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Edited by 

Publication No. 51 of the 


© 1958 

The American Association for the 
Advancement of Science 

Library of Congress Catalog 
Card Number 59-59993 

Printed in the United States of America 

The Horn-Shafer Company 

Baltimore, Maryland 

This volume is dedicated 

to the memory of 

two great zoo geographers, 


Whose observations and reflections on the distribu- 
tion of animals provided much of the evidence that 
led them, just one hundred years ago, to propose to 
the world the epochal concept of Organic Evolution, 
which unshackled the minds of men and helped in- 
augurate the Age of Science. 


i\s science expands and fragments, reviews and 
syntheses of broad areas become increasingly useful and necessary. 
Among the more effective means of review and synthesis are the 
symposia that are being held in increasing numbers at scientific 
meetings. Two such symposia, in 1957, encompassed the field of 
zoogeography, with due attention to the underlying data of geo- 
morphology, paleoclimatology, paleontology, and physiology. The 
fifteen papers that have become available from these two symposia 
comprise a notable and rather comprehensive, though somewhat 
diverse contribution to zoogeography and to its background sciences. 
The extent of the contribution is greatly enhanced by the publica- 
tion of these assembled papers as one of the symposium volumes of 
The American Association for the Advancement of Science. 

The first of these two symposia (Part I) was held under the prime 
auspices of the Pacific Section of The Society of Systematic Zoology, 
as a feature of the joint meeting of the American Institute of Biologi- 
cal Sciences and the Pacific Division of the American Association 
for the Advancement of Sciences, at Stanford University, in August, 
1957. The symposium, bearing the ample title "The Origins and 
Affinities of the Land and Freshwater Fauna of Western North 
America," was abundantly cosponsored by the American Society of 
Ichthyologists and Herpetologists (Western Division), American 
Society of Zoologists, California Academy of Sciences, Pacific Coast 
Entomological Society, Society for the Study of Evolution, and 
Western Society of Naturalists. The fourteen papers ran through well- 
attended morning and afternoon sessions on August 26 and 27, plus a 
final panel discussion that nearly filled a spacious hall on the evening 
of the second day. The large and attentive audiences demonstrated 
the liveliness of the subject. Audience contribution was so spirited 
at the panel discussion that I had difficulty in closing the session at 
a reasonable hour. 

It was my pleasure and privilege to act as general chairman of this 
symposium. In conducting the sessions I was ably joined by the late 
Karl P. Schmidt, as one of the last of his many generous acts, and 
by George F. Edmunds, Jr. Panel members William H. Burt, Alden 
H. Miller, Robert W. Pennak, Herbert H. Ross, and Dr. Schmidt 
helped enliven the informal discussion. 


Gratitude is expressed to the fifteen participants, all of whom 
made notable contributions. Most of the contributors made an ex- 
tensive and thorough analysis of their chosen subjects, and some 
treated their topics in exhaustive and carefully documented style. 

Credit for the success of this symposium goes to the symposium 
committee, all of the University of California, Los Angeles: John N. 
Belkin, chairman, Donald Heyneman, and Marietta Voge. These 
zoologists were the prime actors in the conception of the idea, in 
lining up the able speakers, in arranging and managing the sessions, 
and, as not the least difificult task, in extracting manuscripts from 
thirteen of the participants. They also helped in processing the manu- 
scripts. I am sure that the officers of the meetings, the speakers, the 
audiences, and, now, the scientific public, join me in expressing 
hearty thanks to these tireless and self-efTacing workers. 

The second symposium (Part II), which is herein represented by 
three of the six papers, was a feature of the American Association 
for the Advancement of Science meeting at Indianapolis, and was 
held on December 28, 1957. It was entitled "Geographic Distribution 
of Contemporary Organisms," and constituted Part I of the general 
symposium, "Some Unsolved Problems in Biology, 1957." This was 
a joint program of AAAS sections F (Zoological Sciences) and G 
(Botanical Sciences), and was extensively cosponsored, by the 
Society of Systematic Zoology, Ecological Society of America, 
Genetics Society of America, American Society of Naturalists, and 
Botanical Society of America. The program was arranged by Harold 
H. Plough, of Amherst College, as Secretary of Section F, ably 
assisted by Ernst Mayr of Harvard University and E. Raymond 
Hall of the University of Kansas. Dr. Hall presided at the sym- 
posium and contributes the introductory remarks. 

We of the Pacific Section of the Society of Systematic Zoology 
welcome the privilege of combining the papers resulting from our 
symposium with the three submitted from the Indianapolis sym- 
posium. As editor of the combined symposia, I want to express the 
feeling that they very nicely complement the contributions from the 
first symposium. 

Carl L. Hubbs 

Scripps Institution of Oceanography, 
University of California, 
La Jolla 
October 1958 


George A. Bartholomew, Department of Zoology, University of 
California, Los Angeles 

W. Frank Blair, Department of Zoology, University of Texas, 

William H. Burt, Museum of Zoology, University of Michigan, 
Ann Arbor 

E. Raymond Hall, Museum of Natural History, University of 
Kansas, Lawrence 

William Hovanitz, Department of Biology, California Institute of 
Technology, Pasadena 

Carl L. Hubbs, Scripps Institution of Oceanography, University 
of California, La Jolla 

Philip B. King, General Geology Branch, United States Geological 
Survey, Menlo Park, California 

E. Gorton Linsley, Department of Entomology and Parasitology, 
University of California, Berkeley 

H. D. MacGinitie, Department of Biology, Humboldt State Col- 
lege, Areata, California 

Paul S. Martin, Geochronology Laboratories, L^niversity of 
Arizona, Tucson 

Alden H. Miller, Museum of Vertebrate Zoology, University of 
California, Berkeley 

Robert Rush Miller, Museum of Zoology, University of Michi- 
gan, Ann Arbor 

Kenneth C. Parkes, Carnegie Museum, Pittsburgh, Pennsylvania 

Frank E. Peabody, Department of Zoology, University of Cali- 
fornia, Los Angeles 

Robert W. Pennak, Department of Zoology, University of 
Colorado, Boulder 

James A. G. Rehn, Academy of Natural Sciences of Philadelphia, 

VI 1 


Herbert H. Ross, Illinois Natural History Survey, Urbana 

Donald E. Savage, Museum of Paleontology, University of Cali- 
fornia, Berkeley 

Jay M. Savage, Department of Biology, University of Southern 
California, Los Angeles 

Robert C. Stebbins, Museum of Vertebrate Zoology, University of 
California, Berkeley 


Part I The Origins and Affinities of the Land and Freshwater Fauna 

of Western North America 

1 Evolution of Modern Surface Features of Western North 


Philip B. King 3 

2 Climate Since the Late Cretaceous 

H. D. MacGinitie 61 

3 The Role of Physiology in the Distribution of Terrestrial 

George A. Bartholomew 81 

4 Evidence from Fossil Land Mammals on the Origin and 

Affinities of Western Nearctic Fauna 

Donald E. Savage 97 

5 The History and Affinities of the Recent Land Mammals 

of Western North America 

William H. Burt 131 

6 Origin and Affinities of the Birds of Western North 

America (Editor's Note) 

Alden H. Miller 155 

7 Origin and Affinities of the Present Western North 

American Reptile and Amphibian Fauna (Abstract) 

Robert C. Stebbins 157 

8 Evolution of a Coast Range Corridor in California and 

Its Effect on the Origin and Dispersal of Living 
Amphibians and Reptiles 

Frank E. Peabody and Jay M. Savage 159 

9 Origin and Affinities of the Freshwater Fish Fauna of 

Western North America 

Robert Rush Miller 187 

10 Some Problems of Freshwater Invertebrate Distribution 
in the Western States 

Robert W. Pennak 223 




11 Affinities and Origins of the Northern and Montane 

Insects of Western North America 
Herbert H. Ross 231 

1 2 The Origin and Affinities of the Dermaptera and Orthop- 

tera of \\^estern North America 
James A. G. Rehn 253 

13 Geographical Origins and Phylogenetic Affinities of the 

Cerambycid Beetle Fauna of Western North America 

E. Gorton Linsley 299 

14 Distribution of Butterflies in the New World 

William Hovanitz 321 

Part II Geographic Distributioji of Contemporary Organisms 
Introduction E. Raymond Hall 371 

15 Pleistocene Ecology and Biogeography of North America 

Paul S. Martin 375 

16 The Palaearctic Element in the New World Avifauna 

Kenneth C. Parkes 421 

17 Distributional Patterns of Vertebrates in the Southern 

United States in Relation to Past and Present En- 

W. Frank Blair 433 

General Conclusions 

Carl L. Hubbs 469 

Author Index 479 

Index of Scientific Names 487 


The Origins and Affinities of the 

Land and Freshwater Fauna 

of Western North America 


Evolution of Modern Surface Features 

of Western North America' /<- ^o^s Hn^-^ 

Philip B. King ^*^jl 

United States Geological Survey, " 
Menlo Park, California 

In preparing a summary of the geological 
background of the origins and affinities of the land and fresh- 
water faunas of western North America, I am faced with several 

First is the well-known lack of communication between the 
sciences — a difference in language, in thinking, and in emphasis. 
Thus, items that may be decisive to a zoologist may receive little 
attention from a geologist. I welcome this opportunity to bridge a 
gap between the zoological and geological sciences, to make a con- 
tribution to a problem shared by both of us, and to enhance my own 
education. At the same time, I must admit my present ignorance of 
facets of the problem which are not geological, so that my analysis 
in this paper must be mainly geological. 

Then, too, even in making a purely geological analysis of the 
problem one discovers wide gaps in the record, much evidence that is 
equivocal rather than decisive, and much divergence among geolo- 
gists as to what the evidence means. Broadly, the subject here 
treated is the evolution through time of the geological features of 
western North America, but the aspect of most zoological interest is 
evolution of the surface forms only. For the record up to the middle 
Tertiary, the surface forms must be deduced from rocks and struc- 
tures of various ages, since none of the landscape of that time is 
now preserved. Some fragments of surface forms as old as middle 
Tertiary are preserved, and younger ones are preserved in in- 

1 Publication authorized by the Director, United States Geological Survey. 


p. B. KING 

creasingly larger entitles, but even these surface forms are diversely 

Finally, in so large a subject as western North America, I cannot 
hope to do justice to all items and problems in a single paper. The 
best one can do is to make a sampling and to hope that the samples 
will be sufficiently representative of the whole. In this paper, the 
samples will be chosen mainly from the segment in the United 
States, partly because this is the region I know best, partly because 
it is the region best known to geologists in general. 


Western North America is the region of the Cordilleran system of 
mountain ranges, which extend unbroken along the Pacific Coast 
from Alaska to Central America, and beyond, and inland 400 to 1,000 
miles (Fig. 1). In Canada and the western United States they front 
eastward on the Great Plains of the continental interior, but in 
Alaska they front northward on a coastal plain at the edge of the 
Arctic Ocean, and in Mexico they front northeastward on a coastal 
plain at the edge of the Gulf of Mexico. 

Geographically, the Cordillera north of Mexico is commonly 
divided into two chains of ranges, one along the coast on the west, 
another fronting the Great Plains on the east, with lower, more 
broken ranges and plateaus intervening. Highest summits in North 
America and in the United States are in the chain nearest the coast, 
Mount McKinley in Alaska at 20,300 feet and Mount Whitney in 
California at 14,495 feet. The summit of the interior chain. Mount 
Elbert in Colorado at 14,431 feet, is somewhat lower. Many other 
peaks in both chains project to heights nearly as great as the ab- 
solute summits, and some of these have greater relief relative to 
their immediate surroundings. 

The western mountain chain includes the Alaska Range of Alaska, 
and the Coast Mountains of British Columbia. In the United States 
the chain is double, with low Coast Ranges on the west separated 
by the Puget Trough, Willamette Valley, and Great Valley of 
California from the higher Cascade Range and Sierra Nevada on the 
east. A comparable pattern is expressed to the north, in Canada and 
southeastern Alaska, by the offshore islands and Inland Passage, 
and to the south, in Mexico, by the peninsula of Baja California 
and the Gulf of California. 



Fig. 1. Generalized map of North American Cordillera, showing 
present topographic configuration. 1, Principal ranges. 2, Minor ranges. 
3, Plateaus. 4, Lowlands, including plains of continental interior. 5, Sub- 
merged areas, mainly ocean basins, but including continental shelves. 


p. B. KING 

The lower intermontane belt begins on the north with the wide 
depression along the Yukon River in Alaska, continues southward 
through various plateaus and ranges in Yukon Territory and British 
Columbia, and includes the Columbia Plateau, Colorado Plateau, 
and Basin and Range province in the western United States. 

The eastern mountain chain is represented in Alaska by the Brooks 
Range, and farther south, in Canada and the western United States, 
by ranges that go under the general title of Rocky Mountains. The 
Rocky Mountains end as a continuous barrier in northern New 
Mexico, and for considerable distances southward the eastern ranges 
are discontinuous and are of Basin and Range type. 

In Mexico, the tripartite division of the Cordillera farther north 
is lost. Here the Cordillera is essentially a high plateau, breaking off 
in ranges on the east, west, and south, which form the three Sierra 
Madres of that country — Oriental, Occidental, and del Sur. 

These are the gross geographic forms of the Cordillera today, yet 
to some extent they are accidental, and at most reflect only latest 
warping of the crust. They have slight utility in an analysis of the 
evolution of the surface features of the Cordillera, as each consists 
of diverse geological features that have developed at different times 
and in different ways. For example, the Sierra Nevada is an uplifted 
block of crystalline rocks, whereas the Cascade Range, its orographic 
continuation on the north, was built primarily by volcanic erup- 

Present surface forms, rocks, and structures of the Cordillera have 
developed through a long span of geologic time. Mountains arose 
first in the western part of the region, in the middle of Mesozoic 
time; others farther east developed in later Mesozoic and early 
Tertiary times. Subsequently, in Tertiary and Quaternary times, 
the initial mountains of the whole region were modified into the 
forms we now see — by a continuation of crustal mobility, supple- 
mented by volcanism, erosion, and sedimentation. The eastern part 
of the Cordillera appears to be attaining stability now, so that the 
modifying processes are becoming less active. On the west they are 
still at work, as may be seen by the seismic and volcanic unrest near 
the Pacific Coast, and one may anticipate continuing rearrangements 
of the geography there. It is my purpose in the pages that follow to 
elaborate on the sequence of events thus briefly outlined. 


Nature of Mountain-Building Processes 

Ultimate cause of mountain building is to be sought, not in such 
merely superficial processes as erosion, sedimentation, glaciation, or 
volcanism (however much these may shape the landscape in detail), 
but in forces within or beneath the crust of the earth, which have 
deformed the rocks and raised or lowered large areas of the surface. 
Little is known about these forces themselves, but much has been 
learned about their effects. 

Some of the orogenic phases have been referred to as "revolu- 
tions," because they are supposed to have brought about drastic 
rearrangements of the geography and climate, and so modified the 
environments as to cause far-reaching changes in distribution and 
kinds of life. Detailed study shows, however, that the different 
phases merge into each other, and that the changes they brought 
about were evolutionary rather than revolutionary. Operation of 
crustal forces was persistent through time, and although there were 
certain crescendos, development was orderly and progressive, rather 
than catastrophic. 

Nature of Continental and Oceanic Crusts 

In North America, at least, mountain building was a feature of the 
edge of the continent — the border zone between the continental 
platform and the adjacent ocean basins. 

Sequentially, the processes may be divided into an initial or 
geosynclinal phase, followed by an orogenic phase and a post- 
orogenic phase, the nature of which will be examined later. The 
phases were prolonged. In the Cordilleran region the geosynclinal 
phase endured for at least 350 million years, from Cambrian to 
Triassic; the orogenic phase, for about 100 million years, from 
Jurassic to Paleocene; and the post-orogenic phase, for about 50 
million years, from Eocene to present (Table I). 

Continental platforms and ocean basins are fundamentally 
different elements of the crust of the earth (the crust is the relatively 
thin skin of rocks that overlies the dense material of the interior of 
the earth). Their surfaces stand today at different levels: the con- 
tinental averages about half a mile above sea level; the oceanic, 3 
miles or more below sea level. The two levels reflect contrasting 


p. B. KING 

average compositions of the crust beneath the two areas (Ewing and 
Press, 1955). Crust of the ocean basins is made up of relatively 
dense rock, called sima, with an average composition about like 
basalt, and with a thickness beneath the ocean water of about 6 
miles. Simatic material like that beneath the oceans also forms the 
base of the thicker crust of the continental platforms, but most of 
the thickness of the platforms consists of lighter rock, called sial, 
of about the composition of granite. Continental crust has a thick- 
ness on the order of 20 miles. 

Table I. Subdivisions of Later Geologic Time, and Their Relation to 
the Phases of the Evolution of the Cordilleran Region 




Phases in Evolution 
of the Cordillera 










Post-orogenic phase 





Orogenic phase 


and older 

Geosynclinal phase 

These differences in composition and thickness of the crust under- 
score a widely held belief in the permanence of continents and ocean 
basins, and give little comfort to notions of vanished lands within 
the ocean areas. To create and destroy such lands would involve not 
merely changes in level, but changes in crustal composition. It is 
agreed that the Pacific Ocean basin, in particular, was a permanent 
crustal and topographic feature throughout known geologic time. 
Even the relatively modest ''borderlands" that some geologists have 
believed once existed along or off the present coasts must each be 


appraised critically on their individual merits. Thus, the supposed 
borderland of "Cascadia" which has been postulated along the 
Pacific Coast of North America, if it existed, could hardly have 
extended beyond the edge of the present continental shelf, the sub- 
merged part of the continental crust. 

This is not to say that certain modifications of the doctrine of 
permanence are unworthy of consideration : 

Some geologists believe that the plates of continental crust, al- 
though permanent, have drifted through time across the subcrust, so 
that their positions have shifted with respect to other continents, 
and to the poles. Although there is a great deal of persuasive evi- 
dence for such an interpretation, much more evidence, both geologi- 
cal and geophysical, is against it. The possibility of continental drift 
need not concern us greatly in our present problem ; even under such 
an hypothesis North America has long retained about the same 
position with respect to Asia, South America, and the Pacific Ocean. 

Other geologists believe that, although present oceanic areas are 
unlikely ever to have been continental, the continental plates may 
have increased in area through time by processes of accretion — by 
building of sediments over the edges of the oceanic crust, and their 
subsequent consolidation into continental crust during mountain 
building. Western North America may have increased in area, 
rather than diminished through recorded geologic time, by incre- 
ments along its Pacific margin, especially during the orogenic period 
of the latter half of Mesozoic time. The area of the Coast Ranges of 
California, for example, may have been continental during only the 
last 100 million years of geologic time; before that, open ocean. 


General Concepts 

Growth of a mountain system ordinarily begins with a geosynclinal 
phase, or time of quiet preparation, when marine sedimentation 
went on over the site of the future mountain belt. A geosyncline is an 
area where sedimentation proceeded actively, to the accompaniment 
of more or less crustal movement (Kay, 1947). Many geologists have 
believed that the geosynclines of North America were features that 
developed within the continental platform, between a central nucleus 
and the "borderlands" along the edge. Now, there is a growing 

10 p. B. KING 

suspicion that geosynclines were features marginal to the continental 
platform, that overlapped its edges, it is true, but that, on the farther 
side, may have been built outward into the ocean basins (Longwell, 
1950, pp. 420-422). 

The part of the geosyncline toward the continent, termed the 
miogeosyndine, was a shelf underlain by continental crust that re- 
ceived various sorts of shallow-water sediments. Mobility of the 
crust beneath it was greater than that in the continental interior, yet 
was expressed mainly by subsidence during sedimentation, which 
permitted gradual accumulation of a thick body of sediments. 

The part of the geosyncline toward the ocean, termed the eugeo- 
syncline, was a more mobile area, even during early phases of its 
history, with deeps, shallows, and strips of land that were shaped by 
crustal forces, and with volcanic eruptions whose products were 
mostly spread on the sea floor, but which in places were built up 
into islands. Later, parts of the geosynclinal phase in this area 
blended w^th the succeeding orogenic phase. The extent to which the 
eugeosyncline formed over a continental or over an oceanic crust is 
uncertain, as the basement on which the eugeosynclinal deposits 
were laid has seldom been raised to the surface; at least the outer 
edge of the eugeosyncline was probably built over an oceanic area. 

Our study of western North America can best begin at the start of 
the Mesozoic era, or late in the geosynclinal phase of development 
of the Cordillera, and immediately before the orogenic phase. 

Eugeosynclinal Area of the Cordillera 

A eugeosynclinal environment persisted for a long period in much 
of the western part of the Cordilleran region, with an irregular 
eastern boundary. It extended about to the site of Owens Valley 
east of the southern Sierra Nevada, east of Winnemucca in north 
central Nevada, and across Oregon into westernmost Idaho (Fig. 2). 

The environment is expressed by a characteristic suite of deposits 
— volcanics (lavas, tuffs, and breccias) many times repeated and of 
great thickness, and associated argillites, graywackes, and cherts, 
nearly all of which must have been laid down beneath the sea 
(Eardley, 1947, pp. 316-328). The eugeosyncline originated at an 
early period, for deposits of eugeosynclinal type contain Silurian 
and Devonian fossils in the Klamath Mountains and Ordovician 
fossils in north central Nevada and the eastern Sierra Nevada, but 



its record is most extensively preserved in the later Paleozoic, 
Triassic, and Jurassic rocks. This is not the place to discuss the com- 
plexities and variations of these primarily marine deposits, as we 
are more concerned with the land areas. 


Fig. 2. Map of western United States, showing generalized conditions 
during middle part of the geosynclinal phase of the development of the 
North American Cordillera (Pennsylvanian and Permian time). 1, 
Oceanic area. 2, Eugeosynclinal area; stars indicate approximate posi- 
tions of volcanic centers. 3, Miogeosynclinal area. 4, Foreland area, or 
continental interior; partly land, but intermittently covered by ephemeral 
seas. 5, Deeper sedimentary basins in continental interior. 6, Folds and 
fold belts. 7, Direction of transport of sediments. 

Within the eugeosyncline, indications of any land areas are elu- 
sive. Ephemeral islands are suggested by occasional gaps in the 
sequence (such as absence of any Triassic rocks in parts of the Sierra 
Nevada) and by local conglomerate layers. Many of the volcanic 
units change markedly in thickness within short distances, as though 

12 p. B. KING 

they were built up irregularly on the sea floor, and perhaps in places 
to the surface. It has been thought that in some areas sedimentation 
was interrupted by deformation during Paleozoic time, before the 
close of the geosynclinal phase (Eardley, 1947, pp. 328-334), so that 
fold ridges may have emerged as land areas. Indications of such 
deformation are based on obscure evidence that can be otherwise 
interpreted, so that any occurrence of fold ridges produced by the 
deformation remains to be proved. 

At the eastern edge of the eugeosynclinal area the record of 
emergence is more definite. Differences between Triassic and Jurassic 
deposits east and west of a belt through the center of the Great Basin 
have long been known, and are sufficiently marked as to suggest that 
the two sets of deposits were separated by a land barrier (Nolan, 
1943, p. 158) (Fig. 3). Geologic work in north central Nevada during 
the last few decades has indicated something of the antecedents of 
this barrier (Roberts et al.). Older Paleozoic rocks that had been 
laid down in the eugeosyncline were deformed and thrust eastward 
over the miogeosynclinal area, were then eroded, and were over- 
lapped from the east by Pennsylvanian deposits (Fig. 2). Angular 
unconformities within the higher Pennsylvanian and the Permian 
attest a continued instability of the area. In the Great Basin re- 
gion, the Triassic and Jurassic barrier must have been inherited 
from this belt of Paleozoic deformation. Stratigraphic data indicate, 
however, that the barrier continued northward from the Great 
Basin toward Canada, where its origin and prior history are less 
clearly indicated. 

Miogeosynclinal Area of the Cordillera 

A miogeosynclinal environment prevailed over the continentward 
side of the Cordilleran geosyncline. During Paleozoic time, when the 
miogeosyncline received thick accumulations of limestone, its eastern 
edge extended across the site of the Rocky Mountains to the Great 
Plains near the Canadian border, but farther south in Utah extended 
no farther east than the boundary between the Great Basin and 
Colorado Plateau. 

Through much of the segment in the western United States, there- 
fore, a wide area of the Cordilleran region lay east of the geosyncline 
— the present Colorado Plateau and the Rocky Mountains of Wyo- 
ming, Colorado, and New Mexico. During Paleozoic time most of 



this area had a history Hive that of the remainder of the stable con- 
tinental nucleus, intermittently emergent or receiving the thin de- 
posits of ephemeral seas. In later Paleozoic time, however, part of it 
began to lose its previous stability. On the site of the Rocky Moun- 







Fig. 3. Map of western United States, showing generalized conditions 
late in the geosynclinal phase (Triassic and Early Jurassic time). 1, 
Oceanic area. 2, Eugeosynclinal area; stars indicate approximate positions 
of volcanic centers. 3, Miogeosynclinal area. 4, Sedimentary wedges that 
spread from the geosynclinal area across the foreland: (a) dominantly 
marine, (b) dominantly continental. 5, Land areas that probably did not 
receive deposits. 

tains of Colorado and New Mexico several broad fold ridges were 
raised; troughs subsided rapidly between them and received thick 
accumulations of waste eroded from the uplifts (Fig. 2). These 
"ancestral Rocky Mountains" are the ends of one of the w^estern 
branches of the mountain belt that formed during Paleozoic time 

14 P. B. KING 

along the southeastern side of North America. The zone of weakness 
that they created in the crust greatly influenced the configuration 
of the Rocky Mountain structures that developed there later (Bur- 
bank and Lovering, 1933, pp. 277-301). 

By the first half of Mesozoic time, considerable rearrangements 
had taken place in the miogeosynclinal area. The land barrier be- 
tween the miogeosyncline and eugeosyncline, whose development 
had begun in later Paleozoic time, restricted the extent of Triassic 
and Jurassic sedimentation on the west; troughs along the eastern 
side of the barrier received a considerable thickness of marine sedi- 
ments (Fig. 3). To the east, deposits spread beyond the Paleozoic 
miogeosyncline, wedging out in the Great Plains area east of the site 
of the Rocky Mountains. At least in the south, most of these eastern 
deposits were land-laid, and in the Colorado Plateau include such 
characteristic units as red stream deposits of the Triassic (Moenkopi 
and Chinle formations), great sand dune deposits of the Late Triassic 
and Early Jurassic (Wingate and Navajo sandstones), and vari- 
colored stream deposits of the Late Jurassic (Morrison formation) 
(Baker et al., 1936, pp. 48-55). 

During Cretaceous time, sedimentation continued in much the 
same region as that covered by the Triassic and Jurassic deposits, 
but the Cretaceous deposits are so closely related to the orogenic 
phase of Cordilleran history that it is best to discuss them later. 


General Concepts 

Terminology. The word orogeny means mountain building, yet to 
a degree its use has been perverted by geologists. During early work 
in mountain regions, geologists observed everywhere the strong 
disturbance of their rocks and assumed that such disturbances were 
the cause of the mountains themselves. Now we know that these 
disturbances, while an essential step in the process, did not produce 
strong mountainous relief; such relief was only acquired later, in the 
post-orogenic phase. Use of the term orogeny for the deformative 
phase of mountain growth has nevertheless persisted for want of a 
better name; it is convenient to use it here. 

The Orogenic Process. The geosynclinal phase of mountain 
growth blended, as stated, wath the succeeding orogenic phase, when 


mobility of tlie crust reached its climax. Blending was greatest in the 
eugeosynclinal area, which possessed considerable mobility from the 
beginning; the orogenic climax was reached earliest here. During 
this climax the eugeosynclinal sediments and volcanics were strongly 
compressed and deformed, were more or less metamorphosed, and 
were invaded by small to large masses of plutonic rocks, ending with 
masses of granitic composition. 

Detritus eroded from the newly deformed belt was in part washed 
off its oceanward side, where much of its record has been lost, and 
was in part spread inland as great sheets of clastic rock that tapered 
across the miogeosynclinal area, which was as yet undeformed. 
These clastic sedimentary deposits comprise as much as half of many 
miogeosynclinal sequences. 

As crustal compression progressed, the miogeosyncline itself was 
deformed, sometimes in an orogenic period that appears to be dis- 
tinct from that in the eugeosynclinal area. Its bedded sedimentary 
rocks were thrown into folds and broken by thrust faults along which 
rocks above were moved greater or less distances toward the con- 
tinental interior. Deformation usually progressed as far as the inland 
edge of the geosyncline, where the sediments thin out, and the 
interior region was left undeformed. In places, however, deformation 
was carried beyond the edge of the geosyncline, as in the southern 
Rocky Mountains, within the region we are considering. 

Effect on Surface Features. The orogenic phase so consolidated 
and strengthened the rocks of the eugeosynclinal area that they 
became permanent additions to the continental mass. Also, it 
ordinarily expelled the seas from the whole geosynclinal area for a 
long period — or permanently. Nevertheless, there is much question 
as to how greatly the orogenic phase increased the surface relief. 
Restoration of folds and fault blocks that are now eroded gives the 
impression that orogeny might have produced ranges higher than 
the Himalayas (Fig. 6), but orogeny may have proceeded so slowly 
that various leveling processes nearly kept pace with it — erosion 
wearing off the upraised areas and sedimentation filling the de- 
pressed areas. If so, creation of truly mountainous relief is largely a 
post-orogenic event, resulting from processes different from those in 
operation during the orogenic phase. 

Orogenic Land Bridges. Orogenic belts of this sort are thousands 
of miles long. Some terminate laterally by fading out of effects of 

16 p. B. KING 

deformation, but most, in a sense, are endless. Those along the edges 
of the Atlantic Ocean run out to sea and apparently are broken off at 
the edges of the continental shelves so that their further extensions 
are lost. Those around the margins of the Pacific Ocean, however, 
such as the belt of the North American Cordillera, are continuous or 
nearly so from one continent to the next, and they appear to be 
parts of a single great zone of deformation. In the circum-Pacific 
zone, orogeny created potential conditions for land bridges between 
the continents, and they came into being from time to time during 
the orogenic and post-orogenic phases. Such land bridges were along 
the present and observable orogenic trends; as already noted, no 
land bridges could have formed across the ocean basins. 

The record suggests that land connections along the circum.- 
Pacific orogenic belt were firmer and more frequent between North 
America and Asia than between North America and South America. 
Much of the crust beneath the seas of Middle America, as in the Gulf 
of Mexico and Caribbean Sea, is more oceanic than land-laid and 
seems to be in process of transformation into land-laid crust by 
sedimentation on its surface, and by magmatic transformation 
within it (Ewing et al., 1957, pp. 909-911). At least a part of the firm 
land connection between the two continents in the Central American 
isthmus, especially in Nicaragua and Costa Rica, was built up rather 
recently by volcanic eruptions: "To be sure it is in fact an isthmian 
link. But why is it such an outrageous isthmian link?" (Woodring, 
1954, p. 730). Before development of the isthmus, the lands along 
the orogenic belt between North and South America were mainly 
disconnected islands. 

Deformation of Eugeosynclinal Belt of Cordillera 

Cordilleran eugeosynclinal rocks were deformed, metamorphosed, 
and invaded by granitic rocks in the middle and last half of the 
Mesozoic era, during a time referred to as the Nevadan orogeny (Fig. 


On the west slope of the Sierra Nevada, for which the orogeny is 

named, Jurassic rocks are steeply upturned, altered, and invaded by 

plutonic rocks, whereas Cretaceous rocks lie on their deeply eroded 

edges with little disturbance. From this relation and from more 

detailed evidence we need not mention here, some geologists have 

concluded that at least the deformational phase of the orogeny in the 



Sierra Nevada, and perhaps also the plutonic phase, was accom- 
pHshed during a relatively brief interval near the end of Jurassic 
time, but before its close (Taliaferro, 1942, pp. 102-105). It has been 
inferred, as well, that much of the deformation in the eugeosynclinal 


3 VpA /;// 




Fig. 4. Map of western United States, showing generalized conditions 
during early part of orogenic phase (Late Jurassic and Early to Middle 
Cretaceous time). 1, Oceanic areas. 2, Clastic deposits laid down along 
edges of orogenic belts; arrows indicate direction of transport of sedi- 
ments. 3, Marine deposits of foreland area. 4, Folds produced by Nevadan 
orogeny, late in Jurassic and early in Cretaceous time. 5, Folds produced 
by orogeny later in Cretaceous time. 6, Miogeosynclinal area. 7, Volcanic 

belt to the north and south, where age relations are less clear, took 
place during the same epoch. 

Various considerations suggest that events were more complex 
and prolonged than thus implied, even in the Sierra Nevada region. 
The eugeosynclinal rocks were first folded, steeply upturned, and 

18 p. B. KING 

regionally metamorphosed, then were invaded by successive masses 
of granitic rocks — a sequence which began later than deposition of 
the youngest Jurassic rocks of the Sierra, and must have continued 
for a long time thereafter. Moreover, radiometric determinations on 
the granitic rocks indicate that they themselves were injected over a 
period of more than 60 milHon years, or between Middle Jurassic and 
Middle Cretaceous times, with the oldest to the west in the Klamath 
Mountains and western edge of the Sierra Nevada, and the youngest 
near the east edge of the Sierra Nevada (Evernden et al., 1957). 
Elsewhere in the eugeosynclinal belt where evidence is available, the 
climax of the orogeny varies in age. In the Hawthorne-Tonopah area 
of southwestern Nevada thrust faulting was in progress during 
deposition of Lower Jurassic sediments (Ferguson and Muller, 1949, 
p. 13), whereas in northern Baja California Lower and Middle 
Cretaceous rocks are involved in the orogeny, and are unconformably 
overlain by Upper Cretaceous rocks (Woodford and Harriss, 1938, 
pp. 1328-1330). 

Evidence is inconclusive as to the nature of the lands produced by 
the Nevadan orogeny. Sediments laid down east of the deformed 
belt suggest that the climate there was arid during Triassic and Early 
Jurassic times, and became more humid later, but these conditions 
were influenced by so many unknown factors that they are difficult 
to relate to local topography. As mentioned earlier, a land barrier 
existed on the site of the Great Basin during Triassic and Jurassic 
times, but during initial phases of the Nevadan orogeny the eugeo- 
synclinal belt west of the barrier probably remained low; meta- 
morphism and plutonism of the rocks of the belt indicate that they 
were deformed at a considerable depth, so that first orogenic move- 
ments may have been more downward than upward. Thereafter, 
during forcible injection of the younger plutonic bodies, the surface 
of the deformed belt may have risen, and its erosion may have con- 
tributed to the large volumes of sediment laid down east and west 
of it (described under succeeding headings). Such erosion products 
do not necessarily imply very great relief in the belt ; they might as 
plausibly suggest that leveling by erosion nearly kept pace with 

Be that as it may, it is worth emphasizing that the topographic 
forms produced by deformation of the eugeosynclinal rocks had little 


similarity to any modern features. The present Sierra Nevada, for 
example, was produced much later by tilting and faulting of a block 
within the orogenic belt; other parts were variously raised, broken 
up, depressed, or buried. 

Sedimentation West of Nevadan Belt 

Beyond the strongly deformed and altered rocks of the Nevadan 
orogenic belt, west of the Sierra Nevada and southwest of the 
Klamath Mountains, are less altered Upper Jurassic and Lower 
Cretaceous strata — the Knoxville formation and Shasta series — a 
sequence of marine shales, sandstones, and minor conglomerates. 
These are turned up against the Coast Ranges on the west side of 
the Sacramento Valley, where they are as much as 8 miles thick. 

It has been thought that they were not laid down until after the 
Nevadan orogeny, and that they accumulated in a new trough that 
developed west of the Nevadan belt and east of the ancestral Coast 
Ranges along the Pacific Ocean, with most of the sediments derived 
from the latter (Anderson, 1938, pp. 25-29; Taliaferro, 1942, pp. 
103-104). These views require reexamination, as recent paleontologic 
work indicates that part of the deformed Jurassic rocks of the Sierra 
Nevada on the east (Monte de Oro formation) are of the same age as 
the Knoxville, and that a large part of the Franciscan group of the 
Coast Ranges, once thought to underlie the Knoxville, is as young as 
early Late Cretaceous (McKee et al., 1956, pp. 3; Irwin, 1957). The 
dates of orogenic events and distribution of lands and seas during 
Late Jurassic and Early Cretaceous time must therefore have been 
quite different from those that have been inferred. 

It may be that deformation of the rocks during the Nevadan 
orogeny diminished westward as well as eastward, so that the sites 
of the Sacramento Valley and Coast Ranges were little disturbed 
during the orogeny. The Franciscan, Shasta, and Knoxville strata 
may have been deposited before, during, and after the climax of the 
Nevadan orogeny, and have been laid down along the edge of the 
continent and on the continental slope, in part beneath ocean water 
of considerable depth. Further critical studies are needed to deter- 
mine the source of this great body of sediments, but part of them, 
perhaps the greater part, must have been derived from erosion of 
rising lands in the orogenic belt to the east and northeast (Fig. 4). 

20 P. B. KING 

Existence during this time of lands farther west, along the Pacific 
border, has been stoutly maintained by various protagonists, but 
evidence for such lands seems to have little substance. 

Sedimentation East of Nevadan Belt 

During Cretaceous time, especially during its latter half, a great 
seaway extended along the eastern side of the Cordilleran region, 
from the Gulf of Mexico to the Arctic Ocean (Fig. 4). In mid-latitude 
in the United States its deposits were spread eastward into the con- 
tinental interior as far as Kansas and Iowa and westward into the 
Cordilleran region as far as central Utah. 

The eastern deposits were shallow-water shales and chalks of no 
great thickness, but westward near the front of the Rocky Moun- 
tains these pass into a dominantly shaly mass about 2 miles thick. 
Beyond, wedges of sandstone appear in the shales and thicken west- 
ward, with interbedded layers of coal that formed in swamps and 
floodplains along the edge of the seaway. The westernmost preserved 
Cretaceous rocks, near the west edge of the present Colorado 
Plateau, are nearly 4 miles thick and are dominantly of continental 
origin; they include coarse conglomerates that formed as piedmont 
deposits adjacent to mountainous lands (Spieker, 1949, pp. 60-68). 

The source of these coarse, land-laid beds was clearly to the 
west in the area of the present Great Basin (Fig. 4). The land barrier 
that existed there during late Paleozoic and early Mesozoic time was 
evidently enlarged eastward during Cretaceous time to include the 
former miogeosynclinal area. This enlargement was the result of 
folding and faulting, rather than of mere upwarp, and produced a 
surface of varied relief that was rapidly eroded. 

Deformation of Miogeosyncline and Foreland 

During latest Cretaceous and Paleocene times, orogeny progressed 
into the eastern part of the Cordillera, deforming the rocks of the 
Colorado Plateau and Rocky Mountains as far as the Great Plains 
(Fig. 5). This deformation, which completed the orogenic phase of 
Cordilleran evolution, has been termed the Lar amide oroge?iy. It has 
commonly been thought of as distinct, both in place and time, from 
the Nevadan orogeny, but such distinctions are between end mem- 
bers of a continuing sequence of deformation. Deformation began 
earliest toward the west, then expanded across the miogeosynclinal 



area toward the continental interior; the Cretaceous deformation of 
the Great Basin area occupies an intermediate position in place and 
time. In any particular part of the eastern Cordillera the observ-ed 







Fig. 5. Map of western United States, showing generalized conditions 
during late part of orogenic phase (latest Cretaceous and Paleocene time). 
1, Oceanic area. 2, Marine sediments along Pacific border. 3, Folds pro- 
duced by Laramide orogeny: (a) narrow folds and fault blocks in geo- 
synclinal sediments, (b) broad folds in foreland area, involving basement 
rocks. 4, Volcanic centers. 5, Transverse faults with major components of 
lateral displacement. 6, Sedimentary basins of nonmarine deposition be- 
tween folds and along their eastern border. 7, Land areas; shaded areas 
indicate approximate extent of plutonic rocks of Nevadan age that had 
been unroofed by erosion, 

deformation of the rocks can be placed in this sequence only if 
stratigraphic evidence is available; as a matter of convenience, all 
such structures are ascribed to the Laramide orogeny. 

Laramide movements compressed the sedimentary rocks of the 
miogeosyncline into long, closely spaced folds and thrust blocks, 


p. B. KING 

characteristic examples of which may be seen in the northern Rocky 
Mountains of western Alberta and northwestern Montana, and in 
the central Rocky Mountains of western Wyoming and southeastern 
Idaho. Farther south they have been obscured by later structures 
of the Basin and Range province. 

From central Montana southward, Laramide deformation ad- 
vanced well beyond the miogeosynclinal belt, disturbing part of what 
had previously been the foreland, or border of the stable continental 

I I I I L. 


20 Miles 

Fig. 6. Diagram of a typical mountain uplift in Southern Rocky 
Mountains. The example chosen is the Uinta Mountains of northeastern 
Utah. The block in the background shows the feature without erosion of 
the uplifted strata; that in the foreground the present topography. 
(After Powell, 1876.) a, Pre-Cambrian rocks (here, sedimentary strata; 
in other uplifts of Rocky Mountains, generally plutonic and meta- 
morphic rocks), b, Paleozoic strata, c, Mesozoic strata, d, Tertiary strata. 

interior, and raised the central and southern Rocky Mountains of 
Wyoming, Colorado, and adjacent states. Here, the sedimentary 
cover was mainly thinner than in the miogeosyncline, and deforma- 
tion created structures of a different style — broad-backed ranges of 
diverse trend and spacing, in which Precambrian basement rocks 
were so uplifted along the cores as to be uncovered by erosion, the 
ranges being separated by broad basins (Fig. 6). 

Many of these structures were newly born during the Laramide 
orogeny, but in the southern Rocky Mountains of Colorado and New 
Mexico they were guided by structures of the "ancestral Rocky 
Mountains" already referred to. Here, some of the Laramide ranges 
nearly correspond to uplifts that formed in late Paleozoic time, 


whereas others were produced by close folding of sediments which 
had been deposited in troughs between the earlier uplifts (Burbank 
and Lovering, 1933, pp. 283-301). 

The foreland ranges of the southern Rocky Mountains are sep- 
arated from the miogeosynclinal structures in the Great Basin on 
the west by the Colorado Plateau, which remained as a more stable 
block during Laramide orogeny. Its rocks were broadly upwarped 
and downwarped in much the same manner as those of the Rocky 
Mountains, but they attained less structural relief. A typical uplift, 
in the Kaibab and Coconino Plateaus of the Grand Canyon district, 
is still sheeted over by sedimentary rocks, except where trenched by 
the Colorado River, and it is bounded at the sides by steeply sloping 
monoclinal flexures. 

Record of the Laramide orogeny may be read in deposits of latest 
Cretaceous and Paleocene ages which are preserved to great thick- 
ness in basins between the ranges of the Rocky Mountains, such as 
the Bighorn and Powder River basins of Wyoming — and in the Great 
Plains east of the mountains, as in the Denver and Williston basins 
of Colorado and North Dakota (Fig. 7). The deposits are somber- 
colored land-laid clays and sands with layers of coal, whose upper 
parts contain increasing quantities of detritus eroded from the cores 
of the ranges. 

Much labor has been expended in a search for immense uncon- 
formities that were supposed to be concealed in these deposits, and 
which would mark the time of upheaval of the intervening ranges, 
but it is now clear that the deposits are essentially conformable 
sequences. Very likely the original areas in which the deposits were 
laid did not greatly dififer from the present structural basins, and the 
deposits were thick, local accumulations derived from erosion of 
ranges uplifted in the immediate vicinity. The latest Cretaceous and 
Paleocene deposits are therefore unlike the broad sheet of marine 
sediments of earlier Cretaceous time, which were derived from 
erosion of deformed areas far to the west. 

Laramide orogeny destroyed the great Cretaceous seaway of the 
eastern Cordillera (Fig. 5). Except for a brief marine incursion in 
the northern Great Plains during late Paleocene time, represented by 
the Cannonball member of the Fort Union formation, seas returned 
no more to the region, and all succeeding deposits were land-laid. 
The Upper Cretaceous and Paleocene land-laid deposits evidently 


p. B. KING 


400 Miles 

Fig. 7. Map of central and southern Rocky Mountains, showing up- 
lifts and basins of Paleocene and Eocene time. 1, Folds and fault blocks 
in geosynclinal sediments. 2, Uplifts east of geosynclinal area, with out- 
crops of pre-Cambrian basement rocks in their higher parts. 3, Basins 
that received Paleocene sediments. 4, Basins in which Eocene sediments 
were deposited over Paleocene sediments. 5, Areas of lake deposits, 
mainly of Eocene age. 


formed in forested floodplains and swamps, in a warm humid climate, 
probably at an altitude no more than a thousand feet above sea level ; 
Paleocene rocks contain small mammals that were members of an 
arboreal forest community (Van Houten, 1948, p. 2105). 

The ranges that intervened between the areas of deposition were 
outlined in much their present form during the Laramide orogeny, 
but could not have projected to their present bold heights, or they 
would have prevented an ingress of moisture-laden winds from the 
west and the climate would have been much drier (Mackin, 1937, 
p. 819). More likely, their summits rose no more than a few thousand 
feet above the basin floors ; their rocks were greatly uplifted by the 
orogeny, but were worn down nearly as rapidly as they arose. 


We pass now to that part of our story which is perhaps of greatest 
interest to this audience — the shaping of the Cordilleran mountain 
belt after the orogenic phase, in Tertiary and Quaternary times. 

General Concepts 

Crustal unrest continues in a mountain belt long after the orogenic 
phase. The orogenic phase itself created many modifications in the 
crust and subcrust, which were stable so long as the region was in the 
grip of strong compression. Relatively light sialic crust might be 
thickened as a root beneath the mountain belt, and sialic crust might 
be added along the oceanward edge where only simatic crust was 
present before. Although the orogeny generally thickened and 
strengthened the continental crust, it also produced transverse flaws 
and zones of weakness, by differential movement between adjoining 
segments of the belt. 

With relaxation of compression, there was a shift to a new equi- 
librium. Overthickened parts of the crust might have risen buoy- 
antly, or the mountain root might have been dissipated by subcrustal 
transfer of material. Further movements might have followed the 
zones of weakness, or such zones provided routes for the ascent of 

These processes of readjustment are complex, not well understood, 
and much debated, but their surface manifestations are more evident 
and can be read in the rocks, their structures, and in the changes in 

26 P- B. KING 

the landscape. Such modifications of the Cordilleran region have 
been perhaps as great as in any other mountain belt, and include : 

1. Continued differential movements between mountain up- 
lifts and intervening basins in the epochs immediately succeeding 
the orogeny, or perhaps in the waning stages of the orogeny. Some, 
but not all, of the basins in the central and southern Rocky Moun- 
tains were thus accentuated during Eocene and Oligocene time. 

2. Breakup of extensive areas of the deformed terrain by block 
faulting to produce a succession of mountains and intervening 
basins. Such was the fate of the former miogeosynclinal area and the 
eastern part of the eugeosynclinal area in mid-section in the United 
States — in the Great Basin — but similar structures extend far to the 
south and southeast through the more inclusive Basin and Range 


3. Regional uplift of broad areas without much folding or fault-" 
ing, especially late in the post-orogenic period. The greatest of these 
uplifted regions encompassed virtually all the central and southern 
Rocky Mountains, the Colorado Plateau on the west, and the Great 
Plains on the east ; smaller and more complex areas of regional up- 
lift occur farther west, as in the Sierra Nevada and Cascade Ranges. 

4. Volcanic activity and accompanying shallow intrusions. Some 
volcanism took place locally in the Cordilleran region even during 
the orogenic phase; in the post-orogenic phase it occurred in varying 
degree, at one time or another, in almost every part of the region. 
Volcanism was concentrated more in some areas than others, how- 
ever, and in some of them was long persistent. By far the most 
voluminous and persistent volcanism was in the northwestern 
United States, in the Columbia Plateau and Cascade Range. 

5. Development of faults along which movements were not up- 
ward and downward, but along which one side moved laterally 
against the other. The most famous of these is the San Andreas 
fault of California, but many more occur near it and others else- 
where; some, perhaps, are as yet undetected. 

6. Continued orogeny, marked by local subsidence and sedimen- 
tation, uplift, and deformation along the ocean ward side of the 
mountain belt. In the Coast Ranges of California, strata as young as 
the Pliocene and Pleistocene are strongly folded in places, and the 
seismic record indicates that the crust is still unstable. 


Eastern Part of Cordillera (Central and Southern Rocky Mountains, 
Colorado Plateau, and Great Plains) 

Eocene Environments. We have arbitrarily chosen the end of 
Paleocene time as the close of the orogenic, or Laramide, phase in 
the eastern part of the Cordillera, but environmental changes from 
Paleocene into Eocene were evolutionary rather than revolutionary. 
It is true that in some of the intermontane basins initial coarse 
Eocene deposits overstep the edges of Paleocene and earlier rocks 
with marked unconformity, and that this has sometimes been 
thought to have followed immediately on the climax of the Laramide 
orogeny. We have seen, though, that Laramide structures had been 
in process of growth long before the end of Paleocene time; the 
Eocene deposits thus record merely a resumption of sedimentation 
after the crust had reverted to relative stability. 

Within the mountain belt, subsidence of the basins continued 
through Eocene time; basins which had received Upper Cretaceous 
and Paleocene deposits also received Eocene deposits (Fig. 7). 
Significantly, however, basins east of the mountains became quies- 
cent. The Denver, Williston, and other basins in the Great Plains 
received Upper Cretaceous and Paleocene deposits, but few or no 
Eocene deposits. Here, the surfaces of the earlier basins are over- 
spread by thin sheets of Upper Tertiary sands and gravels. During 
Eocene time the regime of the Great Plains changed from one of 
sedimentation to one of erosion. 

Initial Eocene deposits of the intermontane basins (Wasatch 
formation and equivalents) are red-banded sands and silts of stream 
origin, which pass marginally into coarse piedmont deposits. The 
fluviatile deposits contain fossils of large terrestrial mammals which 
probably lived in savannas and open country; forest-dwelling types, 
such as those of the preceding Paleocene, are less common. Evi- 
dently the passage from Paleocene to Eocene time was marked by a 
restriction of forests and expansion of grasslands (Van Houten, 
1948, p. 2106). Nevertheless, there is no evidence of marked change 
in climate or general altitude ; the environment has been compared 
with that along the present Gulf Coast of the United States (Brad- 
ley, 1948, p. 641). 

In some of the basins stream deposition continued through the 
Eocene (as in the Powder River, Wind River, and San Juan basins), 

28 P. B. KING 

but in later Eocene time some of them on the west became the sites 
of great lakes in which fine-grained, thin-bedded, water-laid sedi- 
ments accumulated, which were in part calcareous or petroliferous 
(Bradley, 1948, pp. 640-647). Lacustrine deposition had already 
begun during Paleocene time in the western part of the Colorado 
Plateau area, where the Flagstaff limestone was laid down widely, 
but during the Eocene the center shifted eastward and a great 
confluent body of water spread north and south of the Uinta Moun- 
tains, in which the Green River formation was deposited ; a smaller 
lake also existed in the Bighorn basin, represented by the Tatman 
formation (Fig. 7). 

Ranges between the basins doubtless continued to rise during 
Eocene time and to shed their detritus into the basins, but the over- 
lap of the Eocene strata along their edges indicates that uplift was 
less active than earlier. The ranges could not have projected more 
than a few thousand feet above their surroundings, else they would 
have created a rain shadow to modify the prevailing humid climate. 
Presence of the same species of mammals in more than one basin 
indicates that the ranges were not barriers to migration. 

These conclusions are incompatible with reports of Eocene glacial 
tills at various places in the Rocky Mountains, especially near Ridge- 
way, Colorado (Atwood and Atwood, 1938, p. 961). On this basis, 
some geologists have assumed that the ranges of the Rocky Moun- 
tains projected to alpine heights at the time. These far-reaching 
interpretations have been built on very local, very dubious evidence, 
which may well be otherwise interpreted (Van Houten, 1957). 

The extensive intermontane and lacustrine deposits of Eocene 
time might suggest that the Rocky Mountains and their environs 
were then a region of interior drainage — that not only were the seas 
driven from the region by Laramide orogeny but also, for some time 
thereafter, no rivers flowed from it to the sea. A little reflection sug- 
gests that this is implausible. Although the region was not lofty, its 
summits must have projected to some height above the lowlands on 
the east and formed a drainage divide. The probable rainfall was 
greater than could have been trapped entirely by basins without 
outlets. The subsiding intermontane basins caught the detritus 
which was being washed down from the mountains, but during most 
of the time the streams which entered them probably flowed on to 
the sea. When subsidence of the basins was excessive, runoff was 


trapped to form lakes, but the nature of their deposits indicates 
that they possessed outlets through most of their existence. 

It is obviously impossible to mark out the courses that were pur- 
sued by the Eocene streams. Even the courses of exterior drainage 
much later in Tertiary time are problematical, and the early history 
of the modern rivers of the Cordillera has been diversely interpreted, 
as we shall see. 

Cenozoic Volcanic Activity. An additional item of the Eocene and 
later Tertiary environments in the eastern part of the Cordillera 
can be discussed appropriately at this point — the widespread and 
persistent volcanism. 

Some trace of volcanic activity can be seen in almost all parts of 
the region, but with variable manifestations — in places, isolated 
volcanic cones, patches of lava, and shallow intrusions; in others, 
extensive volcanic piles that stand as massive plateaus or moun- 
tains. Time relations also vary. Some volcanic fields are so ancient 
that only deeply eroded conduits and dike swarms are preserved; 
others are recent enough that the forms of the cones, calderas, and 
flows are still recognizable; still others present a record of inter- 
mittent volcanic activity through much of Tertiary time, and 
even later. 

Cause of the localization of the larger Tertiary volcanic fields is 
not entirely certain. Many of the Tertiary intrusive bodies are 
clearly aligned along zones of weakness in the country rock, related 
to the Mesozoic orogenies; such alignments may also exist in the 
conduits of the volcanic fields but have been hidden by the eruptives 
that overspread the surface. It is perhaps significant that one of the 
extensive volcanic fields, in the Absaroka Mountains and Yellow- 
stone Park of northwestern Wyoming, lies at the east end of a 
transverse zone of volcanic rocks of various ages that extends west- 
ward across the Cordillera nearly to the Pacific Coast. Another 
series of volcanic fields extends around the Colorado Plateau, from 
the San Juan Mountains on the east through the Mogollon Plateau 
and San Francisco peaks on the south to the High Plateaus of Utah 
on the west, as though the plateau block were separated from its 
neighbors by nearly continuous zones of weakness. 

Volcanism began in the eastern part of the Cordillera during the 
later stages of Laramide orogeny (Fig. 5). Large volumes of andesitic 
debris occur in the Upper Cretaceous and Paleocene deposits of 

30 p. B. KING 

many of the basins. In Colorado, such debris in the Animas forma- 
tion of the San Juan basin and the Dawson arkose of the Denver 
basin indicates that the nearby San Juan Mountains and Front 
Range, during the cHmax of their uplift, were heavily overspread by 
eruptives, nearly all trace of which has now been eroded. 

In the Absaroka Mountains and Yellowstone Park of northwestern 
Wyoming, violent and explosive volcanism began in late Eocene 
time, and built up the "early acid breccias" and "early basic brec- 
cias" of that area (Rouse, 1937, pp. 1262-1272); no doubt their 
edges once extended eastward over the older Eocene deposits of the 
Bighorn and Wind River basins. Other flows and breccias were 
piled over these, probably during later Tertiary epochs, and the hot 
springs and geysers of Yellowstone Park attest that the volcanic 
heat has not yet cooled. 

Climax of the eruptions around the Colorado Plateau appears to 
have been during Miocene time. In the San Juan Mountains of 
southwestern Colorado where the sequence has been worked out 
most completely (Larsen and Cross, 1956, pp. 258-260), the Paleo- 
cene andesitic eruptions were followed by quiescence in Eocene and 
Oligocene times, when relatively thin, non-volcanic deposits were 
laid down. On these, during the Miocene, a mile or two of lavas, 
breccias, and tuffs were piled, but with occasional pauses that per- 
mitted the cutting of canyons as deep as those today. Lesser erup- 
tions continued through the Pliocene and into the Pleistocene. The 
volcanic record of other fields on the periphery of the Colorado 
Plateau resembles that of the San Juan Mountains, although per- 
haps less complete and on a smaller scale (Hunt, 1956, pp. 39-53). 

Volcanism in the eastern part of the Cordillera had a significant, 
though secondary role in the shaping of the geography. Eruptions 
in the larger fields much increased the relief, although upbuilding 
was somewhat compensated by subsidence under the load of erup- 
tives and by transfer of magmas from their subsurface reservoirs to 
the surface. Volcanism changed the regimen of streams by loading 
them with detritus, and in places dammed and diverted their courses. 
In some places these effects may be read plainly; in others, where the 
eruptives have largely been removed by erosion, the effects are 
difficult to assess. 

Contrast between Eocene and Present Conditions. Compare the 


conditions inferred in the eastern Cordillera in Eocene time with 
conditions today — in the Eocene, low general altitude, low relief, 
subdued landscape, and warm, humid climate; today, high general 
altitude, high relief, rugged mountains and deep canyons, and 
sharply contrasted climates. How was this change brought about? 

Geologists agree on many aspects of the stor>% and especially that 
the whole region has been uplifted as a unit many thousands of feet 
since Eocene time, but they disagree as to the manner in which it 
was accomplished, and by what stages. One view, perhaps the more 
customary, is that it came about through a succession of brief up- 
heavals, of which the last great one was during the Pleistocene, sep- 
arated by more prolonged periods of stillstand (Atwood and Atwood, 
1938, p. 978). Another view is that uplift proceeded slowly, with little 
interruption since the waning of Laramide orogeny; with the up- 
ward movement greatest in the first half of the Tertiary and di- 
minishing afterward (Mackin, 1947, pp. 110-111). These divergent 
views result from differences of interpretation of the middle and 
late Tertiary deposits and land forms that are preserved in the 
eastern Cordillera. 

Middle and Upper Tertiary Deposits. During middle and late 
Tertiary time deposits were laid down in the eastern Cordillera as 
widely as during Paleocene and Eocene time, but in a different 
pattern. They are preserved now as erosion remnants of original 
broad sheets of sediment, rather than as downfolds in original 
depositional and structural basins. 

Deposits of the Oligocene White River group are extensive in the 
northern Great Plains of South Dakota, and are preserved in smaller 
remnants in the Central Rocky Mountains of Wyoming; they are 
overlain southward, in Nebraska, by the Miocene Arikaree group. 
Even more extensive in the Great Plains, however, is the Pliocene 
Ogallala formation, which spreads southward from Nebraska to 
Texas, and eastward from the mountain front for nearly 400 miles; 
its caliche-cemented layers ("mortar beds") form the caprock of the 
High Plains (Johnson, 1901, pp. 643-647). At about the same time 
another sheet of deposits, the Bidahochi formation was laid down in 
the south central Colorado Plateau, and is now preserv^ed as rem- 
nants in northeastern Arizona (Repenning and Irwin, 1954). In 
New Mexico, between the plateau and the plains, the Santa Fe 

32 p. B. KING 

formation of late Miocene and Pliocene age occurs in great thickness 
in fault troughs that extend southward near the present course of 
the Rio Grande. 

These later Tertiary deposits were contemporaneous with erup- 
tions in the volcanic fields of the eastern Cordillera, and near them 
contain water-borne volcanic gravels and air-borne volcanic ash. 
The remainder of the deposits were derived from erosion of the 
rocks of the ranges. Those in the Great Plains contain fragments 
derived from the Rocky Mountains on the west; those of the 
Bidahochi formation, fragments from at least as far as the San Juan 
Mountains on the northeast. 

Except in fault troughs, the preserved deposits of middle and 
upper Tertiary times are relatively thin at any locality — a thousand 
feet thick or less, rather than much more than a thousand feet as 
with the Paleocene and Eocene deposits. Their average texture is 
considerably coarser than the latter, not only cobbly or bouldery 
near the mountains, but also with lenses and layers of gravel far out 
in the plains country. Nevertheless, they appear not to have resulted 
from renewed folding of the region, as they overlap the edges of the 
ranges without disturbance, and in places nearly bury a rough 
topography of earlier rocks with complex structure. 

Fossil plants and mammals in the middle and upper Tertiary 
deposits record not only a spread of grasslands at the expense of 
forests, an accentuation of Eocene tendencies, but also an increasing 
regional altitude and aridity. By late Miocene time many of the 
earlier browsing herbivore mammals had disappeared; those that 
survived, such as the horses, had a dentition adapted to feeding on 
harsh grasses. Indications of a semi-arid regime appear first in the 
Oligocene floras and faunas and increase to a climax during late 
Miocene and Pliocene time when the climate seems to have been 
much like that in the present Great Plains. 

The deposits themselves are compatible with this inferred environ- 
ment. In the late nineteenth century it was supposed that the Great 
Plains deposits had been laid down on the floors of a succession of 
great lakes, hence that they were originally horizontal and later 
were tilted regionally eastward. Critical study by many later geolo- 
gists has made clear that they were largely of stream origin, with 
local ponds at most and with finer deposits perhaps brought in by 
the wind. The coarse deposits that were formed in the channels of 


withering streams flowing eastward from tlie mountain are of such a 
texture that, under semi-arid conditions, they could hardly have 
moved down a slope much less than that of the present (Johnson, 
1901, p. 628). 

Erosion Surfaces in the Ranges. So much for middle and late 
Tertiary conditions in the plains and lowlands around the mountain 
ranges. What were conditions in the ranges, which were the sources of 
the streams and of much of the detritus deposited roundabout? 

Wide areas in the ranges are beveled by a subsummit surface, 
marked by accordant crests which extend across the deformed bed- 
rock structures, above which chains and clusters of peaks project on 
the divides, and below which modern valleys and canyons have been 
cut to depths of thousands of feet. The surface has been given local 
names in different ranges, and has been variously dated as Miocene 
and Pliocene. Precise age does not matter greatly, as the surface may 
not have been completed simultaneously everyw^here ; it expresses a 
general late Tertiary erosional condition, hence deserves the general 
title of Rocky Mountain peneplain (Atwood and Atwood, 1938, 
pp. 964-965). 

Analysis of this surface on the north slope of the Uinta Moun- 
tains, where it is unusually well preserv^ed, indicates that it has a 
gradient of 400 feet per mile near the high peaks along the mountain 
axis, flattening to 55 feet per mile toward the plains, where it is 
largely mantled by the coarse gravels of the Bishop conglomerate 
(Bradley, 1936, pp. 170-176). This outward flattening of gradient is 
believed not to have resulted from late differential uplift of the 
range, but to have been inherent in the nature of the surface itself. 
The surface must have been cut under conditions of considerable 
aridity; its graded profile, much steeper and more concave than 
those of humid regions, was just sufficient in an arid climate for the 
transport of materials across it. 

Regional studies indicate that the Rocky Mountain peneplain in 
other ranges is like that in the Uinta Mountains, and that it proba- 
bly formed under similar conditions. They show, as well, that the 
peneplain in the mountains was originally confluent with deposi- 
tional surfaces in the Great Plains and other lowlands where, as we 
have seen, the nature of the deposits suggests deposition on a slope 
nearly as steep as the present slope of the plains. 

Environments of Middle and Later Tertiary times. Between 

34 p. B. KING 

Eocene and middle Tertiary times the eastern Cordillera was proba- 
bly arched upward as a unit by as much as 5,000 feet. During the 
same period, the climate became more arid, partly because of a 
world-wide secular change (Axel rod, 1957, pp. 40-41), partly because 
the crest of the uplift created a rain shadow over the area to the east. 

Climax of uplift and aridity was probably also the climax of 
aggradation in the areas between and east of the mountains. It ap- 
pears well established (Atwood and Atwood, 1938, pp. 965-968; 
Mackin, 1937, pp. 821-823) that extensive areas not now covered by 
later Tertiary deposits, including the earlier Tertiary intermontane 
basins and the lower mountain ends and spurs, were then buried. 
Most of the emergent areas were planed to form the Rocky Moun- 
tain peneplain, leaving, as projections above the general level, only 
the unreduced peaks along the axes of the ranges. 

Opinions differ as to the relief of the aggraded and planed-off 
surface of later Tertiary time. The view of many geologists has been 
that regional relief of the eastern Cordillera was considerably less 
than that of today, and that modern regional and local relief is the 
product of renewed uplift during the Pleistocene. Other geologists 
call attention to the fact that preserved gradients of the Great 
Plains deposits and of the Rocky Mountain peneplain are about 
those to which stream regimen would have been adjusted in an arid 
climate and, by extrapolation, infer that the late Tertiary graded 
surface had almost the same regional relief as that of the present 
country. Regional relief had thus increased greatly from that of 
early Tertiary time, but local relief was about as subdued, and 
differed much from the present strong local relief. 

Quaternary Denudation and Dissection. Transformation of the 
late Tertiary landscape into that of the present was thus an event 
of the Quaternary period, mainly of the Pleistocene epoch. Regard- 
less of ultimate causes, it resulted from accelerated stream erosion, 
which degraded and dissected the whole region. 

Such erosion removed large volumes of upper Tertiary deposits 
from the mountain areas, and excavated the rocks beneath by vary- 
ing amounts according to their resistance. The basins, formed of 
weak Cretaceous and lower Tertiary rocks, were etched out, so that 
the ranges of pre-Cambrian crystalline rocks and Paleozoic stratified 
rocks projected above them. During the period of aggradation 
streams had wandered at will down the slopes of the subdued sur- 


faces, but many of them, as they cut downward, were superimposed 
on hard rocks in the buried mountain ridges beneath, and were 
there forced to excavate deep canyons (Atwood and Atwood, 1938, 
pp. 968-976). 

The same sort of canyon cutting took place in the less deformed 
rocks of the Colorado Plateau, southwest of the Rocky Mountains, 
where uplift and degradation had been in progress since early in 
Miocene time (Hunt, 1956, p. 77). 

Principal cause of the accelerated stream erosion of the eastern 
part of the Cordillera during Quaternary time must have been re- 
newed regional uplift, but there is uncertainty as to its amount. All 
graded surfaces of subaerial erosion and deposition possess an orig- 
inal slope toward the sea ; if the late Tertiary surfaces were produced 
in an arid or semi-arid regime, this original slope would have been 
much steeper than that produced in a more humid regime. How 
much the slopes of the late Tertiary surfaces and the regional relief 
of the eastern Cordillera were augmented by uplift is thus difficult 
to evaluate, but it was probably much less than has been supposed 
by some authors. 

Whatever the magnitude of the uplift, major climatic changes oc- 
curred also, as the ice ages of Pleistocene time brought about both 
refrigeration and increase of rainfall. Under this more humid regime, 
streams that had become adjusted to steep gradients during the 
arid times of the later Tertiary were able to readjust themselves to 
new, lower gradients. Such readjustments were most marked, of 
course, during the glacial periods, and were less marked during the 
drier interglacial periods; thus, general downcutting has been punc- 
tuated by many pauses expressed in the landscape by a succession 
of terraces and intervening steps. 

Origin of Drainage Courses of Eastern Cordillera. All this is very 
well as a generalization but what, specifically, has been the history 
of the individual rivers of the eastern Cordillera? The more specific 
we become, the more the doubts and confusions multiply. 

Streams draining eastward from the Cordillera into the interior 
region need trouble us least. Streams of some sort no doubt flowed 
from the Cordillera in this direction since the Laramide orogeny, 
although their courses must have shifted with time. The greatest 
shift in later times was a deflection of streams that formerly flowed 
into Hudson Bay, southward, around the edges of the Pleistocene 

36 P- B. KING 

continental glaciers, to form the Missouri River (Howard, 1958, 
pp. 585-587). 

Greater problems attend the streams that flow southward and 
southwestward from the Rocky Mountains and find their way 
through long reaches of mountain, plateau, and desert country, 
especially the Rio Grande and the Colorado rivers. 

The Rio Grande flows southward from its source in the Rocky 
Mountains for 500 miles through a succession of desert basins before 
it breaks through the eastern ridges of the Cordillera in the Big 
Bend country of Texas and enters the slope toward the Gulf Coast. 
Deposits in the basins of northern New Mexico contain channels of 
foreign stream-worn gravels that indicate existence there since early 
Pliocene time of a river or rivers ancestral to the Rio Grande (Bryan, 
1938, pp. 205-208), but such gravels are unreported in basin deposits 
of southern New Mexico and Texas. Perhaps the Rio Grande drained 
at first into the lake region of northwestern Chihuahua (Lee, 1907, 
p. 22) , and later found its way across the ridges to the east by filling 
a succession of basins, until it overflowed each in turn at the lowest 
point on its rim (King, 1935, p. 260). 

Very likely the Colorado has drained southwestward from the 
Rocky Mountains for a long span of Tertiary time, during which it 
may have persisted in its present position across much of the north- 
eastern half of the plateau. Its lower course across the plateau is 
more puzzling. It has there cut the Grand Canyon through the south 
end of the Kaibab Plateau, which is one of the highest uplifts of the 
region. Moreover, below the lower end of the canyon, the desert 
basins traversed by the river are filled by the late Tertiary Muddy 
Creek formation, which is made up of locally derived detritus, 
without deposits of any large, through-going river (Longwell, 1946, 
pp. 821-826); the river could not have entered these basins until 
after Muddy Creek time. 

It has been suggested that the river coursed across such uplifts as 
that of the Kaibab Plateau when they were in an early state of 
growth, that renewed uplift ponded the drainage on their upstream 
sides, until the river overflowed through its original valley and cut 
this to its present depth (Hunt, 1956, pp. 65-67). Such a sequence of 
events is possible, but field relations suggest otherwise; so far as 
known the Kaibab uplift was folded entirely by Laramide orogeny. 
It has also been suggested that the Colorado River formerly flowed 


southward through the area of the Bidahochi formation, and so to 
the sea, but was later diverted westward by upHft of the southern 
rim of the plateau (Repenning^/a/.). It is believed that filling of the 
area upstream from the Kaibab Plateau to a depth of about 600 feet 
would be sufficient to allow the river to drain westward, utilizing 
the smaller consequent and subsequent stream valleys that had al- 
ready been established between the Kaibab Plateau and the Grand 
Wash Cliffs. 

Nevertheless, the problem of the course of the Colorado River in 
its lower segment across the Colorado Plateau remains one of the 
riddles of the Cordillera, and will no doubt be debated for years to 

Central Part of Cordillera (Great Basin and Sierra Nevada) 

Basin and Range Topography and Structure. During the post- 
orogenic phase, the Great Basin, or region between the Colorado 
Plateau and Sierra Nevada, acquired its distinctive Basin and Range 
topography — a succession of discontinuous, subparallel ranges, sep- 
arated by desert basins. 

The Great Basin itself is a region of interior drainage; streams 
that flow into its basins have no outlet to the sea. This is in part a 
product of the structure, for some of the basins, of which Death 
Valley is an extreme example, have been depressed lower than any 
possible outlet. To some extent the interior drainage of the Great 
Basin is a product of its arid climate and its remoteness from the 
sea; part of its streams could flow out of the region if they had 
sufficient volume (Hubbs and Miller, 1948, pp. 94-98), Basin and 
Range topography extends far south and southeast from the Great 
Basin into Arizona, New Mexico, and Sonora, which are nearer the 
sea and are drained by the Colorado, Gila, Rio Grande, and other 
through-flowing rivers. 

Some geologists have thought that the distinctive quality of Basin 
and Range topography is primarily a product of erosion of a com- 
plexly deformed bedrock under arid conditions; clearly, the arid 
regime has done much to shape the details of the landscape. Most 
geologists believe, however, that the topography of much of the 
province is related to a distinctive Basin and Range structure, which 
was superimposed on the earlier orogenic structures, in part so 
recently that the forms of basins and ranges are a direct result of 


p. B. KING 

crustal movement. Certain it is that much of the region is still 
unstable, as attested by many fresh fault scarps along the edges of 
the mountains and in adjacent alluvial deposits, some of which can 
be related directly to recorded earthquakes. 

Basin and Range structure is thought to be a mosaic of blocks, 
which have been variously raised, lowered, or tilted along steeply 
dipping faults (Fig. 8). High-standing blocks produced the mountain 
ranges, low-standing blocks the basins; detritus eroded from the 
higher blocks was trapped in the lower ones, and smoothed their 
surfaces into gently sloping plains. The faulted sides of the most 
recently upraised mountain blocks still preserve straight base lines 

10 Miles 


Approximate scs/e 

Fig. 8. Generalized section showing Basin and Range structure as 
commonly interpreted, based on Humboldt Range, western Nevada. 
(After Louderback, 1904.) 1, Deformed bedrock of Paleozoic and 
Mesozoic age. 2, Lava and tuff, mainly of early and middle Tertiary age. 
3, Deposits of the intermontane basins, mainly of late Tertiary and 
Quaternary age. 

and steep escarpments; mountain blocks upraised earlier are more 
frayed and are embayed by erosion (Davis, 1925). Detrital filling in 
the basins has generally overlapped the edges of the mountains 
sufficiently to conceal the faults along their borders, but these faults 
are exposed at some favorable places. 

Basin and Range structure is a post-orogenic feature that suc- 
ceeded the strongly compressed structures of the Cordilleran 
orogenic phase, but opinions differ as to the forces that caused it 
(Nolan, 1943, pp. 184-186). An early view is somewhat naive — that 
it was produced by a breakdown and collapse of the region under 
tension, after relaxation of orogenic compression. But under perva- 
sive tension the whole region would have subsided from an earlier 
high-standing position, the ranges less than the basins, whereas the 


region has been uplifted several thousand feet since the early 
Tertiary, and at least some of the ranges have undergone actual, 
rather than merely relative, uplift. Structures resulting from crustal 
tension are no doubt present in the region, but they may have 
resulted from components of a more pervasive crustal compression. 
This compression, however, manifested itself in a different guise 
from that which deformed the eugeosynclinal and miogeosynclinal 
rocks at an earlier period. 

Time Relations of Basin and Range Structure. In the generalized 
picture sketched above. Basin and Range topography and structure 
were presented as an accomplished fact, although their development 
through time was hinted by the varying degrees of erosion observed 
in different ranges. But the present topography and structure were 
long in the making, and when one attempts to trace their develop- 
ment through time, the picture at once becomes more complex 
(Longwell, 1950, p. 427). 

For example, it was stated that the low-standing blocks, or desert 
basins, were largely filled by detritus eroded from the adjoining 
ranges, but these deposits formed during a considerable span of 
Tertiary time, in which the geography changed as a result of con- 
tinuing crustal movements. Earlier basin deposits were derived 
from ranges in a state of growth different from the present ranges 
and perhaps even in different positions; in places the deposits were 
spread over the sites of ranges that developed later. With further 
movements, the earlier deposits were faulted, tilted, and eroded, and 
those in which resistant lavas were embedded were raised in places 
to mountainous heights. Later Tertiary and Quaternary deposits 
bear a closer relation to modern geography, although even these are 
more or less deformed and eroded. 

Sierra Nevada Topography and Structure. The Sierra Nevada, 
which lies west of the Great Basin, is a single massive block 400 
miles long and 80 miles wide, whose crest attains alpine heights, yet 
its form and structure differ only in degree from the mountain 
blocks of the Basin and Range province, and its development was 
closely related to at least the Great Basin segment of that province. 
The Sierra Nevada block may have been shaped by the great masses 
of granitic rocks embedded in its deformed eugeosynclinal strata, as 
these extend along its eastern side for most of its length. 

The Sierra Nevada faces the Great Basin on the east in a series of 

40 P. B. KING 

lofty scarps that have been outlined mostly by faults, although the 
faults are not continuous and are offset en echelon in many places. 
Minor faults also occur within the range, but most of the range, west 
of its summit, is a tilted block with remarkably even, westward- 
tloping crest lines, below which the tributaries of the Sacramento 
and San Joaquin rivers have cut impressive canyons. 

Early Tertiary (Paleocene and Eocene) Environments. By early 
Tertiary time, the topography that developed on the orogenically 
deformed miogeosynclinal and eugeosynclinal rocks had become 
decadent, but the post-orogenic topography of basins and ranges 
had not yet developed. 

At many places in the eastern half of the Great Basin the Mesozoic 
and older rocks are overlaid by patches of calcareous mudstone, fine- 
grained sandstone, and coarser sands and gravels. These appear to be 
remnants of originally much more extensive deposits that formed in 
floodplains, swamps, and lakes, probably in a warm, humid lowland 
(Van Houten, 1956, p. 2819). Although the deposits have been dated 
only by meager fossil evidence, they are probably westward exten- 
sions of the Paleocene and Eocene deposits of the Colorado Plateau 
and the central and southern Rocky Mountains, which formed in a 
similar environment. 

The western half of the Great Basin seems to have been part of a 
low highland which extended westward across the area of deformed 
eugeosynclinal rocks to the western edge of the Sierra Nevada. Few 
or no early Tertiary sedimentary units exist in the western Great 
Basin, although the lower parts of some of its volcanic sequences 
may be as old as Eocene. At the western edge of the highland the 
marine lone formation of middle to late Eocene age overlaps widely 
on the deformed Mesozoic rocks (Allen, 1929). It is composed of 
clays of remarkable purity, with interbedded sands, and is traceable 
up the slope into the older gold-bearing stream gravels of the Sierra 
Nevada foothills. During lone time the site of the Sierra must have 
been worn down to low relief, and was drained by sluggish streams 
that headed well east of the present mountain crest. The clays were 
derived from deeply decayed granitic rocks that were widely ex- 
posed on this worn-down surface. 

Middle Tertiary {Oligocene and Early Miocene) Environments. In 
Oligocene and early Miocene time lavas, agglomerates, and tuffs of 
varied composition were spread widely over the western part of the 


Great Basin area, and form the older volcanic sequence of that area, 
now much disturbed and mineralized. The northwestern corner of 
the Great Basin was overlapped by basalt flows related to the 
Miocene Columbia River basalt. Most of the volcanics farther south- 
east have also been ascribed to the Miocene, but a tuff member in 
the Alta formation of the Virginia City district contains middle 
Oligocene plants. At some places in the eastern and southern parts 
of the Great Basin, ash-rich sand, mud, and gravel were deposited 
in basins that recently had been outlined by faulting. 

Available floras indicate that the western part of the Great 
Basin stood at an altitude of about 2,000 feet above sea level in 
middle Tertiary time, with the Sierra Nevada to the west projecting, 
at most, only a thousand feet higher. Apparently neither the low 
Sierra Nevada ridge nor the downfaulting of incipient basins inter- 
fered materially with drainage westward to the Pacific. 

During one or more episodes before late Miocene time, and per- 
haps mainly in the middle Miocene, the older Tertiary volcanic and 
sedimentaiy rocks in many parts of the Great Basin were faulted 
and tilted, then widely eroded (Van Houten, 1956, p. 2820). These 
movements, premonitions of which we have seen in the middle 
Tertiary basin deposits, are the first notable disturbance of the 
region since the orogenic phase, and mark the beginning of develop- 
ment of Basin and Range structure and topography. 

Late Tertiary {Late Miocene and Pliocene) Environments. During 
late Miocene and early Pliocene time volcanics and sediments were 
spread widely over the Great Basin and Sierra Nevada, covering an 
eroded terrain that had been more or less deformed by the preceding 
disturbances. As these deposits contain mammals and plants at 
many places, and occasional invertebrates and other fossils, they 
form not only a useful stratigraphic datum, but also an index of the 
environments of the time (Van Houten, 1956, p. 2802; Axelrod, 
1957, pp. 23-28). 

Much of the central and northern parts of the Sierra Nevada were 
covered by several thousand feet of andesitic lava flows, remnants of 
which are still preserved on stream divides and mountain tops. 
Principal centers of eruption were near the modern crest of the 
mountains, along an axis which continued northward into the 
Cascade Range, but the flows also spread eastward into the Great 
Basin. Andesitic debris was transported widely westward and 

42 p. B. KING 

eastward, where it became an Important component of contem- 
poraneous sedimentary deposits. 

Over much of the Great Basin east of the eruptive area a succes- 
sion of andesitic vitric tuff, reworked ash, bentonitic mudstone, 
sandstone, Hmestone, and diatomite was deposited, which has been 
variously termed the Truckee, Esmeralda, or Humboldt formation, 
depending on locality. The deposits were laid down in many sep- 
arate but probably confluent basins, partly in lakes and swamps. 
They not only covered the earlier Tertiary rocks but overlapped 
widely onto low inter\^ening highlands of the Mesozoic and Paleozoic 
rocks. In southern Nevada faulting was more active at the time, and 
the Muddy Creek formation of that area consists of coarse alluvial 
fan deposits along the faulted basin margins, and of finer-grained 
elastics and evaporites in the basin centers. 

Comparison of floras in a traverse eastward across the area is 
instructive as to the late Miocene and early Pliocene environments 
(Axelrod, 1957, pp. 34-38). Conifer forests like those of the modern 
Sierra Nevada were not well developed on its western slope probably 
because of low altitude and warm climate. At Carson Pass on the 
crest of the range, at a modern altitude of more than 9,000 feet, is a 
flora of deciduous trees which could not have lived at altitudes 
higher than 2,500 feet. Farther Inland, In the Great Basin, were 
conifer forests of a type now found at the margins of woodland and 
chaparral country. Annual rainfall at the western base of the Sierra 
Nevada must have been about 25 or 30 inches, increasing to 40 or 
45 inches on the upper slopes, and thence decreasing to 25 inches 
over the lowlands of the Great Basin. The summit level of the central 
and northern Sierra Nevada must have stood at an altitude of less 
than 3,000 feet, and projected about 1,000 feet above the Great 
Basin to the east ; it created no more than an ineff^ective rain shadow 
over that area. Evidence of fossil fishes suggests that the Great Basin 
at this time stood at altitudes well below 2,000 feet, to allow the 
ingress of lowland coastal faunas (C. L. Hubbs, personal com- 

The andesitic eruptions along the Sierra crest, although spread 
over a surface of low altitude and low relief, foreshadowed later 
uplifts along that axis. By late Pliocene time the floras of the Great 
Basin changed from a woodland and forest fades to a savanna and 
grassland fades, adapted to less than 15 inches of rainfall. Evidently 


the Sierra Nevada block was now being uplifted, and was exerting a 
climatic influence on the region to the east. Uplift continued into 
early Pleistocene time, until the block had been raised 5,000 to 
6,000 feet in the north and 7,500 to 9,000 feet farther south (Axel- 
rod, 1957, p. 42). 

At the same time as the Sierra Nevada was being raised, block 
faulting on an extensive scale disrupted the Great Basin, and was 
largely responsible for shaping it into its present Basin and Range 
topography (Van Houten, 1956, pp. 2821-2822). There was also a 
gradual increase in altitude; basin floors which had stood at well 
below 2,000 feet above sea level at the beginning of the Pliocene, 
now stand at 3,000 to 5,000 feet. In part this was a result of sedi- 
mentary filling of the basins, but to a much greater extent to 
regional upwarp. 

The reader may note a discrepancy between the record as here set 
forth for times of uplift in the Rocky Mountain region on the east 
and the Great Basin and Sierra Nevada on the west. In the Rocky 
Mountains, some geologists believe that the principal uplift was 
before the middle of the Tertiary and diminished later, whereas the 
Great Basin and Sierra Nevada seem to have been low up to middle 
Tertiary time, and were greatly uplifted afterward. The inferred 
history of the two areas is based on interpretations of necessarily 
elusive evidence by various competent observers, but if the contrasts 
are real, they had a significant influence on the geographic and cli- 
matic evolution of the middle Cordillera. 

Pleistocene Environments. Events in the Great Basin and Sierra 
Nevada during the Pleistocene are perhaps sufficiently familiar as 
not to require detailed recital — the ice fields along the Sierra crest 
and the valley glaciers below them, the smaller glaciers on higher 
summits in the Great Basin, and the great lakes, such as Bonneville 
and Lahontan, which flooded the lower country, in places to depths 
of more than a thousand feet. Climatic fluctuations are recorded not 
only by successive glacial moraines in the mountains, but by several 
epochs of filling and dessication of the lakes. Existence of the lakes 
indicates a much increased rainfall and implies, as well, that many 
of the basins temporarily possessed exterior drainage (Hubbs and 
Miller, 1948, pp. 21-29). 

The Great Basin has returned now to conditions of aridity ap- 
proximately comparable to those at the end of Pliocene time but if. 

44 p. B. KING 

as many believe, the present is merely an interglacial rather than a 
post-glacial period, far-reaching climatic fluctuations in the region 
may be anticipated in the future. 

Northwestern Volcanic Province (Columbia Plateaus and Cascade 

General Setting. The northwestern part of the United States 
exhibits one of the most drastic later modifications of the orogenic 
structure and topography in the Cordilleran region. Elsewhere in the 
Cordillera, volcanism interrupted or modified other post-orogenic 
processes; here it dominated the scene. The deformed geosynclinal 
rocks are covered, in places deeply, by great floods and piles of lava, 
and by associated breccias, tuffs, and sediments. In northern Oregon 
and southern Washington no rocks older than these are exposed for 
300 miles parallel with the coast, or 400 miles inland ; they also ex- 
tend over an even greater area to the south and southeast where 
older rocks emerge in places (Fig. 9). The volcanic regime was 
prolonged and extended, at one place or another, through most of 
Tertiary and Quaternary times. 

The Nevadan belt of deformed eugeosynclinal strata frames the 
region on the south, east, and north. It is exposed at intervals be- 
tween the Klamath Mountains of southern Oregon and the Cascade 
Range of northern Washington, but describes a great arc eastward, 
which passes through the highlands of northeastern Oregon and 
western Idaho (Fig. 9) . The volcanics are confined by the arc on the 
north and east, but break across it on the southeast, where they 
extend into southeastern Oregon and southern Idaho. 

This extraordinary localization of volcanic activity provides food 
for speculation for which there is no certain answer, especially as the 
substructure upon which the volcanics were built is widely buried — 
and entirely so within the area enclosed by the Nevadan arc. A 
question is worth asking, however, whether the area within the arc 
might not have been an oceanic embayment, floored by simatic 
crust, until well through the geosynclinal phase (Figs. 2 and 3), and 
was only added to the continent later, by volcanism and sedimenta- 
tion. This possibility is suggested by dominance of basalts within the 
arc, which were seemingly derived without contamination from the 
underlying simatic layer, and by more varied lavas southeast of the 
arc, where there was evidently greater mixing of simatic and sialic 
crustal materials. 



\\ it \\ 

X Sierra 

i^°% ^ \ 





>*■>■■ 'I I. . 

2 ^.v.-;.' 3 |.. 

> - » ■■ ' 

• • 


400 Miles 


Fig. 9. Map of northwestern volcanic province, in Washington, Ore- 
gon, Idaho, and adjacent states. 1, Nevadan basement; metamorphic 
rocks Hned, plutonic rocks in heavy shading. 2, Inferred margins of 
Nevadan orogenic belt. 3, Plateau basalts of Miocene and later age. 4, 
Andesitic volcanics of Cascade Range. 5, Volcanic cones of Cascade 
Range, mainly of Quaternary age. 6, Other rocks; mainly sedimentary 
rocks of Mesozoic and Tertiary age, but including some older Tertiary 
volcanics. 7, Edge of continental area. 

The volcanic rocks and their associates assume diverse geographic 
forms: along the Pacific, the low Coast Ranges; east of a longi- 
tudinal depression, the high Cascade Range; and farther inland, the 

46 p. B. KING 

Columbia Plateaus, partly split in their middle by the emerged 
Nevadan rocks in the highlands of northeastern Oregon. 

Early Tertiary Environments. The record of early Tertiary time 
may be seen mainly in the Coast Ranges, where marine clastic 
sedimentary strata several miles thick are turned up in gentle folds. 
Some of them, such as those of the Olympic Mountains of north- 
western Washington, may have been laid down beneath ocean water 
of considerable depth, and have been derived from turbid flows that 
moved westward down the continental slope. Interbedded with the 
Tertiary sedimentary rocks are great lenticular masses of basaltic 
lava, which were largely erupted beneath the sea, as shown by their 
pillow structure (Waters, 1955a, pp. 204-707). Inland, where the 
lower Tertiary rocks are occasionally exposed , the marine beds pass 
into land-laid deposits, including beds of coal, which formed in 
floodplains, swamps, and lakes. 

During early Tertiary time the northwestern volcanic province 
probably was a broad coastal plain with an offshore continental shelf 
and slope, which faced westward on open ocean (Fig. 5). Its environ- 
ment must have resembled that of the present Gulf Coastal Plain, 
except for the much greater volcanic activity. No ranges existed 
near the coast to create a climatic barrier like that today; Eocene 
floras from both the east and west sides of the present Cascade Range 
are closely related, and grew in subtropical lowland forests (Chaney, 
1938, p. 3^Z). 

Middle and Late Tertiary Environments. Miocene time witnessed 
the great eruptions of Columbia River basalt, which spread over an 
area of 100,000 square miles, in places to thicknesses of a mile or 
more (Waters, 1955a, pp. 707-708). The basalt flows cover all the 
plateau country of southeastern Washington and northeastern 
Oregon, within the Nevadan arc (Fig. 9), where in many places they 
still remain nearly horizontal, although in others they have been 
warped and folded. Along the lower course of the Columbia River 
the basalt also spreads westward across the site of the Cascade 
Range. Here its farther edges interfinger with marine deposits. 

The Columbia River basalt is a plateau basalt — it was not erupted 
from volcanoes, but welled out of deep fissures from the simatic layer 
beneath. Single flows are 100 to 500 feet thick, and must have been 
very fluid as some of them are traceable for more than a hundred 
miles. The flows were probably piled thickest near the center of the 


eruptive area, which subsided gradually beneath them, and they 
spread thence in all directions. Along their edges to the north, east, 
and south, they overlapped an eroded surface of the Nevadan 
orogenic belt, damming valleys and ponding their waters. 

At about the same time, a different form of volcanism was be- 
ginning along the Cascade Range. Eruptions of explosive violence 
built up piles of andesitic lava, mudflows, breccias, and tuffs, which 
were probably surmounted by volcanoes. These accumulations 
formed a chain approximately along the axis of the present range, 
from northern Washington southward through Oregon into Cali- 
fornia, where it joined the chain of andesitic eruptions in the Sierra 
Nevada. The andesitic volcanics had a much more complex origin 
than the basaltic, and probably formed on a line of weakness that 
was developing along the Cascade-Sierra Nevada trend (Waters, 
1955a, pp. 709-710). 

In both the Cascade Range and Sierra Nevada, this line of weak- 
ness was first manifested at the surface by eruptions only, but later 
the rocks along it began to be raised by crustal forces. Unlike the 
segment in the Sierra Nevada, however, that in the Cascades was 
neither tilted as a block nor greatly faulted ; the faults that occur are 
minor and local. Moreover, volcanic upbuilding went on hand in 
hand with crustal uplifts so that basement rocks were not laid bare 
by erosion, except at the north end. The cross section of the range 
exposed in the gorge of the Columbia River exhibits both volcanic 
upbuilding and complex arching (Hodge, 1938, pp. 839-886). 

Quaternary Events in Cascade Range. The modern Cascade Range, 
from northern Washington to northern California, is crowned by a 
score or more of great volcanic cones (Fig. 9), whose construction 
apparently began as early as the Pliocene, but whose growth con- 
tinued until recent times — if, in fact, it has yet ceased. The cones 
were built upon a deeply eroded surface of the older andesitic vol- 
canic rocks that form the greater bulk of the range, apparently after 
a time of quiescence of some duration in late Tertiary or early 
Quaternary time. North of the Columbia River the cones stand 
singly, but farther south they have built up a massive range of 
volcanic rocks on the eastern side of the earlier range. 

History of Columbia River. The Columbia River, whose sources 
are in the Rocky Mountains on the east, enters the Pacific in the 
midst of the volcanic province. Much of its drainage basin is blessed 

48 p. B. KING 

with greater rainfall than the country farther south, and its volume 
far exceeds that of any other stream on the western slope of the 
Cordillera. Similar greater rainfall probably prevailed in this north- 
ern segment of the Cordillera through much of the post-orogenic 
phase, so one may assume that an ancestor of the Columbia existed 
there throughout much of the Tertiary and Quaternary. 

With onset of the eruptions of Columbia River basalt, the course 
of the river in the coastal plain downstream from the highlands of 
the Nevadan orogenic belt was obliterated by the flood of lava. Parts 
of the river and its tributaries in the highlands to the north and 
northeast were dammed by the lava, and a series of lakes were 
formed. Each lake drained around the spur ends of the highlands of 
older rocks to the next lower lake on the west, thus establishing an 
exit for the waters along the edge of the volcanic field ; with down- 
cutting, there was thus established the new course of the Columbia, 
part of which it still follows (Fig. 9). Farther downstream in south- 
ern Washington, however, the river is deflected eastward into the 
lava country, probably as a result of outbuilding of andesitic debris 
from the Cascade Range on the west (Waters, 1955b, pp. 681-683). 

In southern Washington the river also crosses several anticlinal 
folds in the basalt, which plunge southeast from the Cascade Range. 
Each anticlinal fold is expressed topographically as a ridge, and in 
each ridge the river and several of its tributaries have cut deep 
gorges. The Columbia and its tributaries were probably antecedent 
to the anticlines (Waters, 1955b, pp. 679-681) — they had much their 
present courses before the folding and maintained them by down- 
cutting as the anticlines were raised. Still farther downstream the 
river cuts a much larger gorge through the complexly upbuilt and 
upwarped Cascade Range. Many geologists believe that the river is 
antecedent to the growth of the Cascade Range also, but some 
would ascribe its course through the mountains to a complex process 
of superposition (Hodge, 1938, pp. 888-918). 

Pacific Border of Cordillera (Coast Ranges of California) 

General Geography and Geology. From the Klamath Mountains 
southward through California and into Baja California, the western- 
most ranges of the Cordillera are the Coast Ranges along the Pa- 
cific Ocean (Fig. 10). Southward to Point Conception they consist of 
numerous parallel ridges, each diverging south-southeastward from 







400 Miles 

Fig. 10. Map of California, showing the two types of basement in the 
Coast Ranges and adjacent areas. 1, Nevadan basement of metamorphic 
and plutonic rocks. 2, Franciscan basement of strongly deformed but 
little metamorphosed clastic sedimentary rocks; probable extent of 
Franciscan basement beneath cover of younger sediments indicated by 
light stipple. 3, Areas covered by younger sedimentary and volcanic 
rocks. 4, Faults, many of which have large components of lateral dis- 
placement. 5, Edge of continental area. 

50 p. B. KING 

the coast at a slight angle. At Point Conception, however, the 
prominent Transverse Ranges run nearly eastward, facing the 
Channel Islands offshore in the longitude of Santa Barbara, and 
rimming the north side of the Los Angeles lowland farther east. 
South of the Transverse Ranges and the Los Angeles lowland the 
Peninsular Ranges resume a trend parallel with the coast, and form a 
more massive set of blocks, somewhat like the Sierra Nevada. 

Dominant surface rocks of the Coast Ranges are mainly of 
Tertiary age, primarily fine- to coarse-grained clastic sedimentary 
strata, but with much diatomite and some volcanics. All of them, 
even the youngest, are folded and faulted, in part heavily so, indi- 
cating that the latest phase of the construction of the ranges was 
late in geologic time. 

Basement Rocks. We have suggested earlier that at least the 
northern part of the Coast Ranges, west of the Sacramento Valley, 
was a marine realm through Jurassic and much of Cretaceous times 
— continental shelf, continental slope, and ocean deep — which re- 
ceived great masses of sediments washed off the Nevadan orogenic 
belt. The Coast Ranges might thus be an element which was built 
up and added to the continental plate from Mesozoic time onward. 

A puzzling feature, incompatible with this concept, is the oc- 
currence in parts of the Coast Ranges of a crystalline basement 
consisting of granitic rocks, shown by radiometric determinations to 
be of mid-Mesozoic age like those in the Nevadan orogenic belt, and 
their host rocks of earlier schists, slates, and marbles. In one area, 
the San Gabriel A'lountains north of Los Angeles, radiometric 
determinations prove the existence of rocks as early as pre-Cam- 
brian, but these probably do not emerge elsewhere. 

Disregarding the cover of Tertiary rocks, the fundamental frame- 
work of the Coast Ranges is an alternation of these areas of crystal- 
line Nevadan basement with a basement of much deformed but 
little metamorphosed Mesozoic rocks, especially the Franciscan 
group which may have been formed on the western, or oceanic side 
of the Nevadan belt. 

Basement of Franciscan age underlies all the Coast Ranges north 
of San Francisco Bay and extends thence southward along the west 
side of the San Joaquin Valley (Fig. 10). Southwest of this northern 
Franciscan area is a long strip of Nevadan basement, termed Salinia, 
which extends southward from Point Reyes and the Farallon Is- 


lands near San Francisco, along Salinas Valley (for which it is 
named) to the Transverse Ranges. Another area of Franciscan base- 
ment, the central Franciscan area, lies west of Salinia (Reed and 
Hollister, 1936, pp. 1547-1550). The Transverse Ranges again are 
largely floored by Nevadan basement, as are the Peninsular Ranges, 
but another, the southern, Franciscan area lies to the south and 
west, mostly beneath the sea, and continues far southward along the 
Pacific side of Baja California. 

The Nevadan basement has been supposed to be the foundation 
of the Coast Ranges and to underlie the Franciscan rocks; remark- 
ably enough, however, the base of the Franciscan has never been 
discovered, and all its contacts with the Nevadan rocks are high- 
angle, through-going faults. For example, the contact between the 
Nevadan mass of Salinia and the Franciscan rocks on the northeast 
is the San Andreas and associated faults. There is thus no evidence 
of the sort of crustal material on which the Franciscan rocks were 
laid ; it might have been quite different from the Nevadan basement. 

San Andreas and Other Through-Going Faults. The high-angle, 
through-going faults thus seem to be a critical feature of Coast 
Range structure, and many of these faults are remarkable enough of 
themselves. Instead of their sides merely moving upward or down- 
ward, one side shifted laterally past the other, and the faults have a 
large component of sideward movement. For example, along the San 
Andreas fault, which has been traced the farthest of any, stream 
courses and stream valleys are offset — a stream draining northeast 
across the fault turns along the fault line, then resumes its north- 
eastward course a half a mile or so to the southeast. This faulting 
has thus altered the geography and surface forms, not merely by 
raising and lowering blocks of the crust, but by shifting the geo- 
graphic positions of large sections of the country relative to country 
on opposite sides; the saying is apt that "San Francisco and Los 
Angeles are coming closer together," the one city being northeast of 
and the other southwest of the fault. 

Offset of stream valleys is an obvious late feature, but study of 
the rocks on the two sides of such faults discloses older and much 
greater anomalies. Gravels in Tertiary rocks on one side of a fault 
may contain material whose only possible source is in some area 
many miles away on the opposite side, suggesting that the source 
area has moved away from the gravels in the time since they were 


p. B. KING 

deposited. Such stratigraphic evidence indicates a sideward shift on 
the San Andreas and some of the other faults of 30 miles or more 
since the mid-Tertiary (Crowell, 1952, pp. 2030-2035; Noble, 1954, 
pp. 44-47). Even greater shifts are suggested when comparisons are 
made between basement rocks on the opposite sides, but they are as 
yet difficult to prove and require further detailed research (Fig. 11). 
There is thus a suggestion that the San Andreas fault has been 
moving progressively for a long period — at least since the close of the 

500 Miles 

Fig. 11. Maps of California during successive periods to illustrate an 
hypothesis of extensive lateral displacement on the San Andreas and 
related faults. A, In late Mesozoic time. B, In late Miocene time. C, 
Present time. (Modified from M. L. Hill, 1954.) 1, Boundary between 
Nevadan basement (to east) and Franciscan basement (to west). 2, 
Boundary between Miocene continental sediments (to east) and marine 
sediments (to west). 

Nevadan orogeny — so that rocks of each older age have been shifted 
by greater amounts (Hill and Dibblee, 1953, pp. 445-451). This 
picture, if valid, is greatly complicated by the fact that the San 
Andreas, or master fault, is only one of many in the same region 
with similar habit; attempts at reconstruction of the geography at 
successive periods thus involve, not a single break, but many breaks 
with diverse movements. 

Be that as it may, the possibility has thus suggested itself that 
the anomalous strips of Nevadan basement are slivers that were 
faulted off the orogenic belt on the east, and have been transported 
scores or hundreds of miles northwestward, into an environment 
foreign to them (Fig. 11). Such movements are strongly indicated in 


southern California, where shifts of as much as 30 miles on the San 
Andreas fault since the mid-Tertiary have been proved, and where 
even greater shifts are suggested in the carher rocks. Farther north, 
however, total movements of less than a mile on the San Andreas 
fault have been claimed (Taliaferro, 1943, pp. 159-161). Such claims 
seem to be based merely on the latest of a series of breaks, and fail 
to consider total offset in a broader San Andreas /aw// zone (Wallace, 
1949, p. 803). Nevertheless, it is puzzling in this northern area that 
there is so little offset of the coast where the San Andreas fault goes 
out to sea south of San Francisco, and no detectable offset of the 
edge of the continental shelf farther offshore to the northwest. An 
offset of the continental shelf of more than 50 miles occurs west of 
Cape Mendocino, but along an east-west fracture system, aligned 
differently from the San i\ndreas trend (Menard and Dietz, 1952, 
p. 273) (Fig. 10). 

Although we now appear to have acquired the rudiments of an 
explanation for the anomalies of the Coast Ranges, this explanation 
is still obscured by negations and contrary evidence. At this stage, 
almost any explanation for a set of anomalies in the Coast Ranges 
creates other, unexplainable anomalies. 

Tertiary Environments. Regardless of the anomalies in the base- 
ment rocks and the possible shifts of large segments of the area along 
through-going faults, the different types of basement have exerted a 
profound influence on the structures of the Tertiary rocks. Areas 
underlaid by Nevadan and Franciscan basement have been land or 
sea at different times and, when compressive forces were exerted, 
the areas underlaid by the weaker Franciscan basement have been 
much more deformed than those underlaid by the stronger Nevadan 

Such compression was exerted at many different times during the 
Tertiary. Some areas show a record of almost continuous deforma- 
tion through long spans of Tertiary time, and the sedimentary 
sequences frequently contain so many unconformities that it is 
diflicult to generalize any orogenic climaxes (Gilluly, 1949, pp. 567- 
569). Nevertheless, two principal climaxes seem to have occurred, 
one near the middle of the Miocene, the other early in the Pleistocene 
(Reed and Hollister, 1936, pp. 1551-1597). It is interesting to note 
that these climaxes of deformation are of about the same age as 
those which have been inferred in the Great Basin area. Effects of 

54 p. B. KING 

the early Pleistocene erogenic climax are especially striking in the 
Ventura and Los Angeles basins of southern California, where thick 
masses of Pliocene and lower Pleistocene marine and land-laid 
strata are steeply upended, and are overlaid by nearly undisturbed 
later Pleistocene deposits. This has been termed the Pasadenan 
orogeny (Stille, 1936, pp. 867-870). 

The influence on the surface features of the varied faulting and 
folding during difi^erent times since the beginning of the Tertiary 
have been portrayed in many sets of paleogeographic maps prepared 
by different geologists. The earlier, or mid -Miocene, deformation 
shaped the ridges and troughs of the Coast Ranges into about their 
present configuration, but left wide tracts of lower country still sub- 
merged ; the later, or early Pleistocene, deformation produced wide- 
spread emergence. During times of greatest submergence, the Coast 
Range area probably resembled the present offshore region of south- 
ern California, with shallow shelves, interspersed with much deeper 
troughs, and linear islands that resembled the present Channel 
Islands. During times of greatest emergence, the Coast Range area 
probably resembled the present topography around San Francisco 
Bay, with mountain ridges and intervening troughs or valleys, in 
which land-laid sediments were being deposited, and whose lowest 
parts, like the present bay, were covered by shallow, ramifying seas. 


Western North America is the region of the Cordilleran system of 
mountain ranges, which extend inland from the Pacific Coast 400 to 
1,000 miles to the Great Plains of the continental interior. The 
landscape of the region has been shaped by surface processes of 
erosion, sedimentation, and volcanism, but ultimate cause of the 
features is deeper in the crust, in processes that have deformed the 
rocks, brought about emplacement of magmas, and raised or lowered 
large sections of the surface. These processes, though spasmodic, are 
persistent through history. In considering the growth of a mountain 
system such as the Cordillera, they may be generalized into a geo- 
synclinal phase, an orogenic phase, and a post-orogenic phase. 

The geosynclinal phase was a time of sedimentation and rather 
mild crustal activity. In the Cordilleran region it persisted through 
Paleozoic time and through the first half of Mesozoic time. 

The orogenic phase began earliest in the western part of the 


Cordillera, broadly in mid-I\Iesozoic time — in places in the Jurassic, 
elsewhere somewhat later. Rocks formed in this part of the geo- 
syncline were deformed, metamorphosed, and invaded by large 
bodies of magma. The deformed rocks were raised into a land sur- 
face, from which detritus was shed westward into the Pacific Ocean 
basin, and eastward as a broad sheet into the interior of the con- 
tinent, across the remainder of the geosyncline. 

During Cretaceous time, deformation progressed eastward from 
the initial disturbed belt, folding and faulting the rocks of the Great 
Basin area, more lightly affecting those on the site of the Colorado 
Plateau, and more heavily affecting those in the Rocky Mountains 
beyond. In the southern part of the Rocky Mountains, zones of 
weakness had already been created by mountain-making during 
Paleozoic time. By the close of the orogenic phase, in Late Cre- 
taceous and Paleocene times, deformation had reached the edge of 
the present Great Plains, but it progressed no farther inland. 

The folding and faulting of the orogenic phase did not produce the 
modern topography. While the surface was raised and lowered by it, 
leveling processes of erosion and sedimentation were active and pre- 
vented development of strong relief; moreover, regional altitudes 
remained low. 

Modern surface features evolved by a multitude of crustal proc- 
esses during the post-orogenic phase, in Tertiary and Quarternary 
times. Intermontane basins subsided (as in Wyoming and Colorado), 
large areas were broken up by block faulting (as in the Great Basin), 
other large areas were overspread by lava (as in the Columbia 
Plateau), and mountains were formed by the building of chains of 
volcanoes (as in the Cascade Range). Besides, extensive regions 
were uplifted relative to their surroundings, with little internal 
deformation. The largest uplifted region centered in the Rocky 
Mountains and extended into the Great Plains and Colorado 
Plateau; it was raised mainly before later Tertiary time, but with 
diminishing uplifts into the Pleistocene. Smaller, more complex 
uplifts took place somewhat later in the Sierra Nevada and Cascade 
Range; in the Sierra Nevada, uplift was accompanied by marked 
faulting along the eastern side. 

The post-orogenic (Tertiary and Quaternary) movements raised 
the Cordilleran region to its present generally high altitude. Streams, 
quickened by the uplift and by increased rainfall during the Pleisto- 

56 p. B. KING 

cene, etched out the mountains and canyons; mountain barriers 
prevented free circulation of moisture-laden winds from the Pacific 
and heightened the climatic contrasts. Since mid-Tertiary time, 
regional relief, local relief, and climatic contrasts have been greater 
in the Cordillera than at any earlier period. 

Throughout geologic time, the Cordilleran system has been 
bordered on the west by the deep Pacific Ocean basin, floored by 
crustal material different from that of the continent. It is unlikely 
that any additional lands ever existed offshore that have since 
foundered to oceanic depths. More likely, continental area has been 
added at the expense of ocean basin by various accretionary proc- 
esses. On the other hand, land connections persisted intermittently 
along the strike of the Cordilleran system, between North America, 
Asia, and South America, as the coastal areas of all three are part of 
a circum- Pacific belt of mountain structures whose origin, like the 
North American Cordillera, extends far back into the geologic past. 


This paper was compiled largely from existing publications, but its 
context has been shaped to a considerable degree by the climate of thought 
and opinion of the writer's many geological friends and colleagues, in 
California and elsewhere in the west. Their observations and ideas, too 
numerous to recall and mention separately, have given the writer many 
insights into the interpretation of the printed record. 

In particular, one or more of the versions of the paper have been 
read by C. R. Longwell and G. D. Robinson of the U. S. Geological Sur- 
vey, J. H. Mackin of the University of Washington, and A. O. Woodford 
of Pomona College. Also, C. A. Repenning of the U. S. Geological Survey 
has furnished helpful information on the history of the Colorado River 
from his unpublished work. Their generous help and their thoughtful 
criticisms are gratefully acknowledged, and have been carefully considered 
in preparing final revisions. 

Nevertheless, decisions as to the context of the paper are those of 
the writer, and he assumes all responsibility for the views herein ex- 
pressed, whether right or wrong. As one critic remarked, no two geologists 
would summarize this complex and diverse subject in the same manner, 
either in the subjects selected for coverage or in the interpretations 
which are made of them. The perfect story of the evolution of the surface 
features of western North America is yet to be written. The present paper 
is an interim report which it is hoped will stimulate further thought, 
especially in that fascinating no-man's land which lies between the 
geological and the biological sciences. 



A complete list of references for a general review of this kind would 
include nearly all the publications on western geology. Some sort of 
selection is thus obviously necessary. Although I have not been entirely 
consistent, I have, for the most part, restricted my documentation to 
papers published in the last decade or two, and especially to papers 
presenting novel or controversial matters. Well-known or long-established 
facts of western geology are for the most part not documented. For these, 
the reader can profitably consult various general works and compila- 
tions, including those listed. 

General References 

Dunbar, C, O. 1949. Historical Geology. John Wiley and Sons, New York. 

Eardley, A. J. 1951. Structural Geology of North America. Harper and 
Brothers, New York. 

Fenncman, N. M. 1931. Physiography of Western United States. McGraw- 
Hill Book Co., New York. 

Special References 

Allen, V. T. 1929. The lone formation of California: Calif. Univ. Dept. 

Geol. Sci. Bull, IS: 347-448. 
Anderson, F. M. 1938. Lower Cretaceous deposits in California and 

Oregon. Geol. Soc. Am. Special Paper 16. 
Atwood, W. W., and W. W. Atwood, Jr. 1938. Working hypothesis for 

the physiographic history of the Rocky Mountain region : Bull. Geol. 

Soc. Am. 49: 957-980. 
Axelrod, D. I. 1957. Late Tertiary floras and the Sierra Nevada uplift. 

Bull. Geol. Soc. Am., 68: 19-45. 
Baker, A. A., C. H. Dane, and J. B. Reeside, Jr. 1936. Correlation of 

the Jurassic formations of parts of Utah, Arizona, New Mexico, and 

Colorado. U. S. Geol. Survey Prof. Paper 183. 
Bradley, W. H. 1936. Geomorphology of the north flank of the Uinta 

Mountains. U. S. Geol. Survey Prof. Paper 185-1, pp. 163-204. 
■ — — — . 1948. Limnology and the Eocene lakes of the Rocky Mountain 

region. Bull. Geol. Soc. Am., 59: 635-648. 
Bryan, Kirk. 1938. Geology and ground-water conditions of the Rio 

Grande depression in Colorado and New Mexico. Natl. Res. Comm., 

Regional Plan., Pt. 6, Upper Rio Grande, pp. 197-225. 
Burbank, W. S., and T. S. Lovering. 1933. Relation of stratigraphy, 

structure, and igneous activity to ore deposition of Colorado and 

southern Wyoming, in Ore Deposits of Western States (Lindgren 

volume). Am. Inst. Min. Metall. Eng., pp. 272-316. 
Chaney, R. W. 1938. Paleoecological interpretations of Cenozoic plants 

in western North America. Bot. Rev., 9: pp. 371-396. 

58 p. B. KING 

Crowell, J. C. 1952. Probable large lateral displacement on San Gabriel 

Fault, southern California. Bull. Am. Assoc. Petrol. Geologists, 36: 

Davis, W. M. 1925. The Basin Range problem. Proc. Natl. Acad. Sci., 11: 

Eardley, A. J. 1947. Paleozoic Cordilleran geosyncline and related 

orogeny. ./. Geol, 55: 309-342. 
Evernden, J. F., G. C. Curtis, and J. I. Lipson. 1957. Potassium-argon 

dating of igneous rocks. Bull. Am. Assoc. Petrol. Geologists, 41: 

Ewing, J. L., C. B. Officer, H. R. Johnson, and R. S. Edwards. 1957. 

Geophysical investigations in the eastern Caribbean ; Trinidad shelf, 

Tobago trench, Barbados ridge, Atlantic Ocean. Bull. Geol. Soc. Am., 

65: 719-732. 
Ewing, Maurice, and Frank Press. 1955. Geophysical contrasts between 

continents and ocean basins. Geol. Soc. Am. Special Paper 62, 

pp. 1-6. 
Ferguson, H. G., and S. W. Muller. 1949. Structural geology of the Haw- 
thorne and Tonopah quadrangles, Nevada. U. S. Geol. Survey Prof. 

Paper 216. 
Gilluly, James. 1949. Distribution of mountain building in geologic time. 

Bull. Geol. Soc. Am., 60: 561-590. 
Hill, M. L. 1954. Tectonics of faulting in southern California, in Geology 

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Climate Since the 
Late Cretaceous 

H. D. MacGinitie 

Humboldt State College, Areata, California 

r ast climates and their changes comprise one 
of the most fascinating subjects in science, since climates have so 
profoundly affected the evolution and distribution of life on the 
surface of the earth. Of one conclusion we can be sure: as we turn 
back the pages into the past, we see that world climates were 
greatly different from those of today. In order to appreciate just 
how different, we have to clear the cobwebs of the present entirely 
out of our minds. Some time ago when I was discussing with a well- 
known western botanist the fossils of Melasequoia and its associates 
found in the far north — the McKenzie basin, Greenland, the Arctic 
Islands, and Alaska — I was astonished at his remark, "Why, how 
could they grow there in all that ice and snow?" His thinking was 
tied to present conditions. Another conclusion we can be sure of, 
in thinking about past climates, is that the conditions of the Recent 
and Pleistocene have been most unusual in the history of the world. 
Our present combination of widely emergent and elevated conti- 
nents, lofty mountain ranges, and polar glaciation has probably 
existed (with recurrences in the past) for less than one-fiftieth of 
geologic time. 

As an illustration of the misconceptions that can result from 
picturing the past too closely in terms of the present, here is a brief 
quotation from a discussion of fossil arctic floras in a paper on the 
evolution of plant associations (Mason, 1947, p. 206): 

An earth, tilted on its axis relative to the plane of its orbit, will inevita- 
bly be characterized by a darkened polar area that will alternate season- 
ally with a lighted condition. The duration of the darkness will vary to 
some extent with position but will range from a few days of total darkness 
to almost six months of total darkness. By total darkness I mean the 



absence of insolation capable of being converted into heat energy and of 
light of sufficient value for use in photosynthesis. The area so involved 
will be a disc approximately 3,000 miles in diameter. Receiving no insola- 
tion, such an area would soon dissipate any residual heat in its soil and 
rock surfaces. There would result extended and bitter arctic cold through- 
out the darkened area that would affect winter temperatures for consider- 
able distances into subarctic areas. 

If we assume now that the poles have been stationary as most astron- 
omers insist that they have, and if we assume that the continents and 
ocean basins have been perpetuated in their present places through 
geological time as many geologists insist that they have, we must con- 
clude that no tropical, warm temperate, or even temperate forest flora 
could possibly live and develop in high arctic latitudes. It would be too 
cold on the one hand and too dark on the other hand. 

Such statements neglect entirely changes in world climates, the 
effects of past oceanic temperatures, and the effects of oceanic and 
atmospheric circulation. 

In order to arrive at a background for understanding later cli- 
matic changes, we may turn now briefly to the world climate of the 
late Cretaceous and early Tertiary. In the Upper Cretaceous the 
continents appear to have been smaller and more occupied by 
epicontinental seas than at any time since the Ordovician (Zeuner, 
1945, p. 164). The continents were comparatively featureless and 
rather uniformly of low elevation. North America was divided into 
two subcontinents by a great inland sea extending from the Gulf of 
Mexico to the McKenzie Delta, with an east-west breadth of about 
12° of longitude. If we could transport ourselves back to the world 
of the Upper Cretaceous, it would be like taking a flight to another 
planet, so different would conditions seem. Just how different we 
may never be able fully to know or appreciate. Tropical to sub- 
tropical floras occupied most of the southern two-thirds of the 
United States. When we investigate the late Cretaceous floras of the 
far north we find an astonishing circumstance in terms of present 
conditions. All around the North Pole, north of latitude 55°, we find 
fossil floras dominated by temperate deciduous trees. Some of the 
more significant localities of such floras are in western Greenland at 
about 75° N. Lat., in Spitzbergen at about 78° N., and in the area 
of the present Yukon Valley in Alaska at about 65° N. It has been 
shown that these northern Cretaceous floras were zoned about 
the North Pole just as floras are today farther south. In his work on 
the late Cretaceous floras of the Rocky Mountain region, Dorf 


(1942, pp. 100-103) has shown a definite change from subtropical 
to warm-temperate floras between southern Colorado and Montana. 
It appears clearly established that the area between the temperate 
northern forests and the tropical forests at the southern border of 
the United States was occupied by an ecotone characterized by a 
gradual transition from the one type to the other. In considering 
the "problem" of the northern floras (which is really no problem at 
all) we have to remind ourselves again of conditions in the past. 
All the evidence points to the fact that the seas were much warmer 
than at present. As an example of this kind of evidence the attention 
of the reader is called to a paper on Cenozoic marine climates of the 
Pacific Coast by Durham (1950), who based his conclusions on an 
intensive study of fossil reef-building corals and the associated 
invertebrate faunas. His fundamental postulate was that living reef 
corals cannot endure a minimum temperature much below 18° C. for 
any length of time. Thus, he took the figure of 18° C for the coldest 
month (February) as the limiting isotherm beyond which reef- 
building corals cannot exist. According to the fossil corals of the 
West Coast, the February isotherm of 18° C must have been located 
at about 53° N. Lat. in the late Cretaceous. That is approximately 
1,500 miles north of its present location on the coast of Lower 
California. It is difficult to appreciate the full significance of such 
a difference in ocean temperatures from that of the present. 

Today a large proportion of the ocean is close to the freezing 
temperature. Polar waters are denser than equatorial owing to the 
low temperatures ; cold water settles in the polar regions and slowly 
creeps along the sea floor to rise to tropical and equatorial regions 
where it is warmed. Warm water from within the tropics moves 
north at the surface to complete the thermal circulation. The layer 
of warm water is comparatively shallow on account of the slow up- 
welling of cold water from below. Thus, "the temperature of 
abyssal waters in the open ocean basins is conditioned by the tem- 
perature of surface waters in the polar regions" (Emiliani, 1954, p. 
854). Even in equatorial regions the abyssal waters are close to the 
polar waters in temperature. All the evidence that we now possess 
indicates that this type of circulation existed throughout the 
Tertiary. Emiliani (1958, pp. 57-58), from his tudy of a deep-sea 
core, has indicated that the abyssal temperatures in the equatorial 
Pacific in the Middle Oligocene were about 10° C, which implies a 


similar mean temperature for the polar seas. Brooks (1951, p. 1005) 
independently arrived at the same figure for polar oceanic tempera- 
tures in the Middle Tertiary. 

When warm surface water extends far to the north, atmospheric 
and oceanic circulation must profoundly modify polar climates. 
Any permanent ice caps would be impossible under such conditions, 
although winter snows north of the Arctic Circle would be probable. 
"Extended and bitter arctic cold" around the poles would not be 
possible with the indicated ocean temperatures of the Upper Cre- 
taceous and Lower Tertiary. The polar forests of those times were 
deciduous, and it is a reasonable assumption that the deciduous 
habit, at least in part, arose in response to photoperiodicity, as an 
adaptation to the long period of winter darkness in polar regions, 
rather than as an adaptation to thermoperiodicity. 

If we turn to the Lower Tertiary, there is again abundant evidence 
for the existence of a temperate deciduous forest occupying a zone 
around the Pole. Several well-known localities are well within the 
Arctic Circle. According to the best evidence available, these i\rcto- 
Tertiary Geo-floras, as they have been called (Chaney, 1947, pp. 
144-146), range in age from Paleocene to Middle Eocene. Some nota- 
ble localities (Seward, 1933, pp. 408, 478-479) are in eastern Green- 
land (70°-75° N. Lat.), Spitzbergen (78° N.), Elsmereland and 
Grinnell Land (to 83° N.), the McKenzie River Delta (64° N.), and 
the New Siberian Islands (75° N.). Farther south, to latitude 55° 
N. in the central part of the continents, are many more fossil locali- 
ties of this northern, summer-green forest. Among the characteristic 
trees are the dawn redwood, ginkgo, sycamore, alder, oak, chestnut, 
poplar, hazelnut, and many close relatives of trees now growing in 
the deciduous forests of the Appalachians and eastern China. It 
was, in no sense, a <:6>/(i-temperate flora. The species would find a 
congenial habitat at present in the mountains of western North 
Carolina at moderate elevations. 

In the early Tertiary as well as in the Cretaceous there was a 
zonal distribution of forests around the Pole that points clearly to 
the fact that the Pole was in the same place as it is today (Chaney, 
1940). There was a gradual transition from the tropical floras of the 
Gulf states to the warm-temperate floras of Yellowstone Park and 
southern Canada and thence to the temperate deciduous floras of 
the far north. We can now amend the quotation given at the begin- 


ning, and say that no tropical, warm-temperate, or even cool- 
temperate, forest flora could possibly live and develop in high arctic 
latitudes under present conditions. However, the conditions of the 
early Tertiary at high latitudes were vastly difi^erent from those of 
today. Durham (1950, pp. 1253-1254) concluded that during the 
Eocene, the 18° C isotherm was at latitude 53° to 55° N., even farther 
north than it was in the late Cretaceous. The fossil floras also indi- 
cate that the temperatures of the Lower Tertiary may have been 
higher than those in the late Cretaceous, since we have subtropical 
floras, such as that at Raton, New Mexico (Knowlton, 1917, pp. 
239-240), growing at moderate elevations, and this in spite of a 
generally emergent continent and mountain building in the Cordilleran 
region. The great inland seaway of the Upper Cretaceous was 
drained at the close of that period. Intermittent mountain building 
occurred throughout the area of the western Cordillera. The west- 
ern mountains of the early Tertiary, with a few possible exceptions, 
were of moderate elevation and did not seem to pose an insurmount- 
able barrier to plant and animal dispersals, and the general elevation 
of the continent was still comparatively low during the Lower 
Tertiary. There seems to have been none of those great continental 
upwarps that characterize the present Cordilleran region. 

By the beginning of the Middle Eocene there were at least three 
botanical provinces in western North America (MacGinitie, 1941, 
pp. 92-95). In the far- western states a subtropical forest extended 
along the coast as far north as latitude 55° N., and, with some modi- 
fications, inland at least as far as the present area of northwestern 
Wyoming. The Eocene flora of Kupreanofi^ Island in southeastern 
Alaska, at Chalk Bluffs on the west slope of the Sierra, and at 
Yellowstone Park have many characteristic plants in common. 
The low-lying shores of the Mississippi embayment were occupied 
by a warmer, practically tropical flora of quite different composi- 
tion. Far to the north were the summer-green Arcto-Tertiary 

Two Eocene floras are particularly significant with respect to 
climatic trends: (1) the flora of the London Clay at latitude 52° N. 
is of Lower Eocene age and is a tropical strand flora — not warm- 
temperate, but tropical (Reid and Chandler, 1933, pp. 47-74); (2) 
the Green River flora of Middle Eocene age, found at many localities 
in northwestern Colorado and southern Wyoming, shows the 


beginnings of climatic trends that were later accelerated. The flora 
represented by the fossil leaves and fruits was a streamside and 
lakeside flora of warm-temperate or subtropical aspect. The abun- 
dance of small and coriaceous leaves and leaflets shows that the 
vegetation on the open divides and higher ground around the lake 
basins was somewhat like our modern subtropical scrub (Chancy, 
1944). The pollen flora of the Green River gives us a picture of 
temperate forests, with oaks and conifers, occupying the surrounding 
uplands. Subhumid or even arid local conditions are indicated by 
pollen of the desert shrub Ephedra. We also find in the Green River 
flora a few representatives of the Arcto-Tertiary flora, the vanguard 
of a dispersal, down the moderate elevations of the Rocky Mountain 
axis, that was later to result in a complete replacement of the Lower 
Tertiary forests. The negative evidence of the Green River flora is 
significant. There is no pollen of grasses or other herbs except that 
of a few primitive aquatic forms. There is no pollen of the sunflower 
family or sagebrush or greasewood and the like. The modern her- 
baceous vegetation or desert shrub vegetation evidently did not 
exist in that area during the Middle Eocene (Wodehouse, 1933, 
pp. 518-522). 

A general view of the Eocene forests of the United States shows 
us essentially tropical floras along the Gulf Coast, slowly merging 
into warm-temperate floras at the north. There appears to have been 
a slow shift to the north of these warmer floras, culminating in the 
late Eocene (Chaney, 1947, p. 143). The most tropical Tertiary 
flora of the West Coast is at Goshen, Oregon. All the Upper Eocene 
floras at Comstock, Oregon, at Steel's Crossing, Washington, and 
at LaPorte, California, have a definitely tropical aspect. 

When the time boundary between the latest Eocene and the 
Lower Oligocene is crossed, we find a marked climatic change, and 
we can look down the vista of cooling and drying climates that 
finally culminated in the glaciation of the Pleistocene. There was an 
irregular, but, in the long run, a continuous change over the whole 
world toward cooler and also, in general, drier climates. This trend 
is clearly shown by the many fossil floras of the Upper Tertiary 
that are scattered over the western states, from the high plains to 
the Pacific Coast, and by the fossil floras of Europe and Asia. In a 
recent study of fossil pollen from localities in southwestern Russia, 
Bogelepov (1955, p. 988) has shown the same sequence of forest 


types and climates from Oligocene to Pleistocene as we can trace 
in the western states. This slow but inexorable climatic change 
(MacDonald, 1953) profoundly affected the evolution of vegetation 
types and their associated faunas. The Middle and Upper Oligocene 
mark the influx from the north of Arcto-Tertiary species over the 
western states. The trend toward cooler climates brought about the 
southward dispersal of a host of temperate-forest trees and the 
beginnings of the modern vertebrate faunas. By the Upper Oligocene 
we find much of the earlier tropical or subtropical elements of the 
floras displaced by northern forms whose ancestors were members 
of the Eocene Arcto-Tertiary forests. A striking aspect of the Upper 
Oligocene floras of the western states is the large number of species 
related to those now living in the forests of eastern Asia. This 
Asiatic aspect is one of the characteristic features of the western 
Oligocene floras and is due, of course, to the fact that the Arcto- 
Tertiary complex, as it dispersed southward, came down into both 
eastern Asia and the western part of North America. Dozens of 
common species in the western fossil floras have their living counter- 
parts in the forests of eastern China (Chaney, 1947, p. 145). Among 
the common genera are Acer, Ailanthus, Castanopsis, Celastrus, 
Dipteronia, Exbiicklandia , Glyptostrohus, Holmskioldia, Afetaseqiwia, 
Koelreuteria, Paliiirus, Pterocarya, Quercus (Asiatic types), and 
Zelkova. The widespread Bridge Creek flora of late Oligocene age 
occupied a large area from northern California into British Columbia 
and eastward to Montana and Colorado. It is characterized by an 
abundance of Metasequoia and Asiatic oaks. The Florissant flora of 
Lower Oligocene age, in central Colorado, is extraordinarily rich in 
warm-temperate species. It comprises many forms derived from the 
earlier Green River flora, together with representatives of the flora 
moving down from the north. 

It is a curious fact that practically none of the western Oligocene 
species having living relatives in eastern Asia was able to get into 
Mexico or into the Appalachian region. A climatic barrier that 
prevented migration either southward or eastward arose in the 
Eocene and was well established in the Oligocene. The evidence 
seems clear that this barrier was one of reduced rainfall. There is 
good evidence, obtained from a study of the Green River and 
Florissant floras (MacGinitie, 1953, pp. 52, 58), that an area of 
subhumid scrub extended across northern Mexico and northward 


across the United States in the region of the present high plains and 
the prairies. While the relationship of the Oligocene floras is mark- 
edly Asiatic, the early Eocene floras of the West Coast contained 
many species that are related to plants now living in the upland 
floras of Mexico and Central America. This indicates a rather free 
interchange of floristic elements north and south at that time. 

The later Tertiary was characterized by repeated flurries of 
mountain growth, in the Cordilleran region and westward, which 
finally culminated in the great uplifts of the late Pliocene and the 
Pleistocene. This orogeny resulted in an increasing complexity of 
climatic barriers and in the local differentiation of faunas and 
floras. According to the coral faunas studied by Durham, the 18° 
isotherm, by lower Miocene time, had moved down the West Coast 
to approximately the latitude of northern California. The climate of 
the western states in the Lower Miocene, though more genial than 
at present, shows none of the subtropical aspects of the earlier 
Tertiary (except along the coast at the south). The flora in Oregon 
and Washington and over the northern Great Basin was essentially 
a mixed deciduous-conifer forest of warm-temperate aspect, with 
many species of deciduous trees having modern counterparts in the 
Appalachian region and in eastern China. There is evidence of 
abundant summer rainfall over the area which at present has little 
or no summer rainfall. The climatic barrier to the south and in the 
plains area that was initiated in the Eocene effectively prevented 
the migration of forest species east-west and also north-south until 
well into the Miocene. There appears to have been little or no ad- 
mixture of forest species between the Appalachians and the Rocky 
Mountains in the interval between the Lower Eocene and the Lower 
Miocene. The Upper Miocene floras of the Columbia Plateau area 
contain many species of oaks, elms, beeches, maples, and the like, 
that are closely related to living species in the eastern states, indi- 
cating a dispersal path between the two areas, probably through 
southern Canada. As the climate cooled in the Upper Tertiary, the 
vegetation of the region between the Mississippi and the Rocky 
Mountains, which was at first a subtropical scrub, was slowly re- 
placed by the modern herbaceous prairie vegetation. 

Evolution of the herbs was comparatively rapid after the close of 
the Oligocene. Pollen of the sunflower family (Compositae) first 
becomes noticeable in the deposits of the Middle Miocene and such 


pollen has not surely been found earlier than the Lower Miocene. 
It is probable that the components of the existing prairies had their 
beginnings about the Middle Miocene, although the prairies as 
such do not seem to have developed until well into the Pliocene 
(Elias, 1942; MacGinitie, 1953, p. 59). The climatic change (Chaney 
and Elias, 1936, pp. 25-34) that stimulated the growth of herbaceous 
vegetation had a profound, indirect effect on the evolution of the 
mammals, since abundant new supplies of nutritious food became 
available for herbivores. The fossil localities of the later Miocene 
and Pliocene offer striking evidence of the astonishing abundance 
of mammalian life on the Great Plains and westward. 

By making comparisons between the present deciduous forest 
floras of eastern Asia and North America we can gain some idea of 
the herbs that came southw^ard with the dispersal of the Arcto- 
Tertiary flora. Here we find closely similar or identical species of 
herbs on the two continents, and these are almost entirely broad- 
leafed, perennial forms with heavy rootstocks. Hui-Lin Li (1952, 
pp. 385-405) has presented this evidence in his excellent paper on 
the related floras of Asia and America. 

The numerous Upper Miocene and Lower Pliocene floras of the 
West have been studied by Axelrod (1956, 1957) and their climatic 
significance has been well set forth. He has recognized about a half- 
dozen climatic provinces — beginnings of the sharply demarked 
climatic provinces now found in the area, but by no means as clearly 
defined. He has also shown that the average temperatures were not 
much higher than those of today, iDut that the summer maximum 
temperatures were reduced and the winter minima considerably 
raised; in other words, there was a much more equable climate. 
The frost-free season in west-central Nevada was probably three or 
four months longer than at present. Axelrod has also emphasized the 
strong evidence for a shift in the pattern of seasonal distribution 
and kind of precipitation, from summer showers and winter rain to 
the present regime of dry summers and winter snows. 

The late Miocene and early Pliocene floras from Nebraska to 
California still indicate comparatively mild conditions, with, on the 
whole, moderate rainfall. The presence of such trees as Cedrela 
(cedro) and Per sea (avocado) in the latest Miocene suggests the 
absence of severe winters, but the majority of the species are 
essentially modern in aspect and are not greatly displaced north of 


their present habitats. The northern oceans were still warmer than 
at present. On the West Coast the 18° isotherm had moved to lati- 
tude 35° N., 5° to 6° north of the existing location. There is no clear 
evidence of permanent polar icecaps at this time. The composition 
of the fossil flora that the writer has been collecting near Valentine, 
Nebraska, at latitude 43° N., the richest late jVIiocene (or lowest 
Pliocene) flora yet found in that area, indicates that the minimum 
temperatures were higher than at present and that the severe out- 
breaks of polar continental air that characterize the present winter 
climate had not yet reached their later intensity. It is surprising to 
find abundant Cedrela and Meliosma in a flora of Barstovian (late 
Miocene) age in northern Nebraska, surprising, because these genera 
are now confined to the tropics, although Meliosma grows at eleva- 
tions of 6,000 feet in the mountains of southern Mexico. A majority 
of the species, however, would find a congenial habitat in southeast- 
ern Oklahoma, some 8° or 9° to the south. 

Fr>'e and Leonard (1957) have been able to reconstruct the 
sequence of late Tertiary climatic changes on the high plains by 
studying the lithologic characters of the beds and the types of fossil 
land snails found in them. The picture is one of steadily deteriorating 
climates with decreasing rainfall, increased seasonal temperature 
fluctuations, and lowered minimum temperatures. Conditions 
essentially the same as those of the present were reached by the 
Upper Pliocene. All except the hardiest and most drouth-resistant 
trees of the once rich western montane floras had become extinct. 
The seasonal distribution of rainfall, with the cooling of the border- 
ing Pacific Ocean, had changed over the area west of the Rockies 
from adequate rainfall at all seasons to the present Mediterranean 
type with dry summers. Along the West Coast of the United States, 
and especially in California, only those plants capable of withstand- 
ing summer drouth were able to survive. Pollen studies show that 
the prairies had become well established by the Middle Pliocene. 

One of the climatic consequences of low^-lying continents and 
warm oceans are truly equable climates, with comparatively small 
seasonal temperature changes. In the modern world such climates 
are found at moderate elevations in the tropical mountains, such as 
the Tierra Templada of southern Mexico and Central America. 
The earlier floras show conclusively that the modern severe winters 
with their cold waves were nonexistent as late as the Upper Miocene. 


The cooling continued until, in the late Miocene or Lower Pliocene, 
winter snows may have occurred along the northern boundary of 
the United States, but the outbreaks of polar air so characteristic 
of the present winters appear to be a development of the late 
Pliocene. The world climatic changes of the late Tertiary were 
intensified and aggravated by the mountain building that reached 
its peak at the close of the period. One of the effects of the climatic 
changes that finally culminated in the Glacial period was an en- 
largement of the area of polar climates and a compression or shrink- 
age of the area occupied by temperate and tropical climates (Brooks, 
1949, pp. 55-62). In the earlier Tertiary the area of warm-temperate 
and tropical climates was enlarged at the expense of the area 
occupied by polar climates, but this situation was gradually reversed 
in the later Tertiary (Craig and Willett, 1951, pp. 381-382). The 
zone of polar-front weather, marked by the succession of moving 
high- and low-pressure areas, was greatly intensified, and moved 
southward. In contrast, the polar front in pre-Miocene time must 
have been nonexistent during the summer and of weak development, 
far to the north, in the winter. During the Glacial stages the zone 
of maximum cyclonic activity was even farther south than at present. 
The southward movement of the polar front and the increased 
temperature gradients caused the Glacial periods to be rainy or 
pluvial periods in the zone just south of the glaciated area. The 
large inland lakes of the Great Basin waxed and waned in response 
to Glacial and Interglacial conditions. At the times of Glacial 
advances the temperature gradient across the temperate zone, 
between the Gulf and the northern states, must have reached a 
maximum. Aianley (1955) has indicated that this temperature 
gradient could have had at least twice its present value and has 
estimated that at the time of maximum cooling the minimum annual 
temperature, on the Fahrenheit scale, was lowered about 13° near 
the Gulf, 16° at latitude 35° N., 20° in the Ohio Valley, and 27° at 
New York. 

Glaciers form wherever snowfall exceeds summer melting, and 
the maximum development of Pleistocene glaciers was in just 
those regions where at present there is maximum winter snowfall 
and cool, cloudy summers. A comparatively slight lowering of 
summer temperatures from that of the present would suffice to 
reinitiate glaciation in those areas. 


One of the distinguishing features of the Glacial ages seems to 
have been the cyclic or periodic character of the climate — the 
alternation of Glacial and non-Glacial stages. A new approach to 
the problem of "fossil" temperatures has been developed by Urey 
and his students (Urey, 1948; Emiliani, 1955, pp. 538-546). The 
relative proportion of the oxygen isotope of mass 18 in carbonates, 
for example, is inversely proportional to the temperature at which 
the carbonate was formed. The ratio of the two isotopes (mass 18 
and 16) can be determined accurately by spectrographic means. 
Although many difficulties are still to be worked out, this method 
of investigating past temperatures holds much promise and some 
interesting results have already been achieved by Urey and by 
Emiliani. Investigation of sea- bottom cores from the equatorial 
and subtropical Atlantic Ocean has shown that there were no 
periodic or cyclic temperature fluctuations during the Miocene or 
Oligocene and that the "cause responsible for Pleistocene climatic 
variations was not effective during Tertiary times" (Emiliani, 
1956, pp. 285-287). 

The distribution of living plants and animals in the present 
temperate regions can be explained only on the basis of the violent 
climatic fluctuations of the Pleistocene. The extent of these climatic 
fluctuations can hardly be overemphasized. For instance, the climate 
on the Michigan Peninsula varied from that of the frigid continental 
icecap to climates warmer than at present. Along the front of the 
glaciers there were changes from tundra through steppe to broad - 
leafed forests, and back again. Studies have indicated that the snow- 
line in all the high mountains of the world descended during times 
of glaciation. It has been estimated (Leopold, 1951; Antevs, 1954; 
Flint, 1957, p. 304) that the snowline on the mountains of New 
Mexico, for example, descended approximately 4,000 feet below that 
of the present. There is evidence from deep-sea cores that the 
surface of the ocean also underwent refrigeration, even in the tropics. 
Through the study of fossil pollen from scattered bogs, it has been 
indicated that a cool-temperate climate extended from western 
Florida to near Austin, Texas (Brown, 1938; Davis, 1946, pp. 
193-196; Potzger and Tharp, 1947, 1954). The lower levels of these 
bogs contain pollen of spruce and fir species now characteristic of 
forests around the Great Lakes. The distribution of the bogs indi- 
cates that these cool-temperate forests could hardly have been small 


isolated islands of such forest types. A few small fossil floras show 
that the climate of southern California was cooler and moister than 
at present. Such examples could be increased almost indefinitely 
(see, for example, Murray, 1957). On the other hand, studies of fossil 
pollen give evidence of the existence of oak-hickory forests during 
Interglacial periods in areas around the Great Lakes that were 
occupied by ice during the Glacial stages. 

The succession of Glacial and Interglacial stages was no doubt 
the impetus for plant and animal dispersals north-south and up and 
down in the mountainous areas. The distributional, ecological, and 
speciational changes may be inferred, as follows. As the climate 
ameliorated in an Interglacial interval, southern forms expanded 
their habitat areas to the north and upward, while withdrawing 
at the south. This northward extension continued until the climatic 
trend was reversed. Isolated, relict areas of occupancy were left 
scattered in favorable, or at least tolerated, locations south (and 
possibly west) of the main occupied area. These relict areas, for 
species dispersing northward, were on the higher elevations and on 
cool north slopes, and may have ofTered especially favorable condi- 
tions for the beginning of further speciation. Uninhabited areas, 
newly exposed by the retreating ice, may have presented somewhat 
different environments and changing competition to the vanguard 
of the northward dispersal. With a turn toward advance of the ice 
sheets, areas of occupancy tended to be driven southward, posing 
new competitors and, perhaps, putting a premium on adaptability 
to unaccustomed foods. There were many changes in local physio- 
graphic barriers, ice sheets, rivers, and lakes. 

Pollen studies indicate that vegetational changes in middle lati- 
tudes were marked. There is evidence that the prairies moved 
northward and, in response to warmer and drier conditions, also 
eastward during Interglacials. During pluvial Glacial stages prairies 
invaded the eastern areas of our south-western deserts. During such 
times of cyclic climatic changes the stimuli to admixture, hybridi- 
zation, and natural selection must have been Intensified. The effects 
on life were naturally greatest along the southern extension of the 
glacial fronts, but these effects are found far to the south (in the 
mountains of Mexico, for instance). Apparently the most favored 
areas climatically were along the Pacific Coast and the southern 
Atlantic seaboard. It is probable that there were dispersals back and 


forth along the Gulf Coast from the Appalachians to the mountains 
of eastern Mexico (Sharp, 1950, pp. 316-318). 

The world climate has undergone striking fluctuations since the 
retreat of the last continental glacier, without physiographic changes 
of any consequence. A gradual warming culminated in the "climatic 
optimum" (about 6,000 years ago), followed by a return to cooler 
conditions. Now a warming trend seems to have been renewed. 
Prehistoric sites of human habitation in the western states show 
clear evidence of great climatic instability since the retreat of the 
glaciers (Malin, 1957). Occupance layers are separated by thick 
layers of wind-blown dust that indicate intervals when the sites 
were uninhabited and when the vegetational cover was at a mini- 
mum. There are historical accounts of severe dust storms in the 
Plains states long before modern settlement and the "plowing of 
the plains." One of the latest effects of climatic changes is the 
spread of the tropical deserts from western India across the 
Mediterranean and northern Africa, and in our own Southwest 
(Wadia, 1955). 

Attention is called to two stimulating papers dealing with the 
present apparently erratic distribution of certain vertebrate ani- 
mals. In dealing with the biogeographical problems concerning some 
American genera of salamanders, Lowe (1950) has plausibly ex- 
plained the puzzling distribution of these animals by a considera- 
tion of late Tertiary and Pleistocene changes. Smith (1957) has 
treated some unusual problems concerning the distribution of mam- 
mals in the north-central states. Almost any type of erratic distri- 
bution and almost any inconsistency of distribution appear possible 
when the effects of climatic changes in the later Tertiary and Pleis- 
tocene are considered. 

The world climate has been comparatively stable throughout the 
ages, but subject, at times, to the most amazing variations. In 
emphasizing certain aspects of past climates the writer has hoped to 
furnish some hints concerning the remarkable effects of climatic 
changes on the evolution and distribution of living plants and 

Space does not permit a critical presentation of all the different 
theories and ideas as to the causes of world climatic changes (Flint, 
1957; Willett, 1953). However, in considering these causes it is al- 
ways necessary to go back to the two fundamental controls of world 


climate: (1) composition of the atmosphere and (2) amount and 
kind of solar radiation. Without doubt there have been changes in 
both of the fundamental controls during geologic time. In addition, 
it is important to note that changes in solar radiation can also affect 
the composition of the atmosphere by changing the amount of both 
water vapor and carbon dioxide. Thus the two controls are not inde- 
pendent. As far as we know now the two constituents of the atmos- 
phere most concerned with world climate are carbon dioxide and 
water, although the concentration of oxygen and ozone aloft may 
also play a part. Carbon dioxide and water both act to absorb earth 
radiation while they are comparatively transparent to short-wave 
solar radiation. Thus the surface of the earth is blanketed by these 
gases and, as a consequence, is much warmer than it would be 
without them, and daily fluctuations are much reduced. Recent 
studies of the absorption bands of carbon dioxide indicate that it 
can have a rather large effect independently of the presence of water 
vapor. Plass (1956) brought up to date the climatic effects of changes 
in the concentration of carbon dioxide. However, he did not explain 
convincingly the role of this gas in initiating world wide climatic 
changes, such as the beginning or ending of the Glacial periods. 
It is only necessary to recall again the climatic changes between the 
spring of 1956 and of 1957 to realize that circulation patterns can 
vary remarkably from one year to another without changes in the 
composition of the atmosphere. We still have much to learn con- 
cerning the true causes of these year-to-year fluctuations, let alone 
those of longer periods. The problem of the function of carbon 
dioxide as an atmospheric climatic control is most complex, and 
several important questions remain unanswered. Removal of carbon 
dioxide from the atmosphere by natural causes might lower world 
temperatures. Removal is accomplished by lime-secreting organisms, 
by the weathering of the rocks, and by the deposition of oil, coal, 
and the like. When we consider the huge limestone deposits of the 
Paleozoic and the Cretaceous, together with the accompanying coal 
deposits, we wonder if the concentration of carbon dioxide in the 
atmosphere has not been tremendously reduced since pre-Cambrian 
days. If the role of carbon dioxide in the atmosphere is of climatic 
importance, there must be some natural means of replenishing the 
atmospheric supply. The glaciation of the late Paleozoic might be 
a natural consequence of the removal of the gas in the formation of 


the Paleozoic limestone beds, but what brought the return of the 
mild climates in the Mesozoic? As far as we know now, the only 
source of carbon dioxide in any quantity is volcanism. Yet intense 
and long-continued volcanism seems to precede rather than follow 
Glacial ages. 

Carbon dioxide is more soluble in cold water than in warm. The 
present cold oceans are a storehouse for incredible amounts of CO2. 
If the climate should become warmer, large amounts of the gas would 
be released to the atmosphere. But here we see that an increase of 
carbon dioxide is an effect of, rather than the cause of, warmer 
climate. Warmer climates also mean an increase in the total amount 
of water vapor in the atmosphere. There is little question that 
changes in the concentrations of these gases tend to emphasize 
climatic fluctuations. The role of continentality in initiating or 
terminating Glacial ages has been greatly overemphasized. No 
known distribution of land and water and no known variations in 
topography are adequate to account for the changes in climate 
since the Upper Cretaceous. Anyone who is familiar with the cli- 
matic change in the central United States between the spring of 
1956 and the spring of 1957 must be aware that some other efifect 
than size, shape, and topographic relief of the continents must be 
the cause of major changes in circulation patterns. Terrestrial factors 
are capable of increasing climatic contrasts and channeling currents 
of air and water, but they cannot, on the basis of our present knowl- 
edge, affect the climate of the earth as a whole (Willett, 1953, pp. 
58-59). The solution of the problem of changing climates is not to 
be found in the theories of wandering poles and drifting continents. 
Any forms of these theories yet developed directly contradict the 
known facts concerning the distribution of fossil floras. In addition 
to the negative biologic evidence there is also direct physical evidence 
against the idea of wandering poles. From his study of the orientation 
of magnetic grains in sediments, Hospers (1955) has "concluded 
that the large amount of polar wandering suggested by Kreichgauer, 
Koppen and Wegner, and Milankovitch cannot be reconciled with 
the new data. If ... at all ... it ha& not exceeded 5°-10° since 
Eocene times." 

The evidence of a recent warming of world climate is clear. If the 
present trend toward warming and drying continues, our south- 
western deserts will eventually expand into Oklahoma, Texas, and 


Kansas, and the prairies will move eastward and northeastward. 
Is this warming and drying trend due to the enormous amounts of 
carbon dioxide being returned to the atmosphere through the 
burning of fossil fuels, as Plass believes, or is it due to some secular 
change in solar radiation? In this connection, accumulating evidence 
indicates that short-wave and corpuscular radiations from the sun 
appear to fluctuate rather markedly, and that the amounts of such 
radiation absorbed by the outer atmosphere may produce rather 
large effects in modifying atmospheric circulation patterns (Craig 
and Willett, 1951 ; Willett, 1953, pp. 62-69). 

In his study of past climates the writer has become convinced 
that the fundamental cause of world climatic changes has its origin 
in small fluctuations in the amount and kind of solar radiation 
(see also Willett, 1953, pp. 57, 61; Flint, 1957, pp. 481-509). Opik 
(1958) has developed what is perhaps the first plausible mechanism 
for long-term changes in solar radiation. These solar changes are 
considerably modified by the resulting changes in ocean tempera- 
tures, concentrations of H2O and CO2, and, on a more local scale, 
by topographic changes. The problem is a complex one, but the 
writer, on the basis of present evidence, always returns to the 
conclusion that the primary cause lies outside the earth itself. 
Brooks' solar-topographic hypothesis (Brooks, 1951, pp. 1016-1017) 
offers an adequate and satisfying explanation of the observed 


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pp. 378-390. 
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development and uses. Florida Geol. Survey, Geol. Bull. 30. 
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High Plains. Geol. Soc. Am. Special Paper 41. 
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New York. 
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Ecology, 28: 274-280. 

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The Role of Physiology 
in the Distribution of 
Terrestrial Vertebrates 

George A. Bartholomew 

Department of Zoology, University of California, 
Los Angeles 

1 he inclusion of this paper in a symposium on 
the origins and affinities of the land and freshwater fauna of western 
North America may be taken as an expression of the tacit assumption 
of most biologists that physiology plays a determining role in the 
complex problems of animal distribution. I have accepted this 
assumption, but in attempting to formulate conclusions available 
from present knowledge, I find that the relation of physiology to 
distribution in terrestrial vertebrates is neither direct, simple, nor 
obvious. All that a brief essay such as this can do is offer a point of 
view with regard to certain groups. To attempt a taxonomically 
extended treatment of a topic so broad would be presumptuous, and 
I shall concentrate on the animals that I know best — the amniotes. 
The literature cited is not exhaustive, but most of the papers are 
quite recent, and all include extensive bibliographies that offer 
convenient access to the literature relevant to the role of physiology 
in the distribution of terrestrial vertebrates. 

Biology is a continuum, but we biologists, because of our limita- 
tions, divide ourselves into categories, and then we pretend that 
these categories exist in the living systems that we study. From the 
functional point of view, of course, an animal is indivisible, and 
physiology is not in any sense an isolatable component of an organ- 
ism. If physiology is defined as the study of vital functions, it be- 
comes inseparable from morphology and behavior. When one defines 
physiology as broadly as this and then undertakes to discuss its role 
in distribution, one attempts the impossible — nothing less than an 



interpretation of all the ways in which the dynamic capacities of an 
organism influence its distribution. In the present paper therefore, 
we shall restrict our discussion to the kinds of data that comparative 
physiologists and physiological ecologists gather. In this way we can 
confine our topic to reasonable limits and also insure that we have 
at least some data on which to base our conjectures. 

Once an organism has been identified, two of the most obvious 
questions to ask are first, "How many are there?" and second, 
"Where do they live?" Simple as these questions are, they are 
usually extremely difificult to answer. But let us assume that, by 
years of unremitting effort, we have succeeded in obtaining approxi- 
mate answers to these obvious questions. Since abundance and dis- 
tribution may be considered as different aspects of the same problem 
(Andrewartha and Birch, 1954, p. 5), two additional and inextricably 
interlocked questions inevitably present themselves: first, "Why are 
there as many as there are?" and second, "Why do they live where 
they do?" We may start our inquiry concerning the role of physi- 
ology in distribution by asking the straightforward question, 
"What information do physiologists supply that relates more or less 
directly to the above questions, particularly to the last one, which is 
a major concern of most students of distribution?" Unfortunately it 
is useless to pretend that answers to these questions can supply us 
with much that is specifically and immediately relevant; first, 
because of the complexity of both physiology and distribution, and 
second, because physiologists have only infrequently considered 
these questions. 

It is obvious that an organism's distribution is a complex integra- 
tion of all facets of its present biology, together with a past history 
in which chance has played an indeterminable but not necessarily an 
unimportant role. Moreover, the occurrence of an organism is 
dependent not only on a complex summation of its present and past 
activities plus chance; it is often profoundly influenced by the occur- 
rence or non-occurrence of other organisms, and these organisms 
may be of quite a different nature and have difi'erent physiological 
tolerances, requirements, and reactions from the one whose distri- 
bution is being studied. 

Viewed in this context it is obvious that most present knowledge 
of the physiology of terrestrial vertebrates is likely to have either no 
apparent distributional importance or to have a contribution so 


broad that It is of little assistance In the analysis of any specific 
distribution. The aspects of physiology that are directly pertinent 
to distribution — and these are the only ones with which it Is ordi- 
narily possible to deal — are not those concerned with internal inte- 
gration, but are those that cither involve the animal's exchanges 
with the environment or control and regulate these exchanges, and 
those that affect reproductive performance. The exchanges referred 
to involve food, water, heat, radiation, and metabolic wastes, and 
are usually studied in terms of rates and limits. The factors con- 
trolling reproductive performance under natural conditions are at 
present only in the first stages of analysis (Lack, 1954) and offer a 
challenging series of problems related to distribution. 

Since an organism is Inseparable from its environment, any person 
who attempts to understand an organism's distribution must keep 
constantly in mind that the item being studied is neither a stuffed 
skin, a pickled specimen, nor a dot on a map. It is not even the live 
organism held In the hand, caged in the laboratory, or seen in the 
field. It is a complex Interaction between a self-sustaining physico- 
chemical system and the environment. An obvious corollary Is that 
to know the organism it is necessary to know its environment. If 
this view is valid, and if the distributlonally relevant data of physiol- 
ogy relate to the dynamics of the complex Interaction between 
organism and environment, then to evaluate the contribution of 
physiological data to knowledge of distribution, one must first 
examine the environment critically, analytically, and in detail. 
Obviously a searching examination of the environment cannot be 
made In a general discussion addressed to only the broad aspects of 
the problem, but for purposes of comparison we may consider the 
sea. From the point of view of this discussion, the most conspicuous 
feature of the open sea is that it offers few places for an animal to go 
to avoid unfavorable conditions that may develop locally. If one 
excludes shore and estuarlne areas, the number of aquatic micro- 
habitats that offer significant possibilities of escape from unfavorable 
conditions is negligible. We can therefore expect that marine organ- 
isms will often be limited in distribution by physical conditions, 
particularly temperature. In contrast, the terrestrial environment 
and to a lesser degree the freshwater habitat offer many mlcrohabl- 
tats that make available an enormous range of temperature, mois- 
ture, and radiation. 


On land an almost infinite series of physical situations is available. 
Plants, generally speaking, meet the impact of the terrestrial environ- 
ment head on, although of course they in turn modify the physical 
environment by adventitious group activity. The individual plant 
cannot select its habitat ; its location is largely determined by the 
vagaries of the dispersal of seeds or spores and is thus profoundly 
affected by chance. Because of their mobility and their capacity for 
acceptance or rejection terrestrial animals, in contrast, can and do 
actively seek out and utilize the facets of the environment that 
allow their physiological capacities to function adequately. This 
means that an animal by its behavior can fit the environment to its 
physiology by selecting situations in which its physiological capaci- 
ties can cope with physical conditions. If one accepts this idea, it 
follows that there is no such thing as The Environment, for there 
exist as many different terrestrial environments as there are species 
of animals. 

We can now take a somewhat closer look at the relation of physi- 
ology to distribution. First of all, we must consider what questions 
the student of ecological animal physiology is trying to answer. (A 
more realistic approach might be to ask to what questions can con- 
veniently obtained physiological data be applied.) It usually de- 
velops that after much laborious and frustrating effort the investi- 
gator of environmental physiology succeeds in proving that the 
animal in question can actually exist where it lives. It is always 
somewhat discouraging for an investigator to realize that his efforts 
can be made to appear so trite, but this statement does not belittle 
the ecological physiologist. If his data assist the understanding of 
the ways in which an animal manages to live where it does, he makes 
an important contribution to the study of distribution, for the pres- 
ent is necessarily a key to the past. 

The contributions of physiological knowledge to an understanding 
of distribution are necessarily inferential. Distribution is a historical 
phenomenon, and the data ordinarily obtained by students of physi- 
ology are essentially instantaneous. However, every organism has a 
line of ancestors which extends back to the beginning of life on 
earth and which, during this immensity of time, has invariably 
been able to avoid, to adapt to, or to compensate for environmental 
changes. By examining in retrospect this prolonged exercise in the 
art of survival and at the same time bearing in mind the physio- 


logical capacities of living forms, it is possible to adduce some obvi- 
ous, familiar, and general statements about the broad relations of 
physiology to the distribution of terrestrial vertebrates. Such an 
effort is greatly facilitated by application of Liebig's law of the 
minimum (Hesse, Allee, and Schmidt, 1951, p. 26), one of the most 
useful of generalizations to which an ecological physiologist can turn. 
In the context of the present essay this generalization may be stated 
thus : the distribution of a species will be controlled by that environ- 
mental factor for which it has the narrowest range of adaptability or 
control. The limiting factors will of course be different at different 
stages in the life cycle and will vary from group to group and from 
time to time. 

The evolution of terrestrial vertebrates has been characterized 
first, by increasingly effective homeostatic mechanisms and second, 
by increasingly variable and flexible behavior. Together these two 
trends mean that the evolutionary history of vertebrates has resulted 
in increasing physiological competence and, at the same time, 
increasing capacity to select from the environment the special physi- 
cal situations that are appropriate to an animal's physiological 
capacity. This increase in ecological versatility allows some forms 
to occupy a remarkably diverse array of habitats and makes the 
determination of distributionally limiting factors an intriguingly 
subtle problem. If we examine the major groups of terrestrial verte- 
brates with regard to the aspects of their physiology that are likely 
to be limiting, we can make several obvious general observations. 

Amphibians. Amphibia show poor osmoregulation (see Sawyer, 
1956, for a recent review), poor control of water loss (Cohen, 1952; 
Thorson, 1956), and complete lack of physiological thermoregulation 
other than the passive cooling incidental to dehydration. 

Reptiles. Of the major homeostatic capacities reptiles lack only 
effective physiological thermoregulation, and they compensate for 
this with surprisingly effective behavioral thermoregulation (Cowles 
and Bogert, 1944; Bogert, 1949; Norris, 1953). A dramatic example 
of behavioral thermoregulation is shown by the Andean lizard 
Liolaemus multiformis, which under some circumstances can achieve 
body temperatures as much as 30°C above air temperature (Pear- 
son, 1954a). 

Birds. Birds have reached a level of homeostatic control com- 
parable to that of mammals. Considering their small size, they have 


remarkable powers of thermoregulation. Their capacity to tolerate 
severe hyperthermia allows them to operate effectively at remark- 
ably high environmental temperatures (Bartholomew and Dawson, 
1958), and their high rate of heat production, effective insulation, 
and peripheral vasomotor control allow them to operate at extremely 
low environmental temperatures (Scholander et al., 1950a; Wallgren, 
1954; Irving et al., 1955). With regard to water, however, birds have 
less independence of the environment than do many mammals. 

In the birds that have been measured, evaporative water loss 
exceeds metabolic water production even under resting conditions. 
(Bartholomew and Dawson, 1953). This unfavorable relationship 
necessitates a high intake of water either through drinking or the 
eating of succulent foods, which places birds, particularly small 
ones, at a disadvantage with regard to the occupancy of arid re- 
gions (Bartholomew and Cade, 1956). 

Documented records of both daily and seasonal torpidity are now 
available for adult birds in four different orders (see Bartholomew, 
et al., 1957, for a summary). Although the advantages of torpidity 
with regard to energy conservation are obvious for birds of extremely 
high metabolism, such as humming birds (Pearson, 1954b), or for 
birds dependent on periodically unavailable food (swifts, poor-wills, 
and nighthawks) , the limited number of species and the fragmentary 
nature of the available data do not warrant rigorous distributional 

Mammals. One of the most impressive attributes of mammals is 
the excellence of the physiological homeostasis that they have at- 
tained ; one form or another is able to meet head on the most severe 
naturally occurring environmental conditions of heat, cold, or 
aridity. Hence, any taxonomically extensive generalizations concern- 
ing physiologically determined distributional limits are apt to be 
particularly unsatisfactory in this group. Large arctic mammals by 
the excellence of their insulation and vasomotor control can main- 
tain a difference of as much as 70° C between air and deep body 
temperatures without increasing metabolism above basal level or 
decreasing the deep body temperature (Scholander et al., 1950b; 
Scholander, 1955). 

Most medium to small-sized mammals living in areas of very high 
environmental temperatures avoid heat stress by being fossorial, 


nocturnal, or both. Such patterns of behavior are often impossible 
for large mammals, but if they can sweat and if drinking water is 
available, they are able to cope with any high air temperatures that 
occur naturally. In at least one large mammal, the dromedary camel 
{Camelus dro^nedarius) , tolerance of hyperthermia contributes 
significantly to effectiveness of adaptation to high ambient tempera- 
tures by allowing heat storage rather than by requiring heat dissi- 
pation through evaporation of water (Schmidt-Nielsen et al., 1957). 

The availability of surface water is of no importance in the distri- 
bution of many desert rodents. Several species in the family Hetero- 
myidae lose so little water through evaporation, excretion, and 
defecation, that as long as they are not forced to resort to evaporative 
cooling, they are able to produce all the water they need through 
their own metabolism even while subsisting on a dry diet (see 
Schmidt-Nielsen and Schmidt-Nielsen, 1952, for an extensive 
review). It has yet to be demonstrated, however, that large herbiv- 
orous mammals can produce enough metabolic water while on a dry 
diet to compensate for water losses. Unlike a rodent, the larger 
mammals cannot escape the heat of the day by burrowing and must 
therefore depend in part on evaporative cooling to prevent harmful 
hyperthermia. Nevertheless, the capacity of some large herbivores 
to go without water is impressive. A dromedary camel exposed to the 
full heat load of radiation from sun and ground during the summer 
at a Saharan oasis survived a 17-day period on a dry diet without 
water (Schmidt-Nielsen et al., 1956). Its performance is attributed to 
its capacity to tolerate a loss in body water equivalent to 30 per cent 
of its body weight. (Most mammals cannot tolerate more than 12 
per cent dehydration.) 

One may summarize by saying that by a combination of behavior 
and physiology mammals can successfully occupy all but the most 
extreme environments on earth without anything more than quanti- 
tative shifts in the basic physiological pattern common to all. With 
regard to dietary limits their performance is almost as impressive. 
For example, ruminant artiodactyls can subsist largely on cellulose 
because of the synthetic capacity of the bacterial flora of the rumen 
(see Blaxter, 1954, for a discussion). (The existence of a fauna of 
ruminant ungulates of course is an essential feature for the survival 
of populations of many of the larger mammalian carnivores.) How- 


ever, a deficiency in critical trace elements in the soil apparently 
represents an unbeatable physiological problem even to ruminants 
(see Underwood, 1956, for a comprehensive review). 

In several groups of mammals there is an additional capacity in 
the repertory of environmentally relevant physiology, namely hiber- 
nation, which allows smaller mammals to avoid for weeks or even 
months climatic conditions too severe for them to cope with other- 
wise (see Lyman and Chatfield, 1955, and Kayser, 1955, for recent 
reviews). Prolonged periods of dormancy may occur at any season, 
and the limited data presently available indicate that there is no 
clear-cut difference between hibernation and estivation except the 
environmental temperatures at which they occur (Bartholomew and 
Cade, 1957). Daily periods of torpor are known among mammals 
only in bats (Hock, 1951). Since hibernating mammals can arouse 
spontaneously from their torpor, this capacity significantly extends 
the range of environmental conditions which they can occupy, by 
allowing them to confine their activity to the periods of the day or 
the year when environmental conditions are favorable. 

In addition to the capacities summarized above, many animals 
including members of all classes of vertebrates have the capacity to 
acclimate to environmental changes. This process of acclimation 
allows the organism to accommodate its own range of control to a 
w^ide range of physical conditions (see Bullock, 1955, for a review of 
temperature compensation in poikilotherms). 

Now that some of the relevant physiological capacities of verte- 
brates have been surveyed very briefly, we may consider some ideas 
concerning the relation of physiological tolerance to distribution. An 
environmental factor that exceeds the limits of an animal's physio- 
logical tolerance will control its distribution, but only at irregular 
intervals in time and only on that perimeter of its range where the 
factor is becoming extreme. On most of the boundaries of the 
animal's range, the distributional limits are set by factors other than 
simple physiological tolerance to the given environmental factor. 
Familiar examples demonstrating that physiological incapacity to 
meet environmental extremes is a factor in distributional control 
only at isolated points in time and space are ofTered by the distribu- 
tion of many species of vertebrates the ranges of which impinge on 
the deserts of southwestern United States and northern Mexico. The 
heat and aridity of the desert may actually limit the occurrence of 


these species, but the desert comprises only part of the perimeter of 
their ranges. On other parts of the perimeters, different factors must 
be Hmiting. 

Locally the distribution of many amphibians and reptiles is often 
determined by aridity and temperature, but even these animals, 
which are relatively dependent on climate, are able by their diurnal 
and seasonal patterns of activity to select from apparently unfavor- 
able physical circumstances the environmental conditions that do 
not exceed their particular physiological tolerances. A result is that 
while it is possible to reason from physiological data to the conditions 
necessary for survival, it is not possible to reason from distributional 
data to physiological capacities in the absence of detailed ecological 
knowledge. Two examples may be cited. Thorson (1955) found that 
the spade-footed toad, Scaphiopus hammondii, which occupies arid 
regions, actually takes up water more slowly than do frogs from 
more moist environments. In western Australia, frogs of the genus 
Neohatrachiis frequent clay soils in which they cannot dig deep 
burrows, whereas all species of the genus Heleioporus occupy friable 
soil in which they can dig deep burrows. In the various species of 
Neobatrachus, rate of water uptake increases with increasing aridity 
of habitat, whereas in Heleioporus no such correlation can be demon- 
strated. Presumably because of the microhabitat occupied during 
estivation, rapidity of water uptake by Neobatrachus is of selective 
importance, whereas for Heleioporus it is not selectively important 
because the latter can dig deep enough to remain in damp soil where 
rapid recovery from seasonal dessication is not critical (Bentley, 
Lee, and Main, 1958). 

The behavioral and physiological virtuosity of birds and mammals 
makes the assignment of distributional control to environmental 
extremes particularly difficult even after detailed studies of ecology 
and local distribution, although some documented instances are 
available in the literature. Opossums {Didelphis marsupialis) on the 
northern limits of the species' distribution frequently suffer frostbite 
of ears and tail and it may be that low temperatures per se are limit- 
ing the northward spread of this species (see Hamilton, 1958, for a 
discussion). At the opposite extreme, Alaska fur seals {Callorhinus 
ursinus) become overheated at air temperatures only a few degrees 
above 0° C, and death from heat prostration is frequent during the 
commercial seal drives in the Pribilof Islands (Bartholomew and 


Wilke, 1956). The inability of these fur seals to prevent hyper- 
thermia even at low air temperatures and low levels of solar radia- 
tion may restrict the location of their breeding grounds to the Bering 
Sea area. In contrast to such situations, wherein environmental 
temperatures may be limiting, several species with very different 
capacities for thermoregulation may successfully occupy the same 
demanding environment. Brown Pelicans {Pelecanus occidentalis) , 
Great Blue Herons (Ardea herodias), and Western Gulls {Lams oc- 
cidentalis), although having comparable thermoregulatory abilities 
as adults, differ markedly in this respect while young. The first 
two species are altricial; the third is precocial. Nevertheless all 
three species nest successfully in unsheltered rookeries on the 
desert islands of the Gulf of California, where they are subjected to 
high air temperature, intense solar radiation, and extreme aridity. 
They are able to breed despite these unfavorable physical conditions 
and despite the profound differences in the capacity for temperature 
regulation of the young, because the parents in the two precocial 
species are extremely attentive and shade the nestlings during the 
hours of intense heat, thus behaviorally compensating for the phys- 
iological limitations of the young (Bartholomew and Dawson, 1954). 
There can be no doubt that in areas such as the deserts, polar 
regions, and high mountains where the environment is so demanding 
that life is extremely difficult or impossible, physiological capacities 
and tolerances limit the distribution of all groups of vertebrates. 
But if one considers the continental areas as a whole and amphibia 
and amniotes only, it becomes surprisingly difficult to find distribu- 
tional limits that are set by physiological tolerance to physical 
factors in the environment, except for those species that occupy one 
of the unusually demanding environments such as mentioned above. 
Ordinarily one species replaces another geographically. Such replace- 
ment may of course on occasion be caused by physiological differ- 
ences between the forms in question. The problems of sympatry and 
competition are so complex, however, that in the absence of detailed 
ecological and physiological knowledge, it seems unwise to assume 
that in an area of contact or overlap each of a pair of geographically 
complementary species is distributionally limited by its physiological 
capacities. (See Dumas, 1956, for a carefully analyzed study of the 
ecological and physiological responses to temperature and humidity 
in two sympatric salamanders.) Although the topic has been one of 


great interest and enormous theoretical importance since the time of 
Darwin, a satisfactory evaluation of the role of competition in the 
determination of distribution in general is obviously impossible at 
the present time. As Hutchinson (1957, p. 419), has pointed out: 

The only conclusion that one can draw at the present from the observa- 
tions is that although animal communities appear qualitatively to be 
constructed as if competition were regulating their structure, even in the 
best studied cases there are nearly always difficulties and unexplored 
possibilities. These difficulties suggest that if competition is determinative 
it either acts intermittently ... or it is a more subtle process than has 
been supposed. 

My obvious reluctance to accept the direct role of physiology in 
the determination of distribution of species probably needs defense 
from the students of geographic variation in western North America, 
where so many subspecies and species have been shown to have 
limits that can be readily correlated with vegetation types and hence 
indirectly with conditions of the physical environment. Since such 
correlations are striking, it is often assumed that the distributional 
limits are physiologically determined and that closely related species 
or even subspecies are characterized by physiological differences. 
There is little a priori reason to presume that animals are any less 
variable in physiology than in morphology. Aside from coloration, 
however, the minute morphological differences separating subspecies 
or closely related species are not necessarily adaptive; similarly, 
small physiological differences between closely related forms need 
not be adaptive. If physiological differences are not adaptive, they 
have little significance in determining the distribution of the forms 
that possess them. Moreover, when one deals with the smallest 
taxonomic categories — subspecies and obscurely delimited species — 
and finds adaptive physiological differences, it is impossible to state 
categorically whether or not these differences allow or follow 
changes in distribution. 

In view of the difficulty of demonstrating physiologically deter- 
mined distributional limits and physiologically determined competi- 
tive success in terrestrial vertebrates, it is reasonable to turn to 
habitat selection and ecological tolerance for help in understanding 
distribution. The correlation of habitat with both local and general 
distribution is familiar to all field zoologists. It is a well-documented 
fact that discontinuities of populations of terrestrial vertebrates 


coincide with changes in plant formations and soil types. These 
discontinuities in distribution are related to active selection of 
habitat by the animals involved. The ability to recognize and react 
to factors in the environment, in such a manner that a given species 
characteristically occupies a certain type of situation, is of course 
referred to as habitat selection. As Miller (1956, p. 269) has pointed 
out, "It does not imply selection of a habitat coincident with the 
limits of environmental tolerance of the species but usually reaction 
to some feature of the habitat far within those limits . . ." In areas 
of great altitudinal relief such as western North America, many 
clear-cut examples of the roles of habitat selection are available 
(Miller, 1942). A spectacular instance is ofTered in the mountains of 
northern Nicaragua where tropical rain forests interdigitate with 
montane pine forests and each vegetational complex supports its 
own characteristic avifauna, so that boreal species such as the Red 
Crossbill (Loxia curvirostra) and tropical species such as the Jacamar 
(Galbula ruficauda) may live only meters apart (T. R. Howell, 
personal communication). Equally spectacular examples can be 
cited for other groups. An unusually clear-cut example of the role of 
the substratum in determining distribution is afforded by the fringe- 
toed lizards of the iguanid genus Uma of the deserts of southwestern 
America. Members of this genus occur only on aeolian sand, and the 
changes in distribution of present day forms are determined by the 
movements of the sand dunes that they occupy. Despite the total 
dependence of this genus on a specific and limited physical habitat, 
it occupies a broad altitudinal zone extending from 244 feet below 
sea level to 3,700 feet above sea level (Norris, 1958). 


It is the thesis of this paper that although the distribution of 
many marine and aquatic organisms and many terrestrial inverte- 
brates may be explicable in terms of physiological tolerances, no 
such general statement can at present be made for terrestrial 
vertebrates. The relationship between physiology and distribution 
becomes progressively more obscure as one ascends the phylogenetic 
series of vertebrates. The homeostatic mechanisms of terrestrial 
vertebrates and the exceedingly complex relations which their 
behavior allows them to maintain with the physical environment 
make any assignment of causality between physiology and distribu- 


tion extremely difficult. In the light of present knowledge it appears 
more reasonable to look for the determinants of distribution of the 
higher vertebrates in behavioral and ecological factors rather than 
in terms of physiological tolerances. Available knowledge of physi- 
ology helps to explain how a vertebrate can live where it does, but 
rarely reveals why it does not occur beyond the observed limits of 
its distribution. Physiological tolerances are permissive in that they 
set the environmental parameters within which a species can occur. 
By habitat choice, seasonal and daily patterns of activity, selection 
of appropriate microhabitats, and acclimation, however, a species 
with sufficient ecological tolerance can assemble the environmental 
conditions necessary for survival and reproduction out of remarkably 
unlikely arrays of environmental factors. Consequently, assignments 
of distributional limits on the basis of assumptions about the physi- 
ology of an animal are unrealistic. An animal's distribution represents 
an integration of all the factors — behavioral, ecological, competitive, 
reproductive, or other — that limit its existence as a population. It 
is, therefore, unrewarding to attempt to explain distribution solely 
in terms of the data presently available from physiological studies, 
which because of the orientation of most physiologists, have been 
neither sufficiently varied taxonomically, sufficiently intensive from 
the standpoint of species and populations, nor often enough oriented 
toward ecology to yield data adequate for the analysis of problems 
as subtle as those involved in distribution. 


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Evidence from Fossil Land Mammals on the 
Origin and Affinities of the 
Western Nearctic Fauna 

Donald E. Savage 

Museum of Paleontology, University of Calif or?iia, 


1 he living nonmarine mammal fauna of Ne- 

arctica is divided into 9 orders. These orders are subdivided into 
about 28 families, about 100 genera, and a minimum of about 175 
species. Approximately 75% of its orders, 60% of its families, 30% 
of its genera, and 1-6% of its species are also found in the parts of 
eastern Asia not occupied by tropical rain-forest. 100% of its orders, 
about 65% of its families, 15% of its genera, and 3% of its species 
occur in the parts of South America not occupied by tropical rain 
forest. But these imposing numbers and their graphic demonstration 
in Fig. 1 do not afford a satisfactory basis for concluding whether the 
mammals of North America have closer affinity with those of eastern 
Asia or with those of South America. The number of taxonomic 
units in the living ensemble and the taxonomic percentage com- 
parisons are figures that serve only as a crude index of the total 
characteristics and affinities. Living mammals are but a small part 
of the total land mammal fauna of this continent, for many more 
lived here in the past, and the exterminated forms must also be 
studied if our knowledge of origins and affinities is to be complete. 
Beginning in force with Sclater, Darwin, Wallace, and Lydekker, 
with tremendous propulsion from Osborn (1910) and Matthew 
(1915), and with recent thorough refinement by Simpson (1947, 
1953), we see the development of our present knowledge of mam- 
malian biogeography, involving millions of years of history. Bio- 
geography "must reckon with time as well as with space" (Hesse, 
Allee, and Schmidt, 1937, 1951, p. 121). The attributes of a living 




fauna are to a large degree, then, reflections of the paleodynamics 
of the fauna. 

Our symposium theme. Origin and Affinity, involves certain rea- 
soning and inferences, probably elementary to most zoogeographers, 












































^1. A graphic demonstration of the approximate percentage of 
living nonmarine mammalian taxonomic units of North America that are 
also found in East Asia and in South America respectively. 

certainly basic to paleozoogeographers, that can appropriately be 
acknowledged and reviewed; for they form a philosophic back- 
ground to our interpretations. It is fitting that a paleontologist 
make the initial review of this background for he is particularly 
concerned with the secularly developed phases in the evolution 


and dispersal of organisms and with tiie ideas tiiat pertain thereto. 
Certain criteria for determination of origin, as Hsted below, apply 
particularly to the expanded field of paleozoogeography — a field 
extending through millions of years. 

Criteria for Determination of Origin 

1. The earliest record of the group in the proposed area of origin. In 
the absence of strong contradictory data, the district in which there is the 
oldest, that is, earliest, occurrence of a group may be taken as the area of 
origin. This procedure is elementary but essential, just as Steno's ride of 
superposition is an essential in the science of stratigraphy (Steno's rule 
states that in an undisturbed succession of sedimentary rocks, the oldest 
formation is at the bottom, the youngest on top.) For example, on this 
criterion, we may claim that Africa, perhaps the restricted area in North 
Africa that was the southern coastal plain of the old Tethyan Seaway, was 
the area of origination of the Proboscidea and that the armadillos origi- 
nated in South America. These statements are based primarily on the 
earliest records. In the case of the proboscideans such claims should be 
employed only as exploratory models of interpretation because of the 
paucity of the fossil record of early forms. Proboscideans may have 
originated in central Asia, as some workers suggest, rather than in North 
Africa; but if the record of late Eocene warm-temperate, savanna, 
gallery-forest habitats in Asia becomes better known, yet does not pro- 
duce remains of proboscideans or pre-proboscideans, the probability 
becomes greater that Africa was indeed the homeland. Already the rela- 
tively complete Eocene records in Europe and in the United States make 
it probable that these territories were not centers of proboscidean origin. 
In the case of the armadillos, contemporary and comparable environ- 
ments are relatively well represented in North America, and we believe 
that armadillos would have been found If they had lived here as early as 
in South America. 

2. An earlier record of progenitors in the proposed area of origination. 
From the standpoint of paleontology, this, along with the first criterion, is 
the ultimate basis for definition of center of origin and dispersal. These 
criteria demonstrate that final statements as to the origin of any taxo- 
nomlc unit of animals whose classification is supported by morphology of 
geologically preservable parts must be based on the complete stratigraphic 
record of the unit. 

3. A group probably originated in the area wherein It has greatest 
taxonomic differentiation (see, also, Emerson's conclusion 13 (1952, p. 224). 
Taxonomic differentiation is here taken as the best available Index of 
general evolutionary differentiation. 

This criterion Is based on the reasoning that with given equality of 
opportunity to diversify, the group has had more time to adapt to the 
various niches, hence has greater antiquity in the area of greatest diversi- 

100 D. E. SAVAGE 

fication. Mayr (1946) uses this criterion extensively; his example (p. 13) 
of the lark family is illustrative: "The larks are a family of more than 70 
species and are represented in all parts of the Old World. Only certain 
subspecies of a single species occur in the New World. There can he no 
shadow of doubt concerning the family's Old World origin" [italics are 
mine]. Perhaps not in Mayr's example but in many similar statements, 
such an approach may be very tenuous and often misleading unless bio- 
stratigraphic, sedimentologic, mineralogic, and geochemical studies indi- 
cate that the proposed center of origin was comparable in ecologic diver- 
sity with the inferred non-origination areas. 

The interpreted center of dispersal, as evidenced by the distribution 
and case history of living forms, may be altogether different from the 
center of origin, particularly in the bradytelic phyla. The environment of 
origin for many groups of organisms has shifted across great distances 
since their inception. See, for example, Chaney (1936, 1940), Axelrod (1952 
and earlier papers), and Stebbins (1950, Chap. XIV). 

A complication may arise also in the consideration of animal groups 
that become less diversified in the later episodes of their phyletic history 
for reasons that may not be apparent in the sedimentary record. The liv- 
ing Didelphoidea (opossums) are most diversified and include possibly 
the most advanced members in the Neotropical region, but all living 
didelphoids show less morphological variation than the late Cretaceous 
Nearctic forms that are presently considered members of the group^ Thus 
we conclude that the Neotropics are an asylum of diversified didelphoids 
and that these Neotropical forms had their ecologic counterparts in late 
Cretaceous Nearctica. Moreover, we must look for the origin of the 
didelphoids in sediments that are lower in the stratigraphic column than 
the presently known fossil sites. 

Finally, the third criterion is the more revealing for the smaller taxa. 
Later diversification within an order, for example, may have little geo- 
graphic relationship to the origin of the first and most primitive species 
of the order. 

4. Phyletic age of the group is important. Phyletically ancient forms, 
groups that have changed relatively little (in hard parts, of course) 
through a long interval of time, are frequently known from restricted 
or from scattered, relict type occurrences. Pertinent examples may be 
found in many living amphibians, reptiles, and invertebrates, and even 
in some mammals. Living lemurids in Madagascar have close relatives 
in the early Cenozoic deposits of North America and Europe. The South 
American, Asiatic and African distribution of living hystricomorph ro- 
dents may represent an unrecorded Paleocene transworld dispersal of a 
primitive stock, as suggested by Landry (1957). There are many records 

1 Only jaws and dentitions are known for the late Cretaceous forms, but greater size 
range and greater diversity of tooth structure are clearly indicated. Paleomammalogists 
infer, therefore, more diversified gross morphologies, diets, and habits in these early 


in the Cretaceous and early Cenozoic in the northern hemisphere of the 
pleurodire turtles, which now live in the southern hemisphere. Gavials 
now live in Asia, but are known from the Oligocene of South America 
according to Langston (1953). Cryptobranchid amphibians live in eastern 
North America and in eastern Asia, but they are represented by the 
renowned Andrias scheuchzeri ("Homo dilmni testis") in the Miocene of 
Switzerland (Schmidt, 1946, p. 149; Romer, 1945, p. 592). These little- 
changing types are in various degrees characterized by fragmented or by 
recessed representation of a once greater geographic range that was 
established during an expanding phase of their dispersal history. 

5. Vagility of the group must be considered. This factor adds im- 
measurable complexity and uncertainty to the interpretation of the fossil 
record. Migratory birds may, theoretically, become a part of the fossil 
record at any resting point on their flyway. Rapidly dispersing land mam- 
mals might be first trapped in the sediments at great distance from their 
district of origin. These uncertainties tend to be overcome by an in- 
creasing probability that correlates with an increasing paleontologic 
sample. Several concordant examples lend an inference greater credence. 

Darlington (1948) and Stebbins (1950, Chap. XIV) have dis- 
cussed other approaches to interpretation of the origin and dis- 
persal of organisms: numbers of animals and of taxonomic units; 
size and continuity of geographic range; distribution of related, com- 
peting, or associated groups. Size and continuity of geographic 
range appear to comprise an especially useful neontologic criterion 
for interpreting origin of the smaller taxa. A large and continuous 
range tokens the origin area. 

Thus to confirm an interpretation of origin for a group of animals, 
we must first explore the diverse paleobiotopes for earliest oc- 
currence. This documentation is fundamental to the historical 
zoogeography of the phyla and is then enriched by the succeeding 
criteria. If, then, an area contains the earliest record, shows a bio- 
stratigraphic sequence from progenitors to the group concerned, 
contains most differentiated subgroups, and exemplifies a large and 
continuous group geographic range, it is probably the center of 
origin and dispersal. 

Matthew (1915) claimed that the more advanced and progressive 
members of a group should be nearer the center of origin because 
evolution was more progressive at this point. He also concluded that 
the less advanced members tend to disperse radially and will be 
peripheral. Because of the known climatic changes through time in 
Holarctica, and because of the concentration of primitive animal 

102 D. E. SAVAGE 

forms in the equatorial and southern hemisphere land areas, Mat- 
thew decided that the Holarctic region has been the principal cen- 
ter of evolution and dispersal of land vertebrates — that the southern 
and tropical areas are refuges for primitive species. This thesis, 
along with Matthew's erudition, had an overwhelming effect on 
North America zoogeographers, as Myers (1938) pointed out. In 
so far as non-mammalian vertebrates and land invertebrates are 
concerned, Matthew's thesis has been strongly opposed by many 
neontologic disciplines. Myers (1938, p. 351) believed that there 
is no evidence for the North American origin of any of the South 
American freshwater fishes. Schaeffer (1952, p. 231), however, as- 
serted that centers of origin for the true freshwater fishes are un- 
known but that some elements were present in South America by 
the late Cretaceous. He concluded that Mesozoic freshwater fishes 
suggest a dispersal relationship between South and North America 
on the one hand, and between Africa and Eurasia on the other. 
Darlington (1948, p. 110) concluded that the main center of evolu- 
tion of dominant groups of freshwater fishes, amphibians, and 
reptiles has been the tropical part of the Old World. Mayr (1946) 
reemphasized that the classic zoogeographic terms such as Holarctic 
and Nearctic cannot be applied usefully to the historical zoogeog- 
graphy of birds. He believes that such terms add nothing, in the 
geographic sense, to the meaning of standard geographic names for 
the areas involved. And he proposes Pantropical, Panboreal, Old 
World, North American, Pan-American and South American cen- 
ters for avian origin and dispersal. Conclusions opposing Matthew's 
generalizations are equally numerous in the literature of nonmarine 
invertebrates, but Emerson (1952) believed that termite history 
is in essential accord. Much of the opposing viewpoint stemmed 
from Matthew's rationalization that the more progressive species 
develop in an area of secularly changing climate — that the warm, 
humid swamp and forest environments promote a "relatively slug- 
ish life." Some of the contradictory statements have been weakened 
by too great a dependence on the natural and organic phenomena 
of the presently arranged and restricted climatic belts. Much of 
Darlington's contention that the Old World Tropics were the main 
center of evolution for cold-blooded vertebrates, for example, is 
based on the knowledge "that the tropical part of the Old World 
is the largest favorable area for existence of cold-blooded life. ..." 


[italics are mine], and on the misconception that north temperate to 
tropical climatic zones have not shifted much during the Cenozoic. 
It has been effectively demonstrated that there was a tremendously 
greater latitudinal expanse of tropical, subtropical, and warm- 
temperate climates during the late Mesozoic and early Cenozoic 
interval when many of the now surviving orders and families and 
some of the genera of animals were actually beginning; even though 
the orientation of climatic belts was similar to the present. 

Holarctica, although defined originally by the fauna living in the 
present temperate and frigid climates, means much more than the 
extant north temperate frigid region. When visualized through the 
span of its geochronologic age, most of Holarctica was tropical and 
subtropical throughout the first two-thirds of mammalian history. 
Perhaps the inception date for Holarctica should be specified as the 
time when oceanic and continental segments of the earth's crust 
were first arranged roughly as at present, whenever that might 
have been. I can see no utility for the term prior to the time of 
abundant land life, however, and probably not before the "Age" of 
endotherms. To the paleomammalogist, Holarctic is a shorthand 
term to signify: (1) the fauna of the northern world continent; 
(2) the northern world continent, characterized by its fauna through 
the geochronologic age of the fauna; or just (3) the world continent 
of North Africa, Eurasia, and North America through a geochrono- 
logic interval. The term is therefore, a generalization, involving 
geography, organisms, and time duration, with varying emphasis on 
these respective constituents. Holarctica, like fauna, flora, strati- 
graphic zone, species, and many other terms in our technical dic- 
tionaries is entrenched by usage and is not vitiated because it has 
been used with differing connotations or because certain organisms 
do not have a dispersal history that can be described most effectively 
by using Holarctic and sister terms. 

Many groups of mammals may have originated in tropical, sub- 
tropical, or warm-temperate biotopes, whether in northern latitudes 
or in the present "tropics." Entire orders of mammals may be auto- 
chthonous and endemic to the warmer and more humid areas, prob- 
ably for varied reasons. As examples we may take the Primates, 
the Dermoptera, and the Chiroptera (with most exceptions). I sug- 
gest to the other contributors in this symposium that, if a "tropical" 
origin is proposed for a group of animals, they carefully specify 

104 D. E. SAVAGE 

whether "tropical" means past or present, for the geographic con- 
notation is much different. 


Mayr, Linsley, and Usinger (1953, pp. 14-15) have reemphasized 
that the study of many living groups of animals has hardly begun. 
If the knowledge of living groups is in its infancy, the knowledge of 
fossil groups is embryonic; for we yet lack complete study series 
in the fossil sample. Darwin (1859, end of Chap. X), remarking on 
the poorness of the paleontological record, said: "... I look at the 
geological record as a history of the world imperfectly kept, and 
written in a changing dialect; of this history we possess the last 
volume alone, relating only to two or three countries. Of this vol- 
ume, only here and there a short chapter has been preserved; and 
of each page, only here and there a few lines. Each word of the 
slowly-changing language, more or less different in the successive 
chapters, may represent the forms of life, which are entombed in our 
consecutive formations, and which falsely appear to have been 
abruptly introduced." Matthew (1915, 1939 edition, pp. 13-14) 
noted: "We know more about fossil mammals in proportion to 
their modern numbers than about any other of the larger groups of 
land animals, yet the number of species of which we have any ade- 
quate knowledge is but a minute fraction of the number which must 
have lived since the class first came into existence." Even in a 
thoroughly studied district such as Crazy Mountain Field of Mon- 
tana, Simpson (1937, p. 69) found that 25% of the species in the 
sample were known from only one specimen each. And new animals 
are yet being discovered in the frequently prospected Chadron 
formation of Nebraska (Cook, 1954). At the present time, and un- 
doubtedly for a long time to come, we can claim little more than 
did Darwin or Matthew. The total taxonomic diversity may be 
usefully represented for some stratigraphic intervals, but only a 
few fossil assemblages adequately portray the populations that they 

Locations of the pre-Pleistocene land mammal localities of 
Nearctica are shown on Fig. 2. The record of earliest mammals is 
from two upper Jurassic localities, one in Wyoming and one in 
Colorado. (Late Triassic representatives of the class are found in 
Europe.) Fortunately the Wyoming site produced a splendid as- 

















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106 D. E. SAVAGE 

sortment of jaws and teeth and is one of the best of the Mesozoic 
mammalian assemblages (Simpson, 1929). The early Cretaceous 
record, at the threshold of dichotomy between eutherian (placental) 
and metatherian (marsupial) mammals, is limited to a few tantaliz- 
ing scraps of bone, isolated teeth and jaw fragments from a site 
in north Texas (Patterson, 1956). The later Cretaceous land mammal 
localities — principally in Wyoming, Montana, and Alberta — indi- 
cate at present a curiously undiversified aggregate of multituber- 
culates, didelphoids, and generalized eutherians. 

The Cenozoic mammals of North America inherited an array of 
nonmarine environments that extended across the entire continent ; 
for our emergent land mass has suffered only marginal inundation 
through the last 70 million years. In the freshwater deposits of the 
middle and southern latitudes, mammalian aggregates have been 
uncovered that are delightfully complete and varied when compared 
with earlier records, but they are woefully small as compared with 
the obtainable living sample of the same area. With the exception 
of the interesting Miocene and Pliocene faunas in Florida, the 
fossil mammal sample of western North America must represent all 
the Nearctic region. Very few pre-Pleistocene fossil mammal speci- 
mens have yet been found east of the Mississippi River. 

Paleocene forms, tokened by skulls, dentitions, and some com- 
plete skeletons, have been collected in the present Rocky Mountain 
province. A few materials have been discovered in California 
(McKenna, 1955), and one jaw came from a deep well in Louisiana 
(Simpson, 1932). The better and more varied Paleocene assemblages 
are in New Mexico, Utah, Wyoming, and Montana. 

Eocene mammalian local faunas extend from the West Coast into 
the Rocky Mountain area and from British Columbia (Russell, 
1954) to southwest Texas (Wilson et al., 1952), and possibly to 
central Mexico (Fries, Hibbard, and Dunkle, 1955). A few frag- 
ments are known from New Jersey (Wood et al., 1941, p. 31 ; Gazin, 
1953, pp. 8, 34). The better and more diversified Eocene assemblages 
are in the Rocky Mountain states and in California. 

Oligocene mammals are known from sites in the central part of 
western North America: from the northern Great Plains to Cali- 
fornia, from southwestern Saskatchewan (Russell, 1940) to south- 
western Texas (Stovall, 1948). Best Oligocene assemblages are from 


Texas, from the world-famous White River group of the northern 
Great Plains, from Montana, and from Saskatchewan. 

Late Cenozoic assemblages are widely scattered through the 
middle latitudes of western North America. Every western state 
claims several local faunas representing the last 30 million years of 
land mammal history on this continent. Pliocene Ncarctic mam- 
malian assemblages have been discovered as far south as Honduras 
(Olson and McGrew, 1941). Pleistocene localities would make a 
dense, stippled pattern for many areas on the map of Fig. 2 and 
have consequently been omitted. Some of the more important 
Pleistocene localities in the West include stream and lake deposits 
of the Great Plains and Texas, cave and shelter accumulations in 
the Southwest and Mexico, "mucks" and gravels in Alaska, and 
breas in California. This suite of samples forms the biostratigraphic 
basis for conclusions as to the origin and affinities of land mammals 
in western Nearctica. 


Since at least the day of Madison Grant's (1904) essay on the 
origin and relationships of the large mammals of North America, 
such statements as the following have appeared in the literature: 
. . . the poverty of animal life which lived in Y area . . . , or . . . in 
the X beds of corresponding age, a similar but more limited fauna is 
found. These statements, usually based on little more than pre- 
liminary surface collecting in newly discovered fossiliferous areas, 
should have been carefully qualified as pioneer generalizations, but 
were not. The authors made no evaluation of the factors of ac- 
cumulation, preservation, discovery, and collection; and the printed 
conclusions, in light of present knowledge, are no more than facile 
verbiage. It is no secret that paleontologists yet lack raw data as 
to the density and relative numbers of individuals, population size, 
species associations and the like in the once living biocenoses. 
Surprisingly, the more common a given fossil is in an area, the more 
likely that there is a poor census for the animal represented. Through 
the years, the common forms have been kicked aside in the quest 
for the "remarkably new" exhibition specimens or the perfect 
study skeleton. Some collectors have been disproportionately in- 
trigued with the remains of giants (alas, the lust for the mighty 



dinosaur!); others spurn the labor-consuming giants for micro- 
sized remains; others collect only complete skulls or skeletons and 
discard individuals represented by only fragmentary specimens. 










Fig. 3. Faunal analysis diagram of the quarry sample from McKay 
Reservoir, Oregon. The divisions of the circle graph represent relative 
abundance of the mammals indicated. The radial bar graph represents 
the number of specimens per individual. The heavy concentric line in- 
cludes genera assigned to the proximal community. Reproduced from 
Shotwell (1955, p. 333). 

Shotwell (1955) demonstrated, as in Fig. 3, that useful census 
and ecological interpretations may be derived from a meticulously 
collected fossil sample. Such a sample will be composed of all the 
obtainable bones and bits of bones from a given site. Shotwell pro- 


vided an objective basis for the evaluation of the numbers of in- 
dividuals of each species in the sample and from this census inferred 
the species whose ranges were more proximal or more distal to the 
accumulation site. No doubt other interpretations of the data will 
differ from Shotwell's, for, as Shotwell notes, many variables and 
assumptions are involved, but a new method of inquiry has been 
pioneered. And this approach to the significance of relative num- 
bers of fossil remains at a given locality will make the formerly 
indifferent collector think twice before destroying or leaving behind 
the identifiable fragments. 

The taxonomic composition of quarry samples may differ sig- 
nificantly from samples made up of specimens picked up only on 
the surface of a fossil-bearing stratum. Simpson (1937) noted the 
differences between two such samples in the Paleocene of Montana 
and concluded that the apparent differences probably represented 
two facies of the fauna. In a footnote (p. 52) he remarked: "Correla- 
tions of faunal types and collecting methods are real but indirect. 
Flood-plain deposition and facies would not normally result in 
concentration of fossils sufficient to permit profitable quarrying." 
Van Houten (1945) concluded that in the continental sediments of 
late Paleocene and early Eocene ages in the Rocky Mountain region 
there is a definite relationship between mamalian faunal facies 
and the lithofacies. He found (p. 444) that the arboreal forest 
faunal facies [micro-mammals] are concentrated in local pockets of 
the drab grayish sediments, whereas the large ungulates and 
creodont carnivores, representing savanna floodplain habitats, are 
sparsely scattered throughout the red-banded varicolored sediments. 
Here the micro-mammal facies were obtained from quarries and the 
mega-mammal facies from surface collecting. A comparison of a 
quarry sample with the surface discoveries from one formation 
shows taxonomic and census differences comparable to those in the 
lithofacies studied by Simpson and by Van Houten. Simpson (1935, 
p. 4) showed the abundance of different species in the Tiffany fauna, 
late Paleocene, from the San Jose formation of southwestern Colo- 
rado. In his chart, here slightly modified (Fig. 4) following later 
work by Simpson, the numbers of micro-mammals from the Mason 
Pocket faunule, contained in less than a cubic yard of matrix, are 
compared with the known surface discoveries on the upper Paleocene 
part of the San Jose formation. In this comparison only one species. 

110 D. E. SAVAGE 

Plesiadapis gidleyi, among the eiglit known from the San Jose sur- 
face and among the eleven from the pocket, is common to the two 
assemblages. The larger animals such as Phenacodus and Periptychus 
are known only from surface finds; so that one's concept of faunal 
composition would be completely different if only the surface ma- 



Ectypodus musculus 12+ 


Peradecfes elegans 20 



Leptacodon tener 2 

Xenacodon mutilatus I 

Zanycteris paleocena I 



Plesiadapis gidleyi 20+ I 


Labidolemur soricoides 2 


Carpodapfes aulacodon I 


Navajovius kohlhaasae 3 


Phenacolemur frugivorus 7 



Chriacus sp. • • I 

Thryptacodon oust rails I 


?Dissacus sp. . . I 



Phenacodus grangeri • • 9 

Phenacodus matthewi • • \ 

Phenacodus gidleyi • • I 

Phenacodus sp. • • I 

Periptychus superstes • • 5 

TOTALS 70+ 20 

Fig. 4. Census of individuals of various land mammal species from 
the Mason Pocket and from elsewhere in the San Jose formation, late 
Paleocene, Colorado. Modified from Simpson (1935, p. 4). 


terlal had been collected. Taxonomic and relative abundance differ- 
ences may be the result of incomplete quarrying at the site of sur- 
face discoveries (one jaw on the surface may indicate fifty at six 
feet down !) , or lithofacies differences may indicate a complete bio- 
facies change, as suggested by Simpson and by Van Houten. The 
final confirmation of one or more of the various possibilities rests on 
the completion of exhaustive quarrying with improved collecting 
techniques in the areas where the variegated, red-banded formations 
are exposed and where the sample is essentially surface pickup at 

During the last fifteen years several institutions in the midwestern 
and western United States have been employing a screen -washing 
technique for the recovery of small fossils. This technique calls for 
the handling of tons of fosslliferous sediment. The sediment Is 
washed through screen boxes. Available bodies of water are used, 
whatever they may be: streams, lakes, stock tanks, or the ocean. 
Fosslliferous matrix, frequently appearing quite barren on its surface 
exposure, is quarried and shoveled into burlap bags for transport to 
the washing site. Experience has shown that the transport distance 
may be 20 miles or more before the method can be considered un- 
profitable in terms of collecting expense. At the water, the matrix is 
screen -washed, dried, and picked; and the number of specimens 
recovered is often astounding when compared to standard quarrying 
methods. During three summer seasons in the lower Eocene of north- 
western Colorado and adjacent Wyoming, M. C. A^IcKenna and 
colleagues of the University of California obtained about 20,000 
individual specimens of teeth, jaws, and bones of ultra-small fossil 
vertebrates. And these were taken from terrain that had been passed 
over and considered unworthy for collecting by earlier workers. 
Through a work period of five months, we have washed slightly more 
than 30 tons of sandstone and have recovered 2,500 museum speci- 
mens of fossil mammals from the late Cretaceous of Wyoming. This 
is about one mammalian study specimen for each 24 pounds of 
matrix. And these mammals are especially significant to the under- 
standing of basic diversification (now largely conjectural) within 
the Class Mammalia. Even greater numbers of specimens represent- 
ing a combined assemblage of lizards, frogs, snakes, fishes, dinosaurs, 
turtles, crocodiles, and birds were obtained from the depositional 
association with the Cretaceous mammals. In both the Eocene and 

112 D. E. SAVAGE 

the Cretaceous, the first and principal sign of the richly fossiliferous 
matrix was an accumulation on an ant hill of tiny teeth, gar scales, 
reptile teeth, and the like. 

These are admittedly the words of an enthusiast. Screen washing 
is not the solution for all collecting problems, and it is efhcient only 
as a mass production technique. Some matrices and some fossils are 
not susceptible to this type of treatment. But the method is useful 
in many areas, and it may be especially useful for census and ecology 
studies in the varicolored flood-plain formations that have been pro- 
claimed barren by previous workers. 

The possible contrast in abundance of adaptive types between 
samples from the drab gray quarry pockets and the varicolored 
flood-plain deposits is also interesting. In the continental late Paleo- 
ceneof the Rocky Mountains, Simpson (1935, 1937) and Van Houten 
(1945) found that the small herbivores abound in the quarry samples 
and that the large herbivores, carnivores, and carnivore-omnivores 
are relatively abundant in the scattered surface finds. Combined 
floral, faunal, and sedimentological data show that these late Paleo- 
cene environments were in intermontane lowlands and were subject 
to humid warm-temperate or subtropical climate (Knowlton, 1917, 
1924; Berry, 1935; Bell, 1949). By contrast, work in the late Mio- 
cene deposits in the Cuyama Badlands of southwestern California 
shows quite difi"erent proportions of adaptive types. Figure 5 gives 
the stratigraphic correlation between red-bed and gray-bed occur- 
rences of land mammals within the Caliente formation in this area. 
Present mapping and studies of the physical stratigraphy of the 
district indicate that the red-bed and gray-bed mammal locations, 
here assigned to the Barstovian (late Miocene) Mammalian Age, 
are geochronologically contemporaneous. Figure 6, a preliminary 
census of the Caliente formation mammals, is based on both surface 
collecting and incomplete quarrying in both lithofacies. In this com- 
parison it may be noted that the small insectivores and herbivores 
(including rodents and rabbits) are relatively abundant in the red 
beds, whereas large herbivores, such as camels, horses, and oreo- 
donts, are the dominant element in the gray-bed faunule. The 
Cuyama example, therefore, suggests a quite different relationship 
between lithofacies and mammalian adaptive types. Combined 
paleontological and geological evidence shows that the Cuyama 
paleobiotope was in coastal intermontane valleys and was subject 


CQ ^ .ti 


P b/) o 

^ o 

"^ "^ 'en 






























































^— 1 


























































n 1 







■ ! .!<.., .M« > ? .. ^ . a .. ^ , T . ,w, ., , .) 

Fig. 6. Census of land mammal adaptive types in the late Miocene 
Caliente formation of southwestern California, showing approximate 
abundance of each type on a percentage bar graph for the red-bed facies 
and the gray-bed facies respectively. 

to probable temperate-mesic to xeric climatic conditions, depending 
upon local topography (Axelrod, 1940, 1950; Dibblee, 1952 ; Durham, 
1950; Schwade, 1954). But this comparison between the paleobio- 
cenoses across western North America provides only tentative con- 
clusions because: 

1 . The compared faunas are dissimilar taxonomlcally. 

2. There was a profound climatic and vegetative difference be- 
tween the two areas. 


3. Approximately 45 million years, a sufficient interval for great 
evolution of morphologies and change of ecological-physiological 
tolerances, elapsed between early Eocene and late Miocene. 

4. There are possible subtle differences between the similar litho- 
facies of the two areas. Similar lithofacies were not necessarily 
formed under the same environmental conditions. The color differ- 
ences in the Caliente formation may mean little more than differing 
sediment-source, and both the red and the gray facies may have 
been deposited in the same physical environment. 

Detailed sedimentological studies have not yet been accomplished, 
and much work lies ahead. Nevertheless, the example from Cuyama 
suggests that conclusions as to relative abundance of taxonomic units 
and adaptive types in certain lithologies are premature and may be 
completely misleading, especially when based on samples collected 
by techniques of disparate refinement. 



Earliest records of the class Mammalia are from the late Triassic 
of England, but generalized reptilian progenitor stocks are known 
from South Africa as well as in various Holarctic districts. There- 
fore, on the basis of the stratigraphic record, the possibility of either 
Holarctic or Paleotropic origin for the class Mammalia must be 

Pre-Paleocene land mammal faunas are so poorly known on most 
continents that little can be determined as to intercontinental dis- 
persal and affinities. From late Paleocene to the present, however, 
the fauna of North America is clearly dominated by groups common 
to many parts of Holarctica, especially such forms as shrews and 
moles, rabbits and pikas, sciuromorph and myomorph rodents, 
creodont and fissiped carnivores, condylarths, uintatheres pro- 
boscideans, perissodactyls, and artiodactyls. All zoogeographers 
know that the Nearctic Cenozolc mammalian fauna differs markedly 
from the prototherian-metatherian fauna of Australasia and is only 
slightly less distinct from the pre- Pleistocene metathere-edentate- 
archaic ungulate assemblage of South America. 

Nearctica is dominant in the recorded range and dispersal of the 
33 recognized orders of land mammals (Fig. 7), but only 9 orders 
(with 27 families) are represented here by living forms: Marsupialia 

116 D. E. SAVAGE 

(1 family) ; Insectivora (2 families) ; Primates (1 family) ; Chiroptera 
(3 families); Edentata (1 family); Carnivora (5 families); Lago- 
morpha (2 families) ; Rodentia (8 families) ; Artiodactyla (4 families). 
However, 14 additional orders were here during various intervals of 
the Mesozoic and Cenozoic, but are now either extinct or survive on 
other continents: Multituberculata (extinct); Triconodonta (ex- 
tinct) ; Docodonta (extinct) ; Pantotheria (extinct) ; Symmetrodonta 
(extinct); Dermoptera (now in the Paleotropics) ; Tillodontia (ex- 
tinct); Taeniodonta (extinct); Condylarthra (extinct); Notoungu- 
lata (extinct); Pantodonta (extinct); Dinocerata (extinct); 
Proboscidea (now in the Paleotropics) ; Perissodactyla (now in the 
Paleotropics, Palearctica, and Neogaea). Of the 23 orders of land 
mammals recorded in Nearctica, 9 have earliest record here, and 6 
have earliest record here and elsewhere. First let us consider the 
possibility that Nearctica was the origin and dispersal center for 
these 15 orders, following the criteria proposed in the first part of 
this paper; then we may consider the possible Nearctic origin for 
other orders. Center of origin or origin area, as here used, of course 
means place where earliest and most primitive members appeared. 

Orders with Earliest Record in North America 

1. Multituberculata (extinct) 

a. Earliest record in upper Jurassic of England and United States 

b. A group of uncertain phylogenetic affinities 

c. Possibly originated somewhere in Holarctica 

2. Marsupialia 

a. Earliest record in upper Cretaceous 

b. Comparisons on the basis of jaws and characters of dentition 
lead to conclusion that this group was derived ultimately from 
the Jurassic mammalian radicle, the Pantotheria; but forms with 
annectant morphologies are unknown 

c. Possibly originated in North America, but comparable Cre- 
taceous biocenoses are poorly known in Asia and are not yet 
known on the other continents 

3. Dermoptera ("flying lemurs") 

a. Earliest record in upper Paleocene 

b. Probably distinct since middle or early Paleocene derivation 
from generalized unguiculate eutherian; intra-ordinal relation- 
ships are uncertain 

c. Possibly originated in North America, but poorly known in the 
North American fossil record and unknown as fossils elsewhere 





















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1 — 1 












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118 D. E. SAVAGE 

4. Chiroptera (bats) 

a. Earliest record in Eocene of North America and Europe 

b. Probable latest Mesozoic or Paleocene derivation from a 
eutherian stock (Insectivora?) 

c. Bat-like forms are reported from the late Paleocene of North 
America, but the group is too poorly known to conjecture as to 
center of origin 

5. Primates 

a. Earliest record in middle Paleocene 

b. An early Paleocene or latest Cretaceous differentiation in the 
radicle Eutheria 

c. Possibly originated in North America, but mammal-bearing 
deposits as old as the early North American records are not 
known on the other continents 

6. Tillodontia (extinct) 

a. Earliest record in upper Paleocene 

b. An early to middle Paleocene differentiation from unguiculate 
(?) stock 

c. Possibly originated in North America, but evidence inconclusive 

7. Taeniodonta (extinct) 

a. Earliest record in lower Paleocene 

b. A probable late Cretaceous differentiation within the Eutheria 

c. Entire record of this group is in Nearctica 

8. Edentata 

a. Earliest record in upper Paleocene 

b. An early to middle Paleocene differentiation from unguiculate 


c. Probable Nearctic origination because the earliest forms known 
lack dermal armor and have a less specialized skeleton; but early 
and middle Paleocene records of mammals are lacking in 
Neogaea, the center of mid-Cenozoic evolutionary radiation of 
the Edentata 

9. Rodentia 

a. Earliest record in upper Paleocene 

b. Presumed origin from early or middle Paleocene unguiculate 
stock, but annectents are completely unknown 

c. Possibly originated in Nearctica, probably in Holarctica, but 
evidence is inconclusive 

10. Carnivora 

a. Earliest record in lower Paleocene 

b. Probably derived from a late Cretaceous eutherian group that 
has been referred to the Insectivora or is not yet recorded; 
possibly became a discrete group before the end of the Mesozoic 

c. Probably of Holarctic origin, possibly in Palearctica 

11. Condylarthra (extinct) 

a. Earliest record in lower Paleocene 


b. A horizontally classified group in which subdivisions are pre- 
sumably derived from a ferungulate stock; some of the families 
are a probable late Cretaceous differentiation 

c. Most of the families (Hyopsodontidae, Phenacodontidae, and 
Periptychidae) may have originated in North America, although 
some paleomammalogists would propose origin elsewhere because 
of the "sudden" appearance of differentiated groups in the 
lower Paleocene here. Didolodontidae, as presently recognized, 
appear to have a South American history, but are only slightly 
divergent from phenacodonts (McKenna, 1956). Meniscotheri- 
idae might have originated in Palearctica 

12. Pantodonta (extinct) 

a. Earliest record in middle Paleocene 

b. An early unique differentiation within the Eutheria, possibly a 
derivative of the ferungulate radicle but annectants with earlier 
eutherians unknown 

c. Probably of Holarctic origin 

13. Dinocerata (uintatheres, extinct) 

a. Earliest record in upper Paleocene of North America and Asia 

b. Unique giants of uncertain phyletic origin within the Eutheria, 
possibly derived from a ferungulate stock 

c. Probably of Holarctic origin 

14. Perissodactyla (horses, tapirs, rhinos) 

a. Earliest record in lower Eocene of North America and Europe 

b. Probably derived from advanced phenacodontid condylarths of 
the type seen in the middle and late Paleocene of North America 

c. Possibly originated in North America but the pre-perissodactyl 
record is poorly known in Eurasia 

15. Artiodactyla (pigs, deer, bovids) 

a. Earliest record in lower Eocene of North America and Europe. 

b. Probably derived from a generalized eutherian group of Paleocene 

c. Probably of Holarctic origin, possibly of Paleotropic origin 

Eight orders of mammals known in North America have earlier 
records elsewhere: Triconodonta, Docodonta, Symmetrodonta, 
Pantotheria, Insectivora, Lagomorpha, Proboscidea, and Notoungu- 
lata. On the basis of prospecting and collecting data for North 
America these orders may be divided into two groups: those that 
may have a yet unknown earlier record in North America and those 
that more probably do not have an earlier record in North America. 
The lagomorph, proboscidean, and notoungulate beds of this con- 
tinent are underlain by relatively well-explored mammal-bearing 
strata; hence, these orders fall into the second group. The other 
orders, all with earliest record in the Mesozoic, may be included in 

120 D. E. SAVAGE 

the first group, and it is pointless to guess as to an origin area, even 
an area of continental size. 

The remaining orders, not presently recognized in the Nearctic 
record, can be discussed briefly. 

1. Monotremata, as Patterson (1956, p. 100) has suggested, may 
be related to forms that are being uncovered in the late Triassic of 
England. This Mesozoic group (Docodonta Kretzoi, fide Patterson) 
has representatives in the late Jurassic of North America. 

2. Pholidota, Embrithopoda, Hyracoidea, and Tubulidentata 
have no presently recognizable North American affinities. The rela- 
tionships between hyracoids and the Holarctic, early Cenozoic 
meniscothere condylarths are yet to be studied thoroughly. The 
affinity of Tubulodon Jepsen from the early Eocene of North America 
with the Tubulidentata is disputed (Jepsen, 1932; Colbert, 1941). 
More fossil material referable to Tubidodon is badly needed. 

In summary, the evidence appears strongest for Nearctic origin of 
the marsupials, edentates, tillodonts, taeniodonts, perissodactyls, 
dermopterans, primates, and rodents. For none of these groups, 
however, is the evidence compulsory. Figure 7 also demonstrates 
that late Paleocene through Eocene was the time when most of the 
modern orders of mammals arose. 


Simpson (1947) so meticulously covered the evidence for origin 
and dispersal direction of families and certain lesser taxa of North 
American mammals that it would be superfluous to do more than 
summarize his conclusions. Figure 8, showing possible origins, is 
presented with the belief that most of the participants in this sym- 
posium will be interested primarily in the families that are now 
living. It is to be remembered that an individual subfamily, genus, 
or species does not necessarily correspond with the origin and dis- 
persion of its family ; for example : 

1. Castor (beaver; Castoridae) evidently dispersed from Pale- 
arctica to Nearctica; Miocene and middle Pliocene members of the 
family dispersed in the opposite direction. 

2. Didelphis (opossum; Didelphidae) and Tayassu (peccary; 
Tayassuidae) appear to be Neotropical autochthons and Nearctica 
is recently marginal to their expanded or expanding range. 





I 1 


Didelphidae E -• L 

Soricidae L -• ? L 

Talpidae L ^L 

Scalopodinae L -• ? L 

Phyllostomatidae^ L -* ?— 

Vespertilionidae^ \J "^ ^ L 

Molossidae^ L' ? L 

Hominidae L' ^ L 

Dasypodidae^ L -* 

Ochotonidae L ? *- L 

Leporidae L *- L 

Aplodontidae E -■ L 

Sciuridae L -• ? L 

Geomyidae^ L 

Heteromyidae^ L 

Castor idae L •" L 

Cricetidae L "?" L 

Microtinae L -• ? L 

Muridoe^ L ■ L 

Zapodidae L ^ L 

Zapodinae L -< ? L 

Erethizonfidae^ L -• 

Canidae L ^?— L 

Ursidae L ^ L 

Procyonidae L ^?-" L 

Mustelidae L ? ^ L 

Felidae L ?- ^L 

Toyassuidae E ^?-* L 

Cervidae L ? ^L 

Bovidae L *- L 

Antilocapridae L 


'-Based on Simpson(l947). 
2-Not discussed by Simpson(l947). 
'-Might have originated in the Paleotropic Region. 

Fig. 8. 


— L 

— L 



— L 
■*■ L 

— L 

— L 

— L 

— L 

A consideration of the time of origin of the 28 Hving Nearctic 
famihes (Fig. 9), supports the generaHzation that the Oligocene or 
possibly late Eocene-Oligocene, was the interval of inception of 
modern families of mammals.'^ 

The living genera of Nearctica are either autochthonous or have 
immigrated from Palearctica or from the Neotropics. Interpretation 

2 Old World and South American families have a comparable geochronologic history. 



of the origin of these genera is shown in Table I. We may say that 
the interval from Miocene into Pleistocene was the time when most 
modern genera of land mammals arose. 

Most species in the living Nearctic land mammal fauna are evi- 
dently autochthonous. Probable exceptions are the transboreal 


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Fig. 9. 

forms, such as the moose, muskox, caribou, and polar bear; certain 
"pan -American" forms, such as Eptesicus juscus (big brown bat), 
Lasiurus borealis (red bat), Tadarida macrotis (big freetail bat), and 
Eumops perotis (Western mastiff bat); and probable Neotropical 
autochthons — Dasypus novemcinctus (armadillo) and Tayassu angu- 
latus (peccary). A species list of land mammals from the Pleistocene 
[including the Holocene of some workers] is given by Hibbard 
(1956; in Flint, 1957, pp. 458-467). No taxonomist will recognize 
exactly the same number of species as appear on the compilation by 


Hiljbard; but it is beyond the intent of this paper to consider the 
taxonomic problems of Pleistocene mammals or the effects of "split- 
ting" or of "lumping" on the species Hsts of fossils. Hibbard's list 
indicates the general stocks that were available for evolutionary 
modification and zoogeographic change through the last few thou- 
sand years. Many of the late Pleistocene animals are very similar in 
hard part structures to the living species and have been so identified. 
Very few of the middle or early Pleistocene forms have been referred 
to living species. 

Intercontinental faunal comparisons show probable trans-Hol- 
arctic mammalian dispersal waves during most of the subepochs 
from late Jurassic through late Pleistocene. Strongest evidence for 
such dispersal is found in the late Jurassic, late Paleocene, early 
Eocene, early Oligocene, middle to late Miocene, and middle Plio- 
cene through late Pleistocene. Sharp peaks in the intercontinental 
faunal resemblance curve indicate, as shown by Simpson (1947), 
that these dispersals were discontinuous pulsations. 


1. A given area may be considered the most probable center of 
origin of a group of animals if: (a) it contains the earliest record of 
the group; (b) it contains the record of suitable progenitors; (c) it 
contains greatest taxonomic differentiation within the group; (d) it 
contains a large and continuous geographic range of the group. 

2. The extant climatic belts and districts are poor geographic 
indices for late Mesozoic-early Cenozoic arrangements. Therefore, 
to propose the Holarctic or Paleotropic or other regions as centers of 
origin and dispersal for a given group of animals we must first 
evaluate the climate and ecology of these regions at the time of 

3. The fossil sample may now give a good picture of the taxonomic 
diversity of once living mammals for some districts, but the study 
of paleobiocenoses, based upon significant numbers of individuals, 
is in its infancy. 

4. The biostratigraphic record is not yet adequate to reveal pre- 
cisely the districts of origin and directions of dispersal for many 
groups of land mammals. 

5. Useful census and ecological interpretations may be derived 
from a meticulously collected fossil sample made up of all identi- 




















Romerolagus^ ? 








Procyon Cynomys? 
Spilogale Geomys 
Conepatus Cratogeomys 
Mephitis Tamiasciurus 
Taxidea Thomomys 
Urocyon 0?iychomys 
Canis? Reithrodontomys 
Lynx Sigmodon 
Tamias Oryzomys 


Probable Old World 
or Nearctic Origin 




















Probable time 
of Origin 



• 1—1 




^ ts ^ -S 

o e S ^ 






Bassariscus Peromyscus 









•■s t? s; 1 s ^ s ^ § 



















126 D. E. SAVAGE 

fiable bones and bone fragments. This statement is trite unless 
considered in the Hght of the actual case history of fossil vertebrate 

6. It is possible that there may be a fixed relationship between 
mammalian faunal facies and the containing lithofacies, but pre- 
vious generalizations as to this possibility were premature and will 
have to be confirmed by exhaustive quarrying and by improved 
collecting methods. 

7. Screen washing is being applied to formations that earlier 
workers believed to be unprofitable for recovery of fossils. The 
abundance of small vertebrates in these formations indicates that 
we may obtain large samples from seemingly barren, red, red- 
banded, or varicolored flood-plain deposits. 

8. Evidence is strongest for the Nearctic origin of Marsupialia, 
Edentata, Tillodontia, Taeniodonta, Perissodactyla, Dermoptera, 
Primates, and Rodentia, but the evidence is not conclusive. These 
orders evidently differentiated within the Infraclass Eutheria in the 
interval extending through late Cretaceous and Paleocene, roughly 
85 to 65 million years ago. 

9. About 35% of the living land mammal families of Nearctica 
are autochthonous, about 7% endemic; most of the families origi- 
nated in the interval late Eocene-Oligocene, approximately 50 to 35 
million years ago, 

10. About 70% of the modern Nearctic land mammal genera are 
probably autochthonous; and as many as 15% were living as early 
as late Miocene, 30% by middle Pliocene. All together, the genera 
originated from about 15 million to possibly several thousand years 

11. About 97% of the modern Nearctic land mammal species are 
probable autochthons that originated in the interval, later Pleisto- 
cene into Recent, possibly two or three hundred thousand years 

ago to present. 


Axelrod, D. I. 1940. The Mint Canyon flora of southern California: a 

preliminary statement. Am. J. Sci., 238: 577-585. 
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Carnegie Inst. Wash. Publ., 590: 215-306. 
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Bell, W. A. 1949. Uppermost Cretaceous and Paleocene floras of western 

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Colbert, E. H. 1941. A study of Orycteropus gaudryi from the Island of 

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Durham, J. W. 1950. Cenozoic marine climates of the Pacific Coast. Bull. 

Geol. Soc. Am., 61: 1243-1264. 
Emerson, A. E. 1952. The biogeography of termites. Bull. Am. Museum 

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Smithsonian Misc. Collections, 121: 1-110. 
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North America. Rept. New York Zool. Soc, 8: 182-207. 
Hesse, R., W. C. AUee, and K. P. Schmidt. 1937. Ecological Animal 

Geography. Wiley, New York; 2nd edition, 1951, 
Jepsen, G. L. 1932. Tubulodon taylori, a Wind River Eocene tubulidentate 

from Wyoming. Proc. Am. Philos. Soc, 71: 255-274. 
Knowlton, F. H. 1917. Fossil floras of the Vermejo and Raton formations 

of Colorado and New Mexico. U. S. Geol. Surv. Prof. Paper, 101: 

. 1924. Flora of the Animas formation. U. S. Geol. Survey Prof. 

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Landry, S. O., Jr. 1957. The interrelationships of the New and Old World 

hystricomorph rodents. Univ. Calif. Publ. Zool., 56: 1-118. 
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Academy Science, 1939 edition. 

128 D. E. SAVAGE 

Mayr, E. 1946. History of North American bird fauna. Wilson Bull., 58: 

Mayr, E., E. G. Linsley, and R. L. Usinger. 1953. Methods and Principles 

of Systematic Zoology. McGraw-Hill, New York. 
McKenna, M. C. 1955. Paleocene mammal, Goler formation, Mojave 

Desert, California. Bull. Am. Assoc. Petrol. Geologists, 39: 512-515. 
. 1956. Survival of primitive notoungulates and condylarths into 

the Miocene of Colombia. Am. J. Sci., 254: 736-743. 
Myers, G. S. 1938. Fresh-water fishes and West Indian zoogeography. 

Smithsonian Inst. Ann. Kept., 1937: 339-364. 
Olson, E. C, and P. O. McGrew. 1941. Mammalian fauna from the 

Pliocene of Honduras. Bull. Geol. Sac. Am., 52: 1219-1244. 
Osborn, H. F. 1910. The Age of Mammals in Europe, Asia and North 

America. Macmillan, New York. 
Patterson, B. 1956. Early Cretaceous mammals and the evolution of 

mammalian molar teeth. Fieldiana: Geology, 13: 1-101. 
Romer, A. S. 1945. Vertebrate Paleontology, 2nd edition, University 

Chicago Press, Chicago, 111. 
Russell, L. S. 1940. Titanotheres from the lower Oligocene Cypress Hills 

formation of Saskatchewan. Trans. Roy. Soc. Canada, 34: 89-100. 
. 1954. Mammalian fauna of the Kishenehn formation, south- 
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Schaeffer, B. 1952. The evidence of the fresh-water fishes. Bull. Am. 

Museum Nat. Hist., 99: 227-254. 
Schmidt, K. P. 1946. On the zoogeography of the Holarctic Region. 

Copeia, 1946, no. 3: 144-152. 
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Div. Mines Bull., 170: Map Sheet 1. 
Shotwell, J. A. 1955. An approach to the paleoecology of mammals. 

Ecology, 36: 327-337. 
Simpson, G. G. 1929. American Mesozoic Mammalia. Mem. Peabody 

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Proc. U. S. Natl. Musuem, 82: 1-4. 
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52: 1-48. 

The History and Affinities 
of the Recent Land Mammals 
of Western North America 

William H. Burt 

Museum of Zoology, University of Michigan^ 
Ann Arbor 

When we speak of the origin of a fauna or 
of some component of a fauna we imply that a more or less definite 
place and time is involved. If our present concept of evolutionary 
process is correct, faunas or parts thereof do not arise de novo. 
Instead, they constitute a continuum. How, then, without being 
strictly arbitrary, can we reasonably designate a place and time as 
a starting point in this continuum — a place and time for the origin — 
when the fauna or taxon is merely changing from one complex to 
another. Can we really talk about the origin of a fauna or a taxon 
without going all the way back to the origin of life itself, which may 
also have been a continuum? Would it not be more nearly accurate 
to speak of a phase in the history of a fauna or a taxon? In mammals, 
for example, we might speak of the reptilian-mammalian phase, 
which must have persisted for some millions of years, then the 
mammalian phase, which has continued to the present. Geolog- 
ically speaking, we might designate a pre-Tertiary phase and a 
Tertiary phase in mammalian history. In this way we would indi- 
cate a gradual change, not an abrupt one. Part of our thinking, 
perhaps, has been influenced by the great discontinuities in the 
geologic record. These break the continuum in the fossil record and 
give to the uninitiated the impression of great steps in evolution. 
They make for easy categorizing, but the animals and plants were 
living and evolving during these great intervals of time when, 
in the history of land mammals, no terrestrial deposits were being 
formed, and no record was left. We are apt to pass over these 
unknown intervals of time and say, for example, that the mammals 


132 W. II. BURT 

appeared in abundance at the beginning of tlie Tertiary. What we 
actually mean is that their fossil remains show up in abundance 
first at the beginning of the Tertiary period. But, they must have 
been abundant and diversified long before the first grain of sand was 
deposited in what we now call Tertiary beds. The paleontologist 
knows all this, but I fear that he sometimes inadvertently conveys 
the wrong impression by the language he uses and the charts he 
draws, stacking one representation of a geologic age, referring to 
the deposits containing fossils, on top of another and not indicating 
lapses of time between them. 

Although the title of the present symposium contains the word 
"origin" I have not used it in this paper for the reasons just given. 
I believe it is more in keeping with the subject of the symposium to 
call it "The history and affinities of the Recent land mammals of 
western North America." There is precedence for this in W. B. 
Scott's monumental work A History of Land Mammals in the 
Western Hemisphere, published in 1913. But, whether we speak of 
origins or histories, it is necessary first to establish space and time 
limits, otherwise the discussion is somewhat meaningless. The area 
about which I shall be concerned in North America is that segment 
of the continent lying principally west of meridian 100° West and 
north of parallel 30° North. In Asia, it is that area principally east 
of meridian 100° East and north of parallel 30° North. In South 
America, I consider the entire continent. These areas admittedly 
are unequal, but each contains diversified ecological conditions, 
and each is sufficiently large to give a good sample of the total 
mammalian fauna. The time interval is from the beginning of the 
Tertiary through the Recent. Bats and marine mammals are not 
included in the following analysis. I shall be little concerned with 
the fossil record since that was discussed in the preceding paper. 
I should like, however, to point up a few criteria used by students 
of Recent faunas in attempts to determine the so-called place of 
origin of a group of animals. I would prefer to call this the area of 
differentiation — where the group passed from one evolutionary 
phase to another. 

1. The Present Geographic Distribution of the Group Indicates 
Its Origin, (a) Some have thought that the central .part of the 
area now occupied may represent the area of "origin" (differenti- 


ation) of the group. This may or may not be so. Here, it is important 
to know what time interval is being considered and, also, the 
taxonomic level of the group — species, genus, family, etc. We 
know that faunas have shifted geographically in the past, and, 
unless we have the fossil evidence we cannot prove that the faunal 
element involved did not move in from some other locality. A good 
example in the mammals, in the area under consideration, where 
we do have a fossil record from the same general area now occupied 
by the group, is the assemblage of pocket gophers, pocket mice, 
and kangaroo rats, involving two closely related families as now 
recognized by specialists, the Geomyidae and Heteromyidae. 
These mammals are, and have been, primarily western North 
American in their distribution, as indicated by the fossil record 
and knowledge of Recent kinds (Fig. 4). This is true also of the 
pronghorn. Family Antilocapridae. If we base our interpretation 
solely on Recent kinds and their present geographic distribution 
and use the criterion just set forth, we would be correct in saying 
that the area of differentiation was in western North America. 
But, if we were to use the same criterion for the camels, Family 
Camelidae, we would be far wrong. None of the latter are now 
found in North America where they had their great development 
in Tertiary times and continued into the Quaternary. 

(b) The periphery of the present range has been considered by 
some as being the most likely place for differentiation of a group. 
This might hold for some of the lesser categories, such as species, 
but for the higher categories, camels, for example, we find the same 
objections as we did in the preceding discussion. As a matter of 
fact, any segment of a population of a species might have the 
potential of evolving in a different direction from the parent stock 
if a barrier is established to isolate it. This barrier need but stop or 
sufficiently dilute the genetic interchange between populations. 
Even in a continuous population over a relatively large area, the 
segments at the extremes may be sufficiently isolated by distance 
that they will evolve in different directions {Peromyscus maniculatus 
is an example). 

2. The Area of Present Greatest Abundance Is Likely the Place 
Where Group Evolved. This theory assumes that the area where 
optimum conditions prevail today was always so. It ignores the 

134 W. H. BURT 

possibility of climatic change and the accompanying changes in 
flora. These changes, if they occurred, would have influenced not 
only distribution patterns but also population densities. 

3. The Area of Greatest Diver sificatioyi {at present) of the Group 
Is Likely the Place Where It Evolved into Its Present Phase. Some 
authors have thought that the area now supporting the greatest 
number of species (of a genus) must be the area where the group 
reached its present evolutionary phase; that far from the place 
where they evolved, individuals of a species are less plastic and 
less able to adapt to diversified conditions. However, this does not 
necessarily follow. It is usual to find diversity in a group (a genus, 
for example) in an area that supports many kinds of habitats, 
where ecological conditions are diverse. If these diverse ecological 
conditions have persisted over a long period of time in the same 
area, it is conceivable that many of the lower categories and, given 
enough time, the higher categories might have developed there. 
But, especially for the larger categories, this is problematical. 
They might or might not have evolved in the area. 

4. The Area Where Individuals Show the Highest Development, 
Are Least Primitive, Is Probably the Place of Differentiation of the 
Group. This is in keeping with Matthew's hypothesis. It is more 
likely to hold for the higher categories (families and orders) than 
for the lower ones. Without the fossil record, the same objections 
apply to this as to other hypotheses. 

5. Ecological Tolerance. Some authors have held that if a 
species can adapt to several kinds of habitat, if it is not confined to 
narrow ecological conditions, it still maintains a certain plasticity 
and some of its initial potential for adaptation. Therefore, this 
area, where the species is adaptable, is likely to be at or near the 
place where it evolved from its ancestral stock. This, of course, 
need not be true. 

These are some of the ideas that have been expressed by students 
of Recent biota. (For others, and a critique of them, see Cain, 
1944; Darlington, 1957, pp. 29-35). They are all indirect lines of 
evidence, but they may be used to advantage where other evidence 
is not available. If any one of the above criteria is used, it should 
be applied with extreme caution, because it may or may not lead 
to a true interpretation of the facts. Darlington (1957, p. 580) 
goes so far as to state: "I doubt whether any existing animals tell 


anything about more ancient times." But he does use present 
situations to explain past events. It is my opinion that the only 
indisputable evidence comes from the fossil record, but we can get 
leads from present distributions and relationships. However, I 
shall not dwell further on this subject here, but shall go directly 
to my principal topic, that of the present affinities of our Recent 
mammalian fauna. 

When one attempts to evaluate, or designate, affinities of two 
or more faunas, he must first indicate the criteria to be followed. 
It might seem simplest to count the species or genera, or whatever 
category is to be employed, apply a formula, and come up with a 
measure indicating degree of taxonomic resemblance between two 
or more faunas. This will give a quantitative measure and make it 
possible for us to communicate our results to our fellow workers 
without elaborate descriptive material. But, the source data are 
subject to errors, as I shall point out later, and the errors, if they 
exist, will influence the result. As in dealing with so many biological 
problems, a certain amount of subjectivity must enter the picture, 
and to reduce everything to numerical terms may be misleading — 
or downright wrong. Many non-taxonomists, and some taxonomists, 
I am sorry to report, think of species and subspecies of mammals 
as discrete entities. When they look at a check list, or faunal list, 
they assume that each name represents a distinct unit, and that all 
names in the same category represent units of equal value. Nothing 
could be farther from the truth. All the categories of mammals are 
to some extent subjective. In addition, they have changed with 
time. What was once a species may now be a genus or a family, 
either through evolution of the animals, if enough time is involved, 
or through changes in man's concepts. Let me give a couple of 
examples that I cited in a previous paper (1954). These have noth- 
ing to do with the evolution of mammals, but they do show the 
evolution of man's ideas. In 1909, when Osgood revised the genus 
Peromyscus, some twenty-eight named species in the literature 
ended up as one (maniculatus) , when he had finished his study. 
More recently, in 1951, Hall reduced what were listed as twenty-five 
species of weasels in the literature to three. I think it is apparent 
that if one were using numbers of species per se, in comparing 
faunas, the results would be quite different if data were taken from 
the 1908 literature or that of 1956. Yet, many biologists continue 

136 W. H. BURT 

to count names in a list and talce them at their face value. They then 
formulate hypotheses on what they innocently, but erroneously, 
think are substantial data. 

These and other problems have confronted me in the preparation 
of this paper, and I have found no good solution to them. I have 
tried various formulas for taxonomic resemblance, and will discuss 
some of these presently. However, no formula will give a correct 
answer unless the basic data are accurate. If we must use a formula, 
and this method has great popularity in biology today, I prefer 
one that takes into account the entire faunas, not just the smaller 
of two. The latter may be best for fossil faunas, as Simpson (1947) 
seems to think, but for our purposes I believe there are better ones. 
After counting the species and genera listed in the literature, 
primarily in Miller and Kellogg (1955) for North America, Ellerman 
and Morrison-Scott (1951) for Asia, and Cabrera and Yepes (1940) 
for South America, I decided to use the genus as my category for 
the application of the various formulas. I have also prepared a 
chart in an attempt to show graphically the relationships of these 
three faunas. Other authorities were also consulted, and when there 
was disagreement on a generic name, I arbitrarily included or ex- 
cluded the name as I thought best. The numbers used, therefore, 
should be considered approximate. I then employed "taxonomic 
intuition." With this system, I came up with similar, but somewhat 
different results. Neither system is accurate, but they show the same 
general trends which fit the concepts of every competent mammalo- 
gist today. My objective here is to test different methods of indi- 
cating taxonomic resemblance — to discover, if possible, how nearly 
accurate they are and where they might be misleading. I shall 
attempt to analyze some of these, but first I should like to indicate 
some of the perplexing problems that confront one in this kind of 

To begin with, our knowledge of the three faunas under con- 
sideration is not equal, so our basic data are not equivalent, and 
this in itself makes comparisons difficult. Our knowledge is best for 
North America, but even here we have many names in the literature 
that no doubt will be omitted from the books in another twenty-five 
years or so. As a matter of fact, our total knowledge of any one kind 
of mammal is inadequate to evaluate it properly in the whole 
scheme of things. 


Secondly, we have conservatives and liberals, or lumpers and 
splitters, among students of Recent mammals. Ellerman and 
Morrison-Scott (1951) tend to be conservative for genera and species 
while Cabrera and Yepes (1940) are quite liberal with the number 
of genera that they recognize. Miller and Kellogg (1955) include 
the findings in the latest revision of each group, with no critical 
analysis of their own, so their list is a mixture of conservatism and 
liberalism. In some groups, such as the Grizzly Bears, the last 
authors, following Merriam's 1918 revision, list no fewer than 69 
species for North America. They also give the black bear different 
generic rank (Euarctos) from the grizzly {Ursiis). In 1953, two years 
before the list by Miller and Kellogg appeared, Erdbrink included 
all the Recent bears in the one genus Ursus, and all the North 
American species of the grizzly, along with those from Asia and 
Europe, in the one species arctos. These two works represent extremes 
in the evaluation of names. It must be frustrating to the non- 
taxonomist to see two such treatments within two years by two 
different authorities. It is also frustrating to the taxonomist who is 
attempting to apply a formula for taxonomic resemblance between 
North America and Asia. 

Thirdly, and somewhat related to the two previous difficulties, 
is the fact that some kinds are considered in the literature to be 
conspecific or congeneric while others, probably just as closely 
related, are not. Some examples of species that are now considered 
by some, at least, to be conspecific for North America and Asia are: 
a shrew {Sorex pacificus), the gray wolf {Cams lupus), Arctic fox 
(Alopex lagopus), wolverine {Gulo gulo), two weasels (Mustela 
erminea and M. ?iwalis), moose {Alces alces), a ground squirrel 
(Citellus undulatus), and two voles {Microtiis oeconomus and 
Clethrionomys rutilus). Such kinds as the red fox (Vulpes), marten 
(Martes), river otter (Lutra), lynx {Lynx), lemmings {Dicrostonyx 
and Lemmus), chipmunk {Eutamias), and several voles and shrews 
are considered to be distinct species, at least in the literature. 
In a case like this, the counting of names without some evaluation 
may give a false impression. 

A fourth problem, but not a difficult one, is what category to 
use. If we simply count the species listed for western North America 
and for northeastern Asia, we come up with about 229 and 160, 
respectively. On the basis of species names, North America would 



appear to have a larger fauna, 229 to 160, but if we consider genera, 
it would have the smaller fauna, 68 to 93. South America, with 
114 generic names, tops them all. But this is not as bad as it might 
seem at first glance. Obviously, if we are comparing faunas which 
are relatively close geographically, and there are no great barriers, 
most of the genera will be common, so we should use a smaller 

Fig. 1. Chart showing relationships of non-flying land mammals on 
three continents. Number of genera is approximate. Shaded areas repre- 
sent parts of total faunas. Formulas at bottom are for taxonomic 

category such as the species. If we are comparing remote faunas 
where few, if any, of the species are common, we must use a higher 
category, the genus or family. 

These are some of the items that one must consider when com- 
paring faunas for resemblance. Now let us look at Fig. 1 and the 
measures we get by using different formulas. Numbers of genera 
listed in the literature are given in the left column and are plotted 
to scale in the others. My intuition tells me that South America 
has too many genera in the indigenous block, relative to North 


America and Asia. However, I am of the opinion that the number 
of common genera is near reaHty. The great variables, then, will 
be found in iV — C for each fauna, in any of the formulas used here. 
But, regardless of the formula used, the trend is the same for these 
three faunas, and all seem to be indicative of the relationships. In 
Simpson's formula, (C/Ni) X 100, if we compare western North 
America with Asia and South America, N2 could vary from 69 to 
infinity and the measure would be the same, 40 for western North 
America and Asia; 1 1 for western North America and South America. 
What his formula actually gives is the percentage of common 
kinds in the smaller of the two faunas, regardless of the size of the 
larger one. This formula is usable as far as it goes, but it is my 
opinion that it should be applied in both directions to give the true 
picture. This gives two measures and makes it more cumbersome to 
use than a formula that takes into account the total of the faunas 
to be compared and gives but one measure. Such a formula is the 
middle one in Fig. 1, [C/(iVi + N^ - Q] X 100. In this formula, 
C appears in both numerator and denominator, and the measure 
obtained is the percentage of common kinds in the total of two 
faunas. This formula works best if the two faunas being compared 
are equal, or nearly so, in size. If they are very unequal in size, 
and the smaller fauna is mostly common to the larger one, the result 
obtained may be misleading. 

The top formula, [2C/(iVi + N2)] X 100, where C appears only 
in the numerator, gives a measure, different from the others, but 
shows the same trend in the faunas here compared. 

In the figure, you will note that twenty-seven genera are common 
to North America and Asia (C = 27). Several genera have close 
relatives on the two continents, but, because of a different name in 
the lists, they will appear in that part of the fauna which is consid- 
ered indigenous. Some of these for western North America are: 
Scapanus (mole), Taxidea (badger), Tamiasciurus (red squirrel), 
Glaucomys (flying squirrel), Phenacomys (vole), Sylvilagus (cotton- 
tail), and Odocoileus (deer). These genera are given the same value, 
on the indigenous side for North America, as Dipodomys (kangaroo 
rat), Perognathus (pocket mouse), Thomomys (pocket gopher), 
and Antilocapra (pronghorn). But, they are related, and fairly 
closely, to their Asiatic counterparts, whereas kangaroo rats, 
pocket mice, pocket gophers, and pronghorns are not. If we use 

140 VV. H. BURT 

a formula based strictly on names in the literature, these relation- 
ships are obscured and given negative instead of positive weight. 
In my subjective system, which presupposes a knowledge of the 
group, these seven kinds would be added to C, to give it a value of 
34, instead of 27. Other adjustments would be made in various 
groups, either combining or separating them. With this system, I 
ended up with over half of the mammal fauna of western North 
America showing affinities with that of Asia, about 57 per cent. 
I believe this is nearer reality than anything the formulas would 
indicate. However, the results are not in a form that is easily 
communicable to other workers. By using this arbitrary system 
further, about 30 per cent, instead of 45 per cent, of the western 
North American mammals are considered as indigenous. In com- 
paring North and South America, I arrived at 13 per cent, instead 
of 19 per cent, of the western North American mammals showing 
affinities with those from South America. This is fairly close. 



Faunal relationships of the nature just discussed, where two land 
masses are now separated by water, indicate a movement of animals 
from one land mass to the other in past times. That there was a 
nearly continuous land connection from the beginning of the Ter- 
tiary to Pleistocene time between what are now the North American 
and Asiatic continents is well established. There is still doubt 
concerning the directions of movements of many kinds of mammals. 
This would be important to know, but it is not essential to the 
present discussion (see Simpson, 1947, for a summary on these 
connections and movements). But, a land connection is in itself 
not sufficient for the transfer of non-flying terrestrial mammals, 
unless it be a very short one which an animal might cross in a 
single journey. The distance from Cape Prince of Wales to East 
Cape, across what is now the Bering Strait, some 75 miles, might 
conceivably have been crossed by some of the larger mammals 
such as caribou, moose, elk, and bear, even though no vegetation 
were present. For the smaller mammals, some of which are restricted 
within fairly narrow limits to specific ecological conditions, I 
think it most unlikely that they would, or could, make the crossing 


without food and shelter. This principle was pointed out several 
years ago by Scott (1913, p. 143) in the following statement. 

In the case of lands newly raised above the sea and connecting formerly 
separated areas, it is necessary that they should first be taken possession 
of by vegetation, before they can become passable by animals, for the 
migration of mammals from continent to continent is an entirely distinct 
phenomenon from the annual migration of birds. 

Not only the land bridge, but the abutments to it must possess 
ecological conditions suitable for those kinds that are likely to make 
the crossing (Simpson, 1947). Simpson {ibid., p. 685), no doubt 
influenced by earlier workers such as Merriam (1894) and Scott 
(1913), stressed the climate as being "Not the only, but probably 
the most important, selective factor..." in the faunal interchanges 
between Eurasia and North i\merica. Further, he stated that 
"the migrants generally are those groups tolerant of relatively 
cold climates," and thereby gave importance to the temperature 
at the time of crossing. But, he did not rule out other ecological 
factors. I am of the opinion that climatic conditions, as regards 
movements of mammals over long periods of time, are important 
in an indirect way, as they affect vegetation and soils, rather than 
in a direct one. It is fairly well established that through Tertiary 
times the climate was more moderate than at present (Emiliani, 
1958). Even in the Pleistocene, the interglacial stages had fairly 
moderate climates (Deevey, 1949). Temperature tolerance in 
mammals is primarily physiological, and most of them can with- 
stand great changes if supplied with food. It is true that those 
mammals that live in cold-temperate climates, especially the large 
mammals that live above the snow, are tolerant of greater fluctu- 
ations in air temperature than are many of the tropical kinds. 
Yet, there are several kinds that range through the tropics to the 
colder regions today (mountain lion, Felis; river otter, Lutra; 
weasel, Mustela; and others). Recent studies, on the bioclimate of 
small mammals that live beneath the snow in winter in an Alaskan 
taiga, show that the temperature at ground surface, where many of 
the small mammals live, ranged through no more than 27°F from 
summer to winter, whereas the air above the snow ranged through 
152° F. The temperature where many of these small mammals 
live rarely goes below + 20° F even in the most severe winter 

142 W. H. BURT 

(Pruitt, 1957). It is misleading to consider air temperatures in 
relation to these forms. The microclimate in which they live is 
the important factor. 

The northern porcupine must have evolved a different physiology 
from that of its tropical ancestors to endure the low temperatures 
in parts of its present range, and this since Pliocene times when the 
Panama land connection was made between North and South 
America. Although the porcupine can den in a sheltered place, it 
must expose itself to the elements when it is feeding. I suspect that 
physiological evolution may proceed more rapidly than morpholog- 
ical change, although I have no direct proof of this. However, I 
think it not too far-fetched to postulate that physiological adjust- 
ment to climate might have kept pace with changing temperatures 
and that temperature per se was no direct selective mechanism 
in the interchange of mammal kinds between Eurasia and North 
America. In some kinds of burrowing mammals, type and depth of 
soil might be the important selective agent (Hardy, 1945). An 
analysis of the Recent mammalian fauna of western North America, 
with these considerations in mind, should throw some light on the 
general problem of what were or were not selective agents. Also, 
we should get some idea of the relative times of the last crossings 
made by each group. Not all mammals have evolved at the same 
rate, but close relationships should indicate recent crossings and 
distant relationships earlier crossings. We must first make one 
assumption, and it seems a reasonable one, i.e., that the habits of 
mammals have not changed markedly since the times when their 
ancestors had the opportunity to cross the land bridge. If this 
assumption is not valid, then we have no way of interpreting many 
of the phenomena of the past. Also, to have had an interchange of 
the kinds that are related and now living on the two continents we 
demand a corridor with the following specifications: There must 
have been soil and vegetation with a fairly continuous forest and 
areas of open savanna country. The two types of vegetative cover 
might or might not have been coexistent. These demands are in 
conformity with modern interpretations of past climate and vege- 
tation in the area of the approaches as well as of the land bridge 
itself (see Darlington, 1957, for a summary of studies in this area). 
In the following discussion of the various groups of mammals I 



have used the excellent summary of fossil evidence by Simpson 



Moles (Family Talpidae). These animals must have required a 
soil cover of the proper kind. This means also a vegetative cover 
and soil organisms for food. Our western moles today range no 
farther north than southern British Columbia. However, the eastern 
representatives go well into Labrador. The present distribution, 

Fig. 2. General distribution of the moles, Family Talpidae, of North 
America. Late crossings of the Bering land bridge are not indicated. 



relationships, and the fossil record would indicate an early Tertiary 
crossing. Late crossings are not indicated. This group has been on 
the North American continent long enough to evolve into two genera 
on the West Coast and three genera in eastern North America. 

Fig. 3. General distribution of shrews of the genus Sorex in North 
America. Late crossings of the Bering land bridge are indicated. The 
genus occurs also in Eurasia (Table I). 

A large area now separates the western and eastern kinds (Fig. 2). 
In like manner the Eurasian moles have evolved into several genera, 
all distinct from those of North America. Temperature probably 
would not have been a factor in dispersal of moles, but soil type 
would. Moles are able to survive in rather heavy soils as well as 


lighter, friable types, but arid conditions, with accompanying light 
soils and a paucity of soil organisms are not suitable for them. 

Shrews (Family Soricidae). Present day shrews live in various 
types of habitats and in various climatic zones (Fig. 3). With a 
vegetative cover of any kind they would find easy passage. Both 
early Tertiary and late passages are indicated by the fossil record 
and present relationships. 

Man (Family Hominidae). There is no problem here, even 
without a land bridge man could have made the crossing. 

Bears (Family Ursidae). There is no problem in getting bears 
from one continent to the other. Polar bears, which are not strictly 
terrestrial, are circumpolar in distribution today, and the other 
bears on the two continents are closely related (the grizzlies are 
considered to be of the same species by Erdbrink, 1953). Exchanges 
probably continued through the period of the last connection. 

Weasel-like mammals (Family Mustelidae). Fossil records in- 
dicate an early Tertiary passage and Recent relationships and 
distributions indicate late passages, particularly of the fisher, 
marten, otter, wolverine, mink, and weasels. The fisher and marten 
would indicate a forested bridge, the others might pass over open 
or forested country. Temperature would not be a factor with these 
animals. However, for some of the skunks (Mephitinae), particularly 
those of the genus Conepatus, climatic zoning could have served as a 
selective agent in late Tertiary and Pleistocene times. Mephitis 
and Spilogale now live under temperature conditions that are 
probably more severe than they were during much of the time that 
the two continents were connected. 

Dogs (Family Canidae). Because of the diversity of habitats 
occupied by this group, we need not look for special conditions to 
effect an interchange. Fossil records and present distributions and 
relationships indicate exchanges from early Tertiary to the last 
land connection. 

Cats (Family Felidae). Members of this family are nearly 
worldwide in distribution and occupy various habitats. Indications 
are that they passed from one continent to another many times 
from early Tertiary to Recent. Although some kinds are now 
confined to the tropics and some to cold areas, others, including 
Felis concolor, range through the different climatic zones. 

146 W. H. BURT 

Squirrels (Family Sciuridae). This is a diversified group with 
many closely related kinds on the two land masses today. Partic- 
ularly close, in the two areas, are the marmots (Marmota), ground 
squirrels (Cilellus), chipmunks {Eutamias), tree squirrels (Sciurus), 
and flying squirrels {Glaucomys in North America and Pteromys in 
Eurasia). For the passage of the marmots and ground squirrels, 
open savanna is required, but for the tree squirrels and flying 
squirrels, there must have been a fairly continuous forest. Climate 
and soil would have been influencing factors only as they affected 
the vegetation. There must have been several crossings up to and 
including the last land connections. 

One group in this family of rodents, the prairie dogs (Cynomys), 
apparently had their entire evolutionary history in North America. 
They are inhabitants of short-grass areas and require deep soil 
for their burrows. These conditions apparently did not prevail to 
the northward and they never reached the land bridge. 

Beaver (Family Castoridae). A forest, or cover of shrubs, and 
fresh water would seem to be required here. Fossil evidence would 
indicate an early Tertiary crossing. Present day relationships and 
distributions indicate a late crossing also. It is possible that there were 
several interchanges. Temperature would not have been a factor. 

New World mice and voles (Family Cricetidae). This group is so 
diversified that any type of vegetative cover would have sufficed. 
The subfamily Cricetinae, long-tailed representatives, probably had a 
fairly early ancestral crossing. Evidence of this is found in their 
present distant relationships and in the fossil record. A Pleistocene 
crossing is not indicated. However, the subfamily Microtinae now 
has close relatives on the two continents (in some genera the same 
species) so crossings must have persisted to the end of the last 
land bridge. Climatic conditions would not afTect this group directly. 
The vegetative cover postulated would suffice, be it forest or 
savanna. Why the North American cricetids or the Old World 
murids did not make the crossing is difiicult to explain. Some would 
argue that because they are ecological homologues, competition 
would keep the two groups separated. I am not convinced that 
this is the answer. It is possible that each group had its evolutionary 
history far to the south, fairly late, and that time was not sufficient 
for them to reach the bridge before separation of the continents. 
However, there is no good evidence of this. 

Mountain beaver (Family Aplodontidae). The little information 


we have on this group indicates a late Tertiary crossing from 
North America to Asia. A rather heavy vegetative cover is required. 

Jumping mice (Family Zapodidae). Conditions suitable for 
the Microtinae would be suitable for this group. Late crossings 
are indicated. 

Pikas (Family Ochotonidae). The fossil record would indicate a 
middle Tertiary crossing for this group, and present relationships 
indicate late crossings also. The pika now lives in talus slopes near 
timberline. For the first ancestral crossings, when climates were 
more moderate, a change in the habits of these little lagomorphs is 
called for. In the Pleistocene, environmental conditions suitable 
to present day pikas would have been more likely. 

Rabbits and hares (Family Leporidae). Either forest or savanna 
would have been suitable for the crossing of these mammals. Climate 
would not, in itself, have been a factor. Fossil evidence and present 
relationships indicate early and late crossings. 

Peccary (Family Tayassuidae). Indications are of an early 
Tertiary crossing. The peccary was then restricted to the North 
American (and later South American) continent from about middle 
Tertiary on. Open or wooded areas would have been suitable for 
the crossing. 

Deer (Family Cervidae). From about middle Tertiary on, 
members of this family probably crossed over the land bridge 
several times. The elk, moose, and caribou now have close relatives 
on the two land masses, an indication of late crossing. Most any 
vegetative cover would have been suitable for the crossing over. 

Bovines (Family Bovidae). The bison and big horn sheep both 
have close relatives on the two continents, an indication of late 
interchange. There is less certainty about the mountain goat 
(Oreamnos). From present relationships with Old World antelopes, 
the indication is that no late passages occurred. 

It will be noted that the groups in this section required only 
soil (moles) and a vegetative cover of savanna and forest (others) 
for a suitable corridor. Temperatures were at no time (except pos- 
sibly during the glacial stages in the Pleistocene) prohibitively low. 


Raccoons (Family Procyonidae). There is no indication of 
intercontinental exchange since the evolutionary phase in which 



Table I. Genera of Strictly Terrestrial, Non-Flying Mammals of 
Temperate North America," 30 of Which Also Occur in Eurasia 



































































































" Designation to eastern or western North America is arbitrary in many instances. 
One species of the genus Eutamias {minimus), for instance, occurs as far east as 
Ontario, yet it is designated western because that is where all the other species are 



Table I. — (Continued) 































































































































150 W. H. BURT 

ancestral forms can first be recognized as raccoons (subfamily 
Procyoninae). Raccoons proper probably had their early evolution 
in tropical America. Climatic zoning might have been a selective 
factor with these animals. However, they do range into southern 
Canada today and it is difficult to see why they did not reach 
Asia in late Tertiary or Pleistocene times. From fossil evidence we 
may assume that the early ancestors passed over in Early Tertiary 
times. The coati {Nasua) is a southern form that likely never did 
get very far north. Climatic factors could have been important in 
limiting the dispersal of this mammal. 

Ringtails (Family Bassariscidae). The ringtail occupies the 
same kind of situation as the coati (Nasua) discussed above. 

Prairie dog (Family Sciuridae). The prairie dog was mentioned 
earlier, but should be included in this section. It is an inhabitant 
of short-grass areas, and ecological factors probably prevented it 
from making the crossing. Although it now inhabits areas where 
winter temperatures are low, it avoids the extreme cold by going 
into hibernation. 

Pocket gophers (Family Geomyidae). The present and what we 
know of the past distribution of pocket gophers is primarily western 
North American. A segment inhabits southeastern United States. 
Their latitudinal range is from southern Canada to tropical America. 
They are excellent diggers and can occupy the regions of heavy 
soils as well as sandy loams. They apparently require soil moisture 
sufficient to grow a good cover of vegetation. Normally, non- 
forested areas are preferred. I suspect that a continuous, dense 
forest would be a barrier to their dispersal — shallow, rocky soils 
might serve the same purpose. Temperature probably would not 
have prevented them from reaching the land bridge — there must 
have been a barrier of forests or soil types, or both. 

Kangaroo rats and pocket mice (Family Heteromyidae). Here 
again, the fossil record indicates a strictly North American evolu- 
tionary sequence. Soil type is probably the most important limiting 
factor in the distribution of these rodents. Although partially 
fossorial, they are weak diggers and, therefore, they require friable 
soil. This kind of soil is to be found primarily in the arid and semi- 
arid western part of North America (Fig. 4). Some of these animals, 
particularly along the eastern border of their ranges, penetrate 
areas of fairly heavy clay soils, but they prefer the lighter types. 



They tolerate temperatures from those found In Death Valley in 
summer (about 120° F) to those of the northern Great Plains in 
winter (about — 40° F). I cannot see that temperature played a 

Fig. 4. General distribution of the genera Dipodomys (broken line 
boundary) and Perognathus (soHd line boundary). All evidence indicates 
that these mammals had their evolutionary history approximately within 
their present range. There is no indication that they ever approached 
the Bering land bridge. 

major role in keeping these mammals on the North American 
continent. I suspect it was soil type with the accompanying vege- 
tation that prevented these rodents from approaching the land 

Porcupine (Family Erethizontidae) . The porcupine did not 

152 W. H. BURT 

find its way to North America until after the Panama land connec- 
tion with South America was established. It has now penetrated to 
the far northern forests and no doubt would have made the crossing 
had it not arrived too late. Time, I suspect, was the important 
factor for the porcupine. 

Pronghorn (Family Antilocapridae). As far as known, this is 
strictly a North American product. Any intercontinental exchange 
must have been by pre-pronghorn ancestors. Why did not this 
animal reach Asia when other artiodactyls did? I suspect that the 
answer is to be found in the ecology of the pronghorn. It is an 
inhabitant of short-grass, semi-arid country. It is tolerant of low 
as well as high temperatures. If the ancestors of pronghorns had 
similar habitat preferences, we may assume that these short-grass 
semi-arid conditions did not form a pathway on the approaches or 
on the bridge itself. In this case, ecological conditions would serve 
as a selective agent to prevent movement of the pronghorn. 

Except for the coati and ringtail, these groups that apparently 
did not cross the land bridge now inhabit areas of lower winter 
temperatures than those that prevailed when the continents were 
connected. General ecological conditions, soil and vegetation, I 
suspect, were more important in restricting their northward move- 
ments than was temperature. For the porcupine it was probably 
the time element. The coati and ringtail conceivably could have been 
restricted by low temperatures. 


It is suggested that the term "origin" as applied generally to 
faunas or taxa be replaced by the term "evolutionary phase." 
Origin implies a fairly definite time and place for the beginning of a 
fauna or taxon. But the evolutionary process is a continuum, and 
a phase may represent a transition in time and space. 

The difficulties in evaluating mammalian faunas in order to 
designate affinities are pointed out. After a somewhat subjective 
analysis, it is concluded that over one-half (57 per cent) of the 
mammalian fauna of western North America shows affinities with 
the fauna of Asia, about 13 per cent with that of South America, 
and the remainder (30 per cent) may be considered as indigenous. 

Present relationships indicate an exchange of faunas in the past. 
Further, they indicate suitable habitats on land connections for 


those kinds that made the crossing from one continent to the other. 
The various groups of mammals of western North America are 
analyzed for habitat selection, and general ecological conditions 
are postulated for those that apparently made the crossing on the 
Bering land bridge. Ecological conditions, soil and vegetation, 
are considered to have been more important than climate, especially 
temperature, in preventing certain kinds from making the crossing. 
From the analysis of the mammalian fauna it is evident that 
generalizations are dangerous. Each kind must be judged by itself. 
What is applicable to one may not be to another. Still more hazard- 
ous would be the application of rules derived from the study of 
mammals to other classes of vertebrates or to invertebrates without 
first understanding those groups. 


Burt, William H. 1954. The subspecies category in mammals. Syst. ZooL, 

3 (3) : 99-104, 3 figs. 
Cabrera, Angel, and Jose Yepes. 1940. Historia Natural Ediar.-Mamtferos 

Slid- Americanos. Buenos Aires. 
Cain, Stanley A. 1944. Foundations of Plant Geography. Harper and 

Brothers, New York. 
Darlington, Philip J. 1957. Zoogeography. John Wiley and Sons, New 

Deevey, Edward S., Jr. 1949. Biogeography of the Pleistocene. Bull. 

Geol. Soc. Am., 60: 1315-1416. 
Ellerman, J. R., and T. C. S. Morrison-Scott. 1951. Checklist of Palaearctic 

and Indian mammals, 1758 to 1946. British Museum (Natural 

History). London. 
Emiliani, Cesare. 1958. Ancient temperatures. Sci. American, 198: 54-63. 
Erdbrink, D. P. 1953. A Review of Fossil and Recent Bears of the Old 

World, Pt. 2, pp. 321-597. Deventer-Drukkerij Jan de Lange. 
Hall, E. Raymond. 1951. American Weasels. Univ. Kansas Pubis., Mus. 

Nat. Hist., Vol. 4, pp. 1-466. 
Hardy, Ross. 1945. The influence of types of soil upon the local distribu- 
tion of some mammals in southwestern Utah. Ecol. Monographs 

15: 71-108. 
Merriam, C. Hart. 1894. Laws of temperature control of the geographic 

distribution of terrestrial animals and plants. Natl. Geogr. Mag., 6: 

. 1918. Review of the grizzly and big brown bears of North 

America. North Am. Fauna No. 41. 
Miller, Gerrit S., Jr., and Remington Kellogg. 1955. List of North 

American Recent mammals. U. S. Natl. Museum Bull. No. 205. 

154 W. H. BURT 

Osgood, W. H. 1909. Revision of the mice of the American genus Pero- 

myscus. North Am. Fauna No. 28. 
Pruitt, WilHam O., Jr. 1957. Observations on the biocHmate of some 

taiga mammals. Arctic, 10: 131-138. 
Scott, William B. 1913. A History of Land Mammals in the Western 

Hemisphere. The Macmillan Company, New York. 
Simpson, George Gaylord. 1947. Holarctic mammalian faunas and 

continental relationships during the Cenozoic. Bull. Geol. Soc, 58: 


Origin and Affinities of the 
Birds of Western North America 

Alden H. Miller 

Museum of Vertebrate Zoology, 

University of California, Berkeley 

In a well-illustrated talk, Dr. Miller presented 
a critical and characteristically lucid analysis of the origin and 
affinities of the birds of western North America, with special ref- 
erence to those of Asiatic and South American origin. He compared 
the eastern and western bird faunas of North America. One of the 
points he stressed is the high incidence of endemism in the Califor- 
nia fauna, conditioned in large part by the isolation of this fauna, by 
the arid lands of the Great Basin and the Colorado Desert. Pressure 
of other duties forestalled the preparation of his paper for publica- 
tion. — Editor. 



Origin and Affinities of the Present Western North 
American Reptile and Amphibian Fauna 

Robert C. Stebbins 

Museum of Vertebrate Zoology, 
University of California, Berkeley 


1 he present distribution of amphibians and 
reptiles in western North America suggests a comparatively recent 
(geologically speaking) trend toward widespread increasing aridity. 
This trend has been especially potent in affecting the course of 
evolution and distribution in the more sedentary, moisture-depend- 
ent species. Examples are presented from among the major groups 
of amphibians and reptiles. 

The origin and affinities of the present salamander fauna of the 
West are discussed. 


Evolution of a Coast Range Corridor in California 
and Its Effect on the Origin and Dispersal 
of Living Amphibians and Reptiles 

Frank E. Peabody^ and Jay M. Savage 

Department of Zoology. University of California, Los 
Angeles and Department of Biology, University of 
Southern California, Los Angeles 

1 hirty years ago, A. B. Howell wrote (1927, 
p. 18) that "the fauna of the Pacific Coast of the United States 
is of unusual interest, and presents many fascinating problems." 
After three decades of intensive study, Howell's statement is no less 
true, and many fascinating problems remain for the solving. How- 
ever, in three decades there has accumulated a great mass of infor- 
mation on the terrestrial fauna and flora of far western North Amer- 
ica. Numerous investigators approaching the region from the varied 
point of view of the zoologist, botanist, paleontologist, and geologist 
have worked to a large degree independently. Perhaps the time is 
right for significant syntheses culled from the data of biological 
and physical disciplines. 

Obviously, any synthesis must draw on the data of geology and 
paleontology as well as on that from the modern biota. A most 
important contribution of geology is that our western region is in 
the throes of violent physical revolution in marked contrast with 
long antecedent epochs of quiescence. Our modern biota exists in 
what we and many others regard as an interglacial stage of the 
Pleistocene epoch. A most important contribution of paleontology 
is the clear evidence of marked southerly shifts of isotherms on a 
continental scale culminating in the Pleistocene and integrated with 
profound topographic changes affecting vast inland areas. While it 
may be charged that the biologist has not sufficiently heeded these 

1 Deceased June 27, 1058. 



major contributions outside his immediate field, it is probably true 
that the paleontologist and even the geologist may profit from a 
closer look at biological data. It is the general purpose of the present 
paper to demonstrate the advantages of a many-sided approach to 
the problems of origin and dispersal of the biota of far western North 
America. Attention is focused on the late Cenozoic era because the 
historical events of that time are most completely documented and 
because these events produced the major patterns of origin and 
distribution of modern species. 

Distribution diagrams are based on the treatise by Stebbins 
(1954), with some emendations by the junior author. The distribu- 
tion patterns are selected to illustrate best the relationship to the 
coastal corridor. It is believed that the pattern of present distribu- 
tion of species provides a general indication of the point of origin 
with respect to the geologically recent corridor. Obviously, fluctua- 
tions must have taken place in the past as at present, as witness the 
northward advance of southern species and northward retreat of 
boreal species which are presently being documented across North 


Fossil remains of amphibians and reptiles are rare in North 
America west of the Mississippi and extremely rare in the far west. 
Some indication of the fact is afforded by the paucity of citations 
from bibliographic sources. For the 41 -year period from 1913 to 
1954, the journal Copeia, of the American Society of Ichthyologists 
and Herpetologists, contains only four papers describing Pleistocene 
reptiles, and only three papers on Pliocene reptiles (Reed, 1956). 
The more complete coverage in the Camp bibliographies of verte- 
brate paleontology over the 20-year period 1928-1948 includes ap- 
proximately eleven papers on amphibians, none concerning far 
western North America, and approximately sixteen papers on rep- 
tiles, none concerning the far west (Camp et al., 1940-1953). More 
current literature includes a few but important contributions, for 
example, the description of the salamander, Paleotaricha, from the 
Oligocene of Oregon (Van Frank, 1955), and contributions by 
Bayard H. Brattstrom (particularly 1954, 1955) and Richard G. 
Zweifel (1955, 1956) on the herpetofauna of the Tertiary and Pleisto- 
cene. In general the described fossils older than the late Pleistocene 


are rare, isolated fragments. Cave and asphaltic deposits of the late 
Pleistocene produce more remains, but nearly all are disarticulated 
and easy to overlook in the quest for larger and more durable re- 
mains of mammals and birds. 

Current interests of paleontologists in the washing and sifting of 
sediments for microfossils are greatly increasing the recovery of 
herpetological remains. For example, students of the University of 
California, Berkeley, have made large collections of small lizard 
remains from Eocene and Cretaceous strata of Colorado and Wyo- 
ming (Malcolm McKenna and Robert Estes, personal communica- 
tion). However, a fossil amphibian, particularly a fossil urodele, will 
continue to be a rare find for the paleontologist because of the an- 
cient trend toward deossification in their skeleton and because bone 
is a prime prerequisite for preservation. Fortunately, the fossil 
record of amphibians is enhanced significantly by the discovery of 
numerous, clear, and distinctive trackways of urodeles in Mio- 
Pliocene sediments of the Sierra Nevada Mountains in California 
(Peabody, 1940, 1954). 

A general conclusion from a survey of the paleontology of the far 
western herpetofauna is that considerable progress is to be expected 
in the future as a result of new techniques and of heightened interest 
in paleoherpetology. However, we cannot ever expect to approach 
the relative completeness of the mammalian record, and discoveries 
in the far west will continue to be infrequent. Also a necessary ad- 
junct to paleontological studies will continue to be more detailed 
osteological studies of living species. 

The fossil record of the herpetofauna, admittedly deficient, is 
complete enough to establish firmly some general considerations of 
historical importance. Fossils from the Cenozoic of Europe and 
North America clearly indicate great antiquity for most living 
genera of salamanders. By the dawn of the Cenozoic the three 
families of terrestrial salamanders, Salamandridae, Ambystomidae, 
Plethodontidae, were evolved, and by the Miocene epoch living 
genera of all urodeles were probably in existence. The most dramatic 
and unusual evidence of modern families and genera comes from the 
Mio-Pliocene trackways of the Sierra Nevada (Peabody, 1940) where 
the genera Taricha, Batrachoseps, and a Dicamptodon-l'ike form 
coexisted in association with a fossil flora described by Condit 
(1944). These trackways and the Oligocene skeleton of Paleotaricha 


from Oregon (Van Frank, 1955) clearly indicate an additional, 
important conclusion. Before the end of the Miocene epoch the far 
west possessed a salamander fauna distinct from those of eastern 
North America and Asia. The fossil record suggests that the antiq- 
uity of anuran development at the familial and generic levels was 
similar to that of the urodeles. However, the anuran fauna of western 
North America has not become as clearly differentiated from the 
eastern fauna. 

On a worldwide basis the antiquity of families and genera of 
modern reptiles does not correspond to that of the amphibians, that 
is, the rate of evolution has been faster. A general impression is that 
whereas most modern families, for example, the Iguanidae and 
Varanidae, were evolved before the beginning of the Cenozoic, the 
majority of modern genera in all families originated in middle to 
late Cenozoic. In any event, the fossil record has little to offer on 
the origin of modern genera and families of reptiles in far western 
North America. 

The fossil record makes little contribution to the origin of modern 
species of the herpetofauna generally. Our knowledge of specific 
characteristics of modern skeletons, of representative herpetofaunas, 
and of stratigraphic controls within the Quaternary epoch is much 
too deficient. Historical insight of the paleontologist would suggest, 
however, that in our far western area, physical events culminating 
in the Pleistocene epoch provided abnormally strong stimuli to the 
rate of evolution at the level of species and subspecies. 


Obviously the above account of purely paleontological contribu- 
tions to the stated theme of the symposium are disappointing and 
inadequate. With this fact all too apparent, the writers groped for a 
more significant contribution in the form of a multi-directional 
approach — essentially a new look at old data from geology, paleon- . 
tology, and herpetology. The senior author has long been fascinated 
by the classic rassenkreis of subspecies of Ensatina as ably described 
by Stebbins (1949). Reflection on possible historic controls of the 
sympatric association of Ejtsatina subspecies in southern California 
suggested that somehow the physical history of California may re- 
veal the vital causative factor — a possibility not entertained by 


Stebbins. Interest was stimulated by the discovery that southern 
Cahfornia is an area of relatively high incidence of sympatry be- 
tween closely related forms in the modern herpetofauna. While 
searching for the explanation for this phenomenon of distribution, 
the writers evolved the concept of a Pacific Coast Range corridor 
culminating in the Pleistocene epoch, accompanied by collateral 
physical changes and affecting directly the origin and distribution of 
the modern herpetofauna. The concept is hopefully presented as a 
useful adjunct to understanding of the problems of origin and dis- 
persal of faunas of far western North America. 

Evolution of a Coast Range corridor essentially involves the 
Central Coast Ranges, consisting of western and eastern segments 
and extending from San Francisco south to Santa Maria, and the 
Southern Coast Ranges extending from the Santa Barbara region 
through the Transverse Ranges. The corridor has important con- 
nections on the south with the Sierra block and with the Peninsular 
Ranges, both of which are genetically related to the Basin and Range 






Fig. 1. Lithologic provinces of California. The present Great Valley 
and Central and Southern Coast Ranges are the site of extensive marine 
deposition (to 50,000 ft. thick) from Cretaceous into early Pleistocene 
time. (After Camp.) 



Province of Nevada. The corridor is bordered on the west by the 
ocean and on the east by a great structural depression, only re- 
cently reclaimed from the sea by continental uplift. 

The data of geology (Taliaferro, 1943; Eardley, 1951) supply 
antecedent chapters in the formation of the corridor. Geomor- 
phologic provinces of California (Fig. 1) show that the site of the 
present corridor was dominated by a large geosyncline receiving 
mainly marine deposits in the approximate position of the Great 
Valley of California during most of the Cenozoic. Adjacent struc- 
tural basins of marine deposition to the south contributed to the 
limiting of the stable edge of the continent to a line running length- 
wise through the middle of modern California. The area of the 
corridor was an archipelago at best during most of the Cenozoic. 

During the Miocene epoch the area of the future corridor was 
essentially "wiped clean" of terrestrial organisms by maximum 
flooding of marine waters (Fig. 2). Flooding was followed by ac- 
celeration of orogeny in the Coast Range belt. The orogeny surged 
to one peak in late Pliocene, affecting mainly the western part of 
the Central Coast Ranges, and to a second peak in the Mid-Pleisto- 



Fig. 2. Late Miocene paleogeography of California, showing extensive 
marine flooding in position of present Central and Southern Coast 
Ranges. (After Camp.) 



cene, affecting the eastern part of the Central Coast Ranges and the 
Southern Coast Ranges generally. The last surge is still in its 
climactic phase as the present is a time of active orogeny. The mid- 
Pleistocene orogeny is associated with the final disappearance of 
Tertiary troughs of deposition and the foundering of considerable 
segments of the Coast Ranges into the Pacific Ocean. Also, and of 
particular importance to the corridor concept, a marked uplift of 


Fig. 3. Pliocene and early Pleistocene paleogeography, showing archi- 
pelagic nature of Coast Range region, and presence of strait connecting 
Pacific with San Joaquin embayment. (After Eardley.) 

epeirogenic proportions affected the continent generally and the 
area of the corridor in particular following the peak of mid- Pleisto- 
cene orogeny. (At present, dissected erosion surfaces exist at levels 
of several thousand feet elevation in the San Gabriel Mountains.) 
Volcanism appears to have occurred sparingly in the area of the 
corridor and has contributed little to its crust, 

Paleogeography of the Pliocene and early Pleistocene (Fig. 3) 
suggests that the Central and Southern Coast Ranges constituted a 
reasonably continuous land mass probably extending far northward 
but separated at the southern end from the continent proper by a 
wide strait. Distribution of terrestrial plant and mammalian locali- 
ties (Fig. 4) of Pliocene and early Pleistocene age suggests that the 



strait at the southern end of the future corridor opened directly 
westward from the southern San Joaquin embayment. In view of 
the many complexities of Coast Range geology it is difificult to 
follow in detail the rapid geomorphic changes attending Coast Range 
orogeny. However, the distribution of the modern herpetofauna in 
California suggests strongly that there was an important marine 
barrier in the position of the present Southern Coast Ranges, in fact 



Fig. 4. Distribution of terrestrial Pliocene and early Pleistocene 
localities for plants and mammals suggestive of southern strait connect- 
ing Pacific with San Joaquin embayment. 

precisely coincident with the strait shown in Fig. 3. Also a con- 
tinuity northwestward from the strait is indicated. The continuity 
need not have been geographic but was almost certainly zoogeo- 
graphic, allowing free access to northern species of the herpetofauna 
but not to southern species. Paleobotanical data (Axelrod, 1957) 
indicate that the marine strait was not a barrier to northward ex- 
tensions of tropical and subtropical floras (Fig. 5). In terms of the 
herpetofauna, it seems reasonable to conceive of a long peninsula 
or a series of closely adjacent islands forming a zoogeographic unit 
extending southward from the San Francisco region and including 
the Santa Lucia basement rocks as a relatively stable component. 





Fig. 5. Distribution of geofiora during Mio-PIiocene time. (After 
Axelrod (reconstructed).) 


Fig. 6. Alternative interpretations of zoogeographic peninsula existing 
in California during Pliocene and early Pleistocene time. 


Alternate maps may be presented (Fig. 6) depending on the pre- 
sumed position of the marine strait, but in both cases demonstrat- 
ing the barrier at the southern tip of the peninsula. The peninsula 
persisted until the second peak of Coast Range orogeny in mid- 
Pleistocene time and the following uplift brought the Clast Range 
corridor into being. 

Physical changes associated with Coast Range orogeny were not 
in themselves sufficient to convert the Coast Ranges into a zoogeo- 
graphic corridor. Entirely coincidental and independent climatic 
changes were in progress. The work of Chaney (1940) in paleobotany 
and of Durham in invertebrate paleontology (1950) has mutually 
documented a continent-wide shift of isotherms southward through- 
out the Cenozoic, reaching a maximum (with fluctuations) in the 
Pleistocene epoch. According to Durham, the 18°C marine isotherm 
was at latitude 35°N, coincident with the Southern Coast Ranges, in 
the late Pliocene, and shifted 7° southward (over 400 miles) at the 
peak of Pleistocene glaciation. Here is the climatic stimulus needed 
to force faunal elements southward into the peninsula, perhaps 
causing "jamming" or peninsular effects. Future study of fossil 
mammals in the presumed peninsular area may show such effects 
to be present. Certainly the marine faunas of the area are extremely 
provincial in character. However, this is commonly attributed to 
the many local, shifting basins of deposition attending the Coast 
Range orogeny. 

Coincidental with the Coast Range orogeny, the vast Sierra 
Nevada block began to tilt westward, so as to form a high crest 
running southward from a point near the present Lake Tahoe and 
curving westward to a junction with the Southern Coast Ranges. 
Axelrod's masterly use of paleobotanical data (1957) graphically 
portrays the rise of the Sierra Crest from an average of 3,000 feet in 
the Miocene to 8,500 feet in the Pleistocene, and the accompanying, 
drastic, climatic effect on vast inland areas of the continent. Un- 
doubtedly the formation of the Coast Ranges also contributed to the 
drying of the interior. The combination of geological and climatic 
changes in the far west resulted in a southward movement of the 
Arcto-Tertiary geoflora, especially along the coast, and a northward 
and northwestward movement of the Madro-Tertiary geoflora from 
a Mexican center of origin. A Neotropical-Tertiary geoflora re- 
treated southward along the coast. 


In summary: Geological data conclusively demonstrate that the 
Central and Southern Coast Ranges were formed largely from sub- 
marine portions of the continental shelf. The Coast Ranges then 
constituted a land bridge between northern and southern California, 
because a San Joaquin embayment to the east persisted as a marine 
barrier well into the Pleistocene. Later withdrawal of the sea from 
the embayment reduced the barrier potential between the Coast 
Ranges and the Sierra Nevada, but the low, wide, dry valley re- 
mains an effective barrier to many terrestrial organisms. 

There is no doubt that the Central and Southern Coast Ranges 
eventually formed a connecting bridge around the seaward side of a 
great structural depression, but the connection remained incomplete 
near the southern end until Mid- Pleistocene time. The area of the 
bridge is cut lengthwise by one of the world's major faults, the San 
Andreas. However, the movement along the fault is largely hori- 
zontal, and although there may have been horizontal displacement 
of several hundred miles in the Plio-Pleistocene, it is thought that 
the zoogeographic effect of the fault movement was negligible. Only 
after the second peak of Coast Range orogeny, accompanied by 
continental uplift, did the land connection become a continuous 
bridge or corridor available to the herpetofauna. 

The original point of view here presented is that the land connec- 
tion existed prior to the mid-Pleistocene as a large peninsula broadly 
connected northward to the continent, as a continuous zoogeographic 
(if not geographic) unit, and with an effective marine barrier in the 
form of a wide strait at the southern tip. The barrier remained until 
mid-Pleistocene time. At this time the Central and Southern Coast 
Ranges became an effective corridor for the dispersal of many ter- 
restrial organisms. 

During late Miocene and early Pliocene the peninsula was largely 
occupied by Neotropical and Madro-Tertiary geofloras. The Arcto- 
Tertiary geoflora was excluded and along with it the associated 
herpetofauna, on the basis of purely climatic control. At the same 
time, herpetofauna of Mexican origin and associated with the 
Madro-Tertiary geoflora may have been unable to reach the evolv- 
ing peninsula because of the marine barrier at the southern tip. The 
barrier, however, was not effective in limiting the northward exten- 
tion of the Neotropical and Madro-Tertiary geofloras. The above 
hypothesis is strengthened by the fact that no endemic species of 


the present herpetofauna exist In the stable Santa Lucia positive 
area of the peninsula. Geological and climatic events of the late 
Cenozoic preclude such endemism. Finally, the profound and com- 
plex influences brought to bear on the biota of the California region 
are shown to be the result of an entirely fortuitous combination of 
interacting geological and climatic changes having peak effect dur- 
ing Pliocene and Pleistocene time: evolution of the Coast Ranges; 
southward shift of marine and continental isotherms on a worldwide 
basis; rise of the Sierra Nevada crestline with concomitant drying 
of the interior; continental uplift. 


Arcto-Tertiary Species 

Major migrations of western geofloras described by Axelrod (1957) 
are important to an understanding of distribution changes in the 
contemporaneous herpetofaunas. The writers believe that the late 
Cenozoic herpetofauna of the west may be correlated broadly with 
the Arcto-Tertiary and Madro-Tertiary geofloras. Salamanders are 
fundamentally boreal and Arcto-Tertiary, the lizards and snakes 
are fundamentally Sonoran and Madro-Tertiary in historical rela- 
tionship. The frogs and toads are transitional in that some forms 
appear to be Arcto-Tertiary elements while others are of Madro- 
Tertiary relationships. Biijo boreas and Rana aurora are examples of 
the former; Bufo microscaphus, Rana boylii, and Rana miiscosa of 
the latter. As a result of the combination of geological and climatic 
events described above, the Arcto-Tertiary salamanders and frogs 
tended to move southward and split around east and west sides of 
the Great Valley depression. However, the western route down the 
corridor was not complete until the mid-Pleistocene. Thus until the 
last half of the Pleistocene a "dam" was in force which would allow 
accumulation of genetic differences between east (Sierran) and west 
(Coast Range) arms of Arcto-Tertiary dispersals. Unless the "dam" 
was in force until relatively late in the Pleistocene, the flow of 
genetic material down the corridor should have merged compatibly 
with the flow down the mainland to eastward. Apparently this was 
not the case. Once the corridor was in operation it was possible for 
an Arcto-Tertiary species to disperse southward, subject to fluctua- 
tions, in a pattern like that of Rana aurora (Fig. 7). Development of 
clines along the route would be expected, and do occur. Few of the 



Arcto-Tertiary species range around the southern end of the Great 
Valley at present, but many range around the northern end. 

Trans-valley "leaks" have occurred across the valley barrier 
but only from west to east at the position of the San Joaquin delta. 
Apparently the "leaks" became possible during relatively recent 


Fig. 7. Distribution of red-legged frog, Rana aurora. Pattern is 
typical of Arcto-Tertiary forms that have moved southward through 
Sierra Nevada and coastal corridor. Arrows in Figs. 7-18 indicate proba- 
ble movements from points of origin. (Figures 7-18 based on Stebbins, 
with some modifications.) 

fluctuation of humidity in the delta region. The subspecies xanthop- 
tica of Ensatina eschscholtzii has established a population in the 
Sierras and is currently showing some interbreeding with the es- 
tablished Sierran sxihs^ecies platensis (Fig. 15). Similarly, the coastal 
Aneides lugubris has established a population in about the same area 
as the subspecies of Ensatina (Fig. 8). In a valuable study of this 
phenomenon, Rosenthal (1957) points out that no Ijiological or 
physical factor, other than time itself, limits the Sierran range of the 



trans-valley leak, hence the Sierran population must be a recent 
introduction across the valley. The only other trans-valley leak 
noted seems to have occurred in the distribution of the limbless 
lizard, Anniella pulchra, which is a Madro-Tertiary species. Again, 
the leak has been from west to east, near the position of the delta. 
It is not known if moisture has been the critical factor here as it 
surely has been for the salamanders, or whether the leak is indeed 



\"LEAK" / 

\ ' 

Fig. 8. Distribution of arboreal salamander, Amides luguhris. Note 
trans-valley leak, which probably occurred in pluvial times and estab- 
lished species in Sierra foothills. 

genuine (the supposed leak may represent an inadequately known 
distribution of the lizard northward along the entire eastern side of 
the Great Valley). The few occurrences of trans-valley leaks em- 
phasize the overall efificiency of the Great Valley as a barrier to 
transverse dispersal between the corridor and the Sierras except at 
the north and south ends. Finally, no Arcto-Tertiary species appears 
to have moved down the corridor and back up the Sierras, or vice 
versa. Dispersals southward along the corridor and along the Sierras 
have remained largely separated in southern California in coastal 
lowland and interior highland, or have achieved only limited 
sympatry there. 



Madro-Tertiary Species 

Species of lizards and an anuran illustrate best the relationship of 
the corridor to Madro-Tertiary elements moving in from Mexican 
centers of origin. Southern mesic elements of the Madro-Tertiary 
complex invaded the corridor from the south end, but in a variable 
manner. The western spadefoot, Scaphiopus hanimondii, appears to 
have "flooded" the corridor (Fig. 9) and the adjacent valley to its 
northern end, meanwhile developing a wide disjunction in the lower 
Colorado Valley. A related, northern species in the Great Basin 
appears to be in the process of invading the San Joaquin Valley via 
Walker Pass. Patterns somewhat similar to that of S. hammondii 
occur in Bujo microscaphns and Ilyla arenicolor, without the pres- 
ence of a related Great Basin species. This suggests that species ap- 




Fig. 9. Distribution of western spadefoot, Scaphiopus hammondii, and 
Great Basin spadefoot, Scaphiopus intermontanus. Former now has 
disjunct distribution in Californias and areas to east. Apparently 5. 
intermontanus has recently invaded western Sierran foothills through 
mountain passes. 



proaching the southern end of the corridor from the interior en- 
counter a barrier at the southern Sierra crest and at the Transverse 
Ranges. Warming and drying trends may enable desert species to 
spread northward into the San Joaquin Valley via Walker, 
Tehachapi, and Tejon passes. Distribution of the desert night lizard, 
Xantusia vigilis (Fig. 10), indicates a relatively recent invasion via 
Tehachapi and up the Sierra foothills, and an invasion via Tejon 






Fig. 10. Distribution of desert night lizard, Xantusia vigilis. Invasion 
of foothills on both east and west sides of Great Valley is apparently 
progressing actively at present. 

and up the dry inner Coast Ranges. A somewhat older invasion 
through the passes into the San Joaquin Valley is suggested by the 
distribution pattern of the leopard lizard, Crotaphytus wislizenii 
(Fig. 11). The San Joaquin subspecies, silus, represents a stock 
difTerentiated from the parent subspecies of the Great Basin, and 
certainly reached the San Joaquin Valley from the south, across 
mountain passes, during a climatic fluctuation. 

Northern elements of the Madro-Tertiary complex have tended 
to invade the corridor from the north, following the path of Arcto- 
Tertiary species. The sagebrush lizard, Sceloporus graciosus (Fig. 
12), has differentiated a Californian subspecies, graciosus, which has, 



SO to speak, made an "end run" around the north end of the Great 
Valley and down the corridor. However, disjunct populations of 
this and the southern subspecies, vandenhurghianus , suggest a post- 
Pleistocene fragmentation and retreat northward. Somewhat similar 
distribution patterns are found in the ringneck snake, Diadophis 
amabilis, and the mountain kingsnake, Lampropeltis zonata. 

Fig. 11 

Fig. 11. Distribution of leop- 
ard lizard, Crotaphytus wislizenii. 
Race silus, is isolated in arid 
southern portion of Great Valley. 



/ V 



^^^^"^•:;il....VANDEN- , 


Fig. 12 

Fig. 12. Distribution of Scelo- 
porns graciosus, sagebrush lizard. 
Effect of coastal corridor on this 
mesic species and fragmentation 
of its range are noteworthy. 

The northern alligator lizard, Gerrhonotus cocruleus (Fig .13), and 
the foothill alligator lizard, G. muUicarinatus (Fig. 14), probably 
differentiated from an ancestral Mexican species. The derived 
species present a curious contrast in distribution. The northern 
alligator lizard appears to have made an "end run" around the Great 
Valley and invaded the corridor part way. The coastal arm is sub- 



specifically distinct. Generally the distribution pattern is like that of 
Sceloporus graciosiis (Fig. 12). The foothill alligator lizard, preferring 
warmer, drier habitat than the northern alligator lizard, ranges 
completely around the Great Valley and broadly up and down the 
California Coast. However, there is subspecilic differentiation, which 



Fig. 13. Patterns of distribution for northern alligator lizard, Gerrho- 
notus coeruleus, and related Sonoran alligator lizard, Gerrhonotus kingi. 
Filter effect of coastal corridor is clearly apparent. 

has highly interesting boundaries. Gerrhonotus muUicar hiatus webbii 
ranges the southern California Coast and up the Sierra Nevada, but 
is differentiated from the northern California subspecies precisely in 
the position of the marine barrier postulated earlier. This coinci- 
dence would be unimportant were it not for the fact that insular 
representatives of the two subspecies (Fig. 14) are also separated — 
multicarinatus occurring on four islands north of the mainland 
boundary, webbii on three islands south of the boundary. There is 



the possibility that the subspecies in the corridor came in from the 
North in the Pleistocene at a time when the marine barrier existed 
at the south end of the present corridor. In any case the coincident 
insular and mainland distribution suggests a certain antiquity of 
subspecific differentiation. It would be interesting to know the rela- 





Fig. 14. Distribution of foothill alligator lizard, Gerrhonotus multi- 
carinatus, and its relationship to range of Gerrhonotus kingi, Sonoran 
alligator lizard. Eastern species is more closely allied to G. muUicarinatiis 
than to G. coeruleus, and the last two forms occur sympatrically in many 

tive degree of differentiation between webbii and midticarinatus on 
the south and north ends of the San Joaquin Valley. 

In summary: Relations of A^Iadro-Tertiary species to the corridor 
and adjacent land features appear more varied than for Arcto- 
Tertiary species. Northern elements of the Madro-Tertiary moved 
around the north end of the Great Valley and down the corridor; 
southern elements moved up the corridor, or if xeric in habitat 
preference, met an effective barrier at the Transverse Ranges and 



the southern Sierra Nevada. Warm, dry trends of cHmate allowed 
xeric elements to move north through mountain passes and into the 
San Joaquin Valley and bordering foothills. 

Sympatry in Southern California 

Four cases of sympatry between closely allied forms occur in 
southern California. Two of the four cases involve amphibians of 
Arcto-Tertiary afTfinities; one of amphibians and one of reptiles are 
of northern Madro-Tertiary affinities. The sympatry is not of the 
same degree in each case, but it is sufficiently clear-cut to draw 
attention to its localized occurrence in southern California. The high 
incidence of sympatry here strongly suggests a controlling, historical 
factor. It is believed that this factor is primarily the evolution of a 
Coast Range corridor as outlined earlier. 

1. A classic rassenkreis of subspecies is represented by the dis- 
tribution pattern of Ensatina eschscholtzii in California (Stebbins, 







Fig. 15. Distribution of painted salamander, Ensatina eschscholtzii. 
Subspecies E. e. eschscholtzii and E. e. klanberi occur together in upper 
San Gorgonio River system, San Bernardino Mountains. 



1954, 1957). The pattern results from a southward movement of a 
boreal species that split around the Great Valley barrier (Fig. 15). 
The coastal arm is characterized by a solid color pattern, the Sierran 
arm by a spotted color pattern. Aside from a trans-valley leak noted 
earlier, the two arms maintain their identity at separate elevations 
in southern California, but are found in true (if limited) sympatric 
association at moderate elevations in the Peninsular Ranges. The 
Sierran arm has undergone more differentiation and more fragmen- 
tation, thus suggesting that it is older than the coastal arm. 

2. Two closely related species of the slender salamander, Batra- 
choseps attenuatus and B. paci'ficiis, are associated in extensive 
sympatry (Fig. 16) in southern California, along the coast (Stebbins 
and Lowe, 1949; Savage and Brame, 1957). The species may live 
together under the same rock or piece of wood. B. pacificus appears 
to be an older species in southern California, if judged from the 
degree of subspecific variation and particularly because of its oc- 



--^ A, PLIOCENE ") . 

^-T-^ / ^FOSSIL }-t 








^^^\CAr ^ 

Fig. 16. Distribution of slender salamanders, genus Batrachoseps. 
Slender salamander, B. attenuatus, is found in sympatry with worm 
salamander, B. pacificus, in numerous localities in Los Angeles and 
Orange counties of California, and on Santa Cruz Island. 



currence on six offshore islands, while the other species has managed 
only one insular invasion. Fossil trackways of Mio-Pliocene age, 
near Sonora in the Sierra Nevadas (Peabody, 1940) suggest that 
B. pacijicus was derived from the north in pre- Pleistocene time. 
B. attenuatus represents the appearance of a younger species in 
southern California, more advanced in a trend toward attenuation, 
and one that shows the forked distribution pattern of a boreal species 
with respect to the Great Valley barrier. 




Fig. 17. Distribution of yellow-legged frogs, Rana boylii and R. 
muscosa. The latter is found at high elevations in Sierra Nevada and in 
montane situations in southern California. Sympatry with R. boylii 
occurs at one locality in San Gabriel Mountains. 

3. The distribution pattern of the two species of the yellow- 
legged frogs, Rana boylii and Rayia muscosa (Fig. 17), displays a 
situation resembling that of Ensatina (Zweifel, 1955). The younger 
of the two species, boylii, ranges around the Great Valley barrier in 
the familiar forked pattern. The range is more or less continuous 
except for a small, disjunct population at the southern end, in the 
San Gabriel Mountains. Here there is a limited sympatry with the 
older species, muscosa. The older species ranges at high elevations in 
the Sierra Nevada and has undergone post-Pleistocene fragmenta- 



tion into populations on several mountain ranges of southern Cali- 
fornia — San Gabriel, San Bernardino, San Jacinto, and Palomar. 

4. Two closely related species of skinks (Fig. 18) show a limited 
sympatry in the Southern Peninsular Ranges of southern California. 
The sympatric relationship is not so well established as for Ensatina 


SYMPATRIC— 3Si!llX z' ^ ^ 



Fig. 18. Distribution of western skink, Eumeces skiltonianus, and 
giant western skink, Eumeces gilberti. 

and Batrachoseps, but appears to be valid. Also, it is more difficult to 
explain reasonably the location of the sympatry. However, the 
sympatry of the skinks is of particular interest for the reason that 
it is unique for closely related species of reptiles in the far west, 
and involves a northern Madro-Tertiary component that has made 
an end run around the northern end of the Coast Range corridor. 
The northern species, Eumeces skiltonianus, appears to have moved 
down the corridor along with boreal species. A few insular popula- 


tions, a derived endemic species {E. lagiinensis) at the tip of Baja 
California, and a disjunct population in southern Nevada suggest 
that the species was an early migrant down the corridor. Eumeces 
gilberti maintains strict separation of range along its western limits 
except for the sympatry in southern California. There may be a 
limited sympatry also at the northern end of the range. The species 
has several disjunct populations in the Great Basin and one in 
Arizona, all suggesting considerable post- Pleistocene fragmentation. 

The relatively high incidence of sympatry between closely related 
forms in southern California suggests a set of well-timed physical 
conditions which must first maintain genetic isolation and then 
allow the isolation to break down. If the Coast Range corridor, Great 
Valley, and Sierra block had possessed their present form and rela- 
tionship from Late Pliocene to Recent, it is doubtful that genetic 
isolation would have been maintained by west and east arms of 
species dispersing southward around the Great Valley barrier, 
whether or not gross climatic changes acted as stimulants. Some- 
thing must have blocked one of the dispersal routes. The evolution 
of a Coast Range corridor, as outlined earlier, exactly fulfills the 
conditions of time, place, and climate necessary to produce the ob- 
served sympatric conditions. Under the conditions that prevailed, 
sympatry anywhere else in the far west was unlikely. Also, it was 
unlikely under prevailing conditions that sympatry would develop 
in Madro-Tertiary species unless a northern element were to make 
an end run from the northern Great Basin to the west and down the 
corridor in company with purely boreal species. That this could 
happen is indicated by the somewhat special sympatry of the skinks 
(of example 4, above). Under the prevailing conditions Madro- 
Tertiary species of more xeric preference could not disperse up the 
corridor, and in fact, were barred from it until relatively recent 
times when dispersal over mountain passes has been possible. Fi- 
nally, it should be emphasized that the areas of sympatric associa- 
tion are precisely where they should be in relation to the presumed 
barrier to dispersal down the corridor in Pre-Middle Pleistocene 
time and to the junction of corridor and Sierran dispersals. (See 
Fig. 19 for summation.) 

The time when sympatry in southern California became possible 
must not be earlier than mid-Pleistocene time, if our concept of the 
evolution of the Coast Range Corridor is correct. Thus one is more 



al)lc to judge the relative age of west and east arms of dispersals 
reaching southern California via the corridor and the Sierran or 
Inland route. At least In the four examples of sympatry cited, It is 
fairly certain that the dispersals down the corridor are the "new-- 
comers" to southern California. The evidence of corridor evolution, 
together with relative development of insular populations and 

^=^-. y- 




Fig. 19. Map showing probable migration paths taken by modern 
amphibians and reptiles with respect to the Coast Range corridor and 
associated geographic features. 

development of post-Pleistocene fragmentation of patterns of 
distribution are keys to relative age determination. 

Coastal Islands and "Waif" Faunas 

Distribution of the far western herpetofauna on offshore islands of 
southern California (Stebbins, 1954) suggests that it may be profit- 
able to reexamine the established theory that the offshore Islands 
have been connected with the mainland at one time or another 
during the late Pleistocene. Among the amphibians, only Bairacho- 
seps, Aneides luguhris, and Hyla regilla have reached offshore Islands. 


These amphibia are well suited for "waif" dispersal and the main- 
land opposite the islands has numerous stream channels that fre- 
quently sweep enormous amounts of sediment and floating debris 
into the ocean. In the case of Batrachoseps, the older species {paci- 
ficus) on the mainland has populated the largest number (5) of the 
offshore islands. The younger species {attenuakis) has reached but 
one island (Fig. 16). 

The reptilian insular fauna appears erratic in distribution, and 
significantly there are no chelonians. Certainly the distribution of 
insular herpetofauna does not support the theory of "tied" islands, 
and the relationship of mainland herpetofauna to the Coast Range 
corridor suggests a generally high degree of sensitivity to land 


The fossil record at present contributes little to a detailed study 
of origins and dispersals of the modern herpetofauna of western 
North America. However, a synthesis of the data from geology, 
paleontology, and herpetology indicates that the far west, particu- 
larly California, was the locus of physical events during the late 
Cenozoic era that shaped the destiny of the modern herpetofauna. 
The synthesis reveals an especially intriguing example of the physi- 
cal factors inherent in biological evolution — the coincidence of time, 
place, and climate contributing to the randomness and opportunism 
of evolution. The synthesis suggests that such fortuitous interac- 
tions of time, place, and climate might be considered a major factor 
in biologic evolution, along with genetic variability, selective pres- 
sure, and geographic isolation. Perhaps this might be considered a 
fourth major factor in biologic evolution along with genetic varia- 
bility, selective pressure, and geographic isolation. Perhaps this 
factor could be included in the term "geodynamics." 

A major result of the synthesis is the concept of a Pacific Coast 
Range corridor which took shape in Pliocene and early Pleistocene 
time as a zoogeographic peninsula connected to the mainland on the 
north, and separated by a marine barrier strait from mainland to 
the south. After mid-Pleistocene time the peninsula became a con- 
tinuous corridor allowing dispersal in both directions, but causing 
a high incidence of sympatry in the herpetofauna of southern Cali- 
fornia. The study of origins and dispersals relative to the evolution 


of the Coast Range corridor would appear to represent a fruitful 
field of investigation, not only in herpetology but also other branches 
of natural history. Evolution of the Coast Range corridor provides a 
unique opportunity to study the influence of a small but efi'ective 
land bridge on its associated biota. Unlike large, classic land bridges, 
such as the Panamanian Isthmus, the Coast Range corridor is a 
phenomenon of small scale lending itself to intensive investigation 
from many directions by biologists and geologists alike. We may 
confidently reaffirm and echo A. B. Howell's assertion of thirty 
years ago that the fauna of the Pacific Coast is of unusual interest 
and presents many fascinating problems. Californians have a land 
bridge laboratory in their own back yard ! 


Grateful acknowledgment is given to Miss Madeline Peabody for her 
most valuable aid in drafting the illustrations and assisting with the 


Axelrod, D. 1957. Late Tertiary floras and the Sierra Nevadan uplift. 

Bull. Geol. Soc. Am., 68: 19-46. 
Brattstrom, Bayard H. 1954. Records of Pleistocene reptiles from Cali- 
fornia. Copeia, 3: 174-179. 
. 1955. New snakes and lizards from the Eocene of California. 

/. PaleontoL, 29: 145-149. 
Camp, C. L. 1952. Earth Song. University California Press, Berkeley, 

Camp, C. L., et al. 1940-1953. Bibliography of fossil vertebrates. Geol. 

Soc. Am.: Spec. Papers 27, 42; Memoirs 37, 57. 
Chaney, Ralph W. 1940. Tertiary forests and continental history. Bull. 

Geol. Soc. Am., 51: 469-488. 
Condit, Carlton. 1944. Pliocene floras of California and Oregon, Chap. 3, 

The Table Mountain flora. Carnegie Inst. Wash. Puhl., 553, pp. 

Durham, Wyatt. 1950. Cenozoic marine climates of the Pacific Coast. 

Bull. Geol. Soc. Am., 61, 1243-1264. 
Eardley, A. J. 1951. Structural Geology of North America. Harper, New 

Howell, A. B. 1927. On the faunal position of the Pacific Coast of the 

United States. Ecology, 8: 18-26. 
Peabody, F. E. 1940. Trackways of Pliocene and recent salamandroids of 

the Pacific Coast of North America. M. A. thesis in Library of the 

University of California, Berkeley. 


■ — ■ — — . 1954. Trackways of an ambystomid salamander from the Paleo- 

cene of Montana. /. Paleofitol., 28: 79-83. 
Reed, C. F. 1956. Index to Copeia 1913-1954. Science Press, Lancaster, Pa. 
Rosenthal, Gerson M. 1957. The role of moisture and temperature in the 

local distribution of the plethodontid salamander. Amides luguhris. 

Univ. Calif. Piibl. ZooL, 54: 371-420. 
Savage, J. M., and A. H. Brame. 1957. The Southern California slender 

salamanders: A solution of the Batrachoseps problem. (1957 meeting, 

Soc. Evolution, Stanford Univ.) (manuscript). 
Stebbins, R. C. 1949. Speciation in salamanders of the plethodontid genus 

Ensatina. Univ. Calif. Picbl. ZooL, 48: 377-526. 
— — ■ — ■. 1954. Amphibians and Reptiles of Western North America. Mc- 
Graw-Hill, New York. 
-. 1957. Intraspecific sympatry in the lungless salamander Ensatina 

eschscholtzi. Evolution, 11: 265-270. 
Stebbins, R. C., and C. H. Lowe, Jr. 1949. The systematic status of 

Plethopsis with a discussion of speciation in the genus Batrachoseps. 

Copeia, 1949: 116-129. 
Taliaferro, N. L. 1943. Geologic history and structure of the Central 

Coast Ranges of California. Calif. State Div. Mines, Dept. Nat. Re- 
sources, No. 118, pp. 119-162. 
Van Frank, Richard. 1955. Palaeotaricha oligocenica, new genus and 

species, an Oligocene salamander from Oregon. Breviora, Museum 

Comp. ZooL, Cambridge, No. 45, pp. 1-12. 
Zweifel, Richard G. 1955. Ecology, distribution, and systematics of frogs 

of the Rana boylei group. Univ. Calif. Publ. ZooL, 54: 207-292. 
. 1956. Two Pelobatid frogs from the Tertiary of North America 

and their relationships to fossil and recent forms. Am. Museum 

Novitates, 1762: 1-45. 


Origin and Affinities of the Freshwater 
Fish Fauna of Western North America 

Robert Rush Miller 

Museum of Zoology, University of Michigan, 
Ann Arbor 

1 he area covered by this paper is primarily 
North America west of the Continental Divide, northward to 
the Stikine River, British Columbia, and southward to the Rio 
Yaqui, northwestern Mexico. The Yaqui is included because it 
contains certain faunal elements derived from the Colorado River, 
and British Columbia is treated since its coastal streams include a 
number of Columbia River types (Lindsey, 1957). Excluded from 
consideration, except in passing, are the Arctic and Bering Sea 
drainages, and only mentioned is the interdigitation of Nearctic 
and Neotropical fishes in Middle America. 

Thirty families comprising nearly 200 species have been recorded 
from fresh water within this area (Table I). These groups form a 
diverse assemblage. Twelve of the families include species in the 
Western fauna that are predominantly marine, although some 
inhabit brackish water or invade fresh water to a limited extent, 
especially toward the tropics, e.g., herrings, flatfishes, silversides, 
mullets, sticklebacks, and gobies. Representatives of four families 
regularly pass only part of their life cycle in the sea or in fresh water 
(lampreys, sturgeons, some smelts, and most trouts). Species repre- 
senting four families were derived from marine ancestors but they 
are now virtually restricted to fresh water (a gizzard shad, Dorosoma ; 
a codfish, Lota; a viviparous perch, Ilysterocarpus ; and the fresh- 
water sculpins, Cottus). Two families, the whitefishes (Coregonidae) 
and graylings (Thymallidae) , are intimately related to the salmons 
and trouts (Salmonidae), which occur in either the sea or fresh water. 

In interpreting origins and dispersal patterns it is essential to 
distinguish the true freshwater fishes from these groups. Although I 







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consider affinities of the freshwater fauna as a whole, emphasis is 
placed on groups designated as primary (I) — made up of those fishes 
that throughout their known history have, with rare exceptions, 
been restricted to fresh water (Fig. 1). These comprise the great 
continental faunas dominant on all land masses save Australia 
(Darlington, 1957, Fig. 11); they fall principally into a single order 





Fig. 1. Primary freshwater fishes of North America. For simplifica- 
tion, the Lahontan Basin (labeled 2-7-8) is mapped too extensively, 
including areas treated separately under Isolated Basin Drainages. See 
text for discussion. See also Tables I-II. 


(Ostariophysi = Cypriniformcs) containing about 5,000 species. 
Also of value are the secondary (II) freshwater fishes representing 
groups largely restricted to fresh water but salt-tolerant and capable 
of occasionally crossing narrow sea barriers. The remaining fishes 
known from fresh water may be divided as follows (Myers, 1938, 
1951) : Diadromous (III), those that regularly migrate between fresh 
and salt water during a definite period of the life cycle. Vicarious 
(IV), essentially or presumably non-diadromous freshwater repre- 
sentatives of partly or primarily marine groups. Complementary 
(V), species that are often or usually diadromous and belong to 
marine groups that become dominant in fresh waters only in the 
scarcity or absence of primary and secondary fishes. Sporadic (VI), 
fishes living and breeding more or less indifferently in salt or fresh 
water or entering fresh water only sporadically. The 30 families 
recorded from fresh water within the area comprise 6 primary 
groups with nearly 100 species and 3 secondary families with only 15 
species. Thus the primary (I) and secondary (II) fishes constitute 
somewhat more than half the total number of species that occur in 
western fresh waters. 

The absence of a large and diverse drainage system, such as the 
Mississippi, and the general scarcity and instability of the aquatic 
environment help to explain why the freshwater fish fauna of the 
West lacks many of the families and genera, especially lowland types, 
that live east of the Rockies (Fig. 1). The depauperate western fauna 
comprises only half as many families and one-fourth as many species 
of primary and secondary fishes as the eastern fauna. It is made up 
of relicts, an abundance of monotypic genera, and a complex of 
endemic faunas with few widespread species in common. Many of 
the species are of restricted distribution (Fig. 2). 

Our knowledge of the systematics of this fish fauna is behind 
that of the other vertebrates. This is especially true of the published 
record. Although the few taxonomists who have worked with western 
fishes in the past quarter century have restricted most of their 
publication to the description of new taxa, I estimate that about 10 
per cent of the species have yet to be described. Rather considerable 
recent field work, begun in 1934, has built up a wealth of preserved 
material and observations that await critical evaluation. No up-to- 
date generic revisions have appeared, and the inadequate fossil 
record provides few hints for speculation on the interrelationships of 



Fig. 2. Approximate location of species of closely restricted distribu- 
tion in western North America. Note the concentration of localized forms 
in the Great Basin and in disrupted waters (in southern Nevada) of the 
Colorado River drainage. Only 14 of the 43 species occur outside of those 

the modern forms, particularly at the generic level. It is not sur- 
prising, therefore, that the affinities of many of the genera are 


The paleontological record of Tertiary and Quaternary fishes in 
western North America is meager. What little material is available 
has not received critical comparative study. For the most part, the 
available skeletal remains, particularly of the Pliocene and Pleisto- 
cene fossils, are hardly adequate for identification below the generic 
level or, occasionally, not even below the family. The only reason- 
ably well-known formation is that of the Green River Eocene, which 
involves a fauna too early in fish evolution to give much help in 
interpreting the modern forms. Tertiary fishes have been treated 
chiefly by Cope, and since his death in 1897, only scattered papers 
have appeared with little attempt at evaluation or reappraisal. 
Vigorous, organized search for and comprehensive study of late 
Cenozoic fish fossils by students thoroughly familiar with the Recent 
fauna is one of the urgent needs for advancing knowledge of the 
origin, dispersal, and evolution of the present fauna. 

Fossils representing nine families have been recorded from fresh- 
water deposits of Miocene to Pleistocene age in western North 


America (Cyprinidae, Catostomidae, Ictaluridae, Aphredoderidae, 
Centrarchidae, Salmonidae, Cyprinodontidae, Cottidae, and Gas- 
terosteidae) . The first five are primary division freshwater fishes; 
the remainder are of diverse origin (boreal, secondary tropical, 
marine types or derivatives). Certain Miocene fossils from the Great 
Basin, e.g., from the Humboldt Formation, Nevada, indicate that 
at this time there were kinds of fishes (a sucker, Amyzoji, and a pirate 
perch, Trichophanes) quite unlike those that now inhabit the West; 
Miocene and Pliocene sunfishes (Centrarchidae) of extinct genera 
from Oregon, Nevada, and Utah demonstrate that this family, now 
largely restricted to eastern North America, was then more wide- 
spread. A minnow from British Columbia, Leiiciscus rosei (Hussakof, 
1916), thought to be of Miocene age, probably represents the living 
genus Richardsonius , and a Miocene minnow from Nevada is of 
essentially modern facies (Hubbs and Miller, 1948, p. 26), From 
these sketchy data it may be inferred that during the long Miocene 
epoch and extending into the Pliocene, one family (Aphredoderidae) 
and a number of genera {Amyzon, sunfishes, Trichophanes) became 
extinct in the West, though relatives have persisted in eastern North 
America, and that, although the Miocene fauna as a whole is quite 
different from the existing fishes, at least one modern freshwater 
type {Richardsonius) probably became established during this 

Two early Pliocene fossils from beds within the Lahontan system 
of Nevada, a killifish {Fiindulus nevadensis) and a stickleback 
(Gasterosteus doryssus), belong to genera of coastal and lowland dis- 
tribution living today in western North America only along the 
Pacific slope. Their entrance into Nevada, perhaps in late Miocene 
or early Pliocene times, may have been from the southwest by way of 
what is now the Death Valley region, since fossil killifishes of the 
same genus occur there (Miller, 1945b) and sticklebacks are found 
as far south today as northern Baja California. 

Middle Pliocene fossils from the Bidahochi formation in the 
Colorado system of northern Arizona represent species of Gila and 
Ptychocheilus similar to the living forms that are adapted to a swift- 
water habitat. This suggests that the Colorado was then a swift 
river, and such an ecological picture is supported by recent studies 
of geologists on the evolution of the Colorado (Repenning et al., 
manuscript), A Pliocene minnow from the Esmeralda formation of 

194 R. R. MILLER 

Nevada, Leuciscus turneri (Lucas, 1900), is likely identical with a 
modern genus (Gila); the age of this formation, first thought to be 
Miocene, was discussed by Stirton (1936, 1939). 

A late Pliocene to early Pleistocene fauna from southern Idaho 
and eastern Oregon contains representatives of 6 families, including 
a catfish of the genus Ictaliiriis and a sunfish likely of the genus 
Lepomis ; the latter genus is now restricted to eastern North America 
and Ictaluriis is not native on the Pacific slope north of the Yaqui 
basin (Figs. 5 and 9). Both genera represent invaders from the East 
whose extinction in the Snake River basin in early Pleistocene times 
is probably correlated with lowering of water temperatures below 
the minimum spawning requirements of these fishes. Most of the 
fossils representing this fauna were discussed by Cope (1883, pp. 

This brief summary of the sketchy fossil record indicates the ur- 
gent need for research on the paleoichthyology of the later Cenozoic, 
particularly for comparisons of the fossils with their living relatives. 
Much of the material is not identifiable because of our inadequate 
knowledge of the osteology of modern fishes. 


The primary freshwater fish fauna of North America (Fig. 1) 
comprises 21 families with approximately 600 species. Although these 
are mapped by areas that generally follow major watersheds, it is 
not intended that these areas portray zoogeographic regions. The 
numbers, representing families, genera, and species, become less 
accurate south of the United States border. The richness of the 
Mississippi Valley fauna is noteworthy, as is the absence of primary 
fishes in the West Indies. In general, there is a trend toward more 
species to the south, perhaps correlated with more equable water 
temperatures and a greater diversity of habitats. The apparent 
richness of the Arctic fauna is largely the result of invasion of the 
Red River by Mississippi fishes during late Pleistocene times. 
Similarly, as a result of Glacial and Postglacial connections, the 
fauna of the Great Lakes basin is strikingly similar to, though 
smaller than, that of the Mississippi Valley. 

The Plateau Region of northern Mexico has provided a broad 
highway over which many Nearctic types have traveled southward. 
Although the bulk of these fishes are stopped by the east-west chain 


of volcanoes lyin^i? at about 19° N. Lat., a sucker {Idiohiis meri- 
dionalis) and a catfish {Ictaluriis meridionalis) have managed to 
reach the basin of the Rio Usumaclnta, Guatemala. The Mexican 
coastal regions, particularly the Atlantic coastal plain, have simi- 
larly allowed the northward penetration of Neotropical groups. A 
single representative each of the characins {Astyanax jasciatus) and 
cichlids {Cichlasoma cyanoguttatiim) has invaded the United States 
in extreme southwestern Texas, and the characin has moved into 
New Mexico (these two are the only primary families shared by the 
United States and South America). 

The southern end of the Middle American peninsula has been 
invaded by a number of South American groups, most of which 
drop out beyond western Panama, although the eel-like Gymnotidae 
are represented as far north as Guatemala. The fish fauna inhabit- 
ing the peninsular-like region between the Isthmus of Tehuantepec 
and Panama is dominated by secondary freshwater fishes, notably 
the Poeciliidae and the Cichlidae. The viviparous poeciliids pre- 
sumably arose within this area, diversified greatly, and spread 
northward and southward ; the cichlids and pimelodids, on the other 
hand, probably originated in South America and speciated in the 
unsaturated environment of Middle America. These two groups, 
with additions from the Characidae and Atherinidae, constitute the 
more tropical portion of Middle American fauna. Intervening be- 
tween this portion of the Middle American fauna and the Nearctic 
fauna of northern Mexico are several transitional faunas and the 
highly distinctive Lerma fauna, which includes a limited representa- 
tion of both middle American and North American genera, and is 
dominated by the endemic cyprinodont family Goodeidae and the 
endemic and diverse atherinid genus Chirostoma. The Lerma fauna 
may be regarded as a distinct element in the Middle American 

The relatively impoverished primary fauna of western United 
States is indicated for the 8 drainage areas shown on the map (Fig. 
1). Within the entire area there are only 6 primary families (Table 
I): the mudminnows (Umbridae), minnows (Cyprinidae), suckers 
(Catostomidae) , catfishes (Ictaluridae), trout-perches (Percopsidae), 
and sunfishes (Centrarchidae). The first three are regarded as of 
Eurasian origin, and the last three as North American. 

The mudminnows (Fig. 3) are represented by two genera, Nov- 




Fig. 3. New World distribution of the mudminnows (Umbra and 
Novumbra) and the blackfish (Dallia). The only other mudminnow, Umbra 
krameri, lives in eastern Europe. Dr. Norman J. Wilimovsky provided 
the northeastern limit of the range of Dallia. 

umbra (Fig. 4), a monotypic relict from the Olympic Peninsula of 
Washington (Schultz, 1936), and Umbra, with two species in eastern 
United States and one in Europe. The suborder (Haplomi = 
Esocoidei) to which these fishes belong contains also the pikes, 
which are circumboreal but most speciose in North America, and the 

Fig. 4. The western mudminnow, Novumbra hiibbsi, a relict species of 
the Chehalis and Deschutes rivers, Washington. (From original drawing 
by Dorothea B. Schultz; see Schultz, 1936, Fig. 38.) 



Fig. 5. Distribution of the North American freshwater catfishes, 
family Ictaluridae. Fossil occurrences of Ictalurus are shown for western 
North America only. (Modified from Rostlund, 1952, maps 18-20; 
Mexican portion original.) 

blackfish (Dallia), which lives in Alaska and Siberia. Although the 
present distribution suggests a North American origin, all known 
fossils, including the primitive genus Palaeoesox (Berg, 1936), are 
from the Eocene to Miocene of Europe. 

The North American catfishes, comprising about 6 genera and 35 
species, barely enter the western fauna with a single species in the 
Yaqui River. That these fishes formerly occurred much farther 
north in the West has already been pointed out. All known fossils 
are North American, as is the present distribution (Fig. 5). 

Trout-perches constitute a singular group represented by two 
monotypic genera, Columbia (Fig. 6) restricted to the basin of that 
name in the West, and Percopsis, of much wider distribution in the 
East. With the closely related monotypic pirate perches (Aphredo- 



Fig. 6. The Columbia River trout-perch, Columbia transmontana. 
(From original drawing by A. H. Baldwin; see Jordan and Evermann, 
1900, Fig. 330). 

Fig. 7. Distribution of the North American trout-perches and pirate 
perches. The fossil pirate perch, Trichophanes, is known only from north- 
eastern Nevada. (Percopsidae greatly modified from Rostlund, 1952, 
map 32, using Walters (1955), Lindsey (1956), and original data. Range 
of Aphredoderidae from unpublished map by Reeve M. Bailey.) 


deridae), they form a North American group known from Eocene 
to Recent (Fig. 7). 

The centrarchids, or sunfishes, comprise a compact family of 
about 11 genera and 30 species, which, except for the rehct genus 
Archoplites of California (Fig. 8), are confined to eastern North 
America (Fig. 9). The present center of distribution is in the middle 
and lower Mississippi Valley. Relatively numerous fossils are 
recorded from Oligocene to Pleistocene deposits of North America ; 
whether or not the Green River Eocene genus Priscacara is a sunfish 
has not been conclusively shown, although Regan (1915, p. 106) un- 
questionably referred it to the Centrarchidae. This freshwater 
group dates from the early Cenozoic and is closely related to the sea 
basses (Serranidae). Since as a whole sunfishes are characteristic of 
lowland waters, the sole survivor in the West presumably attained 
its present distribution prior to the formation of the Rocky Moun- 
tains and Sierra Nevada Ranges. 

The two remaining families, the minnows and suckers, account 
for 95 of the 99 species of primary freshwater fishes in western 
North America. The suckers, a compact group of 14 living genera^ 
and about 80 species, are known fossil and Recent from eastern 
Asia and Alaska, as well as from eastern and western North Amer- 
ica. In the New Worid (Fig. 10) they range southward on the 
Atlantic slope to northern Guatemala {Ictiobus, Rio Usumacinta) 
and on the Pacific versant to western Mexico {Moxostoma, Rio 
Armeria, Jalisco). In the Old Worid there are but two representa- 
tives, an ancient, monotypic genus in China {Myxocyprinus) and 
Catostomus catostomus, in eastern Siberia, representing a recent 
invasion of a species widespread in northern North America (Dar- 
lington, 1957, p. 31, Fig. 9). In the most recent treatment (Nelson, 
1948, 1949), division of the family into three subfamilies (Fig. 11) 
has been made largely on the basis of the morphology of the four 
highly modified anterior vertebrae (the Weberian apparatus) that 
connects the gas bladder with the middle ear. The Cycleptinae, with 
a primitive genus in each continent, might justifiably be segregated 
as two subfamilies with Cycelptiis as the North American and 
Myxocyprinus as the Asian representative. The Ictiobinae includes 
but 2 genera and 9 species in eastern North America and appears to 

1 The following are regarded as synonyms: Deltistes = Catostomus; Megapharynx and 
Placopharynx = Moxostoma; Megastomatobtis = Ictiobus. 



Fig. 8. Sacramento perch, Archoplites interruptus, the only native 
sunfish west of the Rocky Mountains. (From Jordan and Evermann, 
1902, p. 341). 

Fig. 9. Distribution of the Nearctic family Centrarchidae. Fossil 
records are indicated only for areas outside of the present natural range 
of the sunfishes. 



be a conservative group characteristic of lowland waters. The re- 
maining 10 genera belong to the Catostominae ; 2 of its 3 tribes, the 
Moxostomatini and Catostomini, contain over 80 per cent of the 
known species of suckers. Five of the 14 genera are monotypic: 
3 in eastern United States {Cydeptus, Lagochila, and Minytrema), 
1 in western United States {Xyrauchen, Fig. 12), and 1 in China 

Fig. 10. Distribution of the sucker family, Catostomidae, in North 
America and adjacent Siberia; one genus is endemic to China. Northern 
limit between western side of Hudson Bay and Coppermine River from 
Wynne-Edwards (1952, p. 18). 

(Myxocyprinus) . One genus in the East, Moxostoma, and 2 with 
most of their species restricted to the West {Catostomus and Pan- 
tosteus), account for 65 per cent of the modern species. 

The earliest possible fossil sucker remains (Hussakof, 1932, pp. 
16-17) are from Eocene deposits of Central Asia and are probably 
closest to the Chinese genus Myxocyprinus (Nelson, 1949, p. 566). 
The earliest reliably dated remains of the family in North America 


u. R. mii.i.i:k 










Fig. 11. Hypothetical phylogeny of the Catostomidae. The approxi- 
mate number of species in each subfamily and tribe is shown in the 

are from Miocene deposits in British Columbia, Nevada, and 
Colorado, and arc placed in an extinct genus Amyzo7i. Superficially, 
at least, this sucker bears a close resemblance to the living genus 
Ictiobus, but a careful comparison with Myxocyprinus may show 
Amyzon to be closer to that Old \\\jrld representative. Although the 
fossil evidence is inconclusive, it seems probable that the Cato- 
stomidae arose in southeastern Asia and soon crossed a Bering land 
bridge to America, leaving a relict in China, and that in late Pleisto- 

Fig. 12. Humpback sucker, Xyraiichen tcxanus, an endemic genus of 
the Colorado River s>'stem. (From original drawing by S. F. Denton 
(nuchal hump retouched); see Jordan and Evermann, 1900, Fig. 88.) 


cene time the North American species Catostomiis catostomus re- 
crossed to eastern Siberia. The recency of that crossing is indicated 
by the common occurrence, in Siberia and western Arctic America, 
of the same subspecies (Walters, 1955, pp. 295-296). 

It is rather generally held that the suckers are ancestral to (or at 
least more primitive than) the minnows, family Cyprinidae, but a 
comparative study of the upper jaw mechanism in the bony fishes 
led Eaton (1935, p. 168) to conclude that suckers undoubtedly 
descended from minnows. And, after studying skeletal features of 
two groups of Asiatic minnows and comparing them to those of 
certain catostomids, Ramaswami (1955a, pp. 152-153; 1955b, p. 
236; 1957) found certain catostomid skeletal features in members of 
the gudgeons, a subfamily of minnows inhabiting China, and con- 
cluded: "... it is not likely that the Catostomidae could have given 
rise to the Cyprinidae." The weight of present evidence thus indi- 
cates (Fig. 11) a cyprinid prototype as probably ancestral to this 

The carps and minnows comprise the largest of all freshwater fish 
families, the Cyprinidae, with an estimated 250 genera and up- 
wards of 2,000 species, inhabiting all the continents except South 
America and Australia. The group attains its greatest number of 
species and diversity of form in southeastern Asia, where the most 
generalized types also are found. Relatively, the family is not very 
richly represented nor is it particularly diverse in the New World, 
where there are only about 40 genera and 250 species, and the 
paleontological evidence indicates that minnows arrived here in 
comparatively recent times, not prior to the Miocene epoch. Whereas 
a number of distinct subfamilies are recognized in the Old World, 
for example in China (Chu, 1935), it is probable that all of the New 
World cyprinids belong to a single subfamily, the Leuciscinae 
{Notemigonus is possibly a member of the Abramidinae, but its 
relationships to that Old World group are in need of critical study). 
Not only lack of basic morphological diversity but also the readiness 
with which most American minnows hybridize (Hubbs, 1955) sup- 
ports the evidence that the group has not been here long enough to 
develop strongly divergent lines. 

About 27 genera and 58 species of cyprinids live in western North 
America. Of the genera 15 (or 56 per cent) are monotypic. Twenty 



are strictly western In distribution ; another, Gila,"^ has only 4 of its 
approximately 13 species living east of the Continental Divide 
(Miller and Uyeno, manuscript); 5 {Hybopsis, Hybognathus, No- 
tropis, Campostoma, and Pimephales) are clearly recent invaders 
from the East; and one {Rhinichthys) is well represented in both 
areas, although two-thirds of its species live in the West. The 21 

Fig. 13. New World distribution of the minnow family, Cyprinidae. 
The extreme northwestern portion of the range is taken from Wynne- 
Edwards (1952, pp. 18-19). 

genera that are strictly or virtually western may well be autoch- 
thonous, but it is clear that the family originated in southeastern 
Asia around the close of the Cretaceous. It has been suggested that 
there are close relationships between certain western genera and 
ones that occur in China and Japan — for example, between Mylo- 

* Because of inadequate information about the affinities of this genus, I recognize 
Gila, Richardsonius (Fig. 14), and Clinostomus as distinct genera, pending further study 
(see Bailey, 1956, p. 331). 



pharodon (California), Mylocyprinus and Mylocheilus (fossil, Idaho; 
Recent, Columbia River), and Mylopharyngodon (China). The indi- 
cated similarities in this series pertain to the common possession of 
crushing type (molariform) pharyngeal teeth, an obvious feeding 
adaptation subject to independent and repeated evolution through- 
out the family. More likely candidates are the western genus Gila 
and Tribolodo7i of the Japanese fauna. None of the affinities postu- 
lated above has been thoroughly investigated. At the present time, 
only one American genus, Gila, is regarded by some as congeneric 
with an Old World genus, Phoxinus (see Berg, 1949, p. 571), but I 

Fig. 14. Redside shiner, Richardsonius balteatus, of the Columbia 
River basin. Fish of this type represent the earliest known fossils of the 
Cyprinidae in North America. (From Jordan and Evermann, 1900, 
Fig. 105). 

do not accept this allocation for reasons already given. The New 
World distribution of the Cyprinidae (Fig. 13) indicates that this 
family is less tolerant of low maximum temperatures than are 
the Catostomidae. 

The three secondary families have barely been able to invade the 
western fauna from the south and southeast. One species of mojarra 
(Cichlasoma beani), of the tropical family Cichlidae, has managed to 
reach the Yaqui River; the genus to which it belongs is most speciose 
in Middle America, but was derived from a South American ancestor 
(Regan, 1906-08, p. xiii). The viviparous topminnows of the family 
Poeciliidae, exclusively American and essentially tropical, have 
moved a little farther north to the lower Colorado River system, 
where they are represented by a single species of Poeciliopsis in 
southern Arizona (two species occur in the Yaqui). The egg-laying 
killifishes of the family Cyprinodontidae, largely tropical but push- 



ing well into the temperate region of North America (Fig. 15), have 
penetrated Nevada and southeastern and coastal California, where 
they are represented by 4 genera and 1 1 species. This group is 

Fig. 15. New World distribution of the killifishes, family Cyprino- 
dontidae, a secondary freshwater group. 

Fig. 16. Railroad Valley springfish, Crenichthys nevadae, a relict 
confined to warm springs of the enclosed valley (Fig. 15, south central 
Nevada). Another species lives in a former tributary of the Colorado 
River and a related genus, Empetrichthys, inhabits the Death Valley 
system. (From original drawing by Grace Eager; see Hubbs, 1932.) 


dominant in the saline, alkaline, and frequently warm waters of the 
Death Valley system (Miller, 1948). Two of the four genera are well 
isolated relicts, Crenichthys, Fig. 16 (Hubbs, 1932), and Empe- 
trichthys, each with two species, and the two remaining genera 
(Fundulus and Cyprinodon) have their closest relatives in southern 
United States and northern Mexico. The importance of this sec- 
ondary family in indicating past connections of such disrupted 
drainages as the Death Valley system has been substantiated by 
geological evidence. 


In correlation with the physiographic disruption of the West 
during late Tertiary and Quaternary times, the fish fauna has 
differentiated within a group of isolated basins each with a more or 
less high incidence of endemism and generally having few strictly 
freshwater species in common (Hubbs and Miller, 1948). Seven 
main centers of endemism may be recognized constituting the fol- 
lowing drainage systems: (1) Colorado, (2) Sacramento, (3) 
Klamath, (4) Columbia, (5) Bonneville, (6) Lahontan, and (7) 
Death Valley (Tables I-II; Fig. 1). Not all the fishes inhabiting the 
West are included in these 7 systems since there are certain inde- 
pendent basins (for example, between the Lahontan and Columbia, 
Lahontan and Bonneville, and Lahontan and Colorado systems) 
that harbor a few primary species (about 13 in all) unknown else- 
where. The faunas of these extralimital systems are discussed later. 

Most species that occur in more than one of the seven isolated 
drainages belong either to the semi-marine groups (e.g., lampreys, 
sturgeons, smelts, most salmonids, and sticklebacks) or are moun- 
tain-creek types (such as mountain whitefish, cutthroat trout, and 
certain suckers and minnows, particularly the ubiquitous speckled 
dace, Rhinichthys osculus). The montane types probably attained 
their widespread distribution by means of stream captures, head- 
water distributary connections (like Two-Ocean Pass, Wyoming; 
Evermann, 1892, pp. 24-28, PI. II), or through stream shifting across 
low divides. The distribution of the genera of primary fishes that 
are common to a number of the basins (such as the suckers, Cato- 
stomus and Pmitosteus, and the minnows, Gila, Ptychocheilus, 
Rhinichthys, and Siphateles) probably took place largely in Pliocene 
or early Pleistocene times. 



Colorado River Complex 

The primary fish fauna of this basin, including that of the late 
Pleistocene tributary White River of eastern Nevada (Hubbs and 
Miller, 1948, pp. 95-98), is the richest and has the highest per- 
centage of species endemism (87 per cent) of the seven major drain- 
ages. Two factors contribute to this: (1) the basin developed as 
isolated segments for a long period prior to its formation as the 
continuous river we see today ; and (2) it has fewer competing groups 
of marine derivation than the three other coastal drainages (Sacra- 
mento, Klamath, and Columbia) and about half of these {Elops, 
Mugil, Eleotris, Gillichthys) are restricted to the terminal portion of 
the river and the others (Prosopmm, Salmo, Cottus) mostly to the 
higher headwaters. 

The affinities of the fishes vary in different parts of the Colorado. 
Cutthroat trout {Salmo clarki), mountain whitefish (Prosopmm 
williamsoni, Fig. 17) and sculpins {Cottus bairdi and C. annae), all 
confined to the upper portion, have their closest relatives in the 

Fig. 17. Breeding male and juvenile of the mountain whitefish, 
Prosopium williamsoni, a species of cold, clear mountain streams that has 
probably dispersed by stream capture. (From Jordan and Evermann, 
1900, Figs. 200, 200a.) 



Bonneville and upper Snake (Columbia) drainages. The middle 
section, in the vicinity of and including the Little Colorado River and 
the ancient White River, holds in common the species of the endemic 
cyprinid genus Lepidonieda (Miller and Hubbs, in press). The Gila 
River division has 8 endemic species, most of which are likely au- 
tochthonous but at least 2 {Cyprinodon and Poeciliopsis) of which 
were derived from the east and south, respectively. Except for 
headw^ater types, which are identical with or representative of 
headwater species of adjacent basins, 71 per cent of its total of 35 
species are confined to the Colorado. This bespeaks a long isolation 
from surrounding faunas. Only limited faunal exchange has taken 
place with the Rio Yaqui (1 sucker and 2 minnows have moved 
south from the Colorado and Poeciliopsis has moved northward 
from the Yaqui). 

Sacramento Complex 

The Sacramento-San Joaquin, streams entering Monterey Bay 
and San Francisco Bay, and the Russian River and other coastal 
streams north to the Mad River are included in this complex. Nine 
of the 13 families occurring here contain semi-marine species, and 
one {Hysterocarpus traski of the Embiotocidae, Fig. 18) is the only 
freshwater representative of an otherwise wide-ranging marine 
family. The only native centrarchid west of the Rocky Mountains 
survives in the lowland waters but has been greatly reduced from its 


Fig. 18. Tule perch, Hysterocarpus traski, the only freshwater mem- 
ber of its marine family (Embiotocidae). (From original drawing by W. S. 
Atkinson; see Jordan and Evermann, 1900, Fig. 577.) 

210 K. R. MII.I.KR 

one-time abundance, presumably through competition with intro- 
duced fishes. Sculpins are common (5 species of Cottus and 1 of 
Leptocottus) , but suckers are not numerous; minnows have developed 
5 endemic genera (in part, perhaps relicts). The fish fauna shows 
affinities with each of the surrounding basins, the Columbia (Ptycho- 
cheilus, Siphateles) , the Great Basin {Gila, Siphateles), the Klamath 
{Cottus), and the Colorado {Ptychocheilus). High endemism (75 
per cent) at the species level indicates rather long and effective 
isolation for much of the basin. The likely mode of penetration of 
Great Basin types was indicated by Robins and Miller (1957, pp. 

Klamath River 

Studies of the geology and ichthyology of this drainage indicate 
that the part above Klamath Falls has only recently established an 
outflow to the Pacific by the headward erosion of Klamath River; 
certain elements of the fauna largely or entirely restricted to the 
lakes and streams above the Falls strongly suggest former connec- 
tions with the Great Basin (Hubbs and Miller, 1948, pp. 67-68; 
Robins and Miller, loc. cit.). Nine genera and 13 species occur above 
the Falls, and of these, 8 species {Entosphenus tridentatiis, Salmo 
clarki, S. gairdneri, Catostomus snyderi, Gila bicolor, Rhinichthys 
osculus, and Siphateles bicolor) have also been reported from below 
(Snyder, 1908). Catostomus snyderi and Gila bicolor are known from 
single records only but Siphateles bicolor was taken at 3 localities by 
Snyder (1908, p. 159, as Rutilus bicolor). On distributional grounds 
it is clear that these three species were originally present only in the 
upper part of the Klamath basin and gained access to the remainder 
of the river by being carried downstream over the Falls. It is likely 

Fig. 19. Klamath Lake sculpin, Cottus princeps, a vicarious fresh- 
water fish restricted to Upper Klamath Lake, Oregon. (From original 
drawing by Anna L. Brown; see Gilbert, 1898, p. 12.) 


that Rhmichthys osculus (Agosia nuhila and A. klamathensis of 
Snyder) moved in the same direction, since the species does not 
otherwise occur south of the Coquille River, Oregon, or north of 
the Sacramento River system. Ten genera and 19 species have been 
stopped by the Falls; only one of these, Catostomus rimiculus, is a 
primary fish (known elsewhere only from Rogue River, Oregon). 
Two species of Cottus (C. prmceps, Fig. 19, and C. tenuis) are con- 
fined to the Upper Klamath basin. The percentage of endemism at 
the species level is lowest in this system. 

Columbia Complex 

This system, as here expanded to include not only the Columbia 
River but also the Umpqua, Malheur, Fraser, Skeena, and Stikine 
rivers, is the largest of the centers of endemism (Fig. 1). The Snake 
River above American Falls is not included in the complex, as this 
part is faunally allied to the Bonneville Basin and received the outlet 
of Lake Bonneville. In correlation with its size, the Columbia has 
the richest fauna — 15 families, 29 genera, and 57 species. However, 
its primary fishes, though including four families, are not as numer- 
ous as in the smaller Colorado complex (Table I). The accessibility 
of the Columbia to the wealth of marine and semi-marine types ac- 
counts for its large total fauna but also is correlated with a relatively 
weak primary fauna with specific endemism at about the same level 
as that of the Klamath River. A noteworthy element of the fauna is 
the richness of the genus Cottus, the Columbia River system alone 
containing about 12 species (6 endemic). Salmonoids also are nu- 
merous, constituting 6 genera and 13 species, including Thymalliis 
arcticus from the Stikine River only and Coregonas clupeaformis 
from the Skeena and Fraser rivers (Lindsey, 1956, p. 763). 

The primary fauna shows relationships with that of eastern United 
States: 4 species occur on both slopes of the Continental Divide 
{Catostomus catostomus, Hyhopsis plumbea, Hybognathus hankinsoni, 
and Rhmichthys cataractae). Two, Siphateles bicolor and Pantosteus 
platyrhynchus, are invaders from the Great Basin. Novumbra huhbsi 
and Columbia transmontana are ancient (Miocene?) relicts. 

Bonneville System 

This is the largest of the Great Basin drainages with about 21 
species, 67 per cent of which are endemic (Table II). Included is the 

212 R. R. MILLER 

Snake River above American Falls, into which Lake Bonneville 
overflowed in late Pleistocene times. Excluded from consideration 
in the Bonneville fauna, however, are two suckers {Catostomus 
catostomus and C. columbiamis) known from the upper Snake (and 
elsewhere in the Columbia complex) but absent from the Bonneville 
system. These two species are believed to represent part of the origi- 
nal Snake River fauna that survived a volcanic deluge which pre- 
sumably destroyed the other species during or after the formation of 
American Falls but prior to the overflow of Lake Bonneville (Hubbs 
and Miller, 1948, p. 30). 

Table II. Fishes of the Great Basin 










Primary (I) 


5 7 

4 5 

2 5 

2 3 


3 5 

3 3 

2 3 

1 1 

Secondary (II) 


1 1 

2 6 


Coregonidae (III) 

1 4 

1 1 

Salmonidae (III) 

1 1 

1 3 

1 1 

Cottidae (IV) 

1 4 

1 1 

— — 






% Endemism 

Primary (I) 

25 67 

14 78 



All families 

18 62 

10 69 


20 90 

" These include basins between Pluvial Lake Lahontan and the Columbia, Bonne- 
ville, and Colorado systems (see Hubbs and Miller, 1948, pp. 43-67). 

The affinities of the upper Snake and the Bonneville Basin proper 
indicate that 5 species {Prosopiiim williamsoni, Salmo clarki, Cato- 
stomus ardens, Rhinichthys cataractae, and Cottus bairdi) entered 
Lake Bonneville from the Snake River; 4 species {Pantosteus platy- 
rhynchus, P. virescens, Gila atraria, and Snyderichthys copei) moved 
northward into the Snake; and 3 species {Rhinichthys osculus, 
Richardsonius halteatus, and Cottus heldingi) may have moved either 
or both ways. Two primary genera {Richardsonius and Chasmistes) 
are shared with the Lahontan system and 4 montane species {Pro- 
sopium williamsoni, Salmo clarki, Rhinichthys osculus, and Cottus 
heldingi) are common to these two drainages. The Lahontan rela- 
tionships indicate a former connection, perhaps of Pliocene or early 


Pleistocene age, between the Bonneville and Lahontan basins. Three 
of the 4 species (mountain whitefish, cutthroat trout, and Cottus 
bairdi) shared with the Colorado River are headwater types and 
indicate headwater transfers from the Bonneville into the Colorado 
(the fourth species, R. osculus, is too poorly analyzed and too wide- 
spread to be of much zoogeographic value). 

Lahontan System 

This isolated basin is second in size of the interior drainages and 
second also in the number and variety of its fishes, with 78 per cent 
of the primary species endemic (Table II). It has very little of 
significance in common w^ith the Colorado River (for example, that 
basin lacks Chasmistes, Siphateles, and Richardsonius , and Gila is 
absent from the Lahontan basin), but shows afiinities with the 
Klamath, Columbia, Bonneville, and Death Valley systems. Unlike 
Lake Bonneville, Lake Lahontan had no outlet in late Pleistocene 
time and the connections with the surrounding basins were either 
of comparatively recent headwater exchanges across existing divides 
(whitefish, trout, and Cottus) or more ancient low-elevation trans- 
fers, e.g., of Chasmistes (Hubbs and Miller, 1948, p. 40). Black- 
welder (1948, p. 12) felt that a mid-Pleistocene outlet of the Lahon- 
tan basin to the sea via Pit River into the Sacramento or into the 
Klamath, or northward into the Columbia, is a plausible speculation. 

Death Valley System 

This much disrupted drainage is noteworthy for the lack of 
salmonoids and Cottus, the strength of secondary types (6 out of 10 
species), and the weakness of the primary fauna (Table II). The 
highly saline, often warm, and alkaline waters of a large part of the 
system are particularly suited to the family Cyprinodontidae, of 
which all the species and 1 of the 2 genera are endemic (Miller, 1948). 
That this family has been in the system for a long time is attested 
not only by the high degree of endemism but also by the fossil 
record (Miller, 1945b) of Cyprinodon and Fundulus from Tertiary 
deposits in Death Valley. The endemic genus Empetrichthys was 
probably derived from Fundulus. 

The faunal relationships point to a former connection to the south- 
east, probably in Pliocene time, with what we now know as the 
Colorado River, and from the north, with the precursor of Lake 

214 K. R. MILLER 

Lahontan. Evidently the invasions were not simultaneous since the 
movement southward of Siphateles was timed so that this genus did 
not become established in the Colorado complex. The hypothesis 
that Siphateles (as well as Catostomus and Rhinichthys) entered the 
Owens River portion of the Death Valley system from the Lahontan 
basin via the Mono Lake basin (Hubbs and A/Iiller, 1948, p. 79) fails 
to explain why Prosopium, Salmo, and Cottus, common associates of 
Catostomus and Rhinichthys (if not of Siphateles), are absent from 
the Death Valley system. The common occurrence of Siphateles 
points to an earlier, low-elevation connection such as may have per- 
mitted the entrance into the Lahontan basin of Fundulus and 


The fauna of the Rio Yaqui, of coastal streams from Baja Cali- 
fornia to central California, and of certain isolated waters not in- 
cluded in the seven centers of endemism are briefly discussed here. 

Yaqui River 

The fauna of the Yaqui River of northwestern Mexico is distin- 
guished from that of the drainages already discussed by the presence 
of a native freshwater catfish {Ictaluriis pricei), a cichlid (Cichla- 
soma beani), and a host of tropical fishes of marine derivation 
{Dorosoma, Lile, Galeichthys, Centropomus, Dormitator, Trinectes, 
etc.). It has the largest number of families, 16, and is second to the 
Columbia and Sacramento in number of genera. Only 12 of its 31 
species are primary freshwater fishes (Table I). Not included in 
the tabulation are Gila ditaenia (Miller, 1945a), of the Rio de la 
Concepcion, and Catostomus wigginsi (Herre and Brock, in Herre, 
1936), of the Rio Sonora, both independent tributaries of the Gulf 
of California lying between the Yaqui and Colorado drainages. The 
relationships of the minnow are with Gila purpurea of the Yaqui 
and G. orcutti of southern California; those of the sucker have not 
been determined. 

Seven of the 12 primary species are Rio Grande types, which, it is 
plausibly postulated, have entered the Yaqui by stream capture 
across the Sierra Madre Occidental (Meek, 1904, p. xxvii). These are 
Pantosteus plebeius, Campostoma ornatum, Gila'' nigrescens,'' Notropis 
mearnsi, N. ornatus, Pimephales promelas, and Ictalurus pricei. Pre- 


cisely when antl where they or their immediate ancestors arrived lias 
not been stated. Study of the physiographic map of Mexico pre- 
pared by Hoy (1943) and of World Aeronautical Charts 470 (San- 
tiago Mountains, 1950, rev. ed.) and 520 (Lake Santiaguillo, 1951, 
rev. ed.), shows that capture of a tributary of the Rio Conchos by 
the Rio Papigochic (of the Yaqui system) could readily have taken 
place about 28 airline miles south of Minaca, Chihuahua. Also, 
instead of taking the abrupt horseshoe turn that the Papigochic 
now follows northwest of Minaca, this segment of the stream may 
formerly have flowed northward to form the headwaters of Rio 
Casas Grandes, a stream of interior drainage in Chihuahua. In either 
event, Rio Grande types would have been transferred to the Yaqui 

Three species, Catostomus bernardini, Agosia sp. (near chryso- 
gaster), and Gila minacae (= G. robusta; Miller and Uyeno, manu- 
script), are the same as or most closely allied to Colorado River 
species, and thus indicate entry into the Yaqui from the north. The 
2 remaining primary fishes are a sucker (Catostomus) and a minnow 
(Gila purpurea). The former, of uncertain relationships, occurs in 
the headwaters of both the Yaqui and the Casas Grandes, whereas 
the latter, related to G. orcutti and G. ditaenia, inhabits the Yaqui 
and Rio Sonora. No genera are endemic and but one species, No- 
tropis mearnsi, scarcely distinct from N. formosus of the Rio Casas 
Grandes, is regarded as indigenous. 

Minor Coastal Drainages 

Streams and interior springs from central Baja California north- 
ward to San Luis Obispo Creek, California, harbor limited fish faunas 
(arbitrarily combined in Table I). Although 12 families are repre- 
sented, these comprise only 18 species, of which but 3 are primary 
freshwater fishes. One of these, Rhinichthys osculus, is of little 
zoogeographic help. Gila orcutti, with its closest relatives in northern 
Sonora (G. ditaenia) and in the Yaqui (G. purpurea), evidently came 
into southern California from the direction of the Colorado River. 
The third freshwater fish, Pantosteus santaanae, is most closely re- 
lated to species now inhabiting the Great Basin, whence it pre- 
sumably came, perhaps in Pliocene time. 

The two secondary fishes, Fmidulus parvipinnis and F. lima, are 
the only Pacific representatives of a genus that has its center of 

216 R. R. MILLER 

abundance in southeastern United States (Miller, 1955), but which 
was once more numerous west of the Continental Divide, whence 5 
fossil species have been described (Miller, 1945b). 

Isolated Basin Drainages 

Certain isolated basins lying between the Lahontan, Bonneville, 
and Colorado systems harbor a small but interesting remnant fish 
fauna (Hubbs and Miller, 1948, pp. 51-67, 73-75). 

A group of valleys in northeastern Nevada share a peculiar 
Rhi?tichthys-\ike dace, the only native fish in 4 of the 5 basins (Hubbs 
and Miller, 1948, Map 1, Nos. 24-28, 30). The southernmost basin 
(No. 30), Spring Valley, also harbors a species of Pantosteus, which 
is related to species in all surrounding major w^atersheds; the common 
ancestor of this sucker probably originated in the Great Basin. 

Lying north of the Lahontan basin are the Madeline Plains, site 
of Pluvial Lake Madeline (Hubbs and Miller, 1948, Map 1, No. 33). 
This region contains but a single fish, Rhinichthys osculus. The 
remnant populations show remarkable uniformity and are ap- 
parently indistinguishable from the Pit River form, suggesting that 
Madeline Plains received its stock from that source (Hubbs and 
Miller, 1948, p. 59). A very distinctive chub of the genus Siphateles 
occurs in Alvord Valley, mostly in Oregon, and another species of 
the same genus is known from Catlow and Guano valleys. Surprise 
Valley, in northwestern Nevada, has an endemic sucker as well as 
the noncommittal Rhinichthys, and the nearby Warner Valley, 
mostly in Oregon, harbors Catostomus warnerensis (endemic), 
Rhinichthys osculus, Siphateles hicolor, and was probably inhabited 
by Salmo clarki (a Sacramento genus, Hesperoleucus, has likely been 
introduced) . Too little is known about the affinities of these species 
to enable one to draw reliable conclusions as to their origin. 

A number of isolated basins in south central Oregon, lying in the 
desert region between the headwaters of Deschutes River and 
Malheur Lake, were once united into Pluvial Fort Rock Lake 
(Hubbs and Miller, 1948, p. 73). The Recent fauna includes Salmo 
clarki, Rhinichthys osculus, and Siphateles hicolor, each of which has 
relatives in adjacent watersheds. The fossil occurrence of Pacific 
salmon (Oncorhynchus) establishes that the waters of this lake were 
once directly connected to the ocean and the physiographic data 
indicate that the connection was via Deschutes River. Study of the 


fossil minnows and suckers, along with careful comparison of the 
living fishes, should help to determine whether the fauna entered 
this region by more than one route. 

One other well-isolated basin shows a curious faunal mixture. 
Railroad Valley, in eastern Nevada, was the site of a large Pluvial 
lake (Hubbs and Miller, 1948, p. 90, Map 1, No. 60). The sur\dving 
waters contain chubs referable to Siphateles bicolor and an endemic 
cyprinodontid, Crenichthys nevadae (Fig. 16). The only other species 
of Crenichthys, C. baileyi, is known from the remnants of the adja- 
cent Pluvial White River, once a permanent tributary of the Colo- 
rado River. Structural troughs lead from Railroad Valley in a 
southeasterly direction toward the Colorado River suggesting, along 
with the mutual occurrence of Crenichthys, that Railroad Valley 
once drained in that direction, perhaps in early Pleistocene time. 
Siphateles is particularly characteristic of the Lahontan basin and 
presumably entered Railroad Valley from the north after the con- 
nection between that valley and the Colorado system was severed. 



A study of the extralimital ranges of western and eastern fishes 
shows that 29 species have taken part in recent crossings of the Con- 
tinental Divide. Possibly some of these transgressions are the result 
of human intervention (Lindsey, 1956, pp. 780, 782). These fishes 
comprise 23 genera in 9 families, 3 of which are primary. About 
twice as many species have moved from east to west as from west to 
east; where the crossing was effected by stream capture, this sug- 
gests that the western rivers have been the more active in the 
piracy. A total of 19 eastern species has entered the Columbia 
complex of streams and the Yaqui drainage, whereas only 10 western 
species have invaded eastern waters at points from British Columbia 
to Wyoming. 

Stream capture by the Yaqui River of a drainage that once was 
connected with the Rio Grande has given the Yaqui 8 eastern species 
(7 primary, 1 secondary) ; except for a Gila and Ictalurus pricei, none 
of these is recorded elsewhere on the Pacific slope. The eastern ele- 
ment makes up 26 per cent of the total fauna and 58 per cent of the 
primary fishes inhabiting the Yaqui. A well-established route of 
two-way faunal exchange has taken place between the Snake River 

218 R. R. MILLER 

(of the Columbia complex) and the upper Missouri River. Moun- 
tain whitefish {Prosopium williamsoni), cutthroat trout (Salmo 
clarki), and the mountain sucker (Pantosleus) have moved east- 
ward; and the longnose sucker {Catostomus catostomus), longnose 
dace {Rhinichthys cataractae), and mottled sculpin {Cottus hairdi) 
have moved westward. Farther north, the Continental Divide has 
been crossed at several points, notably between the upper Fraser or 
Skeena basins and the MacKenzie Valley in British Columbia 
(Lindsey, 1956), where at least 8 and likely 10 species have crossed 
from east to west and 7 species have moved from west to east. 

Multiple crossings of the Continental Divide are evident from the 
distribution patterns of such western species as Prosopium william- 
soni, Salmo clarki, and Salvelinus malma, and of the eastern 
Catostomus catostomus and possibly Rhinichthys cataractae. Most 
species have not spread far after entering eastern or western waters 
but the cutthroat trout, mountain whitefish, and mottled sculpin 
(Cottus hairdi), all of which ascend tributaries, have extended their 
ranges into isolated basins probably via stream captures, at least in 
part. Two northern species are not included in the above discussion 
since they are unknown from Pacific streams in the area covered by 
this report. Round whitefish, Prosopium cylindraceum, and northern 
pike, Esox lucius, have invaded the Alsek River, a Pacific tributary 
in extreme northwestern British Columbia, which also contains 
Arctic grayling (Lindsey, 1956, p. 789) ; Esox and Thymallus also 
inhabit the Taku River, next to the south. Headwater transfer from 
the MacKenzie drainage furnishes a plausible explanation of their 
limited occurrence on the Pacific slope. Most of these crossings of the 
Continental Divide probably took place in Postglacial times, at 
least in the northern Rockies, and no crossing is thought to be earlier 
than the latter part of the Pleistocene. The identity of most or all of 
the now separated species on each side of the Divide supports the 
view that the transfers were recent. 


Of the 21 families of primary freshwater fishes inhabiting North 
America (Fig. 1), about 30 per cent of the species are judged to be of 
North American origin, 55 per cent of Eurasian ancestry, and 15 
per cent of South American affinities. Two relict families, the 
Polyodontidae and the Amiidae, with a single species each in eastern 


United States, are clearly of northern origin, hut whether Eurasian 
or American is problematical. Hence they are not included in the 
above estimates. Darters (Etheostomatinae) are considered North 
American, but the three other large percids are tentatively assigned 
a Eurasian origin. 

In western North America there are an equal number of families 
of North American and Eurasian origin but the three Eurasian 
groups (Umbridae, Cyprinidae, and Catostomidae) account for 97 
per cent of the primary fauna. The rather sharp differences between 
the western and eastern American fish faunas are of relatively re- 
cent origin, probably post-Miocene except for the three old lowland 
relicts, Novumbra, Columbia, and Archoplites. Excluding the very 
recent. Postglacial eastern invaders, there is an overlap of only about 
5 per cent in the total number of species between the two regions. 


During the approximately 20-year period that I have been studying 
western fishes, Dr. Cad L. Hubbs has provided guidance and repeated 
stimulation both by encouragement of my work and through our joint 
studies. He has also criticized this manuscript. Although I accept full 
responsibility for the conclusions here expressed, my indebtedness to him 
is considerable. My colleague. Dr. Reeve M. Bailey, has also made valued 
suggestions for improving the manuscript and has generously allowed me 
to use the map (Fig. 1) which he compiled and which appears here with 
only minor modifications. Dr. Leonard P. Schultz kindly arranged for the 
use of photographic copies of certain original drawings (Figs. 4, 7, 13, 
18-19). Research grants from the Horace H. Rackham School of Graduate 
Studies, University of Michigan, made possible much of the field work 
that provided the raw data for this report. The maps and charts were 
drafted by Mrs. Betty Anthony. 


Bailey, Reeve M. 1956. A revised list of the fishes of Iowa, with keys for 

identification, in James R. Harlan and Everett B. Speaker, Iowa 

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with emphasis on Glacial and Postglacial times. Bull. Univ. Utah, 38 

(20): 3-16. 

220 R. R. MILLER 

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lakes of western Montana and northwestern Wyoming. Bull. U. S. 

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new callionymid from Celebes and the Philippines. Proc. Biol. Soc. 

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and Sonora, Mexico, with the description of a new subgenus of Gila 

and a review of related species. Copeia No. 2, pp. 104-110. 
. 1945b. Four new species of fossil cyprinodont fishes from eastern 

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the genus Fundulus with the description of Fundulus persimilis 

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cyprinia fishes (Plagopterini) of the Colorado River system. Occ. 

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studies. VII. The skull and Weberian apparatus of Cyprininae 

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Some Problems of Freshwater 
Invertebrate Distribution in the 
Western States^ 

Robert W. Pennak 

University of Colorado, Boulder 

Any brief discussion of the distribution of 
free-living freshwater invertebrates of the West (even excluding 
insects) is a rather large and difBcult matter, chiefly because of the 
great taxonomic and ecological diversity of the many taxa involved 
and because of scanty definitive data. For this reason, I shall deal 
primarily with a few of the basic problems, and I shall limit myself 
largely to generalizations. My remarks are restricted to the Recent 
distribution of freshwater invertebrates, other than insects, of the 
eleven western states. There are six major points which I should 
like to make. 

1. The freshwater invertebrate fauna of the West is not well 
known. Aquatic biologists are relatively far more numerous in the 
eastern half of the United States, where for many years collecting, 
identification, and zoogeographical studies have been actively 
pursued. To an even more striking degree, our familiarity with the 
western freshwater fauna is still farther behind the situation in 
Europe, where such studies have produced a remarkably thorough 
knowledge of freshwater invertebrates. 

Our first point, therefore, is a plea for more field, laboratory, 
and zoogeographical work in our West, especially published work. 
We hope that, as time goes on, more and more students can be 
encouraged to enter these fields of research. Incidentally, we suspect 
that a good deal of unpublished information is already hidden away 
in field notes, master's theses, and unpublished doctoral disser- 

1 Contribution No. 32, Limnology Laboratory, University of Colorado. 


224 R. W. PENNAK 

2. From a purely environmental standpoint, the freshwater 
fauna of the West does not have the advantages of stable flo wages 
and many associated large lakes. Western topography is violent and 
broken, the climates are highly demanding because of wide annual 
variations, and barriers are abundant and rigorous. Many of our 
rivers are laden with silt during much of the year, the gradients 
are steep, and the water levels sometimes vary from trickles (or dry 
beds) in late autumn and winter to rushing torrents during the 
spring runoff. Droughts in the West are often extreme and exten- 
sive; undoubtedly they are effective in inhibiting or exterminating 
local populations. Except in mountainous regions, the West has 
relatively few natural lakes, and many of these are small, ephemeral, 
and pondlike. 

3. We assume that many species of freshwater invertebrates in 
the eastern half of the United States could become well established in 
western areas, but for several important reasons these eastern 
species in certain taxa are apparently prevented from naturally 
spreading westward. The following barriers, for example, are un- 
doubtedly effective: prevailing westerly winds, the topography and 
headwater drainages of the Continental Divide area, steep stream 
gradients, intermittent rivers, streams, and ponds, and extensive 
deserts and semi-arid regions. 

4. Nevertheless, when examined closely, the western states 
appear to present a set of conditions that should encourage isolation 
and speciation, especially in certain taxa containing macroscopic 
forms, and the West should theoretically have a unique population 
of freshwater invertebrates. Some of these conditions may be 
enumerated briefly, as follows: (a) the abundance of barriers to 
gene flow (mountains, deserts, closed drainage systems, variety of 
climates, etc.); (b) the abundance of natural and artificial lakes 
and springs with peculiar chemistry (alkali lakes, saline lakes, 
saline springs, etc.); (c) thermal springs; (d) the generally wide 
variety of lakes and streams. Indeed, there is already evidence to 
show that the western aquatic invertebrate fauna is much richer 
and more varied than is indicated in the literature. Our personal 
experience with alkali lakes, thermal springs, and high-altitude 
lakes and ponds convince us of this. 

Some of the most striking examples of western endemism are to 
be found in the arid and semi-arid Great Basin and adjacent regions, 


notably among the stream snails (Pleuroceridae) . Freshwater 
shrimps in the Family Atyidae, restricted to a few California coastal 
streams, present a further example. 

Perhaps it should be pointed out that the West appears to be 
lacking in extensive limestone caves and associated underground 
stream systems of the sort found in Kentucky, Tennessee, Indiana, 
Illinois, Missouri, and Florida. Such habitats are often marked by 
unusual endemic aquatic invertebrates. Interesting counterparts, 
however, are the occasional western lava-tube caves where a few 
unusual forms have been found, e.g., Kenkia (turbellarian) and some 
species of Stygobromiis (amphipods). On the other hand, it should 
be noted that the West, so far as we know, is lacking in truly archaic 
species, such as amphipods, isopods, Bathynella, Troglochaetus, 
and Marifiigia, that are so typical of southeastern Europe. 

5. Unlike the situation for certain vertebrates and for inverte- 
brate terrestrial groups, it is quite clear that the western freshwater 
invertebrate fauna involves a zoogeographic situation that is con- 
fusing, poorly known, and greatly diverse. Omitting insects and a 
few of the minor taxa, however, an assessment or appraisal of this 
fauna would seem to indicate five zoogeographic categories, as 

Six taxa are characterized in the West by numerous cosmopolitan 
species, most of which produce resting eggs, cysts, and other resis- 
tant and dispersal devices that are remarkably effective in sur- 
mounting barriers. Protozoa and Rotatoria are typical of this 
category and are fairly well known in the West. Four other groups 
(Oligochaeta, Tardigrada, Gastrotricha, and Nematoda) are poorly 
known, but judging from studies in other parts of the world, we 
assume that many common species are widely distributed through- 
out the West. 

A second category includes five taxa that are not necessarily 
cosmopolitan but whose speciation and abundance in the West 
are largely unknown. There are a few records of triclad Turbellaria 
from the West, but little is known about the rhabdocoels, and we 
are greatly in need of studies on pond, alpine, and springbrook 
species in this order. Little is known about the Hirudinea of the 
West; a good many eastern species, however, have highly restricted 
distributions, and a comparable situation may exist in the West. 
Of the thirty species of freshwater Porifera in the United States, 

226 R. W. PENNAK 

only about seven have been reported from the western states; 
presumably many of the turbid low-altitude lakes and streams 
discourage the establishment of sponges, but very little work has 
been done in mountain ponds and lakes that are sometimes fruitful 
places for sponge collecting. Only about four species of hydras have 
been reported from the West; more intensive collecting should 
undoubtly reveal a fauna perhaps even richer than that of the 
eastern states. The same situation applies to the Bryozoa; they are 
easily transported from one place to another by virtue of their 
hibernacula and statoblasts, yet the western species are poorly 

A third category includes four taxa that are known to be well 
represented in the West; they are also groups in which the lists of 
western species will undoubtedly eventually be longer than those 
for the eastern portion of the United States. The Cladocera, for 
example, are represented by many cosmopolitan species, perhaps 
largely owing to the viability and ease of transport of the ephippial 
eggs; in addition, a good many species are restricted to certain 
habitats in the western states, especially species of Moina, Camp- 
tocercus, and Pleuroxus in alkali ponds and lakes. Cosmopolitan 
species of cyclopoid and harpacticoid copepods are likewise abundant 
in the West; the diaptomids, however, are more interesting because 
of their proliferating speciation in western lakes and ponds (the list 
of known species is growing markedly); furthermore, even a few 
Asiatic and Alaskan species are now being reported from certain 
cold-water habitats of the West. Although Ostracoda have been 
subjected to relatively little collecting in the West, each new study 
turns up numerous cosmopolitan and endemic species; further 
systematic collecting should reveal a remarkably large fauna. The 
same is true for the Hydracarina, especially in view of the experience 
of European specialists; the little collecting already done in the 
western states is ample evidence that it is an area rich not only in 
cosmopolitan but also in endemic species, as one might assume in 
view of the wide variety of isolated aquatic habitats. 

A fourth category includes five large taxa that are poorly rep- 
resented in the West. It is, for example, remarkable that this region 
contains relatively few gastropods, especially as compared with the 
very rich fauna of the Mississippi drainage area. To be sure we have 
an interesting assemblage of isolated genera and species in such 


areas as the Great Basin, including Panipholyx, Carinijex, and 
Fluminicola, but these do not constitute a large fauna. The Pele- 
cypoda (exclusive of the Sphacriidae) are very poorly represented 
west of the Continental Divide; for example, only about six species 
of unionids are native to California. One of these, Margaritifera 
margaritifera, is widely distributed in the western states but also 
occurs in the North Atlantic states. But presumably the great 
unionid population of the Mississippi Valley has never been success- 
ful in overcoming the difficulties of the Divide, sandy and silty 
rivers, and the intermittent nature of many western streams. 
Undoubtedly a further problem in the West is the lack of proper 
fish hosts for the glochidia stages of unionids. Isopoda and Amphi- 
poda are apparently poorly represented in the West, although most 
of the few species found there are endemic; the relative abundance 
of species in the eastern states is probably a reflection of speciation 
in springs and subterranean waters. Freshwater crayfishes were 
originally represented by only five species of Astacinae west of the 
Continental Divide, and this same subfamily is represented else- 
where only in northern Europe and eastern Asia, by about ten 
species. The Cambarinae, however, which are so abundant east of 
the Continental Divide, have, in Recent times, apparently never 
been successful in spreading westward from their centers of dispersal 
and speciation in Mexico and the south-central and south-eastern 
parts of the United States. It is, of course, entirely possible that 
the Cambarinae inhabited the western states area in pre- Pleistocene 

A fifth and last category includes three small groups that are 
especially characteristic of the West and that are also abundant in 
comparable geographic and climatic areas elsewhere in the world. 
These are the Anostraca (fairy shrimps), Conchostraca (clam 
shrimps), and Notostraca (tadpole shrimps). All are far better 
represented in the West than in the eastern half of the country. 
Two peculiarities of these groups are perhaps primarily responsible 
for their occurrence here. First, they produce an abundance of 
highly resistant, thick-shelled eggs that are able to withstand 
extremely unfavorable conditions for long periods. Second, many 
species are adapted to living in unusually saline, alkaline, and 
silty bodies of water. Permanent and vernal ponds and pools 
throughout the West thus afford ideal conditions for these phyllo- 



pods, and although they are usually considered more typical of the 
Great Plains, they are just as characteristic of suitable mountain and 
desert habitats west of the Divide. 

Table I. Systematic and Zoogeographic Status of Certain Groups of 
Freshwater Invertebrates in the Western Portion of the United States 





ance of 


species wide- 



spread in the 

of endemic 






in West 



West relatively 



rich in species 









































West relatively 



poor in species 


Certain of the generalizations thus far discussed are summarized 
in an alternate fashion in Table I. The twenty-one taxa in the 
first column are listed in order of their decreasing relative species 
abundance in the West (particularly as compared with the situation 
in the eastern half of the United States). The first five taxa comprise 
a group characterized by a preponderance of cosmopolitan species, 


even though definitive data are lacking for the Oligochaeta, Gas- 
trotricha, and Nematoda, and their inclusion here is based on 
information gathered primarily from European sources. The next 
five taxa of crustaceans form a natural group featured by a high 
percentage of endemic species in the West (with the possible ex- 
ceptions of the Copepoda and Cladocera). The following six taxa 
are a heterogeneous group which, with the exception of the Gastro- 
poda, are poorly known in the West, chiefly because of the lack of 
intensive and systematic collecting. The last four taxa listed in 
the first column are all relatively poor in species in the West, but 
nevertheless most of the species found there are endemic. 

6. The last point I should like to make is concerned with the 
increasingly important role being played by man in the distribution 
of freshwater invertebrates in the West. Residents of California, 
for example, are well aware of the nuisance and economic importance 
of cambarine crayfishes that were intentionally introduced here 
many years ago. In Colorado we are seeing the same process, 
although the end results will probably not be so serious; cambarine 
crayfishes have been introduced into certain Colorado mountain 
lakes, and in some such habitats they have become abundant and a 
welcome addition to the trout diet. In addition, however, they have 
been introduced into the Western Slope drainages, and in a few 
irrigation ditches they are occasionally a nuisance because of their 
burrowing habits. 

Aquarium enthusiasts are often responsible for setting up new 
centers of distribution for both bivalve and univalve mollusks. 
Many species native to the eastern states are well adapted to home 
aquarium use, and, of course, these are commonly shipped west as a 
part of the thriving aquarium business. Frequently, however, 
when the hobbyist is tired of his aquarium, he empties it into the 
nearest pond or lake, and we may thus have a new mollusk popul- 
ation established under natural conditions. 

Fishermen are consciously accomplishing the same ends. We 
have seen fishing parties from Nebraska, for example, bringing 
milk cans full of vegetation and the associated invertebrates to 
Colorado. These they commonly empty into mountain lakes on 
both sides of the Continental Divide. Furthermore, state fish and 
game departmants frequently do exactly the same thing when 
they transport large quantities of invertebrates and vegetation from 

230 R. W. PENNAK 

one "rich" lake to another "poor" lake. Over a period of time these 
activities will undoubtedly assume considerable importance in 
spreading various invertebrates over wider areas of the West. 

A further and unintentional means by which aquatic inverte- 
brates are greatly increasing their ranges and abundance is through 
the extensive system of thousands of farm ponds and stock tanks 
which have been constructed in the West, especially during the 
past twenty-five years. In areas formerly characterized by great 
stretches of unbroken arid or semi-arid land, we now have an 
extremely effective system of "stepping stones" by which inverte- 
brates may disperse much more effectively than was the case many 
years ago. This is no exaggeration. Anyone who will take the trouble 
to examine the invertebrate population of a stock tank or ranch 
pond in the middle of a large semi-arid tract is bound to be impressed 
with the abundance of species occurring there. (Incidentally, this 
facet of aquatic biology seems to have been completely neglected.) 

During the past seventy years the West has become densely 
criss-crossed with an extensive system of irrigation ditches, many of 
them carrying water at all times of the year. Such ditches connect 
with a host of artificial irrigation reservoirs. In our estimation, 
these waterways also provide an enormous transportation and 
dispersal system by which our aquatic invertebrates are becoming 
much more generally distributed. 

Affinities and Origins of the Northern and Montane 
Insects of Western North America 

Herbert H. Ross 

Illinois Natural History Survey, Urbana 

1 he subjects of this paper are the insects 
belonging to the cool-adapted biota and occupying an ecological 
band comprising essentially the cool-temperate and arctic regions. 
The arctic region comprises both the tundra of the Arctic and the 
alpine tundra found above timberline in subarctic areas. The cool 
temperate region comprises the taiga and its equivalents — the 
northern coniferous spruce and pine forests and various higher- 
elevation forests toward the south. In North America today this 
double band — cool temperate and arctic — extends in a wide swath 
across roughly the northern third of the continent and extends 
southward as islands at higher and higher elevations, through the 
mountain chains of eastern and western America. In the West these 
cool-temperate islands are larger and occur much farther south than 
in the eastern part of the continent. 

A large number of insect species are abundant in both taiga and 
tundra, and are almost entirely restricted to these two major 
ecological formations. These insects represent many orders and 
families, including such well-known types as caddisflies, sawflies, 
and mosquitoes. Although today these many species of various 
families form what appears to be a closely knit ecological aggre- 
gation, they must have arrived in this general area of the continent 
by diverse paths and at different geologic times. 

Concerning this cool-adapted biota of western North America, 
we can deduce that some elements arrived from Asia, that other 
elements spread westward from the eastern parts of North America, 
and that still others spread northward from the more tropical 
areas to the south. Present information gives evidence of dis- 
persals of living genera dating from Cretaceous time to practi- 


232 H. H. ROSS 

cally the present. Undoubtedly dispersals between the same areas 
occurred many times, each time involving different ecological 
conditions in the bridging area and resulting in the spread of differ- 
ent lines of insects having corresponding ecological adaptations. 

We know far too little concerning this historic process, however, 
to be able to detail the spread of all the insect species in these 
northern communities, or even that of the plants and other animals. 

Because fossils of northern insects are rarities, we must rely 
chiefly on the biogeographic analysis of living species in delving 
into the past history. Two sets of facts constitute the backbone of 
such an analysis, first, the morphological characters of the species 

Fig. 1. A Baltic Amber caddisfly: right, Lype sericea and left, one of 
its living counterparts, the European Lype phaeopa. (From Ulmer, 1912, 
and Mosely, 1939.) 

on which phylogeny is based, and then the known geographic 
distribution of the species from which the dispersal pattern may be 
deduced. When present, fossil evidence is a welcome and valuable 
adjunct to these data. 

One fact of inestimable importance in attempts at phylogenetic 
reconstruction is deduced from the fossil record, namely that in 
some insect lines evolutionary change may be very slow. The 
caddisfly genus Lype is represented in both the Baltic Amber 
(probably deposited no later than upper Eocene) and present day 
biotas. One of the Baltic Amber species is almost identical in 
diagnostic characters of the male genitalia with a species existing 
today (Fig. 1), and only slight differences can be detected between 
these populations some 50 million years apart in time. In this slow 
rate of evolutionary change found in some of their phyletic lines, 
the insects resemble the freshwater Pelecypoda and certain other 



invertebrates and contrast sharply with the rapid evolutionary 
rates described as characteristic for many groups of Mammalia. 


Fossil records show that many insect genera occurred previously 
in western North America but are now absent from the area. 
Examples from the cool-adapted biota include the fern-boring 

Fig. 2. The phylogenetic tree of the caddisfly genus Wormaldia 
subgenus Doloclanes superimposed on the known distribution of the 
species. This subgenus may be most closely related to more primitive 
Baltic Amber species. 

sawfly Blasticotoma, known only from fossil remains in the Flor- 
issant shales of Colorado and from living representatives in Europe 
(Benson, 1942) ; and the snakefly genus Raphidia, known also from 
the Florissant shales but not now occurring in North America 
(Carpenter, 1953). Since representatives of the caddisfly genus 
Phylocentropus are now known only from Baltic Amber fossils and 
from living species restricted to eastern North America, intervening 
areas must have been populated by this genus at some past time. 
Because considerable evidence indicates that the intercontinental 
connection was between northwestern North America and north- 







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eastern Asia, it is plausible to assume that this genus and others of 
similar range characteristics were former denizens of the American 

A few cases drawn entirely from the distribution of living forms 
give practically conclusive proof of the same phenomenon. An 
example is the subgenus Doloclanes of the caddisfly genus Wormaldia 
(Ross, 1956). The main group of species involved in this subgenus 
evolved in and is now restricted to the eastern part of Asia (Fig. 
2), but one species (most closely allied to one in Japan) occurs in the 
Great Smoky Mountains of eastern North America. The only 
logical explanation for this set of circumstances is that a northeastern 
Asiatic species spread across North America and ultimately became 
established in the Smoky Mountains. During this dispersal, we 
must assume that a species of Doloclanes lived in northwestern 
North America, although we have no definite records for this 
subgenus there. 

Some insect fossils from western localities represent highly 
specialized genera not known from living species and undoubtedly 
have become extinct. The existence of such extinct "side branches" 
of phylogenetic trees cannot be deduced from the study of living 
forms, hence how many of them existed in the past we do not know. 


The oldest dispersals of northern insects involved in the origin 
of the present western North American fauna for which we have 
evidence seem to have been in middle Cretaceous. It may be in- 
ferred that the caddisfly genus Sortosa dispersed at that time to 
almost every continental land mass and that after this great spread, 
many populations of Sortosa became isolated in and persisted in 
various parts of the world. In western North America five species, 
comprising the subgenera Sisko and Fumonta, represent this old 
movement (Fig. 3). It is highly likely that several archaic western 
genera of limnephilid caddisflies, including Dicosmoecus, Ecclisomyia, 
Farula, and Pedomoecus, also are surviving lines dating back to this 
same mid-Cretaceous dispersal (Schmid, 1955). All five of these 
caddisfly genera frequent streams in the extreme north or at higher 
elevations in mountains. 

Judged from their known present distributions, most of these north- 
western genera or subgenera have either remained isolated in moun- 






























































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tain regions of western North America since the time of this supposed 
mid -Cretaceous dispersal, or if they did spread to other areas have 
become estabUshed in no other region. This situation suggests 
that for survival these insects must have streams which are not 
only cold but rapid, and that in the past greater continuity of 
mountainous terrain was a major factor in permitting their dispersal. 

Evidence is highly suggestive that during the height of the 
Laramide orogeny, that is, the very end of Cretaceous and the 
earliest part of Cenozoic, many members of the cool-adapted biota 
spread between western North America and Asia. The mountain- 
inhabiting caddisfiies offer evidence for this dispersal also. The 
genus Wormaldia, which could very well have evolved from a 
Cretaceous subgenus of Sortosa isolated in western North America, 
probably spread in Paleocene into Asia and across to Europe. 
Whichever way the dispersal occurred, it antedated the Baltic 
Amber (in which Wormaldia occurs) and is documented by clusters 
of Wormaldia species in many continental areas (Fig. 4). One 
cluster of nine species occurs in western North America. It may be 
postulated that members of two other caddisfly families dispersed 
in similar fashion at this same time. The genus Rhyacophila, 
belonging to the family Rhyacophilidae, is one of the largest and 
commonest mountain caddisfly genera of the West. Of its 44 species 
groups, 19 occur in the West but 7 are known also from other 
areas. It is almost certain that the ancestors of the other 12 groups 
either reached the West no later than Paleocene or evolved in the 
mountains of western North America from older parental forms. 
The same may be true also of certain of those seven groups that 
now occur in two or more major areas. 

In the family Glossosomatidae (the caddisfiies whose larvae 
construct saddle-like cases) both the archaic genus Anagapetus and 
the subgenus Ripaeglossa of Glossosoma appear to have had similar 
early histories. It is impossible to be sure whether the ancestral 
forms of these groups arose in Asia or North America, but wherever 
they did originate, they dispersed between the two continents at 
some early date. In western North America a remnant of each line 
appears to have evolved in, and to have been restricted ever since 
to, the higher elevations of this area (Fig. 5). 

The next dispersals of cool-adapted insects for which we have 



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Fig. 5. Family tree and distribution of Anagapetus, an archaic genus 
of small caddisflies restricted to western North America. (From Ross, 


plausible evidence occurred in mid-Cenozoic and involved chiefly 
species which may be considered ecologically as forming the warmer 
fringe of the cool-temperate biota. The best evidence involves tree- 
feeding leafhoppers of the genus Erythroneiira and caddisflies of the 
genera Pycnopsyche, Agapetus, and the more warm-adapted 
species of Rhyacophila, which presumably became widespread 
across North America and Eurasia along with the temperate 
deciduous forests of that era. Most of these insect examples had a 
greater eventual effect on the fauna of eastern North America than 
on that of the West, and established nuclei for groups that became 
important elements of the eastern temperate deciduous forest. 

Certain of these mid-Cenozoic dispersals did apparently result 
in colonizations that evolved into species flocks in the West compara- 
ble with those that evolved in the East. The best examples with 
which I am acquainted are the sawfly genus Neodiprion and the 
caddisfly genus Agapetus. We do not know where the ancestral 
form of Neodiprion (Fig. 6) arose, but it seems obvious that an 
eastern and a western population became established, that each 
evolved into a distinctive species flock, that each now constitutes 
an important element in the conifer-inhabiting insect fauna, and 
that the eastern and western branches of the genus have remained 
separate geographically until almost the present time (Ross, 1955). 

A comparable situation may be postulated for the American 
species of the caddisfly genus Agapetus. The larvae of these species 
construct saddle-like cases and inhabit clear, cool, spring-fed streams 
in hilly and mountainous country throughout the Allegheny system 
in the East and much of the western montane region south of 
Canada. Available evidence, based on characters of venation and 
abdomen, indicates that the North American species arose from an 
Asiatic ancestor which spread into North America at the time of the 
Holarctic temperate deciduous forest. The present day North 
American species of Agapetus appear to constitute two primary 
phyletic branches, one in the East and one in the West. Each branch 
has evolved into a moderate cluster of species, many of which 
exhibit striking changes compared with more primitive forms. 
This combination of phylogeny and distribution suggests that when 
the American transcontinental temperate deciduous forest broke up 
in mid-Cenozoic into widely separated segments, one segregate of 
Agapetus persisted in the East and one in the West. There is no 
















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evidence that the two resulting phylogenetic lines ever again 
mingled geographically. 

In addition to these mid-Cenozoic events which can be linked 
ecologically with temperate forest dispersals, we have evidence of 
other intercontinental dispersals of cool-adapted insects that are 
difficult to date. An example (Ross, 1956) is the deduced dispersal 
of the caddisflies belonging to the Rhyacophila sibirica group (Fig. 

























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Fig. 7. Phylogenetic dispersal chart of the Rhyacophila sibirica group, 
comprising caddisflies restricted to rapid, cold streams. (From Ross, 1956.) 

7). Its main evolutionary lines seem to have oscillated between 
northwestern America and northeastern Asia, with many surviving 
species in both areas. The distribution of these chiefly northern 
montane species indicates the possibility of some interchanges in the 
northern elements of our western cool-adapted biota at moderately 
frequent intervals during the Cenozoic. For other groups of montane 
caddisflies of indicated Asiatic origin, a single line seems to have 
spread to and to have become established in western North America. 
Examples are Himalopsyche phryganea (Fig. 8), Glossosoma penitum, 
and the entire Rhyacophila acropedes complex. Beacuse each line 



offers evidence of only one Intercontinental dispersal, it is impossible 
to approximate the date of arrival of these lines in North America. 
We should not forget that during this Cenozoic period many 
lines were almost certainly already present and evolving in the 
cooler habitats of western North America. In the montane caddisflies 
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Fig. 8. Phylogenetic diagram of the caddisfly genus Himalopsyche. 
Note that all the species occur In Asia except the one shown at the extreme 
left, phryganea, which represents the only known dispersal of the genus 
into North America. (From Ross, 1956.) 

Rhyacophila verrula and vagrita groups), whereas others (Fig. 9) 
seemingly gave rise to species that spread into eastern North 
America, e.g., the Rhyacophila invaria and Carolina groups, or into 
Eurasia, e.g., the Rhyacophila glareosa and pepingensis branches. 
The climatic and geologic changes in late Pliocene and the 
Pleistocene are associated with what appears to have been a whole- 
sale redispersal of many cool-adapted insects throughout the Hol- 
arctic region. This phenomenon is especially well illustrated in the 



sawflies. The predominantly northern genera Dolerus, Nematus, 
Amauronematiis, Rhadinoceraea, and many others have entire 
complexes within which all western North American species either 
are Holarctic or have a sister species in Eurasia. It is obvious in 
these cases that probably during the immediate past either an 
existing species or its immediate ancestor became widespread 













Fig. 9. Phylogenetic dispersal chart of several species groups from one 
of the distinctive branches of Rhyacophila, comprising caddisflies which 
inhabit cold, rapid rivers and streams. (From Ross, 1956.) 

across the Holarctic region. The same situation is shown graphically 
by evidence from the herb-feeding leafhopper genus Macrosteles 
(Moore and Ross, 1957). The present distribution of known species 
of this genus can plausibly be explained only by the intercontinental 
dispersal of at least sixteen phylctic lines (indicated by black dots 
on Fig. 10). These sixteen movements were of course not all con- 
temporaneous, but judged by the uniform morphological similarity 
of many pairs of sister species, at least the upper thirteen dispersals 



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within the late Pliocene-Pleistocene period. Similar circumstances 
prevail in many genera of northern grass-feeding leafhoppers and 
also, I am sure, in a large number of other insects abundant in the 
North and Northwest. In Culicoides, an extremely widespread 
genus of biting flies, Khalaf (1954) found evidence of even wider and 
relatively recent dispersals, some indicating a total spread including 
central and northwestern North America, Asia, Europe, and Africa. 
Two Alaskan species, Culicoides obsoletiis (Meigen) and C. tri- 
striatidus Hoff, belong to such widely ranging complexes. 

In addition to these intercontinental movements, dispersals 
from the eastern to the western areas of the continent are illustrated 
by insects. Although there is abundant evidence that members 
from many western species flocks spread to and colonized the East 
at various times in the Cenozoic, present information indicates 
that dispersals to the West from eastern species flocks were much 
rarer and occurred chiefly in the Pleistocene. Of the seven older 
eastern species flocks in the caddisfly genus Rhyacophila, none has 
apparently spread to the West. Some other caddisflies do indicate 
such a dispersal. In the genus Triaenodes nineteen species form a 
fairly old, distinctive, polyphyletic complex which appears to 
have evolved in the eastern deciduous forest area as a series of 
species flocks (Fig. 11). Seventeen of these nineteen species are still 
restricted to the East and Northeast (Fig. 12), but two, baris and 
tarda, extend westward into the Rocky Mountain region. 

Because no morphological differences have been detected between 
eastern and western populations of the two species just mentioned, 
the most logical interpretation is that they evolved originally in the 
East and spread to the West along ecological corridors brought into 
existence by Pleistocene events. An alternative logical possibility 
is that the progenitors of tarda and baris spread from the East to 
the West, that the western populations of each became isolated 
and evolved into distinctive species, and that these two species in 
turn spread eastward during Pleistocene. The restricted western 
distribution and extensive eastern range of T. tarda, however, 
strongly suggests that it was of eastern origin. 

Several species of the related genus Athripsodes, notably cancell- 
atus and tarsipunctatus, exhibit parallel phenomena and may also 
represent recent dispersals from the East to the West. It is quite 


H. ir. ROSS 

I r 

« 5 

o » 

< i» 

I- O. 

z e 

O o 

q: o 

< t:. 



< X 9 

OD O tK 

< Z 1- 



< < 9 

H- Z (t O 

5 uj o -J 

Jt < -I IxJ 

i£ t- li. X 

X <rt 


O 2 

< < < - 

z q: o » ^ 

cc X (E 5 - o: 

iij o < < 2 <J 

Q. O I- S (/) 03 


< Ul 


oit ? 

(^-shorter clasper 

^-short opodeme 
^-long closper 

Fig. 11. Phylogenetic diagram of the North America components of 
the case-making caddisflies belonging to the genus Triaenodes. 

possible that comparable information on other insect groups will 
add greatly to these examples. 

The sum of the Holarctic and trans-American dispersal patterns 
points to a truly extensive faunal interchange associated with the 
colder climates of the Pleistocene. 

The American species of the caddisfly genus Helicopsyche il- 
lustrate another type of range extension into the cool-temperate 
world. The larvae of Helicopsyche live in small clear streams and 
make strong cases shaped like snail shells. All fourteen described 
species occur in the tropical and /or subtropical regions and three of 
them extend northward into the temperate region (Fig. 13). For 
two species, these extensions are slight or small: H. mexicana has 
outpost populations in central Arizona, northern New Mexico, and 
Arkansas, and H. vergelana has an outpost in western Louisiana. 
The species borealis, however, extends northward into the cool- 
temperate zone, reaching Washington in the West and Quebec in the 
East. Thus H. borealis has in some manner acquired an ecological 
tolerance much wider than that of other members of the genus, and 



Fig. 12. Known distribution of certain North American species of 
the caddisfly genus Triaenodes. The category "other species" includes 
all those except tarda and haris listed between tridonta and furcella in 
Fig. 11. 



Fig. 13. Distribution of Helicopsyche horealis and the six other species 
belonging to the same phylogenetic branch. The species limnella, known 
only from Arkansas, is so close to mexicana morphologically that it is here 
considered as merely an outpost colony of mexicana. 



thereby has effected an intrusion of a predominantly subtropical 
group into the cool temperate belt. There is in these data no sugges- 
tion as to when this extension of range developed, but the lack of 
formation of distinctive northern species in the group suggests 
that it occurred relatively recently. 

Adding together the known data concerning cool-adapted insects, 
one gets the definite impression that at three points in geologic 











Fig. 14. Suggested temperature trends during the latter part of 
Cretaceous and Cenozoic time, combining data for the Cretaceous from 
Lowenstam and Epstein (1954), the Cenozoic from Durham (1950), and 
the Pleistocene from Emiliani (1955). These authors stress that the values 
represent trends and should not be construed as indicating absolute 
climatic measurements. 

time — middle Cretaceous, Paleocene, and Pleistocene — conditions 
were such that extensive dispersal of cool-temperate forms took 
place. Various estimates of temperature trends during Mesozoic 
and Cenozoic agree closely (Fig. 14), but they indicate that periods 
of widespread cool conditions were of relatively short duration. 
During the long intervening periods when warmer climates prevailed 
over the lowlands, we must presume that the cool-temperate biota 
existed in higher elevations in the montane regions. Two sets of 
data from the western region of North America fit well into such a 

1. The relatively flat portions of the present day northern tundra 

250 H. H. ROSS 

and coniferous forests are sufficiently extensive to have an air of 
permanence. If, however, they were stable features of the landscape, 
geologically speaking, one would expect some distinctive taxonomic 
units to have evolved, and remained, therein. Among the insect 
groups of my acquaintance, the species of the flat north country are 
either the same as those in the western or eastern mountains, or 
were obviously derived relatively recently from montane species. 
It appeared at one stage in our studies that case-making cacldisflies 
belonging to the Limnephilus suhlunatus complex might be a species 
flock which had evolved in the flat northland. Most of the earlier 
records for many species in this group were from northern Sas- 
katchewan, the Mackenzie River Delta, and Great Slave Lake. 
More recent collections from Yukon and Alaska emphasize the 
possibility that the Limnephilus sublimatus complex may be associ- 
ated historically with the northern ranges of the Rocky Mountains 
rather than with the flatter country. 

2. The two main areas of caddisfly distribution in the mountains 
south of Canada, the Cascade-Sierra Nevada area to the west and 
the main Rocky Mountain area to the east, are separated by an 
irregular strip of arid, less mountainous country, including the 
Great Basin. This pattern is illustrated by the distribution of those 
caddisflies of the genus Glossosoma that comprise the subgenus 
Ripaeglossa, which abounds in large, fast, clear streams in both 
areas. The sixteen species of Ripaeglossa form two major phyletic 
branches. The branch comprising the alascense and traviatum 
species groups apparently evolved primarily in the western ranges 
and the one comprising the parvulum species group evolved in the 
eastern ranges. At the present time the northern six of the sixteen 
species of Ripaeglossa extend around the northern end of the arid 
zone separating the two mountain areas, but no phyletic line appears 
to have divided into sister species in the area to which it spread 
(Fig. 15). From these data it is possible to reconstruct a plausible 
series of events. When the progenitor of all existing forms of Ripae- 
glossa lived, clear mountain rivers of the West formed a sufficiently 
well-connected system to allow this caddisfly to spread throughout 
the West. Increased aridity of the Interior Basin area broke this 
river network and split the ancestral Ripaeglossa species into well- 
separated eastern and western populations. This same condition 
presumably prevailed during the entire subsequent evolution of 



these two populations. Only in comparatively recent times have 
shifts in climates or topography produced conditions under which 
northeastern species of Ripaeglossa spread westward and north- 
western species eastward. This and other similar examples of 
caddisfly distribution indicate that in these mountain areas Pleisto- 

Eostern Ranges 

White, Wosotch, Rockies, etc. 



Western Ranges 

Coscodes, Sierra Nevado, etc. 





Fig. 15. Phylogenetic dispersal chart of Glossosoma subgenus Ripae- 
glossa, a group of caddisflies inhabiting cold, rapid rivers and confined 
to the mountainous area of western North America. (From Ross, 1956.) 

cene events effected a mixing of phyletic lines previously separated 
from each other for long periods. 

In exploring the origin of the cool-adapted western insect fauna 
we have surveyed data from only a small fraction of the insects 
that occur in the cooler parts of the West. It is noticeable, however, 
how most of the data fits readily into the concept of an almost 
cyclic alternation of brief dispersals and long separations. The many 
small but different types of evidence pointing in the same direction 
give us reason to visualize an extensive dispersal and intermingling 

252 H. H. ROSS 

of cool-adapted phyletic lines during mid-Cretaceous, a similar 
series of events occurring again during Paleocene, and a third 
extensive set taking place in the Pleistocene. At each time the 
details of the dispersals were different. Finding out more about 
these details is proving a challenge to our investigations. Each 
dispersal, however, crossed or crisscrossed the West and had a 
tremendous effect on its cool-adapted fauna. In their total action 
these three cool-dispersal periods, with long intervening periods of 
chiefly local movement, were the most important events determining 
the composition of the present northwestern fauna. 


Benson, Robert B. 1942. Blasticotomidae in the Miocene of Florissant, 

Colorado (Hymenoptera: Symphyta). Psyche 49: 47-48. 
Carpenter, F. M. 1953. The geological history and evolution of insects. 

Am. Scientist 41: 256-270. 
Durham, J. Wyatt. 1950. Cenozoic marine climates of the Pacific Coast. 

Bull. Geol. Soc. Am. 61: 1243-1264. 
Emiliani, Cesare. 1955. Pleistocene temperatures. /. Geol. 63: 538-578. 
Khalaf, Kamel. 1954. The speciation of the genus Ciilicoides (Diptera, 

Heleidae). Ann. Entomol. Soc. Am. 47: 34-51. 
Lowenstam, H. A., and S. Epstein. 1954. Paleotemperatures of the Post- 

Aptian Cretaceous as determined by the oxygen isotope method. 

J. Geol. 62: 207-248. 
Moore, T. E., and H. H. Ross. 1957. The Illinois species of Macrosteles, 

with an evolutionary outline of the genus (Hemiptera, Cicadellidae). 

Ann. Entomol. Soc. Am. 50: 109-118. 
Mosely, Martin E. 1939. The British Caddis Flies (Trichoptera). George 

Routledge & Sons, Ltd., London. 
Ross, H. H. 1955. The taxonomy and evolution of the sawfly genus 

Neodiprion. Forest Sci. 1: 196-209. 
. 1956. Evolution and Classification of the Mountain Caddisflies. 

University of Illinois Press, Urbana, 111. 
Schmid, F. 1955. Contribution a I'etude des Limnophilidae (Trichoptera). 

Mitt, schweiz. entomol. Ges. 28: 1-245. 
Ulmer, Georg. 1912. Die Trichopteren des baltischen Bernsteins. Beitrage 

zur Naturkunde Preussens, Konigsberg 10. 


The Origin and Affinities of 

the Dermaptera and Orthoptera of 

Western North America 

James A. G. Rehn 

Academy of Natural Sciences of Philadelphia, 


r or the greater part of a half century the 
assembly of data and evidence bearing on the fields of this symposi- 
um, as relating to the Dermaptera and Orthoptera of North America 
as a whole, has been a major objective of a group of colleagues now 
or formerly associated with my institution. The evidence here 
summarized has been drawn largely — and particularly for the 
United States — from field investigations personally carried on over 
a period of fifty-five years. 

Much of the past literature, and considerable past collecting, is 
not at all helpful. However, very definite and clear-cut conclusions 
are now emerging, as extensive collections, representing many 
seasons of fully documented field work, are being critically studied 
as part of a long-range project assisted by a National Science 
Foundation grant. The general results, systematic, zoogeographic, 
and binomic, are now being made known in a series of papers 
preliminary to a more condensed monograph. In view of these 
circumstances citations to the literature have been omitted in this 

In the present analysis of the subject I am assuming a full under- 
standing of the terminologies that have long been in general use 
for life areas, particularly by the vertebrate school, which in North 
America produced some of the zoological pioneers in biogeography ; 
also that the descriptive terms, based on physiographic areas, such 
as Cordilleran (for the Rockies alone), Sierran, and Campestran, 
are equally familiar and precise. 


254 J. A. G. REHN 


Fossil evidence indicates that the two oldest known members of 
the Dermaptera were present in the Jurassic of Kazakstan, from 
which they were reported in 1925 by Martynov. One of these, 
Protodiplatys, was separated by him as a distinct fossil suborder, 
the Archidermaptera, which has blattoid suggestions. The other, 
Semenoviola has since been regarded as a member of the restricted 
suborder Dermaptera. From the early Caenozoic we know true 
forficulids from the middle Eocene of Italy, the Lower Oligocene of 
Belgium, the Upper Miocene of Germany, and the Florissant 
Miocene of Colorado, as well as from the Baltic Amber. However, 
from the Permian of Kansas Tillyard described a representative of 
what he regarded as a new order, the Protoelytroptera, which he 
regarded as a link between the Paleozoic blattids and the Recent 
Dermaptera. It is therefore within the realm of possibility that 
North America may at one time have been as much a center of 
development of the Dermaptera as the Old World. 

Of the ten genera Dermaptera in North America six (Labidura, 
Anisolabis, Euborellia, Labia, Chelisoches, and Forficida) are clearly 
introduced adventives, and several of these are almost entirely 
riparian types, possibly dating back to "ballast" days, while the 
genus Prolabia is represented in our fauna by two lines, one clearly 
an Old World adventive (now known from southern Texas), the 
other an intrusive Neotropical line of the genus found only in our 
southeastern states west to Texas. 

The three remaining genera are clearly of Neotropical origin as 
far as their presence in our limits is concerned. Two occur outside 
our territory in Central and South America. One, Spongovostox, is 
a pantropical assemblage with probably half the species Ethiopian 
or Malagasian in distribution. The second of these genera, Vostox, 
is clearly of Neotropical origin. Its single North American species 
ranges broadly northward through the eastern United States to 
Pennsylvania, yet does not extend any considerable distance west- 
ward in Texas. 

The third and last genus Doru is also of Neotropical origin, and is 
of very broad distribution in tropical America. In our territory 
it is widely spread in the eastern and southwestern United States. 
In Texas and in the extreme southwest only the widely distributed, 
basically Neotropical, D. lineare, occurs, whereas in the eastern 


United States there are two distinctive endemic members of the 
genus. It is possible that Doru reached North America in two 
separate invasions, the eadier of which established the line that 
developed the endemic southeastern species D. aculeatiim and davisi, 
and the later of which brought in the widely spread D. lineare, 
which is now known from within our territory only from areas of 
Texas, southern New Mexico and Arizona, and California. A 
single species undoubtedly referable to Doru was described from New 
South Wales in 1891. With an intimate knowledge of the hiding 
places that Doru selects, I suggest that a restudy of the unique 
type will probably show it is inseparable from the widely spread 
Neotropical D. linear e, and also that it was introduced from Rio de 
Janeiro, when in 1789 various specimens of Opimtia, the nest-egg 
of the Australian "prickly pear" scourge, were brought in to supply 
food for the similarly introduced cochineal insect. 

One of the really puzzling anomalies in the relationship and dis- 
tribution of the Dermaptera found in America north of Panama is 
the occurrence in areas of south-central Mexico of one species (vara) 
of the genus AnechiLrella, the sole representative known from the 
New World of the otherw^ise widely distributed subfamily Anechuri- 
nae, members of which elsewhere occur from western Europe and the 
Madeira Islands to India, China, Japan, Formosa, and Borneo, but 
not from continental Africa. 

No genera of the Dermaptera are peculiar to North America. The 
areal distribution of the genera of Dermaptera shows clearly that the 
largest number of generally recognized generic entities occurs ex- 
clusively in the Oriental Region, this closely followed in numbers by 
the similarly restricted Neotropical, with the I ndo- Malayan and 
Ethiopian (with its Malagasy subregion) following. The exclusively 
Palearctic genera (12) are equaled in number by those which are 
pantropical, with the Australian, Melanesian, and Pacific, broadly 
paleotropical, and cosmopolitan following in regularly reducing 

No member of the North American dermapterous fauna, except 
those of cosmopolitan distribution, and these usually limited to such 
special environments as sea beaches or river banks, appears to have 
been derived from the Palearctic Re-ion. All other elements have 
clearly come from the Neotropical Region. Several genera of this 
source have apparently been established sufficiently long in the east- 

256 J. A. G. REHN 

ern and southeastern United States to develop distinct specific 
entities. All non-adventive forms found west of central Texas and 
Kansas clearly have entered our limits within geologically recent 

Superfamily Acridoidea 

Family Tetrigidae. The Tetrigidae, or "grouse locusts," are 
cosmopolitan, except for the true arctic and antarctic regions and 
New Zealand ; they are even represented on some of the Pacific island 
groups by distinctive genera. Although terrestrial in habits, they 
almost invariably show close association with moist areas, and many 
species are fully capable of sustaining themselves on the surface of 
water, or of swimming beneath the surface. Their known paleonto- 
logical picture is represented by a fossil genus in the Baltic Amber, 
material referred to a Nearctic and Neotropical genus from the 
Upper Miocene of Bavaria, and an unplaced species of the family 
from African copal gum. 

Very narrowly within our limits, in coastal south Texas, there 
enters the genus Neotettix, an endemic eastern and southeastern 
North American assemblage, possibly developed relatively early, 
either from a primitive Tetrix-\\\<.Q ancestor, or more probably from 
the Neotropical genus Liotettix, to which it has some affinity. A 
similar history is probably that of the Mexican and Central American 
Ochetotettix, which is related to Neotettix and also to Liotettix, but 
Ochetotettix does not enter our territory. Indications point to Neo- 
tettix being one of the number of orthopterous genera apparently 
derived from a relatively early, certainly pre-Pleistocene, invasion 
from the Neotropics; most of these genera are now isolated in the 
eastern or southeastern United States. 

The genus Tetrix, which is represented in western North America 
by five distinct lines, is clearly of Palearctic origin, but it is warranted 
to believe that our North American lines of the genus represent a 
number of distinct incursions from the Palearctic, certainly one or 
two much earlier than the last. From the earlier one or ones three of 
our stocks have probably developed: T. arenosa, presumably the 
earliest, is now confined to the eastern, central, and southeastern 
United States and extreme southeastern Canada; T. ornata is much 
more broadly distributed; T. sierrana, clearly related to Old World 


species, was recently described from Madera County, California, 
in the Sierras at an elevation of 4,300-5,000 feet. The components 
of the Tetrix ornata line, which is confined to North America, are of 
particular interest, as they clearly show reactions to the varying 
aspects of Postglacial climate, as well as the probable results of 
Glacial control. Two subspecies, dominant in eastern and middle 
North America, namely Tetrix ornata ornata and T. o. hancocki, are 
clearly differentiated in certain areas, and are less sharply, probably 
environmentally, segregated in others. The more predominantly 
eastern of the two, T. o. ornata, is far less frequent in large series 
that represent many localities in the western United States and 
Canada, whereas the other, T. o. hancocki, which seems to be more 
partial to steppe country or coniferous forest lands and also is more 
frequent at higher elevations, is the prevailing form in the broad 
sweep of the Great Plains and the Cordilleran region. The Post- 
glacial ebb and flow of prairie land and coniferous and deciduous 
forests appears to account for the mosaic pattern of distribution 
presented by these two elements of this species over a large part of 
its range. However, an isolated subspecies, T. o. ifisolens, is known 
only from the western slopes of the Sierras in California, and is 
broadly isolated from the other localities where the species occurs. 
Another subspecies, T. o. occidua, is limited to the Snake River and 
Columbia River region of Idaho and Washington, reaching north- 
ward to Lake Okanagan in southern British Columbia, in the 
general vicinity of which it intergrades with T. o. hancocki of the 
higher levels about the Okanagan area. It is probable that the 
Columbia-Snake River subspecies represents survival in an area of 
relative aridity of a species once more uniformly distributed, and 
which normally requires a greater degree of humidity. 

The last incursion of the genus Tetrix may have been Inter- 
glacial or even Postglacial, as New World and Old World individuals 
of the one species involved, T. subidata, are inseparable. In the 
New World it is broadly distributed north to the northern border 
of the Subarctic, reaching southward in western America to the 
southern Sierras of California, to relatively high mountain areas in 
southern Arizona and New Mexico, and even to the Sierra Madre 
region of northern Chihuahua, Mexico. In eastern North America it 
does not range south of eastern Pennsylvania and southern New 
Jersey. Another line of the genus developed in North America a 

258 J. A. G. REHN 

species, T. brunnen, which is found in Hudsonian and Boreal 
conditions extending from Alaska to New Brunswick and Quebec, 
north to the northern hmits of the Subarctic and south in western 
North America in mountain areas as far as the Cascades of central 
Oregon and the Rockies of south-central Utah and central Colorado; 
in the eastern United States it is known to occur only in the upper 
Great Lakes region and the Adirondacks; a closely related, or 
possibly inseparable, analog is now known from extreme eastern 
Siberia. It would appear that the brunneri line of Tetrix may owe 
the base pattern of its distribution to the same activating causes 
as the members of the acridoid genus Zubovskya and the blattid 
Cryptocercus, discussed beyond. 

Paratettix is the most widely distributed genus of the Tetrigidae, 
occurring in both hemispheres but not reaching as far northward as 
Tetrix. All representatives of the genus in North America are now 
regarded as developments of lines that have reached us from the 
Neotropical Region. Whether the four chief lines of the genus in 
western North America moved from a developmental point in 
southern Mexico and Central America northward into the truly 
Sonoran areas of more northern Mexico and the western United 
States, or whether they evolved in the latter, at present rela- 
tively more arid district, and then spread southward, can hardly 
be determined from present knowledge. The more pluvial conditions 
which prevailed over much of that country during the late Pleisto- 
cene and/or early Recent clearly were more favorable for tetrigids 
than the severe restrictions of suitable environment there today. 
One North American member of Paratettix, P. cucullatus, has a 
very broad distribution, reaching from southwestern Ontario and 
the northeastern United States to north-central peninsular Florida 
and westward broadly to the lower Rio Grande in Texas and the 
eastern border of the Great Plains to the northward. However, it 
apparently spread, Postglacially in a period of greater precipitation, 
from the Platte drainage across the non-mountainous Wyoming 
Basin into the drainages of the Green and Colorado rivers and certain 
of their tributaries, and also to the Bear and Snake rivers, and 
eventually to the Columbia in northern Oregon and southern 
Washington. In these immediate areas P. cucullatus and the quite 
distinct P. aztecus are the sole members of the genus. The species 
aztecus has clearly reached the northwestern United States from its 


broad sweep in the southwestern United States and Mexico by an 
extension of its range covering much of the state of CaHfornia. 

The tetrigid subfamily Batrachideinae is one that has, funda- 
mentally, a "Gondwanaland" type of distribution and perhaps of 
origin. The genera are limited to the Americas, particularly the 
Neotropical section, and to the Ethiopian, Oriental, Alelanesian, 
and Australian regions. Their greatest development is in South and 
Central America, where eleven of its sixteen genera occur. One 
genus is Melanesian and Australian, one is Oriental, and two are 
Ethiopian, while a single one, Paxilla, is a Nearctic endemic, found 
only in the southeastern United States. The genus Tettigidea is 
clearly of Neotropical origin, as it has many species limited to South 
and Central America, but it became established in our continent, 
and particularly in eastern North America, relatively early in the 
invasion of our continent by Neotropical types. There are four well- 
marked lines of the genus in the eastern United States, with clearly 
marked, related species in Mexico and Central America, the range of 
none of which, however, is contiguous to those of its relatives in the 
southeastern and central United States. One of these lines, T. 
lateralis, is much more broadly distributed than the others over the 
eastern and central portion of North America, occurring westward to 
parts of the Cordilleran region and to certain areas on the Mexican 

Family Eumastacidae. This is, for the Orthoptera, an old assem- 
blage, on the basis of present knowledge probably older than the 
true grasshoppers or Acrididae. The oldest fossil definitely referred 
to the Eumastacidae is Promaslax of Handlirsch, from the Oligocene 
of British Columbia. From the Miocene of Florissant, Colorado, 
three species of the genus Taphacris have been described, and these 
have been considered eumastacoid by Cockerell, Tillyard, and 
Zeuner. A species described from the Oligocene of Baden, Germany, 
by Theobald, has also been referred to this family by Zeuner, who is 
probably the most capable student of fossil Saltatoria in recent years. 
Therefore, the Eumastacidae seem to have appeared in both hemi- 
spheres, relatively early in the Caenozoic, at a time of probably 
greater warmth than today. 

The greatest development of the Eumastacidae at present is in 
the tropics of both hemispheres, with the maximum generic differ- 
entiation in the Indo-Malayan and Oriental Regions, followed by the 

260 J. A. G. REHN 

Ethiopian and Malagasian and the Neotropical. One of the most 
aberrant subfamiHes, hmited to AustraHa and Tasmania, in a num- 
ber of respects approaches the exceedingly distinctive and endemic 
Neotropical family Proscopiidae. No member of the Eumastacidae 
extends into the Palearctic Region except in elevated areas of Central 
Asia and in Japan, and the family is absent from the Pacific Islands 
east of New Guinea and from New Zealand, as well as from Chile 
and southern Argentina. Three genera are known from two of the 
greater Antilles (Cuba and Hispaniola), but the family has not been 
taken in any of the others. 

The southwestern United States is the only part of North America 
in which members of the family now occur. They represent five gen- 
era of two very different subfamilies, both of which, as far as present 
knowledge indicates, are endemic within the area. One of these 
subfamilies, the Tanaocerinae, comprising the genera Tanaoceriis 
and Mohavacris, is localized in certain semi-arid and arid mountains 
and adjacent desert areas of southern California and southern 
Nevada, except for one species of Tanaocerus that is also found in 
northern Baja California. This subfamily in many respects is one 
of the most distinctive assemblages in the superfamily Acridoidea, 
the antennae being the longest in any members of that extensive 
and varied aggregation known as the "short-horned" grasshoppers. 
The Tanaocerinae, which has been regarded by some as of family 
rank, and even considered by one student to represent two families, 
is clearly a Nearctic autochthon, which because of its combination 
of unusual characters certainly may be inferred to have developed 
a considerable time in the past. It is in a number of respects probably 
the most strikingly isolated section of the whole family, and it 
apparently developed from one of its ancestral lines. The other 
Nearctic subfamily, the Morseinae, comprising the three genera 
Morsea, Eumorsea, and Psychomastax, is a cohesive assemblage 
known only from Arizona, extreme southwestern Utah, southern 
Nevada, and areas of southern and coastal California north to Mt. 
Tamalpais. Morsea, the most widely distributed of the three, occurs 
in its preferred habitat over the greater part of the full range of the 
subfamily, although it is not known from southern Arizona. Psycho- 
mastax is peculiar to mountain areas of southern California and 
southern Nevada, reaching northward along the eastern slope of the 
Sierra Nevadas, occurring also in the White Mountain section of the 


Inyo Range, and in the Charleston Mountains of southern Nevada 
as high as 11,500 feet. Both genera are chiefly thamnicolous; Morsea 
occurs largely on chamise (Adenostoma) and manzanita {Ardosta- 
phylos). The genus Enmorsea is known only from a few areas in the 
mountains of what Mearns sixty or so years ago called the "Central 
Elevated Tract," in extreme southern Arizona, where it has been 
found on the foliage of conifers. A^Iost certainly Eumorsea also occurs 
to the southward in the Sierra Madre of Mexico, and the same is 
doubtless true of Morsea and Psychomastax in at least some of the 
mountains of Baja California, although neither has been so reported 
to date. The nearest relatives of the members of the subfamily 
Morseinae are probably those of the central and eastern Asian sub- 
family Gomphomastacinae, of which the five or so known genera, 
range altitudinally upwards to high areas in the Karakoram section 
of the Himalayan uplift (to at least 14,500 feet), and in northern 
Afghanistan (where exact elevations are largely unrecorded). 
Whether the Morseinae and the Gomphomastacinae have had a 
reasonably recent common ancestry remains to be determined but 
this possibility is now under investigation. However, the Morseinae 
clearly comprise a cohesive natural assemblage, occurring in a 
relatively limited Nearctic region, which also shows numerous 
similar parallels in the distribution of other elements of the 

A third subfamily of the Eumastacidae, the Teicophryinae, con- 
sisting of two Mexican genera, is known from the Cape Region of 
Baja California, but has not been taken north of that limited area, 
although the same genus (Teicophrys) occurs in certain areas of 
south-central and southern Mexico. The other genus, Cadomastax, 
is known only from a section of western Mexico. The Teicophryinae 
do not occur south of the Isthmus of Tehuantepec, where several 
other subfamilies of the Eumastacidae of more austral Neotropical 
relationship are present. Presumably the Teicophryinae have 
developed in Mexico. 

Family A crididae. (1) Subfamily Romaleinae. The Romaleinae 
is a well-marked subfamily of the Acrididae, or true grasshoppers, 
with more than two score genera from South and Central America 
and certain areas of the United States. Several Old World genera 
have quite recently been referred to this assemblage, but I question 
this association, which is now under careful study. Within this 


J. A. G. REHN 

subfamily Is found a wide range of structural modifications and de- 
velopments, and adaptations to conditions ranging from those of 
the densest of lowland rain-forest undergrowth to the most arid 
desert environments. In my opinion the subfamily is clearly one of 
Neotropical development. Its members occur over the Americas 
from the Dakotas to central Argentina and Chile, with a single 
endemic genus on one island (Cuba) of the West Indies. 

Within the territory we are covering five genera of the subfamily 
occur, one of which, Brachystola, sweeps north broadly from Mexico 
over the Great Plains to South Dakota, and also is locally abundant 
in central and southern Arizona; another, Taeniopoda, is narrowly 
intrusive from Mexico and Central America, where the genus is 
broadly developed, in border areas of the United States from 
western Texas to central-southern Arizona; a third, Phrynotettix, 
is an inhabitant of Sonoran deserts, brushland, hills, and mountains, 
from western Texas to south-central Arizona, and also extends 
southward in non-tropical Mexico; a fourth genus Tytthotyle, is 
reported from the hottest and most arid Lower Sonoran deserts of 
southwestern Arizona, southern Nevada, extreme southwestern 
Utah, and southern California, although it doubtless occurs in suit- 
able sections of Sonora and perhaps Baja California; while the 
fifth genus, Dracotettix, is known only from the coastal ranges, 
the San Gabriel and San Bernardino Mountains, the lower and 
drier eastern slopes of the southern Sierras, the Panamint Range, 
and other desert mountains of southern California, as well as extreme 
northern Baja California, where the most generalized member of 
the genus has been found. 

The broad center of origin of our Romaleinae has clearly been the 
Neotropical Region, but the genera in western North America have 
doubtless developed as generic entities in our territory and in Mexico 
(particularly in northern Mexico); only one of the genera, 
Taeniopoda, extends as far south as Panama and none is represented 
in South America. Romalea, the sixth genus of this subfamily, in 
North America, is limited to the southeastern United States, ranging 
only as far west as central Texas and not entering semi-arid country. 
It would appear that the North American genera of the subfamily 
indicate a number of incursions from the south, of which the first is 
now represented by Romalea. The ancestral line of Romalea probably 
entered the area at least as early as the Pliocene. Dracotettix, con- 


ceivably just as old in California and Baja California, has no present 
day relatives in Mexico proper (its nearest relative is the rare and 
little known Litoscirtiis of Baja California, which for a number of 
reasons I feel represents the ancestral line of Dracotettix) . The genus 
Brachystola probably entered North America in the grass-dominant 
Pliocene, as it is more frequently encountered in dry or desert 
grass conditions than the other genera. The ancestral stock of 
Phrynotettix, which is more truly an arid land genus, may have 
reached our territory about the same time, as it has developed within 
our limits two well-distinct specific lines. The genus Tytthotyle has 
no very close relatives, and may have evolved within our territory and 
northern Mexico from an old ancestral line, possibly dating back 
of any of the others. It has a very circumscribed distribution, prefers 
areas of creosote bush {Covillea tridenlata), and altitudinally does not 
occur above 2,500 feet, yet is at home under the extremely rigorous 
conditions on the floor of Death Valley in August. The genus 
Taeniopoda, represented within our territory by the northern border 
of the distribution of a widely ranging Mexican species, appears to 
be a post- Pleistocene intrusive from Mexico. 

(2) Subfamily Cyrtacanthacridinae. The great group of the 
"spine-breasted" grasshoppers and locusts, which includes many of 
the world's most important migratory and destructive locusts, is 
represented in western North America by at least four well marked 
tribes, the Leptysmini, the Cyrtacanthacridini, the Vilernini, and 
the Melanoplini. Of these, the Leptysmini and the Vilernini are 
entirely Neogaeic; the Cyrtacanthacridini, or "bird locusts," are 
almost entirely Paleogaeic, and chiefly Paleotropical, with but a 
single genus entering the Western Hemisphere; and the Melanoplini, 
while predominatingly Neogaeic, also share the Palearctic Region 
and, more narrowly, the Oriental. 

Of the Leptysmini the single genus Leptysma occurs within the 
limits of our symposium scope, and is found very locally in suitable 
areas of tall grass and other vegetation growing generally in standing 
water (a preferred habitat for members of the tribe, all of which 
possess definite ability to dive into and swim for short distances in 
water, usually to rest longitudinally on the stems of grasses or 
rushes). In the Neotropical Region, particularly in its South 
American section, are numerous species of Leptysma and certain 
related genera. Within our territory Leptysma is clearly of Neo- 

264 J. A. G. REHN 

tropical origin, and it has broadly established itself, with a related 
genus of similar Neotropical relationship, in suitable environments, 
across parts of the southern United States. However, Leptysma 
occurs across the entire southern border of the western United 
States, and into Mexico, while the other genus (Opshomala) is 
found within North America only in the southeastern United States, 
It would appear probable that the presence of Leptysma in localized 
areas in the southwestern United States is a reminder of a broader 
dispersal, probably in Pleistocene times of a greater degree of 

Of the Cyrtacanthacridini, to which tribe belongs the striking and 
often exceedingly destructive "bird locusts," but a single genus, 
Schistocerca, lives in the Western Hemisphere, and while it has 
developed there a considerable number of endemic species, a single 
member of the genus is limited to the Old World, and is there one 
of their most serious plague forms (the desert locust, Schistocerca 
gregaria). While this species is known to reach as far across the 
Atlantic Ocean from the West African coast as the island of As- 
cension, and has also been captured landing on a ship midway 
between Africa and South America, there is no certainty that the 
numerous New World species of Schistocerca, representing at least 
ten diverse lines of the genus, have entered the New World by 
flying the South Atlantic, as a number of our species are not addicted 
to extensive flights, and also some are definitely localized in their 
distribution and ecological preferences. The optimum differentia- 
tion of the Cyrtacanthacridini clearly took place in the Old World, 
and our stock was certainly derived from progenitors there. It 
is possible that Schistocerca, from a basic ancestral stock of the 
tribe, developed its various lines in the New World, and that the 
one to which gregaria belongs, which is well represented in the 
Americas, North, Central and South, later reentered the Old World, 
giving it its troublesome S. gregaria. If the latter were a local or 
restricted type we could conclude that the genus was Old World in 
origin and is there dying out, but with gregaria in an entirely 
different category, and the genus greatly diversified in the Americas, 
it is plausible to conclude that its ramifications had their base in 
the New World. 

Of Schistocerca five lines occur within western North America, 
and they are restricted to the same general area except that certain 


of them reach into Mexico, with, however, the greater part of the 
known range of three north of the Mexican boundary. One, 6*. 
mexicana, is but narrowly intrusive in our territory from Mexico. 
Also in the eastern, central, and southeastern United States are 
four other lines of the genus, two there limited, one largely re- 
stricted to that area, and the fourth also found rather broadly and 
passing into Mexico, but almost limited westward by the eastern 
border of the Great Plains. Clearly certain of these distinctive lines 
of Schistocerca have been established in our territory for a consider- 
able time. Their history is tied to our area because, where found in 
Mexico, most of them are Sonoran only. One of the lines in the 
eastern and central United States, but hardly encroaching on our 
territory, is broadly developed in Central and South America, 
there having spawned one of the most destructive locusts of the 
New World, the Parana locust {Schistocerca paranensis) of Argen- 
tina and many other areas of South and Central America. 

The Vilernini are a most distinctive Neotropical assemblage of 
a score or more genera, ranging from Argentina northward to 
briefly north of the Mexican boundary, and are found in a variety 
of habitats. Clematodes, the single genus in our region, is an apterous 
thamophilous grasshopper, known only from the border regions of 
western Texas, southern New Mexico, and Arizona, extending into 
Mexico in several areas. It clearly has entered our territory from the 
southward, and with us is probably more widely distributed in the 
Lower Sonoran Life Zone than the records indicate (the secretive 
habits of this grasshopper, which, among other situations, likes the 
main stems of the intrusion-resisting cat-claw (Acacia), are largely 
responsible for our limited knowledge of it). 

European students have broadly assumed that the great assem- 
blage of the Melanoplini is basically a Eurasian group, with an 
Angara background, and that its presence in the New World is 
attributable to a relatively recent extension from the Old. Recently 
this assumption has been challenged, on the basis of a relatively 
critical analysis of the whole picture for the tribe. Little help can be 
drawn from the fossil picture, as the total of such evidence to date 
indicates the presence of two existing species of two genera in the 
Pleistocene of Starunia in the Polish Carpathians. What we do 
know is that in the New World members of the Melanoplini occur at 
localities reaching from the Arctic Circle to at least south-central 

266 J. A. G. REHN 

Argentina and Chile, thus well over one hundred degrees of latitude, 
and occupy stations ranging from extremely arid ones below sea- 
level to others as high as Arctic-Alpine in North America and the 
Paramo in South America. Three major centers of evolution of the 
Melanoplini in the Americas have clearly been indicated: (1) North 
America south to the Isthmus of Tehuantepec; (2) the Venezuelan 
Andes and adjacent, chiefly montane, areas in northern and eastern 
Columbia; and (3) South America from approximately 15° south 
latitude southward. Few genera of the tribe occur over the inter- 
vening areas. In the Old World the tribe is much more circum- 
scribed, for it is absent from the Ethiopian region, from most of the 
Oriental region and from all the Australasian region. In Eurasia 
twenty-seven genera occur, three of which are also in the Nearctic. 
In the Nearctic and Neotropical combined, we find 59 genera, 
including the three occurring also in Eurasia. In the New World 
forty genera are known north of the Isthmus of Tehuantepec, the 
majority only north of the Mexican boundary. 

Within the northern United States we find one line of the Melano- 
plini, the genus Podisma, which clearly is of Old World relationship, 
for it has numerous species in Eurasia and only one in North 
America, P. hesperus, in the Cascades of Oregon, the nearest relative 
of which appears to be a species of northern Japan, P. sapporensis. 
It is probable that the ancestral stock of this species reached our 
continent in the Pleistocene, perhaps Interglacially, or even earlier. 
Another line in North America, comprising the genera Dendro- 
tettix and Appalachia, also represents an older invasion of the same 
stock. (This line is not now present in western North America; 
its two generic members occur, so far known discontinuously, in 
the eastern and central parts of the United States.) These 
two genera clearly developed within our territory. A third line, 
including the single flightless genus Zubovskya, which occurs dis- 
continuously in eastern forested areas of North America and in the 
Cascades of Oregon, is also represented in a limited section of 
eastern Asia by several distinct species. Whether Zubovskya is an 
Asiatic genus that has traveled to North America and spread 
broadly there, or is of North American origin and has narrowly 
entered the Old World, remains to be determined. Clearly, however, 
it has been present in North America since before the Glacial 
period, as there can be little question but that the present dis- 


continuous distribution of the genus in our continent reveals the 
part the ice-sheets had in separating the eastern form of this forest 
land genus from that now occurring in the Oregon Cascades. A 
largely parallel case of discontinuous distribution of this type, 
with apparently the same origin, is that of the flightless wood- 
boring cockroach Cryptocercus. 

It seems that all the other numerous lines of the Melanoplini in 
western North America have developed within our territory, and 
that a single species of the genus Melanoplus has crossed into the 
Old World. The genus Melanoplus developed a considerable number 
of specific lines in North America, with a very marked center of 
speciation in the southern Appalachians and the adjacent lowlands, 
while other lines, clearly representing evolutionary phyla, have 
centered in the grasslands of the Great Plains, the Transition and 
Canadian areas of the Rockies, the Great Basin region and its 
various mountain areas, the Lower Sonoran Deserts of the south- 
western United States and northern Mexico, the Sierra Nevadas, 
and the coastal ranges of California and Oregon. In each of these 
areas one or more definite lines of development of the genus will be 
found. Some lines reach as high in their distribution as Hudsonian or 
even Arctic-Alpine conditions, often with some species quite local- 
ized. To the southward the genus Melanoplus enters Mexico, 
where there is a considerable number of more broadly ranging and 
endemic species, but the genus does not extend south of that country. 
The Melanoplini of Mexico are rich in species and work now under 
way will shortly give us a clearer picture of the richness of that 
fauna, which with the western part of North America has been a 
major site in the evolution of the Melanoplini. 

Of the other genera of the Melanoplini in western North America, 
the Campestran Great Plains apparently produced at least four, 
Campylacantha, Argiacris, Phoetaliotes, and Hypochlora. Phoetaliotes 
is more widely distributed in grassland areas (formerly of greater 
extent, perhaps in the Pliocene, a grassland optimum), and relict 
populations remain in sections of southern Arizona and certain 
other areas. The genus Dactylolum, now widely distributed in 
Sonoran situations in western North America, is doubtless of Mexi- 
can origin, as there the genus has developed a broader specific 
diversity than it has north of the Mexican line, although in the 
latter territory its range is much more extensive. The same is prob- 

268 J. A. G. REHN 

ably true of the array of distinctive genera found broadly over 
areas of central and western Texas {Phaedrotettix, Phaiilotettix, 
Paratdemona, Chloroplus, and Agroecotettix). The genus Aeoloplides 
is of broad distribution in the Great Plains, the Sonoran deserts of 
the southwestern United States, the Great Basin, and areas of 
California, and is probably a relatively old line, very adaptable to 
the distinctly thamnicolous habitat it prefers. The genus Aidemona 
is narrowly present in our territory as an intrusive from Mexico and 
Central America (it ranges southward to Colombia). 

In the Sonoran desert mountains and on the benches of the south- 
western United States we find a group of genera that probably 
originated there, or in adjacent northern Mexico, where they also 
do or may occur. These are Conalcaea, Barytettix, Poecilotettix, 
and Aztecacris. Another clearly Sonoran type is the genus Hes- 
perotettix, which is of wide distribution over most of the lower level 
land areas of the western United States and Canada, where its 
favorite cover of yellow-flowered composites of several genera 
("rabbit weed") occurs. Two lines of the genus undoubtedly entered 
the southeastern United States from more western territory a 
considerable period in the past and there developed a subsidiary 
evolutionary center of the genus, while another line of campestran 
relationship spread in ecologically suitable areas over much of the 
eastern states. In many areas of California and of the Great Basin, 
as well as the Columbia River and Snake River plains, the genus 
Oedaleonotus has developed a marked radiative speclation. It 
apparently is an autochthon which has no very close relatives. 

In mountain areas of the western United States and southwestern 
Canada there have developed a number of apterous, and of course 
flightless, endemic genera, of which three, Bradynotes, Prumnacris 
and Buckellacris, are of Canadian and Hudsonian Zone distribution. 
The most highly specialized is probably Brady?iotes, which occurs in 
isolated areas of the more northern Rockies in the United States 
and adjacent Canada, the Cascades, the pumice plains east of the 
Cascades in Oregon, and in the more northern Sierras. The genus 
also reaches southward to the Kaibab Plateau of northern Arizona, 
although in the main Rockies it is not known from south of South 
Pass, Wyoming. It is possible future work may show that Prumn- 
acris and Buckellacris, as well as the strange Nisquallia of the 
Olympic Mountains of Washington, are more nearly related to 


Old World genera than has yet been determined. Prumnacris and 
Buckellacris are both distinctly northern montane types: Prumn- 
acris occurs chiefly in the northern Cascades, and Buckellacris 
extends from the same range northward to the Chilcotin area of 
British Columbia, and eastward over the northern Rockies to south- 
eastern Idaho. In the Rockies of the northern United States and 
southern Canada, and in adjacent parts of Washington and the 
northern Sierras of California, the distinctive genus Asemoplus 
is localized, and in the southern Sierras only at or near timberline 
do we find Hebardacris, which has nearest affinity to Bradynotes. 
All these montane genera are clearly of relative antiquity, and 
probably survived Glacial conditions by retreating moderate 
distances before the advancing sheets or the encircling spread of 
mountain glaciers. Some of them seem to have reoccupied only 
limited sections of suitable terrain which was heavily glaciated. 

(3) Subfamily Oedipodinae. The Oedipodinae comprise a large 
number of chiefly ground-dwelling grasshoppers, some of which have 
become of economic importance. The subfamily is poorly represented 
in the Southern Hemisphere, and is best developed in Eurasia and 
North America. In South America its members are limited to a few 
genera, one of which, Trimerotropis, is markedly developed in North 
America, while another, Heliastus, narrowly enters our territory. 
The maximum diversity of the subfamily is in semi-arid grass- 
lands, although it is also well represented in true deserts and semi- 
deserts, and a number of types occur in more humid grasslands and 
bush country; a very few are more partial to wooded areas. Some 
of the species live in the most arid environments to be found in this 
continent and in similar areas in Asia and North Africa. Some are 
governed in their occurrence by the presence of favorite food plants, 
but on this point our information is less conclusive than for some 
other grasshoppers. Apparently most, if not all, of the North 
American genera have developed in our territory or in northern 
Mexico, although the possible relationship of a few of the genera to 
those of Central Asia remains to be more accurately determined. 
Broadly speaking, however, the oedipodine fauna of North America 
is autochthonous. A number of the genera probably originated in the 
Sonoran region of our southern Great Plains, the southwestern 
United States, and northern Mexico. Certain of these genera have 
extended their ranges into the more eastern United States and 

270 J. A. G. REHN 

adjacent Canada, and some have developed well-marked subsidiary 
evolutionary centers there. Trimerotropis, an entity with a consider- 
able number of North American species, is probably a relatively old 
type, which has extended locally into boreal conditions, has formed 
certain localized species in the eastern United States, and has further 
intruded itself southward, so that today the genus is also present in 
semi-arid and Andean areas of western South America. Its range 
there is now cut off from the southern limits of its mass distribution 
at the southern edge of the Mexican tableland. This discontinuous 
distribution probably exemplifies a far broader and drier Pliocene 
grassland distribution, and reflects the increased Pleistocene develop- 
ment of forest areas in the intervening territory, which doubtless 
eliminated Trimerotropis from Central America and parts of north- 
western South America. A similar postulate would explain the 
present discontinuous distribution of the grassland mantid Brunneria 
and the acridine grasshopper genus Dichromorpha. 

The genus Chortophaga is probably of southeastern origin, there 
showing two types of the genus, one species of which, present over 
much of the eastern and central United States, is also found in the 
more temperate parts of Mexico and Central America as far south 
as Costa Rica. The endemic Californian genus Chimarocephala is 
rather an anomaly, although its ancestral stock may have had a 
common origin with Chortophaga. The genus Cammda probably 
developed from the same stock as Hippisciis or Encoptolophus, 
possibly in the Cordilleran region, but it now has an unusual type of 
distribution; it is essentially Boreal in the eastern and central 
United States and Canada, broadly present in the Cordilleran 
region, and much more localized westward (in southern California 
it even descends to virtual sea level in coastal Lower Sonoran 
conditions). The broadly spread but often localized genus Xaiithip- 
piis, a close relative of Hippiscus, apparently developed in the 
Sonoran region of our Great Plains, the southwestern United States, 
and northern Mexico, with numerous localized and seasonally limited 
montane forms, but it has not spread eastward, while the related 
Cratypedes is much more definitely an inhabitant of the Cordilleran 
and Great Basin areas. The genera Sticthippus and Agymnastus are 
Californian endemics, clearly derived originally from the same basic 
stock as Hippiscus, Pardalophora, and Xanthippus. The genera 
Leprus and Derotmema are certainly of Sonoran origin, and both 


have spread northward over the Great Plains and entered the Great 
Basin, in which area Derotmema has developed a very distinctive 
type {D. piiite). Hadrotettix, Tropidolophus, and Platyladista are 
also Sonoran. The first two extend to varying degrees northward 
over the Great Plains. Hadrotettix is also known from relict grassland 
areas in northern Arizona. 

The more dominantly eastern genus Spharagemon probably had 
its origin in the eastern United States, where it now has three dis- 
tinct lines. Two of these lines extend westward, but the extent of 
the genus in that direction is virtually limited by the Rockies. 
Spharagemon has four well-marked lines in the Great Plains and in 
Texas, of which two also occur in the eastern United States. The 
genus Dissosteira is widely spread over the United States, narrowly 
entering Canada. One of its species is almost ubiquitous in the east- 
ern United States, but west of the Rockies it chiefly occurs in the 
Transition zone. A second species is basically a Great Plains form, 
a third is largely Californian and Great Basin, and a fourth occurs 
locally only in California. The genus is apparently of Sonoran origin, 
and the same may be true of the related Scirtetica, which has one 
locally distributed stock in coastal areas of the eastern and south- 
eastern United States and in the Great Lakes sections of the 
United States and southeastern Canada, while another stock is 
isolated in the mountains of southern Arizona, with no representa- 
tives known from the interv^ening sections of the territory the pres- 
ent symposium is covering, or as yet from Mexico. The strange 
little genus Microtes is an autochthon of the Californian coastal 
mountains and adjacent valleys, with no very close relatives, and is 
probably an old type. Lactista and Tomonotus are clearly Mexican 
Sonoran entities rather narrowly intrusive in our border states. 

The genera Trepidulus, Shotwellia, and Ciholacris are relatively 
arid land Sonoran types. The last is also coastal in southern Cali- 
fornia. All three probably range into northern Mexico, and doubtless 
all had their origin in that great area on both sides of the inter- 
national lioundary which, even in its diversity of surface features, 
has to a considerable degree had a similar faunistic history. The 
genera Mestobregma and Metator are clearly of Sonoran origin ; each 
extends northward over the Great Plains and the Great Basin, with 
distinctive lines in each of these areas, indicating a considerable 
period of time for divergence and development of differentiating 

272 J. A. G. REHN 

stocks. Trachyrhachts, which clearly has had a similar history, has 
also extended the range of one of its species eastward, probably 
Postglacially, to parts of the Appalachian uplift in the eastern 
United States. The genus Rehnita is an additional Sonoran type, 
probably derived from the same basic stock as Mestobregma. 

The genus Conozoa has more affinity to Trimerotropis, which has 
already been mentioned, than to any other member of the sub- 
family, and it may represent an offshoot from the same stock. If so, 
its divergence was not recent. The genus occurs entirely within the 
area of our coverage, only rarely east of the Continental Divide. 
The chiefly Boreal and generally montane genus Circotettix may also 
originally have been derived from the basic Trimerotropis stock. 
Its distribution is often discontinuous, extending eastward across 
southern Canada and the northern United States into Boreal areas 
in eastern North America. Its species are among the few grasshoppers 
that perform aerial stridulating dances. Another genus with the same 
proclivities, that may be related in some degree to the Eurasian 
genus Bryodema, is Aerochoreutes, which occurs in Upper Austral 
and even Transition areas of the northern Great Plains, northern 
Great Basin, and the Columbia-Snake River semi-arid hills. 

The extremely arid sections of the Lower Sonoran life zone are the 
home of the genus Anconia, which also occurs some distance south- 
ward into northern Mexico. It would appear to be endemic in the 
territory where it now occurs. Its only known relative is Spaniacris, 
which lives in limited, and intensely arid, sections of the same area 
in southern California and extreme western Arizona. These two 
genera clearly are old desert types, with no close relatives, markedly 
specialized in a number of respects, and with distinctive habitat 
preferences. The genera Xeracris and Coniana, smaller desert types 
known only from the most arid sections of the Colorado, Yuma, and 
Mohave Deserts, are similar to Spaniacris in distribution, but 
are of different affinities. They are clearly authochthons without 
any very close relatives, although further study on this matter is 

The genus Heliastus is a Mexican and Central American type, 
which reaches even to northern South America, but in our territory 
is found only narrowly and locally in southern Arizona and coastal 
Texas. This is clearly a Sonoran genus which has spread southward — 
a less frequent pattern. A Sonoran type of higher levels, largely 


Upper Sonoran, is the genus Heliaula, which extends northward 
over the Great Plains as far as eastern Colorado, but does not go 
far west of the Continental Divide. 

(4) Subfamily Acridinae. The Acridinae, or slant-faced grass- 
hoppers, which in our section of the world are in considerable part 
grassland forms, are very well represented in our fauna, and the 
greater part of the forty or more genera reviewed clearly have 
developed within North America west of the Mississippi. Two 
genera, Chorthippus and Stethophyma, are certainly relatively 
recent Palearctic intrusives in North America, the former so recent 
that the single species we have is also widely distributed in Eurasia. 
Chorthippus has a large number of Old World species, and it is possi- 
ble we received C. longicornis in an Interglacial period. Our three 
species of Stethophyma are endemic, two with preferences for Boreal 
or sub-boreal conditions, the other of infrequent and very local 
occurrence over a broad section of eastern North America. The 
species of sub-boreal preferences occurs in widely separated parts of 
western North America, but has been taken at only a few localities. 
Presumably Stethophyma reached North America from Eurasia 
prior to the advent of Chorthippus, as its species are well differenti- 
ated from Old World forms. 

One set of three genera, representing the group Chrysochraontes, 
has presumably also been derived from Eurasia, probably through a 
succession of waves. The earliest invasion was probably that of 
an ancestral stock of the genus Chloealtis, which today is chiefly an 
inhabitant of the more northern parts of eastern North America, 
although it narrowly reaches our included territory in eastern 
Colorado. Apparently a second intrusive line of the same group is 
represented by Chrysochraon, which occurs broadly in the Pale- 
arctic, and of which we have a single endemic species in Cordilleran 
montane localities. A third line of the same group comprises the 
equally endemic genus Napaia of Coastal Range mountains of 
southern Oregon and California, as well as the San Gabriel Range in 
the latter state. The members of the Chrysochraontes are peculiar 
in that they usually oviposit in dead wood, an unusual situation for 
acridids. Another genus of Palearctic relationship is Aeropedellus 
a Cordilleran and high Great Plains genus, which clearly has been 
derived from the same stock as a number of Palearctic genera 
related to, and including, Gomphocerus and Aeropus. A distant 

274 J. A. G. REHN 

relative of Aeropedellus, but without Old World relatives, is Brun- 
eria, which is a northern type, usually found under Boreal, or even 
Hudsonian, conditions, from southern Canada sporadically and 
very locally south in the Cascade-Sierran uplift to northern Califor- 
nia and in the Cordilleran massif at least as far as southern Utah. 
It appears to have developed in the territory where it now occurs, 
with greater diversity in the Cordilleran section than elsewhere. 
Three of our acridine genera, Amblylropidia, Orphiilella, and 
Rhammatocerus, are clearly of Neotropical origin. All have a far 
greater specific development and areal extent southward than in 
our area, extending to southern Brazil and Argentina. Amhlytro- 
pidia is only narrowly represented along our Mexican border by 
one of a number of Mexican species, although a distinct endemic 
species occurs rather broadly over the southeastern United States. 
Rhammatocerus is similarly represented along the Mexican border, 
but not elsewhere in North America. Both of these genera apparently 
are more recent intrusives than Orphulella, which is broadly present 
in North America from Atlantic to Pacific. Because of its habitat 
preferences Orphulella is of much more localized occurrence in the 
western part of its range than in the East. A considerable number 
of the genera of the subfamily in North America, including Paro- 
pomala, Acrolophitiis, Amphitornus, Opeia, Cordillacris, Phli- 
bostroma, Boopedon, Ageneotettix, Drepanoptertia, and Aulocara, 
I would regard as autochthonous in our Great Plains, the adjoining 
Texas Sonoran area, or the Sonoran areas to the westward. Other 
genera, including Achurum, Eremiacris, and Morseiella may, with 
reasonable assurance, be regarded as having developed in Mexico, 
and species there found, or closely related ones since evolved, 
occur on our side of the border. Another genus that should be 
placed in this category is Syrbida, although it apparently entered 
our territory quite some time in the past, as one of its species, 
which also is distributed over much of Texas, is broadly established 
in our more southern and southeastern states. The genus Mermiria 
is represented in the West by four of the well-difi'erentiated lines 
that it has evolved in the United States. In all probability this 
genus developed in the Sonoran region, spread broadly over the 
Campestran, and then extended its range into the southeastern and 
central states, where three of its lines occur. One of its most dis- 
tinctive species, M. texana, is present on both sides of the Mexican 


border, on arid rocky hills and in brush land, while another, definite- 
ly a Campestran (Great Plains) type, narrowly extends into Mexico. 
Pseudopomala, a near relative of Mermiria, is widely distributed 
over the more northern section of the United States, occurring 
sparingly in restricted environments. At least some of its present 
spotty distribution probably can be explained as a subsequent 
readjustment to Glacial displacement, but on this point more 
study is needed. 

The highly specialized genus Radinotatum is largely limited to 
the southeastern United States, but includes a quite distinct species 
in southern Texas. Its nearest relative is apparently Achurutn, 
which is Mexican in origin, although found within our limits in 
southern Arizona. The genus Prorocorypha is of localized occurrence 
in certain mountains of extreme southern Arizona. Its nearest rela- 
tive is the rather broadly distributed and highly specialized, equally 
graminicolous Sonoran genus Paropomala. The genera Acantherus 
and Horesidotes are apparently endemic generic types of the Sonoran 
Mexican border country in Texas, New Mexico, Arizona, and 
California. The same is true of the strictly thamnophilous genera 
Ligurotettix and Goniatron, the former of which does not occur east 
of the Continental Divide and extends northward as far as west- 
central Nevada, while Goniatron lives almost entirely east of the 
Continental Divide in the Chihuahuan Desert area and is much 
more limited in its north and south distribution, but with its range 
definitely known to extend a considerable distance into northern 
Mexico. In habitat Goniatron is restricted to "black brush" (Flour- 
ensia), while Ligurotettix is found on more than one species of 
shrub, but often on creosote bush (Covillea). 

The genus Pedioscirtetes comprises two lines of development, one 
of which occurs in the Mexican border territory from western 
Texas to southern Arizona, as well as some distance southward into 
Mexico; the other is known only from very limited, distinctly more 
elevated areas in northern Arizona, Nevada, Utah, and southern 
Idaho. It appears to me that the genus originally developed in our 
older plateau areas adjacent to the Cordilleran mass, and that one 
element moved southward, perhaps in Pleistocene times, while the 
other remained, survived lower temperatures, and has even extended 
its range northward. The genus Bootettix is always associated with 
the Lower Sonoran creosote bush {Covillea), and is almost never 

276 J. A. G. REHN 

found off of it. It clearly developed in the area of our Mexican 
border. One species occurs on the Pacific side of the more elevated 
Continental Divide, the other on the Atlantic side; both are known 
to extend southward, with their host plant, into Mexico. 

The genera Esselenia and Eupnigodes are Californian endemics. 
The former is found only in the central section of the Coast Range 
region, and has no known close relatives. On the other hand 
Eupnigodes, which is more broadly distributed over the San Joaquin 
Valley and the lower western slopes of the Sierra Nevada, is rela- 
tively close to Ageneotettix, which is a quite widely dispersed 
Sonoran genus, and clearly the stock from which Eupnigodes 
developed in relatively recent times. Another apparent development 
from the Ageneotettix line is Zapata, of which a few species are quite 
locally distributed in southern Arizona, western Texas, and northern 
Mexico. A genus almost exclusively Texan Sonoran is Mesochloa, 
which is clearly derived from Eritettix. The latter, probably also of 
Sonoran origin, is broadly distributed northward over the Great 
Plains and westward along sections of the Mexican borderland. 
One species of Eritettix has deeply penetrated into the central and 
eastern United States, where it occurs from New England and 
Nebraska southward. A related, and apparently derived, endemic 
genus, Macneillia, is restricted to peninsular Florida. 

The genus Dichromorpha is probably of Sonoran origin, but 
ranges northward over most of the central and eastern United 
States, with several species in Mexico, while to the southward, after 
a gap of some thousands of miles, it reappears in areas of Paraguay 
and northern Argentina. It is a grassland type and its distribution, 
like that of the mantid Briinneria, probably reflects the much 
broader extent of grasslands in the Pliocene, and their later restric- 
tion by the moister and colder Pleistocene, with its greater develop- 
ment of forests. 

A dominant genus of largely arid or semi-arid sections of the 
whole Sonoran region, also occasionally entering the Transition Life 
Zone, is Psoloessa, one line of which extends as far northward in 
the Upper Sonoran as the Okanagan Lake country of extreme 
southern British Columbia, and also to sections of the Great Plains 
of southern Alberta, Saskatchewan, and Manitoba. Southward one 
line of Psoloessa reaches as far as the Mexican states of San Luis 
Potosi, Guadalajara, and Mexico. Psoloessa is probably one of the 


types that developed in areas of our Southwest, or it may have been 
intrusive in our area from Mexico, though I am more incHned to 
place its origin as north of the Mexican line, since one of the three 
main elements of the genus does not, as far as we know, reach 
Mexico, and it is, with us, always an Upper Sonoran or Transition 
species. A second of these main elements is restricted to the western 
section of the southern half of California and several areas of Baja 
California, while the third is broadly distributed from east-central 
Texas west to west-central Arizona and northward over the Camp- 
estran region to South Dakota. 

Superfaniily Tettigonoidea 

Family Tettigoniidae. Passing now to the great assemblage of 
what we Americans call the "katydids," but which are elsewhere, in 
the English-speaking world, referred to as "long-horned grasshop- 
pers," or technically the Tettigoniidae, we have first the virtually 
cosmopolitan subfamily of the Phaneropterinae. This is represented 
in western North America by eight endemic genera, none of which is 
Holarctic, and by one, Microcentrum, the " angular-winged katydid," 
that is clearly Neotropical in origin and is much more variedly de- 
veloped in that region. This genus reaches on one hand to California, 
and on the other is broadly spread over the interior and eastern 
United States, but does not reach high altitudes in the Cordilleran 
section. One genus, Platylyra, is endemic in the California coastal 
mountains, and probably represents a relatively early development, 
perhaps from fundamentally Neotropical ancestors. The genus 
Insara was certainly Neotropical in origin, but it clearly has been in 
and has undergone a considerable part of its evolution in the broad 
Sonoran region, developing there at least four lines, one of which 
lives only on the creosote bush (Covillea). Other species of Insara 
range from Mexico to Panama, while related genera are known 
from Panama and northern Argentina. The genus Brachyinsara, 
which as clearly has had a common ancestry with Insara, is known 
only from extreme southern California and Baja California. 

The genus Arethaea, composed of spectral, ghostlike species, is 
clearly a development of the Sonoran center. Certain of its species 
are found in northern Mexico, but the majority occur within the 
limits of the United States, ranging northward in the Great Plains 

278 J. A. G. REHN 

to the Dakotas and western Iowa. A single very distinctive species 
is isolated in the extreme southeastern United States. The greatest 
specific diversity of Arethaea is in southwestern Texas and adjacent 
Mexico, and only one species reaches westward to southern Cali- 
fornia and southern Nevada. Another genus with a similar, and 
clearly Sonoran, pattern of development and distribution is 
Dichopetala, a thamnophilous flightless genus of nearly a score of 
species, which range from Oklahoma, Texas, New Mexico, southern 
Arizona, and southern California southward to the Rio Balsas 
Valley and northern Vera Cruz, Mexico, with several species simi- 
larly referred generically from Peru and Ecuador. However, its 
greatest specific development is in southern Texas and the north 
and central parts of the Mexican tableland and its bordering 
eastern Cordillera. It is possible that the South American species 
may require generic separation or that they represent a southward 
extension of the genus across the "Panama fault," rather than the 
more usually postulated one of a reverse movement. However, the 
maximum diversity of Dichopetala is clearly in the Sonoran region, 
very largely east of the Continental Divide. 

The genus Scudderia, which apparently developed from a Neo- 
tropical center, includes a certain number of species limited to 
Central America, and others intrusive into the western United 
States from Mexico. However, a secondary evolutionary center 
most certainly developed in the southeastern United States. From 
that area, apparently some of the most distinctive members of the 
genus extended. Several broadened their range into the western 
United States, reaching the Pacific Coast, and also into southern 
Canada. The genus Amblycorypha, which probably came from a 
Neotropical ancestral stock, developed an evolutionary center in the 
eastern and southeastern United States. Four of its five lines center 
there, whereas only one is definitely Sonoran. The Sonoran line ex- 
tends narrowly along the Mexican border area from western Texas 
and Coahuila to southern Arizona. The broad north to south range of 
Amblycorypha in western North America reaches from southern 
Manitoba and Wyoming to Zacatecas, Mexico. 

The subfamily Pseudophyllinae, which is a greatly diversified 
and remarkably developed, almost entirely pantropical, assemblage 
is represented in North America by a single tribe, the Pterophyllini, 
which may be called the "true katydids." This tribe is a Neogaeic 


group that has three peculiar genera In North America, two in the 
West Indies and one in South America. The center of development 
of the North American elements of the subfamily seems to have 
been eastern and midland North America, where two (Pterophylla 
and Lea) of the three genera are most diversely developed, while 
the third (Paracyrtophyllus) is essentially Campestran and Sonoran. 
No member of the tribe is found west of the Continental Divide. 

The Copiphorinae is a subfamily of broad distribution, more 
strongly developed in the Neotropical Region than elsewhere. 
While a number of its genera occur in Mexico, Central America, and 
the West Indies, but a single genus, the predominatingly Neo- 
tropical Neoconocephalus, enters w^estern North America. It occurs 
but sparingly In the Campestran area. West of the Continental 
Divide a single species has been taken in southern Arizona and 
southern California. It may be intrusive from Mexico, where the 
same species is broadly distributed. Any such intrusion seems to be 
largely or wholly unrelated to the marked secondary developmental 
center for Neoconocephalus in the southeastern United States, that 
Is clearly indicated by the varied lines of the genus there present and 
In part there limited. 

The subfamily Conocephalinae includes the small species of 
katydids often referred to in economic works as "meadow grass- 
hoppers." One of its two genera found within western North 
America, Orchelimum, is strongly developed in the eastern and 
central United States, and reaches into the Sonoran In Texas and 
eastern Mexico. A single sub-boreal species extends from eastern 
Canada across the northern United States to Montana, Washington, 
and northern California. Orchelimum, while known only from Amer- 
ica north of Tehuantepec, is closely related to the very widely 
spread genus Conocephalus, and probably represents a line that has 
developed in our territory from the Conocephalus stock. Like 
Neoconocephalus, Orchelimum prefers grassy and usually quite 
moist meadows, and unless the continuity of such conditions has 
been assured, as In the eastern and southeastern United States, 
Orchelimum is usually not present, and hence we do not find in west- 
ern North America the varied representation of Orchelimum that is 
present to the eastward. The nearly cosmopolitan genus Conoce- 
phalus has habits rather similar to those of Neoconocephalus and 
Orchelimum, and but four of the eighteen species known from 

280 J. A. G. REHN 

North America occur west of the Continental Divide. Two of the 
three subgenera of Conocephalus known from North America are 
almost entirely confined to the eastern and central parts of the 
continent. We doubtless received the ancestral stock of these lines 
from the Neotropical Region well before the Pleistocene, and they 
probably evolved almost entirely in the southeastern United States 
between their advent there and the present. It is also quite probable 
that the two forms of the genus peculiar to the western United 
States have evolved from eastern species, while the other two there 
present are relatively localized western extensions of broadly 
dominant eastern species. 

Until very recently the subfamily Listroscelinae was not con- 
sidered to be present in North America or even in Mexico. Recent 
work has shown that the genus Rehnia, which occurs from Kansas 
to the Rio Grande and southward into northern Mexico, and there 
westward to Sinaloa, is a member of the Listroscelinae, a subfamily 
chiefly of pantropical distribution, with a number of most distinc- 
tive genera in South America. Apparently Rehnia is a bush- and 
tree-loving Sonoran development from a line of the subfamily, 
the entry of which into our general region from a Neotropical stem 
probably dates back a considerable time. Another genus of the 
same subfamily Neobarrettia is an inhabitant of the very hot Rio 
Balsas Valley of Guerrero, Mexico, while the remainder of the 
Neogaeic genera of the subfamily occur almost exclusively in South 
America and more southern Central America. 

The subfamily Decticinae is made up of a very extensive array of 
genera occurring almost entirely in the Nearctic and Palearctic re- 
gions. A very few narrowly extend southward and several isolated 
genera are known from South America. A large percentage of the 
members of the subfamily are bush- or thicket-loving species, 
but some are grassland types, and others live entirely on the ground 
in forested areas; a very few, such as the Mormon cricket {Anabrus) 
and the coulee cricket (Peranabrus) are often economic problems, 
and these latter, although flightless, have well-developed migratory 
instincts when in search of food. In North America only one genus 
{Atlanticus) is limited to its eastern part, while twenty-one genera 
are known from, and all but one are peculiar to, the western part of 
our continent. One interesting peculiarity is that the one eastern 
genus, Atlanticus, is the only one having its greatest diversity in 


our continent that is also found outside of North America (in the 
last few decades a fair number of species of the genus have been 
made known from eastern Asia). This distribution is paralleled in 
part by the acridid genus Zubovskya, the blattid genus Cryptocercus 
and also by numerous genera of trees and shrubs which have similar 
patterns of discontinuous distribution and are now unrepresented in 
western North America. 

Of the various genera of the Decticinae in western North America, 
a single genus {Metrioptera, s. 1.) is shared with the Palearctic 
region. This genus with us is a truly boreal type, not occurring south 
of Alberta. Its nearest relative is considered by some European 
authorities to be M. iissuriana of the Soviet Far East. Of truly 
Sonoran development we would regard the genera Eremopedes and 
Pediodedes. Genera limited to, and probably developed in, the very 
arid western section of the Sonoran are Anoplodiisa and Ateloplus. 
The genus Aglaothorax is limited to the Mohave Desert and the 
Great Basin, and to the latter the exceedingly rare and local Za- 
cydoptera is also restricted. Plagiostira, although chiefly a Great 
Basin genus, extends southward over parts of the Arizona Plateau 
and eastward into sections of New Mexico, and Capnobotes, which is 
chiefly a western Sonoran type, also extends northward in mountain- 
ous portions of the Great Basin. 

Probably originally of Sonoran origin, but now extending its 
distribution widely over the Great Basin and the Columbia Plains, 
and even to very considerable elevations in the Rocky Mountains, 
is the genus Anabrus, the dreaded Mormon cricket. In the north- 
western United States are two endemic decticid genera, Pemnabriis 
the economically important coulee cricket, and Apote, which is 
chiefly localized in the Columbia Plains, but reaches southern 
British Columbia and is apparently restricted in its occurrence. It 
is possible that further study may show that both Anabrus and 
Peranabrus have Palearctic relationships, and the same also may be 
true of Apote. Material for such study is now available and will be 
used in the near future. 

In the broadly Pacific area from British Columbia to southern 
California are a number of clearly endemic genera of Decticinae, 
such as Neduba, which often is taken on the ground in heavy conif- 
erous forests from British Columbia to the mountains of southern 
California, and Idiostatus, from more arid regions of the same 

282 J. A. C;. REHN 

general territory east to Montana, while the little-known Oreo- 
pedes and Crytophylliciis are Sierran endemics, occurring respectively 
on the eastern and western slopes. Only at high elevations in the 
Sierras, generally above timberline, occurs the flightless Acrodectes, 
which is known from the summit and vicinity of Mount Whitney, 
and which also may be found to have Palearctic affinities. Californian 
endemic decticid genera of lower levels are Idionotus, Decticita, 
and Clinopleura. The last-named genus apparently developed from 
the same basic line as the genus Steiroxys, which is chiefly a Cordill- 
eran and Great Basin type, with, however, a few records from east 
of the Rockies (its distribution as a whole is at present poorly 
understood). It is possible that Clinopleura and Steiroxys may be 
found to have Palearctic affinities. 

It is possible, and even probable, that a comprehensive study, 
now outlined, may show that the very complex and greatly dif- 
ferentiated decticid fauna of western North America represents 
several lines of infiltration of Palearctic elements, and that they 
have come into our territory long since the sole eastern representa- 
tive of the subfamily, Atlanticus, either moved into our territory 
from eastern Asia, or conversely traveled to the latter area from 
eastern North America, where today it has a number of distinct 
specific lines. Clearly, however, a number of our genera of western 
North American Decticinae, such as Aglaothorax, Neduba, Zacy- 
cloptera, Capnobotes, and Plagiostira, have no approximate counter- 
parts in the Palearctic region, while others, such as Eremopedes, 
Pediodectes, Ateloplus, Idiostatus, and Idionotus, exhibit almost as 
well-marked differences and represent distinct lines from the many 
Old World genera of the subfamily. Certainly a very considerable 
period of time, isolation, and evolutionary pressure and oppor- 
tunity has been required to make evident what we see in our western 
American Decticinae. 

Family Gryllacrididae. The Gryllacrididae, for which the most 
generally used vernacular name is "camel crickets," are an ex- 
tremely complex and difficult group systematically. Their ancestral 
stock, according to Zeuner, who is probably our most able scholar 
in this respect, diverged from the Protorthoptera probably in the 
Mesozoic. What he regards as ancestral stocks have been found in 
the Upper Jurassic of Solenhafen, although typical Gryllacrididae 
are not known from earlier than the Tertiary. Several genera from 


the Florissant Miocene have been referred to the family. The 
majority of fossil forms, which can in a general way be associated 
with this family, or superfamily as some regard it, belong to the 
family Prophalangopsidae, or the subfamily Prophalangopsinae, 
depending on the rank accorded it, and occur in deposits as old as 
certain Mesozoic formations of Turkestan. Two living genera have 
been referred to this assemblage, one Prophalangopsis of India 
(known only from the unique type taken nearly ninety years ago), 
and Cyphoderris of the northwestern United States and adjacent 
Canada. Cyphoderris, however, has by some authors been referred 
to the gryllacridine subfamily Heniclnae, in which nearly two 
score existing genera have been placed (the majority of these genera 
occur only in the Southern Hemisphere, from which several reach 
northward in the Neotropical Region to Central America and the 
Greater Antilles). The Henicinae are also regarded as having a 
single representative within our territory in Cnemotettix, an endemic 
genus of San Clemente, one of the Californian coastal islands. 
Except for the two Nearctic genera which have been placed in it, 
the members of the Henicinae occur in areas which could be asso- 
ciated as parts of the often postulated "Gondwan aland." There can 
be no question but that Cyphoderris is a relict genus, and of a line 
that definitely has long passed its optimum development. It also 
should be noted that the area where Cyphoderris occurs is also the 
chief center in the New World of Grylloblatta, which is probably the 
most aberrant and primitive orthopteron still existing. 

The subfamily Stenopelmatinae, which has fossil representatives 
as far back as the Lower Miocene of Croatia, is well represented in 
western North America, but only by the typical genus Stenopel- 
matus, which apparently developed from a Sonoran center, thence 
spreading southward at least as far as Costa Rica, and northward 
over the campestran Great Plains to the Dakotas and Montana, 
over the Great Basin to southern Idaho, and along the Pacific 
Coast area to British Columbia, whereas eastward it does not 
extend beyond the Great Plains. It is a highly specialized apterous 
burrowing genus, whose existing relatives are of South African and 
Indian distribution. Its pattern of relationship would indicate the 
fragmentation, well in the past, of a once widely spread assem- 
blage adapted to subterranean life. The presence of Sienopelmatus 
in the New Worid cleariy is not a matter of very recent times. As a 

284 J. A. G. REHN 

genus, it evidently has evolved in our liemisphere, probably within 
the broad limits of the semi-arid and arid Sonoran life center. 

In the subfamily Rhaphidophorinae one definitely placeable 
genus, Prorhaphidophora, is known from as far back as the Lower 
Oligocene amber of East Prussia. Existing members of the subfamily 
are wingless, usually nocturnal, and many are cavern-dwelling. 
More than a score of genera are represented in Europe, Asia, North 
America, Australia, and New Zealand. Only one of the thirteen 
genera in North America occurs outside of this continent, and this 
genus, Tachycines, is a rather recent accidental introduction from 
eastern Asia, now well established under protected conditions in the 
eastern and central United States as far west as the Dakotas and 
Colorado. The remaining twelve North American genera are all 
endemic. They are related to two genera occurring to the southward, 
Phoheropiis in the mountains of Central America and Argytes on the 
Pacific side of the Mexican Plateau. It is clearly evident that this 
assemblage of more than one hundred species, which Hubbell, who 
has done detailed work on it, regards as the tribe Ceuthophilini, 
has as a whole developed in North America, and to a lesser 
degree in adjacent Mexico and northern Central America. 

Three of the genera of the Ceuthophilini are western North 
American endemics: Tropidischia, which ranges northward in Pacific 
territory to British Columbia; Rhachocnemis , which is known only 
from the unique type from "California"; and Gammarotettix, which 
occurs in various non-desert parts of California, with one species 
also occurring about the headwaters of the Gila River in eastern 
Arizona. The genus Pristoceiithophilus occurs solely in western 
North America from British Columbia to north-central Mexico, 
often in montane localities. Styracosceles is limited to areas of the 
southwestern United States east to Colorado. The very unusual 
recently described genus Salishella is known only from the mountains 
of north-central Idaho and the Olympics of Washington. It is a type 
of marked specialization, that probably developed in a north- 
western center, as it has no close relatives in any surrounding 
territory. The genera Daihiniodes and Daihiniella are definitely 
Sonoran in their distribution. Ammobaenetes has a similar pattern, 
in sand areas. The genus Udeopsylla is truly Campestran. Daihinia 
has a similar range, but reaches into adjacent Cordilleran territory. 
The widely spread genus Ceuthophilus is represented by some scores 


of species in North America south only to northern Mexico, and 
they are considered to have had as their main centers of differentia- 
tion (a) the Eastern Deciduous Forest, {b) the Sonoran region, and 
(c) the northern Great Basin. In the more arid regions of western 
North America specific Hnes of Ceuthophilus appear Hmited to 
mountain areas, probably as hot lower levels are less favorable for 
their existence. It is very probably that the tribe had a broader and 
less localized range in western North America in the moister and 
cooler Pleistocene, and that present distributional patterns, as for 
many other groups, reflect an average greater aridity in Recent 

Superfaniily Gryllodea 

The second superfamily of the existing suborder Ensifera, the 
Gryllodea, has, in a conservative evaluation of its component 
major groups, three families in our fauna, the Gryllotalpidae, or 
mole crickets, the Tridactylidae, or pygmy crickets, and the 
Gryllidae, to which belong the true crickets. 

The oldest fossil of an undoubted mole cricket, from the Upper 
Miocene of Germany, is considered to represent an existing genus, 
Gryllotalpa, and to be closely related to the existing European 
G. gryllotalpa. Zeuner believes that both the Gryllotalpidae and the 
Gryllidae have developed independently from the Liassic Proto- 
gryllinae, and that the Gryllotalpidae have not evolved through 
the medium of the Gryllidae. In western North America we find 
but one genus of the Gryllotalpidae, which is variously referred to 
as generically identical with Gryllotalpa of the Old World, or 
representative of a New World genus Neocurtilla. It is clearly evi- 
dent, however, that the two distinct species of this genus in North 
America are of Neotropical derivation, as one, found broadly over 
the United States west to the Rockies, is also widely spread over 
eastern South America, and the other, the sole species occurring 
very locally and infrequently from Texas to California, is closely 

The position of the Tridactylidae, or pygmy locusts, which were 
long considered gryllids, is now regarded broadly as with the 
acridids. I mention the group here, as this is the position given in 
most past literature. Their ancestral stock is now known from the 
Tertiary, but the single genus found broadly in North America 

286 J. A. G. REHN 

is the almost cosmopolitan Tridactyliis, one of the very few genera 
of these strangely specialized orthopterons. 

Passing to the true Gryllidae, of which a number of subfamilies 
are generally recognized, the Myrmecophilinae, composed of ant 
inquilines, is represented in our fauna by the single widely spread 
genus Myrmecophila. While members of the genus occur in certain 
tropical countries, most of our knowledge of the group has been 
drawn from representatives found in more temperate regions. At 
least four species occur in western North America. No fossil forms 
are known and any postulate as to centers of origin seems at present 

The subfamily Mogoplistinae, of which also no fossil forms are 
known, is represented in western North America by two genera, one 
of which, Cydoptiliim, is distributed broadly over the southeastern 
United States, narrowly enters the Campestran region, extends 
from Texas to coastal southern California, and is intrusive in the 
Colorado- Virgin rivers area to southeastern Utah. Cydoptiliim is 
broadly distributed in tropical regions, even occurring in Polynesian 
islands, but it apparently developed certain centers of evolution or 
radiation, where a number of distinct species occur, one in the south- 
eastern United States, and another in its southwestern section, 
Baja California and apparently extreme northern Mexico. The 
second genus, Hoplosphyrum, is peculiar to the Sonoran region of 
North America, Baja California, and mainland Mexico, with one 
species in each of these areas, but it does not, as far as we know, 
extend greatly to the southward. 

The single genus of the subfamily Nemobiinae in western North 
America is virtually cosmopolitan in distribution. The subfamily 
is known fossil only from the Oligocene, in Prussian amber and 
Isle of Wight deposits. The dominant and widely distributed genus 
Nemobius clearly developed an evolutionary center in the eastern 
and central United States, where a number of endemic species occur. 
Six species and subspecies of the genus occur in western North 
America which the genus appears to have entered by this group 
from both Mexico and the eastern United States. Several species 
are but narrowly present in the southwestern United States. Another 
is a Campestran subspecies of an eastern species and reaches the 
foot of the Rockies in eastern Colorado. Of two subspecies of a dom- 
inant and widely spread eastern species, N. fasciatus, one reaches 


westward as far as Salt Lake City, Utah (possibly an accidental 
introduction) and eastern New Mexico, and northward to southern 
Manitoba, Saskatchewan, and Alberta, and the other, a more 
southern race, extends west to central Texas. 

The subfamily Gryllinae is represented in western North America 
by three genera, each with a very limited representation of species. 
A single species, A. assimilis, of the virtually cosmopolitan genus 
Acheta ranges over the greater part of the Neogaeic from Canada 
to southern South America. It is now regarded by some as comprising 
a group of probably physiological subspecies, as morphologically 
these subsidiary elements intermingle to an inextricable degree, 
and also they have no clearly defined gc§graphic allocations. 
Members of the genus Gryllulus are known from the Tertiary of 
both Europe and Argentina, and it is probable that in the New World 
Gryllulus has had a very ancient history, but fossil evidence is very 

The genus Miogrylliis, which is represented in western North 
America by two species, is clearly of Neotropical origin. Members 
of the genus, including one of those found in North America, ran ge 
southward to central Argentina, while others are more closely lim- 
ited in the Neotropical Region. One of the North American species 
is known in our territory only from a portion of the southwestern 
United States, reaching from southern California to portions of 
Texas and eastern Colorado. The second species, which is that also 
of wide Neotropical distribution, occurs rather broadly over the 
southeastern and central United States westward to Nebraska, 
Kansas, Oklahoma, and central Texas. 

The genus GryUita is also Neotropical. The one species known in 
the southwestern United States, has been found only in the 
Baboquivari Mountains of Arizona, only a few miles from the 
Mexican border, south of which undoubtedly the species also occurs. 
Other members of the genus GryUita are known from more southern 
Mexico, Central America, and the Greater (Cuba) and Lesser 
(St. Vincent) Antilles, and its occurrence within our territory has 
clearly been due to extension from a more austral center. 

The subfamily Oecanthinae is a cosmopolitan assemblage, includ- 
ing the so-called tree crickets, because many of them frequent the 
foliage of trees or bushes. The little we know about them as fossil 
forms is that specifically unidentifiable remains have been found 

288 J. A. G. REHN 

in the Lower Oligocene and Upper Miocene of Germany and France. 
In the present world fauna members of the subfamily are to be found 
wherever their chosen environment exists in virtually all parts of 
the temperate and tropical regions. They are represented in the 
Nearctic fauna by two genera, one of which Neoxabea occurs in 
Nearctica only in the eastern part of North America, but other 
members of that genus are well distributed over the Neotropical 
Region south of Mexico, as far as northern Argentina. The other 
genus, Oecanthus, is cosmopolitan over the temperate and tropical 
parts of the world, but its greatest concentration of species is in 
North America. A definite area of marked specific differentiation is 
in eastern North America, and three of the four specific lines of the 
genus represented in western North America, are there at the 
extreme western limits of distribution of more widely spread and 
dominant eastern species of the genus. The status of at least one of 
the endemic species reported from the western United States is at 
present uncertain, but another one, 0. calif ornicus, is clearly autoch- 
thonous and doubtless will be found to extend into northern 

The subfamily Pentacentrinae is an aberrant group of small 
crickets broadly distributed within the tropics. A single genus, 
Trigonidomimus , enters our territory in central Texas, while to the 
southward it ranges across Mexico and Central America to Panama. 
The other genera of the subfamily are known from Brazil, Cuba, 
Madagascar, West Africa, Ceylon, and Formosa. Clearly Trigoni- 
domimus entered our territory from the Neotropical Region. No fossil 
members of the subfamily are known. 

A single genus, Anaxipha, of the subfamily Trigonidiinae is 
represented within western North America by one species which is 
largely eastern in its distribution, reaching to central Texas and to 
the eastern parts of Nebraska and Kansas. The subfamily is found in 
virtually all the warmer parts of the earth, on foliage or in low 
plant cover, and is also represented in Pleistocene or post-Pleisto- 
cene African copal. The genus Anaxipha is entirely New World 
in its distribution, with many tropical American species. A secondary 
evolutionary center for the subfamily and also for the genus Anaxi- 
pha apparently developed in the southeastern United States, 
where several other distinctive genera of the subfamily occur, one of 
which is entirely restricted to that area. 


Superfamily Grylloblattoidea 

Family Grylloblattidae. The exceedingly strange orthopteron 
Grylloblatta, which was first made known by my old friend, Dr. E. 
M, Walker, in 1914, from material taken near Banff, Alberta, has 
probably provoked more discussion as to its relationship and its 
phylogenetic position than any other living insect discovered in 
the last half century. Its original describer fully realized the 
unique character of the insect and modestly created the family 
Grylloblattidae for it. Crampton in 1915 erected the order Notop- 
tera to include it, and while some have followed this ordinal arrange- 
ment, another school inclines toward the belief that in Grylloblatta 
we have a connecting link between the saltatorial Orthoptera (the 
true Orthoptera of some present day scholars) and the Oothecaria 
(or Dictyoptera) and the Phasmatoidea (or Cheleutoptera). Zeuner 
recently succinctly stated, "Since it has a number of features 
which are more characteristic of the true Orthoptera, it might 
rightly be called a living, though specialized representative of the 
ancient Protorthoptera." 

Our knowledge of the family Grylloblattidae has grown con- 
siderably since Grylloblatta was described. It is now known to be 
made up of Grylloblatta, which is entirely Nearctic, Grylloblattina , of 
the southern Maritime Provinces of Siberia, and Galloisiana, of 
Japan. The genus Grylloblatta contains six species, all from montane 
localities in southwestern Canada and the western United States. 
They are known from localities in southern British Columbia, 
montane Alberta, similar areas in Washington, Montana, Yellow- 
stone National Park, the Cascade region of Oregon, and the Sierran 
section of California as far south as Mammoth Crest. Almost all 
the species seem to have very special humidity and temperature 
requirements, occasionally are found in contact with snow or ice, 
grow with exceeding slowness, and exhibit numerous attributes 
that clearly indicate their overall primitive character. It is clearly 
evident that today the Grylloblattidae is a Holarctic assemblage. 
Its segregation into three distinctive generic units was probably 
accomplished well in the past, as the genera are well defined and 
regionally limited. The species of Grylloblatta also show in their 
distribution, that the relatively numerous forms of the genus (five) 
now known from California, Oregon, and Washington (the last also 
reaching northward into British Columbia) apparently differenti- 

290 J. A. G. REHN 

ated at different periods from the line represented by G. campodei- 
formis (the genotype), which ranges in the Cordilleran region from 
as far north as Jasper Park, Alberta, to the Yellowstone National 
Park. The fact that the Cascadan and Sierran species are more 
divergent from campodeiformis, would indicate to me that these 
more southern representatives have been established as divergent 
entities for a longer time. The greatest known specific differenti- 
ation in the family has taken place in North America, and it is fair 
to assume that the family had its beginnings in western North 
America, and that ancestral lines probably traveled eastward over a 
Bering Sea land bridge well in the past. We have parallel cases in 
the Orthoptera, such as the decticid genus Atlanticus and the 
acrid id Zubovskya. 

Superfamily Phasmatoidea 

(Cheleutoptera of some authors) 

The Phasmatoidea, or "walking-stick insects," are a very dis- 
tinctive assemblage, much more diversely developed in the number 
of genera and species in certain tropical areas than in more temperate 
ones. The areas of optimum differentiation are the Neotropical, 
the Indo-Malayan, and the Australian. Africa has in proportion a 
relatively smaller representation, even its great forested area 
having a much less marked diversity than similar regions in the 
Neotropical and Indo-Malayan regions. 

In North America we find representations of four entities of 
higher rank (variously regarded as families or subfamilies), one of 
which, elsewhere entirely Neotropical, occurs in the southeastern 
and central United States but does not enter more western territory. 
One very distinctive line, which is almost universally regarded as a 
family, the Timemidae, with the single genus Timema, is as far as 
known restricted to certain areas of the western United States. 
Timema possesses a number of unusual, possibly primitive, char- 
acters, and its six species are known from well-separated areas in the 
mountainous areas of California and of extreme southeastern 
Arizona. The species are, as far as known, tree or bush dwelling. 
The family is clearly an autochthon of the general area where it is 
now found, and it shows a pattern of distribution essentially 
parallel to that of the three genera composing the Morseinae of the 
Eumastacidae. Perhaps as our knowledge becomes more compre- 


henslve we may find that this, and similar correlations, indicate 
parallel spreads of widely distinct entities, but of similar faunistic 
histories. While it is purely a postulate, it is my belief that the 
distributional evidence here reflects Pleistocene conditions, and 
heavier precipitation and lower temperatures then over extensive 
areas now largely desert or semi-desert, and that the genesis of the 
Timemidae probably took place in California very much before 
the Pleistocene. 

The subfamily Pachymorphinae, a group widely spread over the 
world is represented in much of the western half of North America 
by the genus Parabacillus. Its range extends northward over the 
Great Plains to the Dakotas and elsewhere into New Mexico, Ari- 
zona, southern Nevada, and southern California. While it also ex- 
tends a considerable distance into Mexico, its greatest distribution 
is northward over the Great Plains, and I would regard it as Cam- 
pestran in origin, with closest relationship probably to certain rather 
poorly known Asiatic genera. 

The subfamily Heteronemiinae is entirely one of Neogaea, with 
representatives distributed from Canada to at least Paraguay. 
Five genera have been reported from western North America, and 
all but one of these I would regard as of Sonoran development. 
The exception is Sermyle, which is clearly a Mexican and Central 
American Neotropical type, with a single species found in southern 
Texas. Of the other four genera, Megaphasma is an endemic usually 
infrequent in forest, generally bottom, land of eastern Texas, Okla- 
homa, Louisiana, and other Mississippi valley areas, but narrowly 
entering the territory we are considering. Two of the three remain- 
ing genera, Rhabdoceratiies and Psendo sermyle, are limited to west- 
ern North America, except for narrowly reaching into Sonoran 
sections of Mexico. They doubtless have developed in the great 
Sonoran area, where Pseiidosermyle in particular is a dominant 
type. The remaining genus, Diapheromera, is probably also a Sonoran 
derivative, for several of its species are limited to that area. One 
species of the genus, however, has spread more broadly eastward 
over most of eastern North America, and there also has developed a 
very distinctive species in the southern Appalachians. The south- 
eastern and central United States apparently have served as a 
secondary developmental center for the Heteronemiinae, not only 
for Diapheromera, but also in producing there an endemic genus 

292 , J. A. G. REHN 

(Manomera) which Is not found to the westward. However, I would 
regard the basic developmental center for Diapheromera as Sonoran 
on account of the specific diversity in the genus there. 


(Dictyoptera of some authors) 

Superfamily Mantodea 

The Mantodea are represented in western North America by 
members of five subfamilies or families (the exact rank of the higher 
entities is debatable). Two of these subfamilies are known only from 
the New World, while the others are found in both hemispheres. 
One of the latter is the Amelinae, which has two genera in North 
America, both found only within its western part and in northern 
Mexico. These are curious, almost entirely terrestrial mantids, one 
of which, Yersiniops, has considerable saltatorial powers. The genus 
Litaneutria occurs rather broadly over western North America 
and northern Mexico, reaching northward to North Dakota, Mon- 
tana, Washington, and extreme southern British Columbia. Yersini- 
ops has a more limited distribution, extending from western Texas 
westward to central southern Arizona and northward to parts of 
Colorado. A related genus, Yersinia, occurs in northern Mexico. 
All three genera clearly developed in a Sonoran faunal center. 

The widely distributed subfamily Manteinae is represented in our 
territory by a single genus, Stagmomantis, which is clearly of 
Neotropical origin. Species of this genus range southward to Ama- 
zonia. The greatest diversity of Stagmomantis is in Central America, 
where a number of lines of the genus not present elsewhere are de- 
veloped. It later, probably, spread both to the north and to the 
south. In western North America there are four species of Stag- 
momantis. S. Carolina, a dominant eastern species, which is also 
widely spread southward over Central America and northern South 
America, reaches as far westward as the Great Plains in the pan- 
handle of Texas, eastern New Mexico, and the Arkansas Valley of 
eastern Colorado. 5. gracilipes, a very distinctive type, is known 
only from several mountain areas in southern Arizona. 6". californica 
occurs rather broadly in desert conditions from western Texas to 
southern California, southern Nevada, Utah, and western Colorado. 
S. limbata is broadly intrusive from Mexico, where it is widely 


distributed. In our limits it occurs from central Texas and eastern 
and northern New Mexico to Needles and Calexico, California. 

Within our territory the subfamily Oligonicinae is represented 
only by the genus Oligomcella, which, like the subfamily, is clearly 
of Neotropical derivation. The two species of the genus within our 
limits are known there only from Texas and southern Arizona. 
One, which elsewhere has a broad distribution in the southeastern 
United States, extends across Texas to its trans-Pecos section. 
The other, an intrusive from Mexico, is known only from extreme 
southern Texas and southern Arizona. 

The subfamily Vatinae, a Neotropical assemblage, includes two 
genera that narrowly enter our territory from northern Mexico. 
Both also range broadly over Central and South America. One of 
these genera, Phyllovales, has a single species of much broader 
distribution occurring with us only in extreme southern Texas, and 
the other, Vates, is represented by one endemic species in certain 
mountain areas of extreme southern Arizona. 

The subfamily Photininae, all the other members of which are 
entirely Neotropical, is represented in our territory by one species 
of the striking genus Brunneria, which ranges from the grass 
prairie country of east-central Texas to central North Carolina. 
The North American species of Brunneria, B. borealis, is partheno- 
genetic — no male has ever been taken, although hundreds of females 
have been secured at a considerable number of localities. The genus 
has a discontinuous distribution; no member other than B. borealis 
is known from north of central Brazil, Paraguay, and northern 
Argentina, where other species occur with the male sex as frequent 
as the female. All members of the genus are strictly grassland forms, 
and the postulate that what we see is a reflection of the far greater 
extent and former broader prevalence of grasslands in the Pliocene, 
with their marked restriction in the more humid Pleistocene, 
with the correlated augmentation of lowland forests in that period 
in the tropics, seems to be the logical explanation. A theory of 
drift across the Caribbean has been advanced to explain the sit- 
uation, but the genus does not occur in northern South America as 
far as known, in fact at no place between Texas and territory much 
south of the Amazon. Somewhat parallel conditions exist in other 
genera of the Orthoptera which are grassland forms, and for which 
the same postulate seems applicable. 

294 J. A. G. REHN 

Superfaniily Blattodea 

The superfamily Blattodea or cockroaches is represented in 
North America by twenty-seven genera, of which eleven are re- 
garded as adventives. Some of these were probably introduced 
several centuries ago in the early historic periods of the Atlantic 
states and provinces. Others were brought in during the early years 
of the present century, particularly from the West Indies. The 
original home of a number of these adventives was Africa, and the 
early transport was by cargo or slave ships. Of these eleven ad- 
ventives, six are now known to be present in western North x'\merica, 
namely Supella, Blattella, Neostylopyga, Blatta, Periplaneta, and 
Pycnoscelus. Of these Periplaneta was doubtless brought in by the 
slave trade, as the genus, while now almost cosmopolitan in the 
warmer regions, is clearly a native of Africa, where feral species 
of the genus also occur. Supella probably had a similar history in 
reaching the West Indies, as it was not known from the United 
States until the early years of this century, although its dominant 
species, 5. supellectilium, the only one that has reached America, 
had long been established in the West Indies. The genera Blatta and 
Blattella reached America in much the same way as the black rat 
{Rattus rattus) and the Norway rat (Rattus 7iorvegicus) , and their 
spread westward across Europe coincided very much in sequence and 
time with the spread of the two species of domiciliary rats. Both of 
these cockroach genera are probably natives of northeastern 
Africa, where a number of feral species of each genera occur. 
Pycnoscelus is of Oriental origin, and wild species of the genus 
are known from Farther India. Today the domiciliary species, 
P. surinamensis, is frequent in subtropical, as well as tropical, 
America. It presents another case of usual parthenogenesis. 

The Oriental genus Neostylopyga, very readily recognized by 
its form and coloration, is common in the Philippines and also over 
much of Indo-Malayia, and west to Madagascar and the eastern 
coast of Africa. The first report of its one domiciliary species, 
A^. rhombifolia, in America was made in 1865. It was reported from 
Acapulco, Mexico, and from Venezuela and Argentina. From 
Acapulco it has spread to the Cape Region of Baja California, 
northward over Sinaloa, and even to the railroad entry port of 
Nogales, southern Arizona. Acapulco was the port at which in 
colonial days the Spanish galleons from Manila landed their cargoes 


for land transfer across Mexico for shipment to Spain. In coming 
years Neostylopyga probably will gradually become established in 
parts of the southwestern United States, as well as in much of the 
warmer parts of Mexico. 

Seven of the blattid genera that are endemic in western North 
America can definitely be called Neotropical in origin. The majority 
belong to the subfamily Pseudomopinae, which is a cosmopolitan 
assemblage that is highly developed in the Neotropical Region. 
Of these the genus Euthlastoblatta is known in our territory only 
from extreme southern Texas, although other members of the genus 
occur southward to Panama. Latiblattella, another basically Neo- 
tropical genus, has a single species in western North America, 
restricted to certain mountain areas of southern Arizona. A number 
of other species of Latiblattella occur in Mexico and Central America, 
and one is endemic in peninsular Florida. The genus Ischnoptera is 
another very diverse and basically Neotropical genus, of which 
two species reach North America: the endemic /. deropeltiformis, 
which is widely distributed in eastern North America and reaches 
westward as far as central Texas, and /. rufa occidentalism a race of a 
widely spread Neotropical species, which has a broad range in 
Mexico and Central America, entering our territory only on the 
Gulf Coast of Texas. 

The flower-haunting harlequin-patterned cockroach Pseiidomops 
is another very widely spread Neotropical genus, of which a single 
species enters our territory, and is found in Texas north to the 
central part of the state. The remaining genus of the Pseudomopinae 
in our territory is Parcoblatta, which, unlike all the other genera of 
the subfamily, is strictly limited to North America. Of the twelve 
species of this genus four eastern ones narrowly impinge on our 
territory in eastern Texas; bolliana is found westward to central 
and southern Texas, and north to Nebraska; desertae is distributed 
from eastern New Mexico to central Texas and Oklahoma ; /zz/^e^- 
cens ranges westward to central and southern Texas, north to the 
Red River, but not west of Texas; pensylvanica extends west to 
central and southern Texas, north to Nebraska; americana is a 
Pacific species distributed from Oregon to western Arizona and 
Nevada; and notha is an endemic species of certain mountain 
areas of central and southern Arizona. Apparently Parcoblatta has 
developed from a relatively early Neotropical ancestor, and the 

296 J. A. G. REHN 

center of differentiation, on the basis of present diversity, pre- 
sumably was in the eastern and central United States. 

Another subfamily of the Blattodea, the Panchlorinae, aside 
from the already mentioned Pycnoscelus, is represented in our terri- 
tory by a single species of Panchlora, which may be autochthonous 
with us in a circumscribed area. The genus is greatly diver- 
sified in tropical America, and also has a few endemic species in 
forested West Africa. The single species we have within our bound- 
aries, P. cubensis, is broadly distributed to the southward, but 
reaches its northern natural limit in the Brownsville area of southern 
Texas. This insect is often brought in accidentally in bananas, 
but cannot survive our usual winter conditions. The subfamily 
Chorisoneurinae is a Neotropical assemblage made up of a large 
number of species, although but a single genus and species, Choris- 
oneura texensis, reaches our territory, where it ranges rather broadly 
over the southeastern United States from North Carolina to eastern 
and southern Texas in the Brownsville area. The genus, with us, is 
clearly intrusive from the south, for our representative is the most 
northern member, and the number of species represented regularly 
increases as one goes southward in Mexico and Central America. 

The subfamily Attaphilinae, the members of which are ant 
inquilines, is represented in our territory by the single genus Atta- 
phila, of which the genotypic species is known only from central 
Texas. This genus is represented by a number of other species in 
South America, and a number of allied genera are found in the 
Neotropical Region. It is evident that Attaphila, along with its 
host Atta, has been derived from that great center. 

The subfamily Corydinae is represented in North America by a 
single genus, Compsodes, the sole species of which in our territory is 
known from the mountains of southern Arizona and from localities 
in south and central Texas and Baja California. The genus, as well 
as a number of related ones, is clearly Neotropical in origin. A 
number of genera of this subfamily are inquilines with various 
Hymenoptera, as well as with Isoptera. 

The morphologically very distinct subfamily Polyphaginae is 
made up of genera that are largely desert forms, and that show 
marked antigeny between their sexes. The greater number of the 
genera, and the bulk of the species, are Palearctic, with others 
arid Ethiopian. In Neogaea we have representatives of the sub- 


family in North America and in Mexico. The North American 
species represent two quite distinct genera, one of which, Arenivaga, 
is now considered by Russian colleagues also to include certain 
Central Asian species. Of Arenivaga seven species are now recognized 
in North America, all but one of which are found within the territory 
covered by this symposium. Several also occur in northern Mexico. 
The one exception is known only from Florida, but it clearly has 
been derived from the Sonoran area where the other species have 
developed. The forms of Arenivaga in our territory range from 
east-central Texas west to southern California, and north as far as 
Monterey, California, St. George, Utah, and Oklahoma. The other 
genus Eremoblatta, is more exclusively a desert type. Its distribution 
extends from eastern New Mexico and extreme western Texas to 
the Mohave and Colorado deserts of California, north to Kern 
County, California, and to Las Vegas. Nevada. 

The last genus of the Blattodea to be considered is in some 
respects one of the most interesting of our North American blattids. 
This one, Cryptocercus, is the sole member of the subfamily Panes- 
thiinae in the New World. Like many of the other species of the 
subfamily it lives in dead wood, can digest cellulose, bores channels 
in dead logs, preferably of fir or chestnut, and is also wingless. In 
North America the genus, and its single American species, is dis- 
continuously distributed. It is found in the eastern Appalachians 
and the Appalachian Plateau from New York to Kentucky and 
Georgia, and again is present in western Washington, the Cascades 
of Oregon, and possibly the Sierras of California. It is absent from 
virtually all the Middle West, the Great Plains, the Rockies, and 
the intervening basins, even where these are heavily timbered. 
Apparently the separation of the two distinct areas of the distribu- 
tion of the species has been due to the southward advance of the 
lobes of the various Glacial ice sheets, which severed previously 
connected areas and isolated the two elements of the species, in the 
same way the two segments of the acridoid genus Zubovskya were 
developed (but in that case specific entities were established). 
The particularly interesting feature in connection with Crypto- 
cercus is that it, with several distinct species, also occurs in eastern 
Asia. Clearly we have here a case basically parallel to those of the 
acridid Zubovskya and the decticid Atlanticus, although the ex- 
planations for each may not be identical, but in their patterns they 

298 J. A. G. REHN 

are clearly expressive of the roles of Bering Sea connections and of 
Glacial ice in past biogeographic movements or controls. 


In the absence of adequate fossil evidence which would integrate 
with living elements we must draw our relevant evidence from the 
known centers of existing genera and their allies. Of the 229 genera of 
Dermaptera and Orthoptera that occur west of the eastern edge of 
the Great Plains, exclusive of purely Mexican ones, 35% (82 genera) 
are clearly Sonoran types, using this term in its broad sense or, 
when limited, to that area of the same east of the Continental 
Divide. This great evolutionary center has been the outstanding 
North American center of generic differentiation for Orthoptera. 
In descending importance 14.8% (36 genera) clearly were derived 
from the Neotropical Region; 7.3% (17 genera) represent a dis- 
tinctive and endemic coastal and non-Sierran montane California 
fauna; 6.5% (15 genera) are endemic there and probably developed 
in Lower Sonoran Zone deserts; 5.6% (13 genera) are introduced 
adventives; 4.8% (11 genera) are at present Sierran endemics and 
most probably autochthons, and 5.2% (12 genera) holds for a 
group of genera also of Palearctic occurrence or relationship; while 
3.9% (9 genera) similarly are Cordilleran in their present distribution 
and probable origin. A number of the genera here regarded as 
developed in the Sonoran center also moved eastward, and sub- 
sequently established specific evolutionary centers in the eastern 
and southeastern United States. I regard 8 genera (3.5%) as 
derived from purely eastern centers of development. The remaining 
4% (13) represents basically Sonoran types that developed sub- 
sidiary radiative centers in eastern North America, Mohavan and 
Great Basin endemic types, cosmopolitan genera, and others 
considered purely Nearctic Boreal and restricted Campestran. 
The occurrence of certain genera in both western North America 
and eastern Asia leaves unanswered the natural query as to whether 
their original center was in the one or the other, with much of the 
weight of evidence in some of the genera in favor of a North Ameri- 
can, and also definitely pre-Glacial, origin. 


Geographical Origins and Phylogenetic Affinities 
of the Cerambycid Beetle Fauna 
of Western North America 

E. Gorton Linsley 

University of California, Berkeley 

1 he two previous papers deal with dis- 
tributional patterns, respectively, of groups of cool-adapted an- 
imals, including northern and montane insects, particularly caddis- 
flies and sawfhes, and of certain free-living terrestrial forms (Orth- 
optera and Dermaptera). The Cerambycidae, or long-horned 
beetles, as larvae, are mostly internal feeders in living, dead, or 
dying woody plants, a fact that has greatly influenced the dis- 
tributional and evolutionary history of the family. Nearly 900 
species are now known from America north of the Mexican bound- 
ary. The adults of a few groups are flightless, but most are relatively 
strong but somewhat inefficient fliers. They seek the appropriate 
host plant before or after mating and subsequently oviposit in 
cracks or crevices in the bark or in notches cut by the female. 
The degree of host specificity varies. The forms that attack living 
trees and assemble on the host plant for mating usually exhibit the 
greatest specificity, and those that attack dead or decomposing 
wood, the least. The fact that many of the latter group congregate 
on flowers for mating precludes or weakens selection for host 
specificity. Thus the close association of Cerambycidae with woody 
plants and the varying degrees of intimacy in relation to particular 
trees and shrubs must be considered in any analysis of the origins 
and affinities of the North American elements of the family. 

Based on analyses of contemporary distributions, on phylogenetic 
and ecological relationships, and on the limited fossil record, the 
North American cerambycid fauna appears to be a complex of 
diverse distributional elements or subfaunas, of which five are 
rather readily identified: a Holarctic element (largely Ijoreal), 


300 E. G. LINSLEY 

a Neotropical element (largely austral), an Alleghenian element 
(centering mainly in the Appalachian and Ozark plateaus), a 
Vancouveran element (centering along the Pacific Coast), and a 
Sonoran element (centering in southwestern United States and 
northern Mexico). 

The modern Holarctic and Neotropical constituents are of 
relatively recent derivation and endemism is expressed largely at 
the species level (Table I). The Alleghenian, Vancouveran, and 
Sonoran elements are of more ancient origin, although the first two 
were apparently derived largely from an early Holarctic fauna, 
and the last originated almost entirely from the early Neotropical. 
Much of the endemism in these subfaunas is at the generic level 
(Tables I and II). 

Table I. Primary 

Geographical F 


ges of 

Contemporary Species ^ 

North American Ci 




Per cent 













Rocky Mountain 



Great Basin 


















Table II. Con tern 

iporary Occurrence 

of Genera of Cerambycidae No 

Represented in 

North America 


Per cent 
















Rocky Mountain 









Eastern Austral 











In North America, fossil Cerambycidae have been found only in 
the Florissant beds of Colorado. The lacustrine deposits at this 
site contain abundant plant remains and the richest modern-type 
insect fauna yet discovered on this continent. MacGinitie (1953) 
made a critical taxonomic and ecological study of the fiora, which he 
regards as of Lower Oligocene age but, based upon vertebrate 
evidence, R. A. Stirton (w litt.) treats the beds as middle Oligocene. 
In any event, by comparing the fossil plant community with 
living plant communities and considering the chemical and physical 
aspects of the sediments, MacGinitie has reconstructed the en- 
vironment as follows: 

The Oligocene forest occupied streamside and lakeside habitats in a 
piedmont of low relief and moderate elevation which bordered the Rocky 
Mountain uplift on the east. The drainage was disorganized and partly 
ponded by successive volcanic outbursts which covered the area with 
dust, pumice, and mudflows. 

The fossil fauna and flora were deposited in the resulting shallow and 
ephemeral lakes. The climate was subhumid and warm temperate, not 
unlike the present climate of Monterrey, in the state of Nuevo Leon, 
Mexico. Warm winters and hot summers prevailed, and abundant sun- 
shine is indicated. The vegetation on the high ground, away from the 
stream and lake borders, was characterized by pines and evergreen oaks 
and was most probably of an open, scrub-forest type, with grass and 
microphyll shrubs in the drier areas. 

MacGinitie has provided a useful table of the fossil gymnosperms 
and angiosperms together with the modern occurrence of the most 
similar living species. Of these last, 57.1 per cent are found in 
habitats encompassed by a circle of radius 400 miles, centered in 
southwestern Coahuila, Mexico, especially in the southern Rockies 
of San Luis Postosi and Texas and northeastern Mexico. The west 
Mexican and southern Arizona area now contains only three or 
four additional species. The Ozark-southern Appalachian area and 
the Asiatic area have nearly equal representation and together 
comprise 57.1 per cent of the list. These living forms are very 
largely mesic, streamside types of warm-temperature aspect, and 
many of their fossil equivalents were found by MacGinitie to be 
relatively abundant forms. However, nineteen of the Ozark species 
are also found elsewhere; only six are unique to the region. The 
species now living in California he regards as having no particular 



ecological significance as a group, being either wide-ranging forms 
or species with restricted distribution isolated by events of the 
late Tertiary and Pleistocene. 

Less than thirty species of Cerambycidae have been named from 
these beds (Linsley, 1942). Among the species that are well enough 
preserved to permit interpretation (Table III), about two-thirds are 
northern types and some of these are very close to, if not identical 
with, living forms. About half of these belong to genera that are 

Table III. Modern Occurrence of Some Genera of Cerambycidae 
Represented in the Oligocene Beds of Florissant, Colorado" 




























2 + 



























































— - 









« Modified from Linsley (1939, 1942). 

^ Numerals indicate approximate number of known endemic species (widely dis- 
tributed species excluded). 

now more or less equally represented in the present day Vancouveran 
and Alleghenian subfaunas. Grammoptera, Anoplodera, Leptura, 
and Gaurotes are flower-visiting forms of low host specificity associ- 
ated with dead and decomposing conifers and hardwoods; Callimoxys 
attacks Ceanothus and certain other shrubby plants (the fossil 
form suggests the modern Alleghenian subspecies); Semanotus is 
now associated largely with Taxodiaceae and Cupressaceae ; and 
Phymatodes includes some species that attack conifers and some that 
attack hardwoods (the fossil species resemble the latter). Six species 
belong to genera better represented today in the Alleghenian sub- 


fauna than in the Vancouveran (Pidonia, Leptostyhis, and Saperda, 
now associated with broad-leaved deciduous trees) and four belong 
to genera found in the present Alleghenian but not in the Van- 
couveran (Dryobius, Slenosphenus, Psapharochus, and Megacyllene, 
which are also associated with hardwoods, the last with Gary a and 
Robinia, which were represented in the Florissant flora). Among the 
fossil genera with recognizable affinities, Protospondylis is apparently 
related to the living genera Spondylis (with one species in the 
Palearctic Region, one in the Vancouveran subfauna, another on 
the Mexican Plateau, but none in the Alleghenian) and Scaphinus 
(one living species in the Alleghenian). All known members of this 
group are associated with conifers (Pinaceae). Protipochus and 
Parolamia appear to be related to forms now living in the Med- 
iterranean region. The affinities and/or interpretations of the 
remaining fossil genera are obscure. 

In Europe among the oldest records for species that might belong 
to modern cerambycid genera are fragments from the Middle 
Eocene of the Geisel Valley near Halle (Pongracz, 1935). Baltic 
Amber contains many fine examples, but these have not been 
adequately studied, although modern Holarctic genera are well 
represented (Klebs, 1910). From Early and Middle Tertiary, 
Handlirsch (1908) listed 70 species, but most need to be reexamined 
in the light of current classifications. However, Statz (1938) re- 
ported on a small sample of cerambycids from the Middle Oligocene 
sediments at Rott am Siebenbirge, all of which could be placed in 
modern genera (about half are now Holarctic in distribution, the 
remainder Palaearctic) . He emphasized that the varied and rich 
growth of deciduous trees and shrubs of the Rott environment 
provided an abundance of living and decaying wood for larval 
development and numerous composites, umbellifers, and flowering 
shrubs for pollen-feeding adults, yet cerambycids represent only 
0.6 per cent of the known beetle fauna in contrast to the 9 per cent 
of the living forms. Although, in part this may reflect lower pop- 
ulation levels in the family, Statz considers that their over-all 
representation in the Tertiary record as from 3 to 4 per cent of the 
beetle fauna reflects a less highly developed group, at least in the 
Early and Middle periods, than at present. 

Although no later fossil Cerambycidae are known from North 
America, Axelrod (1956) has characterized several Mio- Pliocene 

304 E. G. LINSLEY 

floral provinces in the Far West. These represent the beginnings of 
our modern floral and climatic provinces and undoubtedly had a 
profound influence on the distribution and evolution of the present 
fauna of cerambycid beetles. In his words: 

... a North-coastal province, extending along the coast from Washington 
to central California, supported a relict warm-temperature facias of the 
Arcto-Tertiary Geoflora. At the north it graded inland into the Columbia 
Plateau province which was characterized by a typical temperate Arcto- 
Tertiary Geoflora, and which gave way at higher levels and eastward to 
a cool-temperate conifer facies. Near its southern margin the North-coast 
province merged eastward into a floodplain facies of the Arcto-Tertiary 
Geoflora which occupied central California, extending to the foothills of 
the ancestral Sierra Nevada. On these better-drained slopes the floodplain 
forest was replaced by vegetation representing an ecotone between the 
Arcto-Tertiary and Madro-Tertiary Geofloras; owing to its near-coastal 
position this ecotone included more humid types than that in west- 
central Nevada. At higher levels in the Sierra, Madro-Tertiary species 
were supplanted by the more mesic, temperate Arcto-Tertiary plants. 
A South-coastal province, extending from coast-central into southern 
California, was characterized by arid subtropical climate in which a 
relict Neotropical-Tertiary Geoflora was in ecotone with the subhumid 
Madro-Tertiary Geoflora. To the eastward, in the drier interior Mojave 
province, the Madro-Tertiary Geoflora was dominant, grading northward 
rapidly into an ecotone with the Arcto-Tertiary Geoflora in west-central 

MacGinitie has contributed to this symposium a vivid account of 
the Tertiary climates of western North America. These have pro- 
foundly influenced the distributional and phylogenetic histories of 
the modern floras of western North America, including the redwood 
forest, the black oak-madrone forest, the North Coast Douglas 
fir forest, the upland conifer forest of the Sierra Nevada, and the 
Rocky Mountain forest (Mason, 1947), which support large seg- 
ments of the endemic cerambycid fauna. 

According to Axelrod (1948), most of the important trees and 
shrubs now characterizing the Redwood, Sierra-Cascade, Rocky 
Mountain, and North-coast conifer forests have close equivalents in 
the West American Element of Miocene floras from the Columbia 
Plateau and adjacent areas. These species are in such genera as 
Abies, Acer, Alnus, Amelanchier, Betula, Castanopsis, Chamaecy- 
paris, Corniis, Fraxinus, Gaultheria, Libocedrus, Lithocarpus, Ma- 
honia, Rhododendron, Rosa, Salix, Sequoia, Sorbiis, Thuja, Tsuga, 


and Vacciniiim and their modern counterparts are largely hosts of 
Vancouveran Cerambycidae with northern affinities. Regularly 
associated with these plants are fossil species that find their nearest 
relatives in the temperate, summer-wet eastern portions of North 
America and Asia. In the East American Element are fossil species in 
genera no longer indigenous to the region west of the Rocky Moun- 
tains, such as Carya, Carpinus, Castanea, Fagiis, Liqiiidamhar , 
Nyssa, Taxodmm, and Ulmus, whose closest counterparts are now 
found in eastern North America and serve as hosts for Alleghenian 
Cerambycidae. Also included in this element are fossil species 
of genera such as Acer, Betula, Crataegus, Fraxinus, Popiilus, 
Prunus, Smilax, Quercus, and Vaccinium which have their nearest 
relatives in eastern North America. Members of the East Asian 
Element are distributed in Ailanthus, Cercidiphyllum, Ginkgo, 
Keteleeria, Metasequoia, and Pterocarya, genera no longer indigenous 
to North America; in species of Carya, Ilamamelis, Hydra?igea, 
Ostrya, Lindera, Sassafras, and other genera that are represented 
also in eastern North America; and in certain fossil species of 
Acer, Abies, Picea, Populus, Quercus, and Prunus, which have 
their nearest homologues in the temperate forests of eastern Asia. 
Another important modern ecological type, the Woodland 
formation, with dominant live oaks and such associated conifers as 
pinyon pine, juniper, and digger pine, according to Axelrod, makes 
up a prominent part of the Madro-Tertiary Flora, which ranged 
widely over southwestern North America in middle and later 
Tertiary times. Members of the Sierra Madrean Element have 
their nearest equivalent species in summer-wet areas extending 
from the Cape region of Baja California across the Sierra Madre 
of eastern and western Mexico and into the southwestern United 
States. This element includes plants that are no longer represented 
generically in California, Nevada, or Colorado, such as Bumelia, 
Clethra, Eysenhardtia, Ilex, Pistacia, Rohinia, Sapindus, Ungnadia, 
and Zanthoxylum, as well as certain species of Arbutus, Cupressus, 
Forestiera, Fraxinus, Populus, Quercus, and Rhiis that now have 
their closest homologues in areas with summer rains and mild 
winters. The California Woodland Element, with species in such 
genera as Celtis, Juglans, Lyonothamnus , Platanus, Pinus, Populus, 
Prunus, Quercus, and Umbellularia, finds its nearest relatives 
making up living California woodland associations. Cerambycidae 

306 E. G. LINSLEY 

attached to these woodland associations exhibit both northern and 
southern affinities. 

Chaparral, according to Axelrod (1948) in such genera as Arcto- 
staphylos, Ceanothus, Cercocarpus, Dendromecon, Fremontia, Garrya, 
Photinia, Quercus (scrub oak), and Rhus, has a large representation 
in the Madro-Tertiary Flora. Close relationship is apparent with 
the sclerophyllous associations now in California, Arizona, and 
Coahuila. The Cerambycidae now associated with this formation 
include several forms with southern affinities discussed below as 
"Californian" as well as overflow species classed as Vancouveran. 



The modern Holarctic elements of the cerambycid fauna appear 
to be more or less equally represented in the northern forests and 
mountainous regions of Europe, Asia, and eastern and western 
North America. Their distribution reflects Postglacial dispersal and 
their hosts are largely spruces and other northern and high-elevation 
Pinaceae or northern-type deciduous trees as Salix and Populus 
(Salicaceae). In western North America these are the dominant 
Cerambycidae of the Canadian and Hudsonian life zones, but occur 
also in dilute form in the coniferous phases of the Transition and 
Upper Austral life zones, and a few species are represented in the 
high-altitude coniferous forests at least as far south as Guatemala. 
Representative genera of this Holarctic fauna include: Asemum, 
Arhopalus, and Tetropium of the Aseminae; Callidium, Semanotus, 
Xylolrechiis, and Clytus of the Cerambycinae ; Toxotus, Pidonia, 
Grammoptera, Leptura, and Anoplodera of the Lepturinae; and 
Monochamus, Acanthocinus, and Pogonocherus of the Lamiinae. 
In addition to genera, there are a number of species with a similar 
circumpolar or Holarctic distribution. Among these are Tragosoma 
depsarium (Linnaeus), Asemum striatum (Linnaeus)^, Arhopalus 
rusticus (Linnaeus), Stenocorus inquisitor (Linnaeus), Acmaeops 
pratensis (Laicharting), Pachyta lamed (Linnaeus), Judolia sex- 
macidata (Linnaeus), and Saperda popidnea (Linnaeus). The last 
of these is associated with poplar, the remainder with conifers. 

The recent neotropical elements, derived from areas of high 
temperatures and humidity and attached largely to southern-type 


hardwoods and Leguminosae, have penetrated northward very 
unequally. They are largely restricted to the Austro-Riparian belt 
bordering the Gulf of Mexico, the Atlantic coastal plain, and a few 
warm river valleys as those of the Mississippi, the lower Rio Grande, 
and the lower Colorado. About a half dozen wide-ranging species 
in this category reach southeastern California, e.g., Achryson 
surinamiim (Linnaeus), Dendrobias mandibidaris Audinet-Serville, 
Lissonotus flavocinctus Dupont. 

Representatives of the recent Neotropical elements of the Ne- 
arctic region include the following genera: Archodontes and Steno- 
dontes (Prioninae); Strangalia, Euryptera, and Ophistomis (Lep- 
turinae) ; Sniodicum, Eburia, Elaphidion, Chion, Psyrassa, Heter- 
achthes, Ibidion, Plinthocoelmm, Megacyllene, Euderces, Rhopalop- 
hora, Ancylocera, Agallisus (Cerambycinae) ; and Lagocheirus, 
Leptostylus, Leiopus, Lepturges, Eupogonius, Oncideres, Ecyrus, 
Ilippopsis, and Spalacopsis (Lamiinae). Some of these groups 
apparently came into North America by way of the Antilles and 
are poorly represented on the coastal plain of Mexico, e.g., Spala- 
copsis. The majority of the species of West Indian origin are not 
found north of the southern tip of Florida, most appear to be recent 
arrivals, and none has reached western North America. However, 
the largest representation of subtropical Cerambycidae in the United 
States is found in the lower Rio Grande Valley of Texas. More than 
eighty species have been collected in this area, and all have southern 
affinities. Twenty-two occur also in the Austro-Riparian or Carolin- 
ian life zones of southeastern United States, ten in the Sonoran 
subfauna, and the remainder are strictly Neotropical. Thus these 
faunal elements bear little relationship to those of western North 
America. Only one austral genus, Neoclytus, has successfully in- 
vaded all the northern forests, and it is extremely doubtful if this 
is a recent arrival. The genus is most highly developed in South 
America and is entirely absent from the Old World, thus suggesting 
southern affinities, yet its wide distribution in North America 
indicates that it must have been established very early in the 
Tertiary. The majority of the species feed upon broad-leaved and 
hardwood trees, but N. nubiliis Linsley and A^. muricatuliis Kirby 
are restricted to conifers. 

The term "Alleghenian" was proposed by Wallace (1876) to 
designate a large area covering much of eastern North America 

308 E. G. LINSLEY 

More recently it has been used in reference to the subfauna that 
centers in the Appalachian and Ozark plateaus. It includes a large 
number of endemic cerambycid genera and species. The affinities of 
these beetles are predominantly and clearly northern, but in many 
respects their relationships appear to be nearer to those now found 
in the Japano-Manchurian region than with those in the present 
day Vancouveran of western North America. Unlike the recent 
Holarctic elements, which are associated mainly with conifers and 
northern type hardwoods, the Alleghenian species are mostly found 
on lowland hardwoods, where they exhibit a preference for areas 
with warm, humid summers, and apparently have little tolerance 
for cold and for high altitudes. Few of the Alleghanian species have 
successfully penetrated the Canadian and Hudsonian life zones. 

One of the most interesting of the old, relict endemics in the 
Alleghenian subfauna is the primitive monotypic genus Scaphinus, 
which represents one of the two living genera of its subfamily. Its 
only relative is Spondylis, with a single species in the Palaearctic 
regions, another in the Vancouveran, and a third in the high moun- 
tains of the Mexican plateau. Other endemic genera with relatives 
in eastern Asia or southern Europe are: Cytrophorus and Micro- 
clytus (the only New World Anaglyptini), Zammodes, Tylonotus, 
Physocnemum, Cyrtinus, Psenocerus, Hetoemis, and Dorcaschema. 
At least one genus, Michythisoma, is now phylogenetically isolated, 
but all its living relatives, although distant, are associated with 
northern coniferous forests. 

Some endemic Alleghenian species fall in Old World genera not 
found elsewhere on this continent (Table IV). Genera like Ropalopus, 
Hesperophanes, and Clytanthus, highly developed in the Palearctic 
region, have one species each in the Alleghenian subfauna. Other 
species, numerous in the Alleghenian, represent Holarctic genera 
absent, or nearly so, from the Vancouveran subfauna. The genus 
Saperda, with two postglacially dispersed, poplar- feeding species 
occurring from coast to coast, includes fifteen endemic species 
associated with various deciduous elements of the Alleghenian 
forest, and one in the Vancouveran subfauna, S. horni Joutel, 
attached to Salix. Similarly, Oherea has eighteen Alleghenian 
endemics with various deciduous hosts, and one (0. quadricallosa 
LeConte, also attached to Salix) in the Vancouveran. The Old 
World-Alleghenian genera Tetrops and Typocerus are both absent 



from the Vancouveran, and Gaurotes is represented by only a single 
species in that subfauna. 

The present Alleghenian subfauna is not, however, entirely 
composed of northern elements. A few southern derivatives became 
established at a date early enough for them to persist as endemics, 
e.g., the clytine genera Glycohius and Sarosesthes, and the lepturine 
genera Bellamira, Charisalia, and Strangalia. Several Neotropical 

Table IV. Discontinuous Distribution of Some Holarctic Genera of 
Cerambycidae Differentially Represented in the Vancouveran and 
Alleghenian Faunas of North America" 





A merica 

A merica 





















8 + 


8 + 




9 + 






8 + 


18 + 






Rosalia s. str. 






10 + 

25 + 













« Numerals indicate approximate numbers of known endemic species. 

genera e.g., Neoclytus, Leptostylus, Lepturges, and Leiopus, also give 
evidence of having come into the fauna at an early date, and indeed, 
some of these are represented in the fossil beds at Florissant. The 
early southern elements may be eastern counterparts of the "Cal- 
ifornian" discussed below, but in the absence of climatic barriers 
that have maintained the integrity of the "Californian" they have 
apparently blended with the northern Alleghenian elements and 
shared their late Tertiary geological history. 

The Vancouveran subfauna (Van Dyke, 1919, et seq.), in its 
purest form, occurs along the coast of western North America from 
the Aleutian Islands to central California, more broadly in the 



Bitter Root and northern Rocky Mountains, the Cascades, Sierra 
Nevada, and the detached mountain systems of southern Cahfornia 
and northern Baja Cahfornia (San Bernardino, San Jacinto, and 
San Pedro Martir Mountains). In more dilute form, elements are 
recognizable in the southern Rocky Mountains as well as in the 
high coniferous forests of southern Arizona and northern Mexico 

Fig. 1. Primary geographical ranges of some Cerambycidae classed 
as Vancouveran in the narrowest sense (dark shading), broader sense 
(with addition of intermediate shading), and widest sense (with addition 
of lightest shading). 


(Fig. 1). These are the dominant Cerambycidae of the Transition 
Life Zone of Merriam (1898) and show closer afifinities with those of 
Europe and eastern Asia than with their Alleghenian counter- 
parts in eastern North America. Thus, in the Vancouveran subfauna, 
we find the endemic Opsimus and Dicentrus (only New World 
Saphanini), Synaphaeta (only New World genus of Mesosini), 
and Brothylus, Leptalia, Ulochaetes, Hybodera, and Lophopogotiius, 
all with related genera in the Old World. Several other genera 
share species with both the Vancouveran subfauna and those of the 
Palearctic Region, but not the Alleghenian (Table IV). These include 
Plectrura (one species in Japano-Manchurian region, one in Van- 
couveran) ; Spondylis (one species Palearctic, one Vancouveran) ; 
Megasemum (one species in Japano-Manchurian, one in Vancouver- 
an) ; Callimellum (eight species in southern Europe and Asia Minor, 
two in Vancouveran) ; Cortodera (numerous species in both Europe 
and Vancouveran) ; Xylosteus (one species in southern Europe, one 
in Vancouveran) ; and Rosalia (one species in Japano-Manchurian, 
two in south China, one in Europe, one in Vancouveran). Other 
genera endemic in the Vancouveran fauna are Xylocrius (two 
species), Poecilobrium (one species), Enmichthus (one species), 
Holopleura (one species), Ortholeptura (three species), Piodes (one 
species), and Pyrotrichiis (one species). Presumably all these have 
ancient northern affinities. 

The relict trees of the genus Sequoia, growing within the area 
occupied by the Vancouveran subfauna, are hosts of several endemic 
cerambycid species or subspecies (all members of the tribe Callidini). 
These include Callidium vandykei Linsley, C. sempervirens Linsley, 
and Semanotus ligneus sequoiae Van Dyke, which are limited to the 
coast redwood {Sequoia sempervirens), and Callidium sequoiae 
Fisher, on the big tree [S. gigantea). A more striking group of 
Cerambycidae is found on the Sargent Cypress (Cupressus sargentii) 
which grows only in a few restricted areas of serpentine rock in the 
foothills of northern California. Confined to this host are Vatidykea 
tuber culata Linsley, Atimia helenae Linsley, and Callidiellum cup- 
ressi (Van Dyke). The last species has a close relative, C. rufipenne 
(Motschulsky, in Japan, associated with Crytomeria japonica and 
Chamaecyparis obtusa, another, C. villosulum (P^airmaire), in China, 
on Cunninghamia lanceolata, all members of the Cupressaceae or 

312 E. G. LINSLEY 

Taxodiaceae. However, Vandykea is isolated taxonomically and 
apparently has southern rather than northern affinities, and I 
have classed it as "-Calif ornian" (see below). 

In Oregon and California, the Sierra-Cascades (arid) phase of the 
Vancouveran subfauna is quite distinct from the coastal (humid) 
phase, although the two approach each other more closely in Wash- 
ington and merge in British Columbia. In general, most Ceram- 
bycidae that occur in the Sierra-Cascade Vancouveran are found 
also in the coastal phase. Apparent exceptions include: Desmocerus 
auripennis Chevrolat, Tetropium ahietis Fall, Oeme calif ornica 
Linsley, Pachyta armata LeConte, Leptura obliterata soror LeConte, 
Semanotus amethystinus LeConte, Clytus planifrons LeConte, C. 
clitellarius Van Dyke, Neoclytus mibilus Linsley, and Leptostylus 
nehulosus Horn. Species of the coastal Vancouveran not known to 
occur in the Sierra-Cascade phase include: Evodinus vancouveri 
Casey, Leptura obliterata obliterata LeConte, Desmocerus cribri- 
pennis Horn, Callidium vandyke, C. sempervirens Linsley, Clytus 
blaisdelli Van Dyke, and Plectrura spifiicauda Mannerheim. Mela- 
nism is a marked characteristic of the humid Vancouveran and is 
particularly pronounced in Piirpuricenus dimidiatiis Horn, Necyd- 
alis laevicollis LeConte, and Judolia quadrillum LeConte. 

The Rocky Mountain area, lying between the Vancouveran and 
Alleghenian endemic reservoirs, has few endemic cerambycid genera 
of its own (e.g., Elatrotrypes, with ancient northern affinities), 
and the intermountain or Great Basin area contains only one, 
the monotypic Megascheuma, obviously derived from the austral 
Megacyllene and adapted for life in the roots of shrubby compositae. 
The present cerambycid fauna is made up primarily of Holarctic 
elements of recent origin, with an intrusion of Vancouveran forms, 
especially in the north and, to a lesser extent, of Sonoran elements 
in the south. A few Alleghenian representatives are to be found on 
the eastern slopes of the mountains, emphasizing a long separation 
of Vancouveran and Alleghenian elements, and these are mostly 
recent arrivals, many of which have followed up the river courses 
from the Mississippi Valley, e.g., Neoclytus caprea Say. The Great 
Plains area to the east, which apparently began to develop some of 
its present characteristics in the Miocene, has produced the prionine 
subgenus Homaesthesis, and this, like Megascheuma, exhibits 


specialization for life associated with plant roots (in this case, of 
prairie grasses). 

The endemic Sonoran elements among the Cerambycidae are 
almost entirely of early Neotropical derivation (in the geographic 
sense) and exhibit various modifications of structure and habit 
associated with the arid conditions under which they now exist. 
They are characteristic of the Lower Sonoran Life Zone of Merriam 
and occupy most of the central and northwestern plateaus of Mexico, 
western Texas, much of New Mexico and Arizona, southeastern 
California and eastern Baja California, and they are associated 
with desert trees, shrubs, and Cactaceae, e.g., Anefliis, Osniidus, 
Anepsyra, Rhodoleptus, Metaleptiis, Schizax, Tylosis, PUonoma, 
Taranomis, Sphaenolhecus, Batyle, Moneilema, Peritapnia, Coenopiis, 
and Glaucotes. Other genera, dominantly Neotropical, but well 
represented in the Sonoran (and also in the Austro- Riparian) 
are: Derobrachus, Methia, Elaphidion, Ophistomis, Euryptera, 
Stenosphenus, Elytroleptus, Stenaspis, Dendrobias, Acanthoderes, 
Oncideres, and Ataxia. A major derivative of the Sonoran fauna 
occupies the intermountain area of the Great Basin. It is represented 
by genera (e.g., Crossidius, Tetraopes, Mecas) associated with the 
roots of shrubby Compositae ( as Artemisia and Chrysolhamnus) 
and asclepiads. However, in the mountains, Eucrossus and Haplidiis 
are present. These are endemic genera with southern affinities, 
primarily associated with pinyon pine, which I have classed as 
"Californian" in the broad sense. The small endemic subfauna, 
designated by Van Dyke (1919) as the " Calif ornian"^ is also 
deserving of brief discussion. In its restricted form it occurs from the 
middle of the west coast of Baja California to Santa Barbara County 
and in the interior from the San Pedro Martir Mountains to the 
Tehachapi region of southern California (Fig. 2). This area is 
characterized by many endemic groups of insects, particularly in 
the Tenebrionidae, and corresponds generally to the center of 
distribution attributed to the broad-sclerophyll vegetation of the 
Pacific Coast by Cooper (1922), although many of the forest elements 
included in his classification could be called " Vancouveran" on the 
basis of the Cerambycidae associated with them. In a broader 

1 This term is applied in various senses by students of biogeography and ecology. 
I have not attempted to determine priority of usage. 



sense the "Californian" includes some elements now occurring in 
the foothill region of the western Sierra Nevada and in the eastern 
Coast Range, surrounding the great valley of California, and in the 
Chiricahua and certain other mountain ranges of southern Arizona 

Fig. 2. Primary geographical ranges of some Cerambycidae classed 
as Californian in the narrowest sense (dark shading), and intermediate 
sense (with addition of the lighter shading). Note that some of these over- 
lap the ranges of forms classed as Vancouveran (Fig. 1). 

(Fig. 2), and is sparsely represented in the Great Basin montane 
(not shown in Fig. 2), Generally speaking, this is the cerambycid 
fauna of the Upper Sonoran Life Zone of Merriam, but it is often 
mixed with elements derived from the Sonoran and Vancouveran 
subfaunas, especially the latter in so far as the Cerambycidae are 


Like the Sonoran, the "Californian" subfauna has southern 
affinities but it is older, perhaps comparable in age with the Vancou- 
veran. It exhibits relationship with elements now found in the mon- 
tane phases of the Mexican Plateau, but, judging from the beetles, 
at least some of its affinities suggest a closer relationship to the 
contemporary faunas of the arid and semi-arid west coast of South 
America (Peru, Galapagos, Chile, etc.) than to those of humid 
tropical America. As has been emphasized previously (Linsley, 
1939), it appears probable that some time during the later Tertiary 
a series of arid or semi-arid environments permitted the dispersal of 
elements between the west coasts of North and South America. 
It is possible that these environments were associated with mountain 
ranges or chains of islands. At present, portions of the peninsula of 
Baja California and the islands off the coast of southern California 
exhibit arid (landward) phases and humid (seaward) phases, the 
former usually characterized by desert or semi-desert conditions, 
and Michener (1954) has emphasized that xeric communities now 
exist in the vicinity of the Canal Zone in Panama. Such arid phases 
might well have offered north-south dispersal routes for plants and 

Among the Cerambycidae, a typical Californian genus is Ipochus, 
a wingless group of closely related species or subspecies which 
occupies an area from the middle of Baja California north to Santa 
Cruz, California, including Guadalupe and Catalina islands, and 
is also represented in the Huachuca Mountains. Other groups with 
southern (but not Sonoran) affinities, apparently assignable as 
endemics of the Californian in the broad sense, include the mono- 
typic genera Megobrium, Eiidistenia, Meganoplium, Paranoplium, 
Hesperanoplium, Neobellamira, Triododytus, and Sternidocinus 
(associated primarily with oaks and chaparral shrubs); Vandykea, 
which is attached to Sargent Cypress; Eucrossus and Haplidus, 
occurring primarily with pinyon pine; and the polytypic genus 
Poliaenus, with one species limited to Fremontia (a chaparral type), 
others to pinyon and digger pines (woodland types). 

The California insular fauna has been treated as a subdivision 
of the Californian, but among the Cerambycidae, except as noted 
for Ipochus (above), no endemic elements are known and typical 
Californian elements are present (Fig. 2). Mason (1934) has shown 
that the modern closed -cone pine forest now occupies areas that 

316 . E. G. LINSLEY 

can be demonstated to have been islands in the late Tertiary or 
which are insular today (islands off the coasts of southern Califor- 
nia and Baja California). Insect distributional patterns reveal a 
similar discontinuity, not only among phytophagous wood-boring 
forms but in such flightless groups as Pleocoma (Scarabaeidae) and 
Omus (Cicindelidae). Among the Cerambycidae, this distribution 
is evident in Megobrium edwardsi (LeConte), Ortholeptura insignis 
(Fall) (hosts: Piniis muricata, P. radiata), and Paratimia conicola 
Fisher (in cones of Pinus attenuata and P. holandari) . Other species 
of the old California insular fauna apparently include Sternidocinus 
barbarus (Van Dyke) and Necydalis barbarae Van Dyke. The 
distribution of the former centers in the Santa Inez Mountains, 
the latter in the region from Santa Barbara north to the Santa 
Cruz Mountains. The Californian species Ipochus fasciatiis LeConte 
and Atimia maritima Linsley, the Vancouveran Xylotrechus insginis 
LeConte, and the widespread but austral Romaleum hispicorne 
(Linnaeus) all occur today on one or more of the southern California 
islands but, with the exception of the first two, give evidence of 
being recent immigrants. 


Judging from an analysis of present day distribution and the 
limited fossil record, the North American cerambycid fauna is a 
complex of diverse elements of which five are rather readily identi- 
fied: the Holarctic, Neotropical, Alleghenian, Vancouveran, and 
Sonoran. The modern Holarctic and Neotropical constituents are 
of relatively recent derivation, and endemism is expressed largely 
at the species level. The Alleghenian, Vancouveran, and Sonoran 
elements are of more ancient origin, although the first two were 
apparently derived largely from an early Holarctic fauna associated 
with the Arcto-Tertiary flora, the last almost entirely from the 
early Neotropical. Much of the endemism in these subfaunas is at 
the generic level. 

The modern Holarctic elements are more or less equally represen- 
ted in the northern forests and mountainous regions of Europe, 
Asia, and eastern and western North America. Their distribution 
reflects Postglacial dispersal. Their hosts are largely conifers and 
northern-type deciduous trees as Salix and Populus. In western 
North America these are the dominant Cerambycidae of the 


Canadian and Hudsonian life zones, but they are also represented 
in the coniferous phases of the Transition and Upper Sonoran. 

The recent Neotropical elements, derived from areas of high 
temperatures and humidity and attached largely to southern-type 
hardwoods and Leguminosae, have penetrated northward very 
unequally. They are largely restricted to the Austro-Riparian belt 
bordering the Gulf of Mexico, the Atlantic coastal plain, and a few 
warm river valleys like those of the Mississippi, the lower Rio 
Grande, and the lower Colorado. About a half-dozen wide-ranging 
species in this category reach southeastern California. 

The Vancouveran elements, in their purest form, occur along the 
coast of western North America from the Aleutian Islands to 
Central California, in more dilute form in the Bitter Root and north- 
ern Rocky Mountains, the Cascades, Sierra Nevada, San Ber- 
nardino, San Jacinto, and San Pedro Martir Mountains. These are 
the dominant Cerambycidae of the Transition Life Zone and they 
show closer affinities with those of Europe and eastern Asia than 
with their Alleghenian counterpart in eastern North America. 

The endemic Sonoran elements are almost entirely of early 
Neotropical derivation and exhibit various modifications of structure 
and habit associated with the arid conditions under which they now 
exist. They are characteristic of the Lower Sonoran Life Zone and 
occupy most of the central and northwestern plateaus of Mexico, 
western Texas, much of New Mexico and Arizona, southeastern 
California and eastern Baja California and are associated with 
desert trees, shrubs, and Cactaceae. A major derivative of the 
Sonoran fauna occupies the intermountain area of the Great Basin. 
It is dominated by genera associated with the roots of shrubby 
Compositae (as Artemisia and Chrysothamnus) and asclepiads. 

A small endemic cerambycid subfauna with southern affinities 
occurs from Monterey County, California, to the middle of the west 
coast of Baja California and in the interior from the Techachapi 
area to the San Pedro Martir; its influence is also seen in the foothill 
areas surrounding the central valley of California and in some of 
the mountain ranges of southern Arizona. This subfauna, sometimes 
called the " Calif ornian," also has an insular phase. Some affinities 
with the subfauna now occurring along the arid west coast of South 
America but the Calif ornian also has characteristics of its own, 
and about a dozen endemic cerambycid genera, mostly mono- 

318 E. G. LINSLEY 

typic, have been assigned to it. It appears to have been associated 
with the Madro-Tertiary Flora. 


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during the Quaternary Period. Stockholm. 
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Inseln, der Insel Sitkha und New-Californiens. Bull. Soc. Naturalistes 

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der Insel Sitkha. Bull. Soc. Naturalistes Moscow, 19: 501-516. 
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ischen leander des Russischen Reiches. Bull. Soc. Naturalistes Mos- 
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floral analysis. Madrono, 3: 181-190. 
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European Species. New York. 2 vols. 
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Distribution of Butterflies in the New World 

William Hovanitz 

Department of Biology, California Institute 
of Technology, Pasadena 

1 he butterfly fauna of North America is proba- 
bly better known than that of any other large group of insects. 
The reason for this is clear: butterflies are day fliers and thus are 
apparent to everyone. They are brightly colored and therefore have 
been collected for non-scientific purposes, for collection hobbyist etc. 
The result of this activity has been both advantageous and disad- 
vantageous to the knowledge of the group from a scientific stand- 
point. On the advantageous side is the tremendous job done by the 
non-scientific or semi-scientific workers on ferreting out butterfly 
haunts over the entire world and making this information available 
in collections and the literature, so that the geographic distributions 
of this group of insects is better known than that of any other. On 
the disadvantageous side is the lack of organized study on the 
butterflies due to lack of biological education by the hobbyists on the 
one hand, and lack of much work by scientific workers created by 
fear that work in this field will place them in the light of immature 
or peculiar "butterfly collectors." 

Butterflies are a major evolutionary branch of Lepidoptera, 
adapted to day-flying habits. It is not certain that the group as a 
whole has had a common origin, or is therefore a natural group. It is 
almost certain that the skippers (Hesperiidae) originated inde- 
pendently. No data are given for the Hesperiidae because they are 
not regarded as naturally related to the other families, even though 
they have commonly been considered to be a part of the butterflies, 
and because the taxonomy of the group involves special problems 
that do not lend themselves well to this analysis. 

The families of butterflies other than the Hesperiidae are fairly 
distinct, but appear to be closely related. All groups seem to have 
had a past history of tropical origin. Since their body temperature 




approximates that of the environment, their activity depends on 
warmer temperatures. The PapiHonidae, Pieridae, Danaidae, 
Morphidae, Satyridae, Brassolidae, NymphaHdae, Erycinidae, and 

•< o 


Fig. 1. New World distribution of butterfly families. 

Lycaenidae are all represented by far more genera or species in the 
tropical parts of the world than in the temperate or boreal parts. 
Independently, certain genera or species of some of these families 
appear to have become adapted to life in colder regions, so that 
some of these would be considered as arctic types or temperate types, 
despite the fact that the family as a whole is tropical. 




The distribution of the major taxonomic groups In North and 
South America is shown by a series of histograms (Figs. 1-19). The 
histograms are constructed In the following manner. Blocks indi- 
cating distributional range are drawn on a scale from left = north to 
right = south, reading from 82° N. Lat. to 55° S. Lat. Each block 
covers 5° of latitude and 1,000 meters of elevation above sea level. 
For example, in the charts on distribution of the Paplllonldae (Figs. 
2-3), if a species exists at an elevation of 1,500 meters at 46° S. 
Lat., this fact is indicated by a block extending from right to left 
at 45°-50° S. Lat. and up and down from 1,000 to 2,000 meters. On 
some histograms, where the data warrant and the distributional 
relations are thereby clarified, the bars are terminated between the 
arbitrary 5° class limits, and, occasionally, the altltudlnal limits are 
set at 500-meter intervals. Where the ranges are disjunct, a line has 
been drawn to connect the base of the separated parts. Where the 
altltudlnal information on a genus Is inadequate, the latitudinal 
distribution is indicated by a thin line. 

For comparison with these ranges, a histogram is shown at the 
top of each figure to indicate the extent of land and habitat avail- 
able in North and South America, for the absence of a butterfly 
group in any area may be caused by the absence of a particular 
elevation at a certain latitude so that no habitat Is available there. 

This comparative chart is drawn In the same way as those for the 
butterflies, with the exception that blocks of 1° latitude are used in- 
stead of 5°. Also, since in some areas high elevations are represented 
solely by a few mountain peaks, these are indicated by the sign A , 
while short ranges are Indicated by H, mountain passes (breaks In 
distributional ranges) are indicated by U, and three areas of nearly 
complete break in the cordillera are indicated by v . 

All areas potentially inhabitable by butterflies are shaded ; areas 
of perpetual frost or cold, in Greenland and southern Chile, are 

Generic names of the butterflies are taken from Seitz's Macro- 
lepidoptera of the World, even though it is now known that many of 
these are not correctly used. The reason for this usage is to avoid 
difficulty in identification due to conflicting opinions. 

From the chart of the families (Fig. 1) it can be seen that the 


Papilionidae inhabit America from 68° N. Lat. to 35° S. Lat., and 
range to their highest elevations (4,000-5,000 meters) in the lati- 
tudes 35° N. to 49° N. only. South of 35° N. Lat., the elevation drops 
ofif to less than 3,000 meters, south of 10° S. Lat. to 2,000 meters, 
and south of 20° S. Lat. to 1 ,000 meters. This distribution indicates 
a large tropical group of Papilionidae that does not exist in the 
higher, colder parts of the Andes, and also indicates a northern 
group that exists in the far north and in the mountains of the tem- 
perate zone. This northern group apparently has not been able to 
extend southward into the mountains of the tropical regions. 

The Pieridae on the other hand have a wider range, extending 
from 82° N. Lat. to 55° S. Lat. — the entire possible range of land. 
They also inhabit the largest part of available elevations at all 
points, and are absent primarily only from the higher elevations in 
the extreme north and south. For further understanding of this 
group one must study its constituents in the following charts. 

The Danaidae occupy primarily a centralized tropical position, 
from 40° N. Lat. to 30° S. Lat., and occur at high elevations only in 
the equatorial regions. Summer extensions of range are shown by 
white bars to 55° N. Lat. and to 55° S. Lat. 

The Morphidae are indicated to be even more tropical, as they 
probably do not reach the Tropic of Cancer and extend little beyond 
the Tropic of Capricorn. Within these limits, however, they range 
locally up to 3,000 meters. The range in the south (to 28° S.) is 
greater than in the north (to 20° N.). 

The Satyridae are indicated to have a very complex distribution, 
covering most available habitats from north to south and at all 
elevations. In distribution they resemble the Pieridae, but they do 
not extend quite so far north. 

The distribution of the Brassolidae is shown to be almost equiva- 
lent to that of the Morphidae, as each is wholly tropical. As for 
certain other tropical groups, the distribution of this family ranges 
upward to 3,000 meters and farther southward than northward. 

The Nymphalidae are a large group, with a range equivalent to 
that of the Pieridae in both elevation and latitude, but they usually 
do not extend so high in the equatorial regions. 

The Erycinidae are largely tropical, but extend northward to 
50° N. Lat. and southward to 35° S. Lat., and upward to 3,000 meters 
in the broad center of the range. This family thus has a range similar 


to that of the Danaidae, Morphidae, and BrassoHdae, except for the 
greater north-south distribution. 

The Lycaenidae occupy a strangely tropical-appearing range, but 
extend to 82° N. and to 40° S. Lat. In the equatorial regions they 
range up to 5,000 meters, and from 45° N. to 15° S. they continuously 
extend up to 4,000 meters. These ranges must be studied individually 
by analyzing their constituents, since some forms in the group are 
clearly cold-adapted. 

Observation of the charts as a whole shows that members of the 
Pieridae, Nymphalidae, and Lycaenidae extend farther to the north 
than do any other families. The first two are joined by the Satyridae 
in extending to the southern tip of South America. There are, by 
the way, no butterflies in Antarctica. 

The Lycaenidae equal the Pieridae and the Nymphalidae in 
northernmost range, and in southernmost range nearly equal those 
families, as well as the Satyridae and the summer migrants of the 
Danaiidae. Next in order of northernmost occurrence are the Satyri- 
dae and the Papilionidae, each of which nearly reaches to 70° N. 
Lat. The Satyridae extend all the way to the tip of South America, 
along with the Nymphalidae and the Pieridae, but do not extend so 
far north. All the other families have much more restricted north- 
south distributional ranges, and should be considered tropical in 
their entirety. 

The same families that extend far into the north and south lati- 
tudes are also found at high elevations in the mountains of the middle 
latitudes of North America: the Papilionidae, the Pieridae, the 
Satyridae, the Nymphalidae, and the Lycaenidae. Contrary to 
expectation, these families are not necessarily the same ones that 
are found at the highest elevations in the mountains of the equatorial 
belt, here treated and charted as from 20° N. Lat. to 20° S. Lat. 
Instead, some of the purely tropical families exceed the northern 
ones in elevation in this belt, where they occupy cold zones high in 
the mountains. For example, the tropical Danaidae exist up to 4,000 
meters in a broad equatorial belt, where the Papilionidae do not 
exceed 3,000 meters. Elevations reached by the Papilionidae, the 
Satyridae, and the Nymphalidae are considerably higher in the 
middle latitudes of North America than in the central equatorial 

Of the six families with resident examples in the northern lati- 


tudes north of 40° N., only three extend beyond 40° S. South of the 
equatorial belt the butterfly fauna is quite depauperate, because of 
the relative lack of typically cold-adapted forms of northern origin. 
On the other hand, many typically tropical forms are seen to extend 
farther southward than northward for reasons that can only be 
conjectured but are probably a combination of (1) lack of competi- 
tive forms in the far south and (2) warmer winters at the same lati- 
tudes south of the equator than to the north. 


Following the chart (Fig. 1) that compares the distributions of the 
families of American butterflies, block histograms (Figs. 2-19) are 
presented to show the latitudinal and altitudinal distributions of the 
genera and of certain lesser groups, when this is deemed desirable. 
The histogram for each family is repeated, in finely crosshatched 
form, at the head of the series of black histograms for the contained 
genera. Within the family divisions coarsely hatched histograms for 
the recognized subfamilies head the appropriate series of black 
histograms. As a variation in the scheme, below the black histogram 
(on Fig. 2) showing the distribution of the first-entered genus, 
Papilio, there are given three coarsely hatched histograms, each of 
which gives the range of one of the main "groups" into which this 
large genus is first divided. Each of the hatched histograms is in 
turn followed by black histograms for the contained natural species 
groups; and the first of the three main divisions, the Aristolochia 
Papilios, is first divided into sections A and B (also shown in black). 
Under the papilionid genus Parnassius black histograms portray the 
distribution of the three American species. In the Satyriidae, under 
the genus Euptychia, black histograms show the ranges of the 27 
species groups. Otherwise, the black histograms portray the dis- 
tribution of genera. 

Papilionidae (Figs. 2-3) 

This family is represented by only four genera, of which one 
{Papilio) is very large and is subdivided many times. It probably 
should be divided into many genera or subgenera, but so far no 
other really good natural division has gained acceptance. The 
groups as organized by Jordan are satisfactory for our purpose. 

The genus Papilio has almost the same distributional range as the 




Fig. 2. New World distribution of Papilionidae (1). 



< 'J 




eo 70 60 50 40 30 20 10 

20 30 40 50 

Fig. 3. New World distribution of Papilionidae (2) and Pieridae (1). 


family, being exceeded by the family only in the northern parts of 
the range and only by the genus Parnassius. The latitudinal range 
is greater in the north than the south, going to 65° N. and to only 
35° S. Also, the elevations attained are higher in the north than in 
the south: to 4,000 meters at about 35° N. Lat. and to only 1,000 
meters at 35° S. Lat.; to 3,000 meters at 10° to 20° N. Lat. but to 
only 2,000 meters at 10° to 20° S. Lat. The distribution of the genus 
has a northern skew, because, as shall be seen below, some groups of 
northern origin are superimposed in the north on groups of tropical 
or equatorial origin. 

The genus is subdivided into three natural groups, the Aristo- 
lochia, the Fluted, and the Kite Papilios. The Aristolochia group, 
extending from 42° N. Lat. to 35° S. Lat. has a tropical range, ex- 
tending into the non-equatorial regions only where winter tempera- 
tures are not too cold and long. Elevations to 2,000 meters are 
attained in the equatorial range. Of two sections of the Aristolochia 
Papilios, only one, comprising the Polydamus group, extends north 
of the equatorial area more than 5°. The other section (A) is tropi- 
cal, but extends farther south (35° S.) than north (25° N.). This 
section consists of three natural groups {Ascanius, Aeneas, and 
Ly Sander), which have about the same range in the equatorial region. 

The Fluted Papilios have nearly the same range as the genus 
itself, and comprise both northern and tropical members. The 
species groups considered here are clearly seen on the chart to be 
divisible into two parts, a northern part consisting of the Machaon 
and Glaucus groups and an equatorial part consisting of the re- 
maining six groups. The Machaon and Glaiccus groups extend to 
65° N. Lat. and the Machaon group reaches 3,000-4,000 meters in 
elevation in the region of 35-40° N. Lat. Both groups extend into 
the equatorial regions at middle elevations (2,000-4,000 meters) 
and the Machaon group extends as far as 10° S. Lat. in the Andes. 
The Glaucus group does not reach across the barrier presented by the 
Panamanian isthmus. Of the tropical groups, only Thoas extends 
much north of the Tropic of Cancer and then only to 42° N. Lat. 
Except for the Homerus group, the others are strictly equatorial 
and tropical, not exceeding 1,000 meters in elevation. The Homerus 
group ranges up to 3,000 meters in the equatorial belt. 

The equatorial Kite Papilios are represented north of the Tropic 
of Cancer only by the Marcellus group. The Lysithiaus and Thyastes 


groups extend slightly farther south than north. The Marcellus 
group extends to 40° N. and to 30° S., with an apparent gap of 
some 25°. 

The genera Euryades and Baronia are considered as primitive 
members of the Papilionidae. Their distributional ranges are typical 
of relict species at the far corners of a once wider range. Euryades 
exists in the southeastern part of South America where it has a 
latitudinal range of 15° on the plains. It extends to 35° S. Lat., 
which is as far south as is reached by only one group in Papilio. 
Baronia is isolated in southern Mexico, where it exists with a range 
of less than 5° latitude and of less than 1,000 meters elevation. 

Parnassius, the remaining genus in the Papilionidae, is northern 
in origin and distribution. It has a range from nearly 70° to 35° N. 
Lat. and occurs at elevations from sea level to 5,000 meters. The 
three species that comprise the genus in America are indicated 
separately: P. thor is restricted to a range of less than 10° latitude 
at near sea level in Alaska ; P. smintheiis occurs from sea level in the 
north (65° N.) to 5,000 meters in the south (35° N.); P. clodius is 
found from sea level in the north (65° N.) to both sea level and 5,000 
meters in the south (35° N.) (it accomplishes this dual range in the 
south by existing along the cool-summer Pacific Coast as well as in 
the cool-summer mountains of the interior). 

Pieridae (Figs. 3-5) 

This large family covers the entire range of land from north to 
south and at nearly all elevations. It is subdivisible into four natural 
groups, the Pierinae, the Rhodocerinae, the Euchloinae, and the 
Dismorphiinae. Except for the last, each of these is large in itself 
and covers almost the same range as the family. The range of the 
Pierinae is less than that of the Pieridae only in that it extends in the 
far north only to 68° N. Lat. instead of to 82° and reaches lower 
elevations in North and South America. The subfamily consists of 
several genera, most of which are divisible into types with narrow 
temperature tolerance. Neophasia is limited to a range of 30° to 
55° N. Lat., and should be considered one of the rare types of 
temperate origin. Eucheira is a relict type found only from 20° to 
30° N. Lat. at elevations of from 2,000 to 3,000 meters. 

Tatochila has an unusual distributional range in that it exists 
from 55° S. Lat. to 10° N. Lat., wholly within the continent of South 




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Fig. 4. New World distribution of Pieridae (2). 



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Fig. 5. New World distribution of Pieridae (3) and Danaidae (1). 


America, from sea level in the south to 3,000-4,000 meters in the 
north. It has a counterpart in the north, Pieris, which extends from 
68° N. Lat. (at sea level) to 15° N. Lat. (at 2,000-4,000 meters). 
The ranges of these two nominal genera are separated by low- 
elevation barriers in Central America. There is good reason for 
considering them to be congeneric, since the differences between 
them are not greater than those between species within each group. 

The remaining genera of the Pierinae are all equatorial; only one, 
Ascia, ranges north of the Tropic of Cancer. The altitudinal range 
of some of the genera is narrow (less than 1 ,000 meters) , of others 
wide (up to 4,000 meters). Catasticta ranges from 20° N. Lat. to 
20° S. Lat., and at all elevations from sea level to 3,000 meters. 

The range of the Rhodocerinae is wider than that of the Pierinae 
and is equivalent to that of the Pieridae as a whole. The genera are 
divisible again into temperature-tolerance groups as is shown by the 

Eurema is equatorial; it ranges to 30° N. Lat. and to 25° S. Lat., 
and up to 3,000 meters in the central Andes. Phoebis is equatorial 
but extends farther north than Eurema (to 35° N. Lat.,) although it 
has a more limited altitudinal distribution. Anteos is also equatorial; 
it extends north and south only to 25° and has a limited elevational 
distribution (to 2,000 meters). Kricogonia is subtropical with a 
range extending only from 10° to 30° N. Lat., at near sea level. This 
is unusual in that most species or genera that inhabit the tropics 
cover the entire tropical area from the Tropic of Cancer to the Tropic 
of Capricorn with little in the way of further limitations. 

Colias is low-temperature dependent, as is shown by the histo- 
gram. It ranges from 82° N. Lat. to 55° S. Lat., is present across the 
equator at high elevations, but is absent in the low elevations in the 
tropical regions and exists farther north and at higher elevations 
than any other butterfly genus. The altitudinal range in North 
America (to 5,000 meters) and in the Andes is as high as any or- 
ganism can live. The range is broken by a gap of 5° latitude from 
Guatemala to Venezuela and Colombia. 

Zerene resembles Colias in pattern of distribution, but usually 
lives in warmer regions and at lower elevations. It exists only to 40° 
N. Lat. and 30° S. Lat., is absent from lower elevations across the 
equatorial regions and inhabits the middle-equatorial altitudes 
(1,000-3,000 meters), in a zone intermediate between the hotter 


tropics at lower elevations and the cooler regions higher in the 

Nathalis resembles Kricogonia in having a limited distributional 
range from 5° to 35° N. Lat. ; within this range, however, it occupies 
a wide altitudinal belt up to 4,000 meters (but typically only to 
3,000 meters). It has failed to pass from the North American tropics 
into the South American tropics despite the apparent absence of a 

The Euchloinae comprise six genera the distribution of which, for 
such a small group, is especially diverse: two are wholly northern, 
three are wholly southern, and one is equatorial with a southern 
expansion. Euchloe, a typical northern type, is found as far north as 
60° N. Lat. with a sea level extension along the Pacific Coast to 
30° N. This pattern is nearly duplicated by that of Anthocharis , 
with the exception that the latter extends farther south, to 25° N. 
Lat. at elevations of 3,000-4,000 meters, and thence to 15° at 2,000 
to 3,000 meters. 

Eroessa duplicates, to a certain extent, these distributions south 
of the equator, covering elevations of from 1,000 to 3,000 meters 
with a latitudinal range from 25° to 40° S. Lat. Hesperocharis is the 
connecting link between the genera of the southern hemisphere and 
those of the northern hemisphere. It covers all elevations from sea 
level to 3,000 meters, from 20° N. Lat. to 20° S. Lat., and, in addi- 
tion, extends southward up to 1,000 meters to 45° S. Lat. It thus 
overlaps in distributional range all other genera except Eiichloe. 

Andina is represented by a very limited distributional range at 
4,000-5,000 meters elevation in the Andes, from 15° to 20° S. Lat. 
Phalia extends this range downward to 2,000 meters, over a lati- 
tudinal range from 15° to 25° S. Lat. These distributions appear to 
indicate that the Euchloinae are a closely knit group with specific 
temperature tolerances, with the possibility that the basic origin of 
the group was tropical and that its northern {Euchloe, Anthocharis) 
and southern (Eroessa, Andina, Phalia) representatives were inde- 
pendently derived from the tropical Hesperocharis, or from its 
ancestors. Of course it is always possible that the entire American 
group was derived from Asiatic representatives, via Euchloe and 
Anthocharis, that Hesperocharis was derived from these, and the 
southern types from Hesperocharis. The direction of derivation 
cannot be deduced from present day distributions alone. 


The Dismorphiinae comprise a small group that may not be 
derived from the Pieridae. Its range is wholly tropical, with a slightly 
greater extension to the south than to the north of the tropics. Of 
the two genera, Dismorphia has the same distribution as the sub- 
family and P seudopieris is restricted to a range from 15° N. Lat. to 
15° S. Lat. 

Danaidae (Figs. 5-7) 

The Danaidae comprise thirty-five genera, all but one of which 
are restricted, or almost confined, to ranges between the Tropics of 
Cancer and Capricorn. The only genus not so restricted is Danais, 
one species of which extends its range annually to latitudes of 55° N. 
and 55° S. by seasonal migration. In addition, this species manages 
to remain at home at latitudes up to 40° N. and 30° S. The distribu- 
tional range of the family as a whole forms a pyramidal histogram 
with the median point centered at about 10° N. of the equator, 
rather than being centrally placed across the tropics. Higher eleva- 
tions are inhabited north of the equator than southward, but it is 
possible that this apparent phenomenon is due to the lack of suffi- 
cient information for the humid region on the east side of the Andes 
south of the equator. 

The Lycoreinae with two genera are equatorial at low elevations. 
The Mechanitinae are also equatorial but extend to 25° S. Lat. 
This is a very large subfamily ranging from sea level to 2,000 meters. 
All thirty genera are found within this range; some occupy the 
whole range, others only a narrow segment. For example, Athesis 
occupies a range from 10° N. Lat. to 5° S. Lat. at elevations of only 
1,000 to 2,000 meters. Sais is found only from 5° N. Lat. to 0°. No 
reasons for the restricted ranges of some of these genera are apparent 
from the histograms. A great proportion of genera occupy the area 
from 10° or 15° N. Lat. to 10° or 15° S. Lat., although there are no 
geographic barriers in these regions to hinder their expansion to 20° 
in either direction. The family as a whole should be considered as 
one of entirely tropical origin, for no representative lives perma- 
nently in cold regions. 

Morphidae (Fig. 7) 

The Morphidae are represented by one genus (Morpho), which is 
entirely equatorial though extending to considerable elevations (up 



80 70 60 50 40 30 20 10 

10 20 30 40 50 

Fig. 6. New World distribution of Danaidae (2). 



E P I S C A A 


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80 70 60 50 40 30 20 10 

20 30 40 50 

Fig. 7. New World distribution of Danaidae (3), Morphidae, and 

Satyridae (!)• 


to 3,000 meters). As is usual for a number of tropical or equatorial 
groups, the range southward (to 28° S. Lat.) is greater than north- 
ward. There is no indication of any but a tropical origin for this 

Satyridae (Figs. 7-12) 

The Satyridae comprise a huge family that extends from the arctic 
regions at 70° N. Lat. to 55° S. Lat. They occur at nearly all eleva- 
tions throughout this range. Tropical genera, however, are far more 
abundant than northern genera. The family is an interesting one 
since many genera have highly restricted habitats both within and 
outside the tropics. 

Callitaera, Haetera, Pierella, and Antirrhaea are confined almost 
wholly within the tropical regions; except for Callitaera they range 
up to 2,000 meters. Sinarista has a restricted range from 7° N. Lat. 
to the equator and from 1,000 to 2,000 meters in elevation (it exists 
only in the northern Andes of Colombia and Ecuador) . Coerois and 
Tisiphone are equatorial ; the former is the more restricted. Tisiphone 
extends southward to 30° S. Lat. and up to 2,500 meters between 
the tropics. 

Enodia, on the other hand, occupies a north temperate habitat 
ranging from 25° to 45° N. Lat. in the eastern part of North America. 
Since it has no northern affinities but only tropical ones, it may be 
assumed to be of tropical origin. 

Taygetis has a full range between the tropics up to 2,000 meters 
and extends south to 30° S. Lat. Amphideda, on the other hand, is 
restricted to lower elevations south of Panama. 

Euptychia is a large genus of certainly tropical origin, but includes 
at least four groups that extend northward to 45° N. Lat. and several 
that extend southward to 35° S. Lat. The genus is subdivided into 
groups in the histograms, to show how some groups are restricted 
tropical, some are extensive tropical, and a few are restricted 
temperate types. In the first classification (restricted tropical) are 
the Nossis, Pronophila, Liturata, Gera, Lea, Tolumnia, and Agaga 
groups. In the second classification (extended tropical) are the 
Hesiofie, Mollma, Saturnus, Harmonia, Necys, Pacarars, Batesii, 
Cephus, and Arnaea groups. In the third category (restricted tem- 
perate either north or south) are the Paeon, Cluena, Phocion, and 
Pyracmon groups. A fourth set might be recognized, namely, those 



Fig. 8. New World distribution of Satyridae (2). 









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Fig. 11. New World distribution of Satyridae (5). 


with panequatorial distributions that extend far into the temperate 
zones. These are the Ocypete, Renata, and Hermes groups. 

The restricted range (15°-20° N. Lat. at 1,000-2,000 meters sug- 
gests that the genus Pindus is a relict group similar to Baronia. 
Cyllopsis has a similar distribution but extends from 10° to 25° N 
Lat. and from 1,000 to v3,000 meters in elevation. Oressinoma ex- 
tends from 10° N. Lat. to 20° S. Lat. Paramecera is restricted to the 
same general area as Pindus (17° to 25° N. Lat. and 1.000-2.000 
meters elevation). It too suggests a relict group. 

Satyrodes, Coenonympha, Neominois, Cercyonis, Oeneis, and 
Erebia are all northern genera that have no contact with the tropics. 
The charts show typical histograms of forms with cold-temperature 
tolerances, by increasing in elevation in the south. In distribution 
these northern forms are somewhat duplicated south of the equator 
by Argyrophorus, Cosmosatyrus, Tetraphlebia, Faunida, Neosatyrus, 
Neomaenus, Epinephele, Elina, and Eteona. No other family has 
developed so many genera south of the equator. It may be assumed 
that they developed from tropical relatives independently of 
northern genera. 

Many of the genera (perhaps not good ones) have very restricted 
distributions in equatorial habitats. Many have very restricted 
altitudinal ranges as well; for example: 

Manerebia, 15°-20° S. Lat., 2,000-3,000 meters 

Indioneura, 5° N. Lat., -0° 2,000-3,000 meters 

Pseudomaniola, 15°-20°S. Lat., 3,500-5,000 meters 

Calisto, 16°-27.5° N. Lat., 0-2,000 meters 

Pseudosteroma, 5° N. Lat. -15° S. Lat., (discontinuously?) 2,000- 

3,000 meters 
Steremnia, 10° N. Lat. -15° S. Lat., (discontinuously?) 2,000-3,000 

Gyrocheilus, 13°-35° N. Lat., 2,000-3,000 meters 
Eretris, 10° N. Lat., -5° S. Lat. 2,000-4,000 meters 
Daedalma, 10° N. Lat.. -15° S. Lat. 2,000-3,500 meters 
Polymastus, 5° N. Lat., -10° S. Lat. 2,500-3,500 meters 

The great prevalence of restricted, narrowly ranging genera in the 
Andes suggests a center of rapid divergence of these forms in the 
area. This may not have been the center of origin of the family, but 
almost certainly has been a secondary center of origin for many 

The northern genera of the family have affinities with Asia, and 


it is possible that these have had their origin there, and that the 
tropical forms of the family have been derived secondarily from 
these (or from their ancestors). From existing distributions, it is not 
possible to decide in which direction the migrations went. The 
systematics of the remaining groups (Figs. 8-12) are too uncertain 
to warrant extended discussion. 

Brassolidae (Fig. 12) 

All nine genera of the Brassolidae are equatorial, although as usual 
for distributions of this type the ranges extend farther south (to 30° 
S. Lat.) than north (to 20° N. Lat.). The altitudinal range is only to 
2,000 meters, except in a restricted part of the range of Caligo. The 
origin of the group is to be regarded as tropical since there are no 
indications of affinities elsewhere. 

Nymphalidae (Figs. 12-16) 

This huge family is not exceeded in its diversity by any other, 
and it is equaled in its distributional range only by the Pieridae. 
Many of the subfamilies are wholly tropical, but others are northern. 
Some of the most interesting distributions are found in this family. 
The distributional range, as in the Pieridae, is from 82° N. Lat. to 
55° S. Lat. and from sea level to 5,000 meters in elevation. 

The four subfamilies are not of equal size or character. The three 
smaller ones are tropical, or nearly so, and the larger one has the 
same distributional range as the family itself. The Acreinae are 
represented by only one genus, which has an equatorial range from 
20° N. Lat. to 30° S. Lat. and an altitudinal range to 3,000 meters. 

Actinote provides no exception to the rule already indicated for 
other groups that the ranges of equatorial species often extend 
farther south than north. 

The Heliconiinae are another equatorial subfamily, larger than the 
preceding, with five genera. Three of these extend slightly beyond the 
confines of the equatorial belt, one as far as 35° N. Lat. and 35° S. 
Lat. Except for Metamorpha these exist as high as 2,000-3,000 
meters in elevation. Heliconius, Eulides, Colaenis, and Dione have 
the full range from north to south ; the range of Metamorpha ceases 
at Panama (10° N. Lat.) as is typical of the range of many southern 

The Clothildinae are represented by one genus, Clothilda, having a 



80 70 60 50 40 30 20 

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Fig. 12. New World distribution of Satyridae (6), Brassolidae, and 

Nymphalidae (1). 



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Fig. 13. New World distribution of Nymphalidae (2). 



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Fig. 14. New World distribution of Nymphalidae (3), 



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Fig. 15. New World distribution of Nymphalidae (4). 



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Fig. 16. New World distribution of Nymphalidae (5) and Erycinidae (1). 


narrow range from only 10° to 20° N. Lat. It is absent from South 

The Nymphalinae comprise the major part of the family Nympha- 
lidae, and are not easily subdivided into further parts. The family 
Pieridae can be divided into several large natural subfamilies. On 
the other hand, the Nymphalidae can be subdivided only by remov- 
ing a few odd forms since no large natural cleavage lines are ap- 
parent. In fact, even the line between the Nymphalinae and the 
Heliconiinae is poorly defined. 

The genera of the Nymphalinae do not fall into definite classes 
such as tropical and northern. Instead, each seems to have its 
specific range of temperature tolerance. One may be wholly tropical, 
another subtropical, and another cold adapted. 

Euptoieta is tropically adapted but exists north and south to 3>S°, 
and to 3,000 meters in the central equatorial region. Probably all 
temperatures short of freezing are satisfactory, as colonies are quite 
common at 3,000 meters in the Tierra Fria of the equatorial belt. 

Argynnis, on the other hand, is a cold-adapted genus. It exists to 
82° N. Lat. and to 55° S. Lat., but it is absent in the equatorial 
regions between 25° N. Lat. and 15° S. Lat., even at the higher 
elevations. As is typical of northern types, the elevations at which it 
survives are higher southward in the northern hemisphere and higher 
northward in the southern hemisphere. Argynnis is a large genus 
that exists around the world. If is best considered subdivided into 
various subgenera. If this were done for the /\merican forms, at 
least four subgenera would be recognized for North America and a 
fifth for South America. Two of the groups that would be treated as 
subgenera in North America extend nearly to the Bering Straits 
and are represented in Asia. Thus, there is recent gene continuity 
between America and Asia. The third subgenus is separated by a 
considerably greater distance and, at least during the quaternary, 
has been completely severed from the nearest relatives in Asia. 
There has developed in the North American temperate zone a par- 
ticular type not represented elsewhere. Likewise, the South Ameri- 
can subgenus has been isolated so long that its type is not represented 
elsewhere in the world. 

The genus Melitaea occupies the temperate part of North America 
(also Eurasia) and is not represented south of 20° N. Lat. Phyciodes, 
on the other hand, covers somewhat the same territory in the north, 


but it occupies in addition the equatorial zone at 3,000 or 4,000 
meters altitude to 20° S. Lat. and extends to 25°. 

The genus Chlosyne is equatorial and occupies the lower elevations 
(less than 2,000 meters), with extensions to 35° N. Lat. and 25° 
S. Lat. 

Microtia, Gnathotriche, and Morpheis occupy narrow zones in the 
northern part of the equatorial region. Undoubtedly, revision of 
these genera would prove desirable and would indicate relationships 

Polygonia is a northern type that extends from 68° to 20° N. Lat. 
and occurs at higher elevations in the south. Nymphalis {Vanessa) 
is slightly less a northern type, extends less far to the north (to 
50° N. Lat.), but farther to the south (to 10° N. Lat.). Vanessa 
(Pyrameis) is also not such a northern type, having about the same 
northern distribution as Nymphalis but extending over the tropics at 
2,000-3,000 meters elevation and existing south of the equatorial 
regions as well. Representatives of this genus exist throughout the 
world in cold or temperate regions. Contact with Eurasia is broken 
by a considerable distance across the Bering Straits, but probably 
only a little increase of ocean temperatures would be sufficient to 
connect them again. 

All the remaining genera of this subfamily are equatorial and 
seem to owe their origin to America. A few, however, have been able 
to survive colder temperatures and are found north or south of the 
equatorial zones. Victorina extends to 30° N. Lat. and to 30° S. Lat. 
Didonis extends to 30° S. Lat. Cystineura and Megalura ( = Timetes) 
extend to 27° N. Lat. and to 25° S. Lat. Myscelia extends to 30 N. 
Lat. and to 25° S. Lat. Historis and Pyrrhogyra extend to 25° S. Lat. 
A few genera, for example Lucinia, Balboneura, and Peria, have very 
restricted ranges. These suggest relict genera. Several genera extend 
northward only to Panama (for example, Cybielis, Callithea, Haema- 
tera, Panacea, Agris, and Zaretes). Others that extend north or south 
of the equatorial zone by 5°-10° are Cybielis, Eunica, Callicore, 
Dynamine, Cyclogramma, Adelpha, Ageronia, Chlorippe, Prepona, 
and Anaea. Some of these extend only to the north; others only to 
the south. 

Two of the genera having equatorial affinities, Limenitis ( =Basi- 
larchia) and Asterocampa, are found only in the northern temperate 
latitudes. Limenitis extends from 15° to 50° N. Lat. and Asterocampa 


from 15° to 43° N. Lat. A reconsideration of these genera may indi- 
cate that they are not of generic stature; for example, Leminitis is 
possibly congeneric with Adelpha. 

A number of genera of very restricted ranges in the tropics are 
insufficiently known to be able to offer reasons for their restriction. 
Judging from distributions alone, some of these, for example Gnatho- 
triche, Morpheis, Lucinia, Peria, Balboneura, Libythma, Batesia, 
and Coenophlebia, appear to be relict types. However, study of 
other relationships is required before differentiations can be made 
between those that are newly adapted to a localized habitat and 
those that are relicts. 

Contrary to the distributional patterns in the Satyridae, few 
genera of the Nymphalidae are restricted to intermediate or high 
elevations in the equatorial regions, or, on the other hand, to a 
wholly Southern Hemisphere distribution. 

Erycinidae (Figs. 16-19) 

Few genera of the Erycinidae occur outside the equatorial regions, 
or nearby. Only two of the genera range far into northern latitudes. 
The histogram shows, however, a range from 50° N. Lat. to 35° S. 
Lat. and to 3,000 meters in the equatorial and desert mountains. 

Most of the equatorial genera extend farther south of the Tropic 
of Capricorn than they do north of the Tropic of Cancer. In fact, 
in this family 23 of the 28 equatorial genera whose ranges reach the 
Tropic of Capricorn extend beyond at least to 30° S. Lat. The 
equatorial genera are nearly all adapted to the lowest elevations 
(0-1,000 meters), though a few extend upward in the Cordillera to 
2,000-3,000 meters. Only one genus is restricted to higher eleva- 
tions, namely, Imelda at 1,000-2,500 meters. 

The genus Charts has an equatorial range but extends also to 42° 
N. Lat. and to 33° S. Lat. Apodemia, on the other hand, is restricted 
to the North Temperate zone, from 50° to 20° N. Lat. A Southern 
Hemisphere range from 20° to 30° S. Lat. is also indicated, but is a 
basis that requires further generic study for certainty. 

Lycaenidae (Fig. 19) 

The Lycaenidae is a very large family extending from 82° N. Lat. 
to 55° S. Lat., and from sea level to 5,000 meters in elevation. Over 
much of its range it exists together with the Nymphalidae and 




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Fig. 18. New World distribution of Erycinidae (3). 



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Fig. 19. New World distribution of Erycinidae (4) and Lycaenidae. 


Pieridae. The family contains some huge and diverse genera, which 
are badly in need of comprehensive study. On the whole, the genera 
are northern rather than tropical, such as the genera of the Ery- 
cinidae. However, since the largest genera are tropical, it is likely 
that the bulk of species exists in the equatorial range. 

Eumaeiis has a tropical range extending northward to 30° N. Lat. 
and up to 2,000 meters in elevation, but southward only to 15° 
S. Lat. 

Theorema has a very limited range near sea level from 15° N. Lat. 
to 0°. Trichonis is even more restricted, to from 0° to 5° N. Lat. 

The largest genus from the standpoint of species, but also the 
most difficult to subdivide naturally, is Thecla. This genus has a 
tropical core that ranges from tropic to tropic at elevations from 
to 4,000 meters (some species even to 5,000 meters). But it also 
exists northward in cold areas as far as 60° N. Lat., and at eleva- 
tions up to 4,000 meters as far north as 40° N. Lat. In addition, it 
extends southward to 55° S. This genus is virtually a family in itself 
and probably ought to be considered at least a subfamily. 

Theclopsis has a limited equatorial range from 10° N. Lat. to 15° 
S. Lat. at elevations not over 1,000 meters. Scolitaritides has a limited 
distribution south of the tropics; it ranges from 0° to 40° S. Lat., 
at elevations from 3,000 to 4,000 meters in the equatorial region 
and at sea level southward. 

Chrysophanus has a strictly northern distribution ; it ranges from 
72° to 25° N. Lat., and at high elevations toward the south. This 
genus is also Eurasiatic, as might be expected. 

Feniseca is restricted to a narrow latitudinal range from 35° to 
45° N. Lat. at lower elevations. Few genera of any family are so 
restricted to the North American temperate zone. 

Leptotes is equatorial, extending from tropic to tropic at 0-2,000 
meters, but extending also northward to 40° N. Lat. 

Brephidiiim is North American tropical and temperate, extending 
from 10° to 45° N. Lat. at all elevations from to 2,000 meters. Few 
butterfly genera have such a restricted North and Central American 

Hemiargiis lives at elevations from to 3,000 meters and extends 
slightly farther north (to 30°) than south (to 25°). 

Hylos is found only in the cold temperatures of the Andes from 
2° N. Lat. to 20° S. Lat. and occurs at elevations between 3,000 


and 5,000 meters. In this zone of endemism it is accompanied by 
some Pieridae, Nymphalidae, and Satyridae. 

Everes along with Leptotes has a tropical core but exists also north- 
ward to 50° N. Lat. and southward to 25° S. Lat. 

Plebejus, Philoles, and Glaucopsyche are North Temperate genera. 
Plebejus ranges from 82° to 15° N. Lat., at higher elevations south- 
ward, especially at about 40° N. Lat. Philotes is restricted to the 
range 25° to 40° N. Lat. Glaucopsyche has a similar range but goes 
to 50° N. Lat. Plebejus and Glaucopsyche are also Eurasiatic. 

Lycaeniopsis exists at low elevations from 10° to 65° N. Lat., but 
at the higher elevations of 2,000-3,000 meters only in the central 
part of its range. 


The generic and family distributional charts have indicated a 
number of recurring and characteristic distributional patterns. 

The distribution of the families of butterflies (Fig. 1) can be 
divided into two kinds: (1) the tropical distribution (or nearly so) 
and (2) the non-specific or general distribution. These are as follows: 

(1) (2) 

Tropical General 

Danaidae Papilionidae 

Morphidae Pieridae 

Brassolidae Satyridae 

Erycinidae Nymphalidae 


The genera of the second grouping can be classified according to 
the nature of their distribution. Two major classifications are 
readily apparent. These are the strictly equatorial genera ranging 
generally between the Tropics of Cancer and Capricorn, or at most 
only a little north or south. Examples of this type of distribution are 
those of CatasHcta and Appias (Fig. 4). Few genera of this classifi- 
cation are found in Eurasia or Africa. 

The second major distributional pattern is that of the northern 
types, which extend to far northern latitudes and typically occur at 
increasing elevation to the south. Most of these genera live also in 
Eurasia or Africa. Included in this group are a few genera that occur 
also across the equator at high levels and in southern latitudes. 


An enumeration of the genera (including "groups") of these two 
types for each family shows : 















































Many genera of the northern distributional pattern have close 
relatives, or even continuity of species, in Eurasia, or, if they do not 
at present, did in the immediate past when the northern latitudes 
were warmer. Except when particular circumstantial evidence pro- 
vides a measure of plausibility, there seems to be no sound basis for 
inferring that any given form of this type originated in the Old 
World or the New. 

It can be seen from the figures above that no family has more 
genera of northern distributional pattern than of panequatorial 
pattern. If numbers alone were important, this would seem to 
indicate that all families were, or could be, tropical in origin. Only 
three families completely lack genera classed as of the northern type. 

Except for the Morphidae, containing the one well-known Neo- 
tropical genus Morpho, all the families contain genera that do not 
appear referable to either the panequatorial or the northern cate- 
gory. In four families, more than half the genera are regarded as of 
other types. The Papilionidae, however, have but 2 such genera out 
of 19 genera or groups (Figs. 2-3). These are Euryades and Baronia 
(Fig. 3), both of which are clearly relict types of restricted distribu- 

The Pieridae (Figs. 3-5) have 7 such types out of a total of 30 
genera. One of these, Eucheira, is similar to Baronia in range, for it 
is restricted to a narrow elevated range near the Tropic of Cancer 
Tatochila complements Pieris in the southern hemisphere and 
probably should be considered at most a subgenus. Two of these 


seven genera display a common equatorial distributional pattern in 
which the distribution would be panequatorial were it not that the 
northern range stops at 10° N. Lat., that is, at the Isthmus of Pan- 
ama. Since these are usually well-adapted tropical types existing at 
low elevation, there is no discernible reason for this abrupt termina- 
tion except for the few that cannot cross the Andes from the eastern 
to the western tropical regions in Colombia or Venezuela. The two 
pierid genera of this category are Leucidia and Leodonta (Fig. 4). 
Complementary distributions from 10° N. Lat. northward are less 
common. These are in effect circum-Caribbean types, which are 
represented in the Pieridae by Kricogonia and Nathalis (Fig. 4), the 
latter of which reaches as far south as 5° N. Lat. In the Eiichloinae 
three genera, Eroessa, Andina, and Phalia (Fig. 5), are restricted to 
southern latitudes at high elevations. 

In the Danaidae (Figs. 5-7), 19 out of a total of 34 genera fit into 
neither the northern nor the panequatorial pattern. Since all these 
are tropical, the reason for their restricted range is not immediately 
apparent. Ten of the 19 reach their northern limit at 10° N. Lat., 
but most of these also do not extend far southward. The other 9 are 
limited to belts of varying degrees of latitude in the vicinity of the 
equator. This would seem to indicate that temperature is not the 
limiting factor in their distribution. 

In the Satyridae (Figs. 7-12), fully 60 of the 85 genera have ranges 
that do not fit into the two major categories. The Panamanian limit 
(10° N. Lat.) characterizes only 18 of the genera. The others are 
limited in various ways. The most common limitation in this family 
is restricted altitudinal range for a short latitudinal distance in the 
equatorial Andes. This family is rich in genera of limited distribu- 
tion in the Andes and in the Central American Cordillera. Included 
are genera of very small range at almost every latitudinal belt from 
30° to 40° N. Lat. to 30° to 40° S. Lat. In fact, this family has more 
genera than any other, and most of them are limited in range. No 
other family has so many genera (fully 14) restricted to a south 
latitudinal distributional range or so many (22) restricted to a range 
of less than 10° of latitude. 

In the Brassolidae (Fig. 12), of the four genera not included in the 
panequatorial distributional pattern, two cease their northern range 
at the Panamanian 10° N. Lat. limit, and two are restricted to a 
narrow (10°) range south of the Tropic of Capricorn. 


In the Nymphalidae (Fig. 12-16), 25 of the 70 included genera are 
neither fully panequatorial (38) nor northern (7). The Panamanian 
10° N. Lat. limit disqualifies only 3 genera, Metamorpha, Cybielus, 
and Agrias, from the panequatorial category. Others having narrow 
distribution are Gnathotriche, Lucinia, Peria, Balboneura, Libythinia, 
Batesia, Morpheis, and Caenophlebia with 5° limits; Vila and Poly- 
grapha with 10° limits; Napeodes and Megistanis with 15° limits; 
Haematera, Panacea, Callithea, and Zaretes with 20° limits. Clothilda 
like Kricogonia, has a pan-Caribbean distribution (10°-20° N. Lat.). 

In the Erycinidae (Figs. 16-19), 19 of the included 49 genera are 
neither panequatorial (29) nor northern (1). Ten of the 19 are limited 
in the north by the Panamanian 10° N. Lat. barrier, even though all 
exist at the lowest altitudinal ranges. The others are tropical but 
limited in latitudinal distribution, usually at the lowest altitudinal 

The 15 lycaenid genera (F'ig. 19) are equally divided into the 
three major groups. None seems to be affected particularly by the 
Panamanian 10° N. Lat. barrier. One of the 5 has a 25° equatorial 
range, another 15°, one 10° in the temperate zone of the north, one 
at the higher levels of the southern Andes, and one (Brephidium) in 
the tropics and temperate zones north of 10° N. Lat. 

Altogether 45 genera out of the total of 311 have a distributional 
range that is equatorial save for the 10° N. Lat. limits. This number 
exceeds the combined total (28) of northern genera. Nearly one- 
third (96) of the total genera have ranges that do not fit into the 
normal patterns, largely because the ranges are too limited. Only 4 
genera, Kricogonia, Nathalis, Clothilda, and Brephidium, are both 
tropical and restricted latitudinally north of South America (pan- 
Caribbean). Some genera are restricted to less than 5° latitude, 
mostly in the mountain belt between 30° N. Lat. and 30° S. Lat. 
Exceptional areas of endemism of this sort are: (1) the Mexican 
mountains, especially in the south, (2) the higher parts of the Andes, 
especially in Peru and Bolivia, and (3) the plains of South America 
from 20° to 35° S. Lat. 


Butterflies are directly temperature-controlled (i.e., cold-blooded). 
The larvae are plant feeders. The adults are day fliers, mostly 
dependent on direct solar radiation for flight. These three factors 


appear to be the most significant in controlling the distribution of 

Because they are dependent on the heat of the environment for 
their activity, butterflies become inactive at temperatures below 
freezing. The tropical environment therefore appears to be ideal. 
This is reflected by the facts that 262 of the 311 genera (and species 
groups) are equatorial and that 142 of these occupy the whole, or 
almost the whole, distance from the Tropic of Cancer to the Tropic 
of Capricorn. Adaptation to existence in northern or southern 
latitudes with seasonal cold weather has been attained by members 
of 7 out of 9 of the families in one of two ways: (1) by remaining 
during the cold time of the year in an inactive state (diapause), or 
(2) by migrating out of the area. The former method has been em- 
ployed most successfully by members of 6 families, which thereby 
are enabled to exist in areas of freezing winters. The members of the 
seventh family (Danaidae), without diapause, avoid the hazard 
of cold by migrating into warmer regions each winter. In fact, it is 
not unusual for many species of several families to migrate south- 
ward in winter and northward in summer, especially in areas on the 
fringes of their ranges. 

Most species appear to have a limited range of temperature toler- 
ance. This is obviously narrower for species than for genera, but 
even for most genera it appears from the charted distribution to be 
narrower. Genera adapted for cold climates seem to be unable to 
exist in areas of continuous high temperatures. Their ranges typically 
rise in altitude as they progress southward in the northern latitudes, 
or northward in the southern latitudes. Even the distribution of 
genera appears to be partly controlled by temperature tolerances. For 
example, Colias is cold-adapted and skips over the tropics and sub- 
tropics, whereas Zerene is adapted to subtropical conditions and 
remains below the cold regions (altitudinally and latitudinally) and 
above the hot temperatures (Fig. 4). Other genera occupy the hot 
areas. The species within a genus occupy belts of latitudinal diversi- 
fication. The species of Colias can be arranged in consecutive order 
from those most cold-adapted to those most warm-adapted. The 
most warm-adapted species {Colias enry theme) lacks a diapause and 
depends for its survival in the winter either on migration or on 
resistance to the relatively short winters in the temperate zone. It 
cannot survive in the far north. It migrates northward in the Mis- 


sissippi Valley in summer and southward in winter. The species 
Danais plexippus does so also throughout the whole of its temperate 
zone range. 

Nearly all plant-eating insects develop a high degree of specificity 
in their food habits. One species or race of insect is commonly re- 
stricted to one species or group of plants. Such restrictions naturally 
limit the geographical ranges of the insects to the range of the nec- 
essary plants. These restrictions of temperature or habitat further 
narrow insects to but a portion of that range. The limited ranges of 
many tropical genera, indicated before, are undoubtedly related to 
the distribution of food plants. 

With few exceptions, all butterflies depend on direct solar radia- 
tion for activity. The few exceptions are certain genera of the Brasso- 
lidae Danainae, and Ithomiinae, which fly in the partial shade of the 
tropical forest. A close relationship exists between temperature and 
solar radiation, with regard to the tolerances of certain butterflies. 
These tolerances are controlled even to groups as small as the color 
phases of a single species. For example, the white and orange color 
phases of Colias eury theme have been shown to respond differentially 
to these two environmental factors, which operate in combination 
(higher temperatures partly compensate for lower solar radiation 
and vice versa). 

Areas with little or no direct solar radiation, especially where the 
temperatures are low, do not support butterfly populations. This is 
true in the Aleutian Islands, Iceland, and southwest Chile. 


Distributional maps, or the histograms here shown, give an undue 
impression of permanence. The distributions change in time: over 
many years (as with climatic changes), over one year (annually), 
during part of one year (seasonally), or even daily. 

There is much circumstantial evidence for distributional changes 
in past time. Restriction of colonies of northern species in southern 
mountains with no recent contact suggests a once wider range with 
continuity during a colder period. For example, the population of 
Colias philodice in Guatemala is separated now from its nearest 
relatives by the whole of Mexico; the population of Colias interior 
in the southern Appalachians is separated now from the nearest 
northern stock in the White Mountains of New Hampshire; Colias 


behri is located in the southern Sierra Nevada from its presently 
nearest relative in central Oregon. Many other examples of such 
disjunction could be cited. 

Tropical forms occasionally invade more northern areas, where 
they may stay for a season or two. Extremes of climates are usually 
the limiting factors controlling distributions, but they do not always 
occur annually. Thus colonies can often survive out of their more 
permanent range for several years until an unusual year wipes them 
out. Colias eurytheme periodically invades the colder regions of 
northern Canada where it may survive for a number of generations. 
Then a cold winter kills all individuals. Phoebis periodically invades 
northern areas during the summer and may even survive mild 

Ice age distributions may or may not have been very different 
from what they are now, but great areas were undoubtedly denuded 
of all populations by the glaciers. Such areas are still being repopu- 
lated. Some of the reinvasions from opposite sides of the former 
continental glacier of North America have led to interesting read- 
justments of species relationships. Colias hecla and Colias nastes, for 
example, hybridize in that area to form a third species, not found 
elsewhere. There is often a narrow line of demarcation between two 
species, one that existed south and east of the glacier, and one that 
held out in the unglaciated area to the northwest. For example, in 
Limenitis, the two species astyanax (south) and arthemis (north) now 
narrowly overlap in the Great Lakes area. Similarly, Colias interior 
(south) and Colias palaeno (north) narrowly overlap across central 


Colias eurytheme is absent from the Gulf Coast of the eastern 
United States in summer, since the temperatures there are unsatis- 
factory for its existence. However, it is reestablished by migrants 
from the north in autumn, and passes through two or three genera- 
tions before the hot summers arrive again. In the meantime, cold 
winter weather forces the adults to disappear for a month or two. 

Daily differences in activity and distribution have been indicated 
for the genetically determined color phases of Colias. It is of course 
the selective effect of climate on individuals that determines in a 
broader sense the distribution of species, of genera, and of families. 
The groups are no more important than the individuals of which 
they are composed. 



Genetically speaking, the point of origin of any species, genus, or 
family can be any location inhabited by the genetically aberrant 
individual ancestor. Origins can ordinarily be determined only by 
circumstantial evidence and thus are no more certain than the evi- 
dence used. Inferences on the origin of any group depend on the 
distributional pattern of the group, particularly on its isolation, and 
on the number of forms that have remained isolated in a particular 

It has been seen that for the American butterflies an Old World 
origin can plausibly be postulated for all those types having a 
northern range, as they all have affinities in Eurasia. However, it 
could be proposed with similar plausibility that these forms origi- 
nated in North America and dispersed into Eurasia. Moreover, 
since all these northern types also have affinities in the American 
tropics, it is possible that they originated in the tropics or at least 
from the tropical forms. It seems probable that the tropical forms as 
we know them have originated in the American tropics. The degree 
of differentiation of the New World butterfly fauna from the faunas 
of Eurasia and the African-Australian region increases progressively 
in proportion to the distance from Bering Straits. This suggests long 
and great isolation of the American tropical fauna from the faunas 
of the Old World tropics. Such continuity as exists is only through 
the few northern types. 

Primary origins, whether of the northern or the tropical groups of 
butterflies, can seldom be securely determined, or even plausibly 
suggested. Secondary origins or centers for butterfly types, however, 
are indicated for various regions, including the zones of endemism 
already discussed. In the North American temperate region there 
has been an extensive development of characteristic subgenera in 
such genera as Colias, Argynnis, Melitaea, Oeneis, Satyrus, Pieris, 
Limenitis, Plebejiis, and Glaucopsyche. Colias and Argynnis give 
evidence of other secondary origins in the temperate zones of South 
America. The tremendous development of satyrid genera in the 
Andes is unique, as is the development of a number of genera in 
several families on the Altiplano of Peru and Bolivia. The Caribbean 
region shows relatively little endemism, but four genera are re- 
stricted thereto. 

By analogy and by theory it seems plausible to postulate that 


centers of origin for many species and genera of butterflies have 
often been places where invading species have encountered many 
new, unoccupied habitats, for, it is generally assumed, adaptive 
speciation is rapid and extensive in such places. Such a process has 
probably led to the evolution of the endemic genera of Satyridae in 
the Andes, during the relatively recent grand uplift of the Cordillera. 
A similar basis may be inferred for the development in northern 
regions of new species of Colias, Argynnis, and other genera that 
probably invaded the disturbed lands of North America, some in 
relatively recent time. Such centers of origin are areas where diverse 
genetic types on new arrival have found readily available habitats 
for their occupancy. The trial and error system of natural selection 
probably succeeds best under such conditions. 


Below is a partial compilation of the literature that has provided a 
large part of the data for the present digest. Nearly every paper published 
on American butterflies is important in providing geographical or ecologi- 
cal information. A bibliography such as this cannot, however, list every 
paper seen or read. The author's observations have also been essential in 
providing accuracy on the altitudinal and geographical distributions in 
Alaska, the Northwest Territories, the Yukon Territory, Alberta, and 
British Columbia, the Sierra Nevada, the Rocky Mountains, Mexico, 
Central America, Colombia, and Ecuador. Without these observations, it 
would probable have been impossible to have constructed the histograms. 
Accuracy in the Mexican region is due in large part to the data of Hoff- 
mann. The region poorest known is that of the central to southern Andes, 
in Peru, Bolivia, Argentina, and Chile. Data obtained from collections 
should also be mentioned, even though many of these do not give alti- 
tudinal details. 

Barnes, William, and J. J. McDunnough. 1911-1922. Contributions to the 
Natural History of the Lepidoptera of North America, Vols. 1-5. 
Decatur, 111. 

Bates, Marston. 1935. The butterflies of Cuba. Bull. Museum Comp. Zool. 
Harvard. 78: 61-258. 

Bowman, Kenneth. 1919. Annotated Check List of the Macrolepidoptera of 
Alberta. Alberta Natural History Society, Red Deer, Alberta. With 
revisions 1919, 1920, 1921, 1924, 1928, 1934, 1938, 1944. 

Breyer, Alberto. 1936. Lepidopteros de la Zona del Lago Nahuel Huapi 
Territorio del Rio Negro. Rev. soc. entom. arg., 8: 61-63. 

. 1939. Uber die Argentinischen Pieriden. VII Intern. Kongr. 

Entom., Berlin, 1938: 26-55. 


Brooks, G. Shirley. 1942. A check list of the butterflies of Manitoba. 

Can. Entomologist, 74: 31-36. 
Brown, F. Martin. 1941-43 (continued series). Notes on Ecuadorian 

butterflies. Various journals. 

. 1943-45 (continued). Notes on Mexican butterflies. I-V. 

. 1950. The American Papilios. Lep. Neivs, 4: 39-42; 63-67. 

. 1953. The Papilios of Ecuador. Rev. Ecuatoriana Entomol. y 

Parasitol., 1: 41-60. 
Carpenter, G. D. Hale, and C. B. Lewis. 1943. A collection of Lepidoptera 

from the Cayman Islands. Ann. Carnegie Museum, 29: 371-396. 
Clark, Austin H. 1932. The butterflies of the District of Columbia and 

vicinity. Smithsonian Institution, U. S. Natl. Museum Bull. 157. 
Comstock, John A 1928. Butterflies of California. Los Angeles. 
Comstock, Wm. P. 1944. Insects of Puerto Rico and the Virgin Islands: 

Rhopalocera or butterflies. N. Y. Acad. Sci., 12, Pt. 4: 419-622. 
Davenport, Demorest. 1941. The butterflies of the satyrid genus Coeno- 

nympha. Bull. Museum Comp. Zool. Harvard, 87: 215-349. 
Dillon, Lawrence S. 1948. The tribe Catogrammini. Part 1. The genus 

Catogramma and allies. Reading Museum Sci. Pubis. No. 8. 
Dyar, Harrison G. 1904. The Lepidoptera of the Kootenai District of 

British Columbia. Proc. U. S. Natl. Museum, 27: 779-938. 
. 1914. Report on the Lepidoptera of the Smithsonian Biological 

Survey of the Panama Canal Zone. Proc. U. S. Natl. Mus., 47: 139- 

Edwards, William H. 1868-1897. The Butterflies of North America. Boston 

and New York. 
Elrod, Morton J. 1906. The butterflies of Montana. Univ. Montana Bull. 

30, Biol. Ser. 10. 
Elwes, H. J. 1898. A revision of the genus Erebia. Trans. Entomol. Soc. 

London, 1898: 169-207. 
Field, Wifliam D. 1938. A manual of the butterflies and skippers of 

Kansas. Bull. Univ. Kansas, 39 (12): 1-328. 
Fiske, W. F. 1901. Butterflies of New Hampshire. New Hampshire Col- 
lege Agr. Expt. Sta. Tech. Bull. No. 1. 
Forbes, William T. M. 1945. The genus Phyciodes. Entomol. Americana, 

24: 139-207. 
Fox, Richard M. 1940. A generic review of the Ithomiinae. Trans. Am. 

Entomol. Soc, 66: 161-207. 
. 1947. Ithomiinae of Rancho Grande, Venezuela. Zool., 32: 173- 

Garth, John S. 1935. Butterflies of Yosemite National Park. Bull. South- 
ern Calif. Acad. Sci., 34: 1-39. 
. 1950. Butterflies of Grand Canyon National Park. Grand Canyon, 

Ariz. Nat. Hist. Assoc, Bull. 11. 
Gay, H. 1849. Fauna Chilena. Santiago de Chile. 


Gibson, Arthur. 1920. Report of the Canadian Arctic Expedition 1913-18, 

Vol. 3, Insects: Pt. 1, Lepidoptera. Ottawa, Canada. 
Godman, Frederick D., and Osbert Salvin. 1879-1901. Biologia Centrali- 

Americana. Insecta-Lepidoptera-Rhopalocera. Vols. 1, 2, 3. 
. 1891. in Whymper's Travels among the Great Andes of the Equator, 

Appendix, Lepidoptera, Rhopalocera. 
Grinnell, Joseph, and F. Grinnell, Jr. 1907. Butterflies of the San Ber- 
nardino Mountains, California. /. TV. Y. Entolol. Soc, 15: 37-50. 
Grossbeck, John A. 1917. Insects of Florida. IV. Lepidoptera. Bull. Am. 

Museum Nat. Hist., 37: 1-147. 
Hayward, Kenneth J. 1931. Los Nymphalidoes Argentinos. Rev. Soc. 

entomol. arg, 4 (1-3): 1-199. 
Hoffmann, Carlos C. 1940. Catalogo Sistematico Zoogeografico de los 

Lepidopteros Mexicanos. Primera Parte. Papilionidea. Anales inst. 

hiol. {Univ. nac. Mex.), 11 (2): 639-739. 
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Ecology, 22: 259-284. 
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callippe in California. Am. Naturalist, 77: 400-425. 
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Mus. Hist. Nat., Buenos Aires, 28: 427-520. 
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Trinidad. Trans. Entomol. Soc. London, 1904: 159-228. 
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and Tobago, Port-of-Spain, Trinidad. 

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Mem. Dept. Agr., Trinidad and Tobago. 
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Pubis. Biol, 9: 47-63. 
Longstaff, G. B. 1914. Butterflies of Tobago: On some butterflies of 

Tobago. Reprinted from Trans. Entomol. Soc. London, 1908. 
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Michigan. Occ. Papers Museum Zool. Univ. Mich. No. 54. 
Macy, Ralph W., and Harold H. Shepard. 1941. Butterflies (esp. Min- 
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San Bernardino, Calif. 


Geographic Distribution of 
Contemporary Organisms 


E. Raymond Hall 

The University of Kansas, Lawrence 

W hen a biologist accurately depicts the geo- 
graphic distribution of species of contemporary organisms, he does, 
in a sense, about what the merchant does when he completes an 
inventory of his stock of goods. When the biologist maps also the 
geographic distribution of these same kinds, and also other kinds, of 
organisms of the immediately preceding geological epoch, he does, 
in a sense, what the merchant does when he examines his inventory 
list of a year ago. Paleontology for the biologist and history of stocks 
of goods for the merchant better than almost any other information 
permit the biologist and merchant, respectively, to forecast what lies 

For the biologist who studies evolution and its modus operandi, 
speciation is of major importance because "species" means "kinds," 
and the biologist has to distinguish one kind of organism from all 
others before he can plot the distribution of any one kind. Further- 
more, the biologist must, on the one hand, decide on a subjective 
basis whether a particular morphological ensemble is a species or a 
genus and, on the other hand, on an objective basis whether that 
ensemble is a species or a subspecies. In order to decide on species 
versus subspecies much field work, especially collecting at the right 
places and times, is required. If the two kinds intergrade in nature, 
they are subspecies of a single species. If the two kinds do not any- 
where in nature intergrade, they are two species. 

Therefore, the nontaxonomist should remember when he views a 
reasonably accurate map of the geographic distribution of an or- 
ganism that the map represents several steps along the road to an 
understanding of how evolution occurred in nature. 

From what the speakers showed and told and from what was 
said in the ensuing discussion, I judge that (1) several problems have 
been solved, but that the solution of a particular problem ordinarily 


372 E. R. HALL 

poses new unsolved problems; (2) the geographic distributions of 
many kinds of organisms in the temperate region of North America 
are explained by Quaternary climates — climates of the immediate 
past geologically speaking; and (3) shifts of geographic range now in 
progress are primarily northward. 

On the second point, it seems that the alternation of dry and moist 
periods in the central part of what is now the United States left their 
marks on contemporary organisms. These alternations of climate 
are thought to have been associated with recessions and extensions 
of glaciers in the northern part of North America. There is reason 
to suppose that each of several mammalian stocks now separated 
into two species (eastern and western) formerly ranged as one species 
across the United States from the Atlantic to the Pacific. For ex- 
ample, the Eastern Cottontail of the eastern region that supports 
shrubs and trees and Nuttall's Cottontail of the western region that 
supports shrubs and trees probably owe their existence as separate 
species to a period of aridity, south of the glacial front, so marked 
that the common stock withdrew from most of the region that we 
now designate as the Great Plains. In the now still arid Great Plains, 
albeit less arid than at some times in the past, the two stocks have 
reinvaded the region but only by following the few ribbonlike 
riparian plant associations that extend from west to east across the 
grassy plains. Where the two stocks of cottontails now meet, they 
do not intergrade (crossbreed), having evolved, while separated from 
each other, along different physiological and physical lines. The 
Shrews of the Sorex vagrans group recently reported on by Dr. James 
S. Findley {Univ. Kansas PubL, Mus. Nat. Hist., 9: 1-68, 18 figures, 
December 10, 1955) provide a second example of the effect of a 
period of aridity, in this instance in the Great Basin of the western 
part of the United States. While the two stocks of Sorex vagrans — 
east and west — were separated, evolution did not proceed quite so 
far as in the Cottontails and so the two stocks of shrews crossbreed 
at a few of the places where their geographic ranges ultimately met 
again. At other places they do not crossbreed. Indeed the geographic 
ranges broadly overlap and provide one of the few examples in 
mammals of two subspecies of the same species occurring together 
over a considerable geographic region. 

Incidentally, it seems to me, that the effectiveness of the grass- 
lands of the Great Plains, extending from Mexico to Canada, in 


isolating closely related stocks of land vertebrates from each other 
has seldom been recognized by zoogeographers and certainly has 
not been carefully assessed. 

In illustration of the third point I again draw on the Mammalia. 
Shifts of geographic range now in progress are evident in the Nine- 
banded Armadillo, in the Hispid Cotton Rat, and seemingly in the 
Southern Bog Lemming. The northern margin of the geographic 
range of the Bog Lemming seems to have shifted northward in the 
past 30 years in the eastern part of the Great Plains. In the same 
region in the past 40 years the Armadillo has extended the northern 
margin of its range 75 miles and in the same region and period of time 
the Cotton Rat has done the same thing by moving approximately 
200 miles. 

Pleistocene Ecology and Biogeography of 
North America' 

Paul S. Martin 

Geochronology Laboratories, 
University of Arizona, Tuscan 

Uuring the past ten years, the related fields of 
Pleistocene chronology, biogeography, palynology, and prehistory 
have experienced vigorous growth. This growth may be attributed in 
part to methods of isotope dating, fresh interest in periglacial 
geomorphology, the application of pollen stratigraphy to archaeo- 
logical and chronological problems, and increased appreciation of 
"vertebrate microfossils." Students of animal and plant distribution 
find themselves increasingly committed to archaeological and 
geological data. The information exchange is mutual and poses a 
challenge in interdisciplinary communication. For attempting to 
unify Pleistocene concepts within archaeological, biological, geologi- 
cal, and climatological specialities we are especially indebted to 
Braun (1955), Clark (1952), Deevey (1949, 1953), Flint (1957), 
Frenzel and Troll (1952), and Moreau (1955). In North America 
Dillon's mapping of Pleistocene life zones (1956) has filled something 
of a vacuum in the area of biogeographic reconstruction. 

My present purpose is to identify some of the problems that 
appear important in the terrestrial ecology and biogeography of 
North America during the late Pleistocene. This project follows the 
logical principle advocated by Deevey (1949) that students of 
plant and animal distributions are obligated to consider the Pleisto- 
cene before working backward. To do so does not mean ignoring or 
neglecting the instructive record of Tertiary environment and life. 
The adopted course, however, is based on the belief that Pleistocene 
climatic change was not confined to the glacial border. Until 
proved otherwise, the more useful working hypothesis is that 

' Contribution No. 9 of the Program in Geochronology, University of Arizona. 


376 P. S. MARTIN 

existing range gaps and relict populations date from the Glacial 
period. From the viewpoint of the biologist the foremost events in 
terrestrial ecology of North America during the Pleistocene appear 
to include the following: (1) the climatic sequence proper with its 
attendant displacement of biotic zones; (2) the arrival of prehistoric 
man; (3) the extinction of late Pleistocene vertebrates. To an un- 
unknown degree these events appear interrelated. The first part of 
my analysis is devoted to problems of climatic and environmental 
change, the second to extinction and the effect of man. 


In view of the relatively poor pre-Wisconsin fossil and sedimen- 
tary record, it is expedient to concentrate on the last (Wisconsin) 
glacial sequence. Environmental change during the Wisconsin 
glaciation can be considered subequal to that which accompanied the 
earlier (Nebraskan, Kansan, lUinoian) glaciations. This assumption 
is based on the coincidence of the four glacial drift borders in eastern 
North America, the four equivalent periods of glacial temperature 
drop as recorded in oxygen-isotope analyses of marine foraminifera 
from the equatorial Atlantic (Emiliani, 1955), and the apparent 
sequence of cool and warm mammalian faunas found in unglaciated 
North America (Hibbard, 1958). 

Generally, biogeographers keep abreast of modern findings in 
glacial geology and are not deterred by such views as that of Scharff 
(1912, p. 156) that glacial drift was formed by marine deposition 
and that the climate of the Pleistocene was never colder than at 
present. Admittedly, there is lack of agreement concerning Pleisto- 
cene environment and life in the region where glacial geology pro- 
vides least information, namely in the temperate and tropical zones 
south of the drift border. Braun (1951, p. 145) felt that "... the 
deciduous forest zone, although narrowed, maintained itself on the 
Appalachian Plateaus in southern Ohio and Kentucky while glaciers 
extended southward in Ohio." Thomas (1951, p. 166) followed suit: 
"The distribution and the ecology of many Ohio animals, I believe, 
raises strong presumption that they survived the Wisconsin, or 
perhaps the entire Pleistocene, close to the glacial border; some 
species in refugia within the limits of glaciated territory." Plants in 
question include buckeye (Aesculus octandra), sweet gum {Liqui- 
dambar), Agave, and Magnolia. Animals with distributions that also 


parallel the Wisconsin drift border in Ohio include the fence lizard 
{Sceloporus undulatus), copperhead {Agkistrodon contortrix), and 
upland chorus frog {P seiidacris brachy phono). To date there is no 
sound paleontological support for the postulated ice margin popula- 
tions of temperate biotas. 

On the contrary, evidence of Pleistocene spruce in southern 
Louisiana and spruce and fir pollen in northern Florida and eastern 
Texas seems impeccable (cf. Deevey, 1949; Braun, 1955). The 
interpretation of the evidence, however, is not immediately shown. 
Does it prove the existence of boreal forest at this latitude? Or does 
it reflect an azonal mixture of temperate and boreal floras through- 
out the unglaciated east as Braun (1955) and Drury (1956) main- 
tained? Presently spruce grows near sea level in Connecticut and 
southern Michigan, 400 to 500 miles beyond the southern limit of 
spruce-fir-jack pine boreal forest. The Florida and Texas records of 
boreal elements may also represent marginal populations of species 
whose position of dominance lay farther north. We need not insist 
that fossil spruce meant boreal forest in Texas and Louisiana, but it 
may well represent population outliers of boreal forest occupying 
Kentucky and the Carolinas. 

An area of intense frost action extending 50 to 100 miles south 
of the ice sheet is generally accepted by geologists (Flint, 1957), 
at least for eastern North America. Denny's studies (1951, 1956) of 
periglacial land forms in unglaciated Pennsylvania are relatively 
conservative, Peltier's (1949) more sweeping in their paleoclimatic 
conclusions. Quite recently a series of herb-dominated pollen zones 
have been reported from inorganic sediments in eastern North 
America (Andersen, 1954; Davis, 1957; Deevey, 1951; Leopold, 
1956; Livingstone and Livingstone, 1958; Martin 1958a). I consider 
these findings as palynological confirmation of Full- and Late-glacial 
tundra zones. 

At this point it may be helpful to insert a definition. Within the 
scope of the term tundra I would include the following: (1) treeless 
vegetation in the Arctic; (2) treeless Alpine zones on temperate and 
tropical mountains; (3) pollen zones in Pleistocene sediments featur- 
ing high percentages of herb pollen plus a small amount of spruce 
and other boreal tree pollen. 

There is no question of floristic identity between these communi- 
ties. As an example. Ambrosia, an element in the Late-glacial pollen 

378 p. S. MARTIN 

zones of New England and Michigan, is not found in the Arctic. 
Both Ambrosia and Ephedra, another steppe species in the Late- 
glacial of Europe and America, present the problem of how we might 
distinguish cool prairie from tundra in a pollen diagram. Today these 
vegetation types are separated by a belt of woodland and forest. 
Is it possible that they were in contact during the glacial periods? 

Perhaps the periglacial landscape was not entirely treeless. If 
scattered spruce, larch, or jack pine grew near the ice margin, they 
would have formed a taiga or boreal savanna. Presently the taiga 
lies between boreal forest and treeless tundra (Rousseau, 1952 ; Hare, 
1954). Occasionally pieces of coniferous wood are found in glacial 
drift (Flint, 1957, p. 323). Rather than indicating that forest was 
overridden by ice, they may mean that the glacier swept through a 
taiga type woodland, a more plausible ice-margin environment. The 
relatively well-known and widely discussed Two Creeks "forest" 
bed, silted and covered by Valders ice (Wilson, 1932, 1936) is not an 
exception. In stump diameter, taper, and growth rate the Two 
Creeks trees resemble spruce woodland in central Ungava (see 
Hustich, 1954, for comparative data). In brief, fossil wood is not 
proof of forest ! 

We may expect that Full-glacial tundra, boreal forest, and 
deciduous forest formations were not identical in species composition 
or even in vegetational structure with their present bioclimatic 
analogues. Nevertheless, if there is an adaptive relationship between 
vegetation and climatic zones, it seems unreasonable to postulate an 
azonal system during the glacial period, as Drury has done (1956, 
pp. 80-90). The model proposed by Dansereau (1957), with nar- 
rowed tundra bordering the ice at one point and maple or oak forest 
at others, also does not agree with either the concept of bioclimatic 
gradients or with Late-glacial pollen diagrams. In general the suc- 
cession of pollen zones, tundra -^ boreal forest — » deciduous forest 
in New England and boreal forest — > mixed deciduous forest -^ oak- 
pine forest in North Carolina (Frey, 1953)^ shows, I believe, the 

2 My interpretation of boreal forest in North Carolina is based on Frey's pollen zone 
M2 in Singletary Lake and Jones Lake J-1. This reveals dominance of pine, including 
many small grains, with up to 9% spruce, 7% oak, 1% birch, and 1% hickory. In fair- 
ness to Frey (1953, 1955) it should be noted that, although he regarded his results as 
evidence of climatic change, he does not advance the hypothesis of Boreal Forest in the 
Carolinas. The case I would make for Boreal Forest rests chiefly on the small but crucial 
percentage of spruce and the scarcity or absence of broad-leaved species. 

Another authority on this region, D. R. Whitehead (personal correspondence) takes 
strong exception to such an interpretation of Frey's work, noting: (1) Size-frequency 


historical integrity of generalized vegetation zones. On this convic- 
tion I have attempted to map late Pleistocene vegetation zones in 
two periods (Figs. 2 and 3). They are based on pollen stratigraphy, 
periglacial geomorphology and scattered plant and animal fossil 
records. Presumably, such a map will be of more value to the bio- 
geographer than one based largely on biogeographic evidence that 
leads to a circular argument. If boreal forest replaced temperate 
deciduous forest in the Cumberland Plateau and southern Appala- 
chians, it seems preferable to attempt to establish this fact in terms 
of pollen analysis, buried soils, and other fossil evidence. 

Modern Vegetation Zones (Fig. 1) 

Dansereau (1951) has stressed the importance of structure to the 
geographer and general ecologist, a viewpoint that I believe to be 
profitable also in paleoecology. Reconstruction of forest community 
composition from pollen data is beset with difficulties, for example in 
evaluating relative pollen rain among different wind-pollinated 
species and correcting for underrepresentation of insect-pollinated 
plants. However, it seems possible to determine structure of the 
simplest type, to distinguish forest, savanna, and grassland biochores 
and, within the first, coniferous and deciduous formations (for 
definitions of these and other vegetational concepts, see Dansereau, 
1957). The six major vegetation zones or formations in eastern North 
America include: (1) treeless tundra; (2) boreal woodland or taiga, 
a savanna formation of needle-leaved trees scattered in a shrub and 
lichen mat; (3) boreal forest with a continuous canopy dominated 
by needle-leaved evergreens; (4) temperate forest dominated by 
broad-leaved deciduous trees and shrubs; (5) temperate prairie and 
savanna; (6) subtropical savanna of evergreen sclerophylls and tall 
grasses. These six zones represent arbitrary divisions of an adaptive 
gradient controlled in general, if not always in detail, by climate. Is 
it unreasonable to assume that this gradient maintained its struc- 
tural features and sequence during the glacial periods? 

features have not been worked out carefully for all the species of pine which are, or 
might be, expected in this area. Thus the allocation of small grains to the boreal species 
P. bankesiana is premature. (2) Zone M2 from Frey's core LS-2 contains fairly high 
percentages of oak (about 15%) and hickory (about 10%) as well as some pollen of 
Taxodium, Nyssa, and other temperate elements. (3) The predominance of pine might 
be the result of "over-representation" of a species such as P. serolina, which surrounds 
boggy sites in the southeast today. In other words, oak, hickory, and associated tem- 
perate plants occurred at sites some distance from the bay lakes but were "swamped- 
out" by the well-known heavy rain of pine pollen. 



Fig. 1. Vegetation zones of eastern North America. Small, isolated 
mountain-top populations of boreal forest in parts of the Appalachians 
are not shown. The southeastern pine forests are considered part of the 
deciduous forest formation in a broad sense. Taiga is mapped on the 
basis of its savanna-like structure; floristically it is not very different 
from boreal forest. P = prairie. 

Full-Glacial (Fig. 2) 

Of utmost importance to the student of animal and plant distri- 
butions is the extent of Full-glacial biotic displacement. Following 
Flint we may date this period as ending roughly 17,000 years ago. 
In New Mexico the San Augustin Plains, 7,000 feet in elevation, 
were occupied by forest with a spruce pollen frequency of 20% 
(Clisby and Sears, 1956). In Postglacial time the spruce has dis- 
appeared and non-arboreal species have become more important. 

In eastern North America there are only two radiocarbon-dated 
pollen diagrams that may represent pollen sedimentation of the 
Full-glacial period. From a piedmont marsh in unglaciated Pennsyl- 
vania the peak in non-arboreal pollen lies 80 cm below a radiocarbon 
date of 13,500 B. P. (Martin, 1958a). Apparently the formation of 


Pennsylvania piedmont swale marshes 50 miles beyond the ice 
margin dates from the Full-glacial period and coincides with a 
tundra-taiga vegetation of grasses, sedges, other non-arboreal 
species, and scattered spruce and jack pine. 

A longer late Pleistocene pollen sequence, perhaps extending 
back into the middle Pleistocene, has been found in the Carolina Bay 
lakes (Frey, 1951, 1953, 1955). Possibly rebedding and truncation 
have occurred (Wells and Boyce, 1953; Frey, 1955). If the upper 10 
feet of Frey's sequence is continuous, his zones Ml, M2, and MS 
should correspond to the Full-glacial period. In these pollen zones 
oak and other deciduous trees are scarce or absent; pine predomi- 
nates with a high frequency of small-sized grains suggesting Pinus 
banksiana. There is a low but constant frequency of spruce. In terms 
of structure, the M zones indicate boreal, needle-leaved forest, with 
dominance of jack pine attributable to its well-known preference 
for sandy situations. 

The local records of spruce pollen in Texas, Florida, and Louisiana 
are undated and, except for Potzger and Tharp's work (1947, 1954), 
unaccompanied by detailed stratigraphic study. If maximum dis- 
placement is represented, the difference between Full-glacial and 
present southern limits of marginal spruce populations would seem 
to be the same as the corresponding past and present southern limits 
of the boreal forest formation, that is, 800 miles. 

Some type of mixed deciduous forest occupied the extreme south, 
with subtropical vegetation largely driven from Florida. Further 
discussion of Florida awaits expansion of the pollen studies begun 
by Wilson (Davis, 1946). 

Certain periglacial land forms including boulder fields, colluvial 
soil mantles, and various types of patterned ground constitute rea- 
sonably secure evidence of climatic change. Others, such as loess, 
are apparently less reliable indicators of ice-margin conditions 
(Hack, 1953; Dylik, 1954). Uncritical identification of all "peri- 
glacial" features with a Full- or Late-glacial tundra climate is to be 
avoided. A few of these features can form at midlatitudes today. 
Yehle (1954) described soil tongues similar to periglacial frost cracks 
appearing in calcareous soils under the present climate. Goodlett 
(1954) reported patterned ground in miniature appearing on bare 
earth in central Pennsylvania. Recent colluvial creep and earthflows 

382 p. S. MARTIN 

in the unglaciated Appalachian Plateaus "... appear to be most 
common in pastures, but field and woodland areas are not entirely 
free from such movements" (Sharpe and Dosch, 1942). 

Wolfe's description (1953) of frost-thaw basins and related peri- 
glacial features in unglaciated New Jersey has been subjected to 
certain criticism. Yehle (1954) questioned the authenticity of the 
alleged frost cracks. Rasmussen (1953) and Deevey (1957) noted 
that basins of rather similar appearance occur in the Carolinas and 
coastal Texas, beyond the limit of possible periglacial frost action. 
However, the involutions and ventifacts which Wolfe described 
would appear to remain sound evidence of a periglacial tundra 

Farther south, in the latitude of Washington, D.C., Hack (1955) 
and Nikiforoff (1955) found little geomorphological indication of a 
"periglacial climate," beyond stabilized dunes and a soil hard pan of 
uncertain origin. For this reason, I have included this area within 
the Boreal Forest (Fig. 3). 

In the Appalachians the block fields or stone streams (Flint, 1957) 
and glades including "bear wallows" may mark the lower limit of 
Full-glacial alpine tundra (Braun, 1955; Martin, 1958a). Cranberry 
Glades in West Virginia at 3,350 feet (Darlington, 1943) is perhaps 
the best known of the anomalous glade bogs; Core (1949) discussed 
others. In the Smoky Mountains inactive block fields covered with 
mosses and ferns and occasional yellow birch trees extend down to 
at least 4,500 feet. Braun (1955, p. 361) believed that they indicate a 
vertical tree line depression of 2,000 feet. It seems the present 
regional tree line does not lie at the top of the peaks as Braun im- 
plies. Spruce and fir grow as forest at 6,500 feet, the top of the 
Smokies (Whittaker, 1956). I would allow an additional 2,000 feet 
for subalpine taiga and "krumholtz" and locate the theoretical 
present alpine zone at 8,500 feet. This would bring the relative 
depression of the Alpine Zone in eastern North America into line 
with that observed at the same latitude in the west, 4,000 to 4,500 
feet (Antevs, 1954). In either case the distribution of glade bogs and 
inactive block fields reveals that a Full-glacial treeless zone extended 
down into the Great Smokies. 

To the south of the region of a periglacial treeless zone we might 
expect buried organic soils, fossilized "string bogs," or organic ter- 
rain of the type that typifies subarctic taiga and boreal forest (Drury, 



1956). Drury (pp. 86-87) believed that fossil peat and muck deposits 
resembling those of Alaska are absent from the unglaciated east. It 
would appear, however, that serious search for ancient boreal forest 
landforms has not been made in the latitude formerly occupied by 
this vegetation type (Fig. 2). The famous buried soil of Spartans- 
burg, South Carolina (Cain, 1944), might possibly represent such a 

BOREAL FORES T ^f^fii^ 2 p 

18,000 B.P. 


1. Marsh, Po. 

2. Slngletory Lake, N,C. 

Fig. 2. Vegetation zones during the Full-glacial of the late Wisconsin. 
Tundra and taiga are mapped as a single zone with no attempt to dis- 
tinguish them. Shelf exposure following sea level depression permitted 
some extension of vegetation beyond the present coast line. 

feature, lying at the southern margin of the Full-glacial boreal forest. 
In addition to some hickory and oak these soils contain high per- 
centages of spruce, jack pine, and fir pollen. ^ 

Vertebrate fossils may provide some independent support to the 
existence of a narrow Full-glacial tundra zone. While uncritical ac- 
ceptance of large mammals as climatic indicators is to be avoided, 

' D. R. Whitehead (personal correspondence) is presently analyzing pollen from these 
soils and thinks that they are more likely Interglacial than Full-glacial. He reports 
finding less spruce and fir than Cain (1944) encountered. 

384 P. S. MARTIN 

the fossil distribution of Ovibos (see map of Kitts, 1953) fits the Full- 
glacial tundra zone fairly well. The barren ground caribou, Rangifer 
arcticus, is reported from late Pleistocene deposits and its Full- 
glacial range should be roughly similar to that of Ovibos. Apparently 
the Postglacial distribution of these species has been so modified by 
both prehistoric and modern man that their value as tundra indi- 
cators is uncertain. 

Rather than in eastern North America, the main Full-glacial 
refugia for tundra mammals and birds (Rand, 1948) lay in ungla- 
ciated Alaska. The tundra lemmings, Dicrostonyx and Lemmus, have 
not been found as fossils south of the ice sheet. The present range of 
the Peary Caribou, Rangifer ardicus pearyi, in northern Greenland 
and Ellesmere Land dramatizes the ability of caribou to survive at 
high latitudes under existing glacial conditions. It is barely possible 
that cyclonic nourishment of the Laurentian ice sheet in central 
Canada was accompanied by very low precipitation and sufficient 
ablation to expose the northern part of Greenland and the Arctic 
Islands. Mercer (1956) indicates ice of uncertain depth, but evidently 
not very thick, on Baffin Island in the glacial period. The evidence 
that Banks Island was largely unglaciated (Manning, 1956) adds 
support to the concept of local, restricted glacial activity in the 
Arctic during the Full-glacial of the Wisconsin, and of earlier periods. 

The poverty of mammalian biotypes in the tundra of north- 
eastern Canada compared with northwestern Canada and Alaska is 
noteworthy. Tundra species of the northwest include Sorex timdren- 
sis, Citellus undulatus parryi, Clethrionomys ruHlus, Microtus 
oeconomicus, and M. micrus. These lack vicariants in eastern Canada. 
A faunal parallel to Hulten's Beringia rejiigium for the Arctic flora 
seems obvious. 

Late-Glacial (Fig. 3) 

It is sobering to recall that pollen evidence of a North American 
tundra dates back no farther than Deevey's study of Aroostook 
County in northern Aiaine (1951). Since then, Livingstone and 
Livingstone (1958) have confirmed Deevey's tentative recognition 
of an Allerod type sequence and, by a radiocarbon date of basal 
organic material, have shown that it was indeed contemporaneous 
with the Lower Dryas-Allerod-Upper Dryas period in Europe. The 
subsequent history of Late-glacial tundra, presumably moving 



rapidly into central Canada during the Post-glacial period, remains 
a mystery. 

Although they document changes in forest composition, Potzger 
and Courtemanche's Quebec profiles (1956) fail to throw much light 
on this problem. How was the glaciated portion of the Arctic re- 

Fig. 3. Vegetation zones during the Valders readvance. Tundra and 
taiga are not distinguished; the tundra may have been absent west of the 
Appalachians. Gillis Lake, Nova Scotia, within the tundra-taiga zone at 
this time (Livingstone and Livingstone, 1958), is not shown. Horizontal 
ruling marks Lake Agassiz and the proglacial Great Lakes. East of Michi- 
gan the position of the Valders drift border is uncertain. P = prairie. 

populated? For the present it may be wise to avoid the issue, noting 
simply that it is unnecessary to assume a direct continuity of tundra 
from mid-latitudes to high latitudes. If the last ice to stagnate and 
melt was the Laurentian sheet, it may have "trapped" the retreating 
Late-glacial tundra in southern Quebec during deglaciation of 
northern Quebec, and permitted tundra plants to invade north- 
eastern Canada from the partly unglaciated Arctic Archipelago. 
In eastern L^^nited States the Late-glacial, from 17,000 to 10,200 

386 p. S. MARTIN 

B.P., represented a period of stagnation and retreat, with several 
climatic reversals and readvances of ice. Pollen records are still 
scattered, and dated diagrams are not as abundant as we might 
wish. However, they begin to approach in detail those available for 
Postglacial time. The stratigraphic break between the Postglacial 
and Late-glacial, which generally marks a rise in organic sedimenta- 
tion, is a convenient level for a radiocarbon date. Partly for this 
reason, I have found it possible to assemble sufficient dated pollen 
horizons to attempt a vegetation map for the end of the Late-glacial 
during the Valders readvance. Even though ice returned to central 
Michigan, considerable climatic improvement is indicated over the 
Full-glacial conditions. In northern New England Deevey's dis- 
covery of Valders tundra is confirmed by Livingstone (see Table I). 
C^^ dating of pollen zone A-4 in Connecticut indicates the presence 
of boreal forest rather than taiga or tundra. The Valders readvance 
did not affect radically the forests of southern New England. 

Mixed hardwoods and conifers, including spruce, occupied Glade 
Bog (2,700 feet) in Tennessee (Johnson, personal correspondence). 
Pine-spruce-birch-hemlock dominated the Cranberry Glades of West 
Virginia (3,400 feet). Alpine tundra had retreated or perhaps en- 
tirely disappeared from the southern Appalachians. Small ice fields, 
almost certainly surrounded by tundra, excavated circs in the 
Catskills, Adirondacks, and other high mountains of New England 
(Manley, 1955). Perhaps of greatest interest is the evidence from 
pollen studies that mixed deciduous forest had replaced the pine- 
spruce forest of the Carolina Coastal Plain (Frey, 1953). The Valders 
forests of that area supported mesophytes such as beech and hem- 
lock, temperate species no longer part of the regional pollen rain. 

West of the Appalachians the situation is less clear. Andersen 
(1954) considered a typical Late-glacial profile from the George 
Reserve in southern Michigan to be of Younger Dryas age (Valders 
as currently understood in North America). However, if the C^^ dates 
from the George Reserve (M-223, M-224, each 11,450±600 B.P.) 
are from the same core as was used in Andersen's study, his NAP 
zone is older. Possibly it represents the Older Dryas (Port Huron) 
period. Andersen presented a thoughtful and skilled analysis of the 
problem of "rebedded" and "redeposited" pollen in Late-glacial 
sediments and made a strong case for allochthonous origin of such 
temperate genera as oak, sweet gum, and ash. The regional pollen 




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388 P. S. MARTIN 

rain represented in the George Reserve clay is predominantly of 
spruce, various sedges, and grasses. With an NAP pollen sum not 
exceeding 40%, it appears that the vegetation may have been a taiga 
rather than a treeless tundra. For my immediate purpose, which is 
to map vegetation zones during the Valders maximum, it seems best 
to withold judgment on the age equivalent of Andersen's profile. It 
does tell us that there was a taiga-tundra period during deglaciation 
of Michigan. 

Pollen studies of Potzger (Zumberge and Potzger, 1956) reveal 
Postglacial events in the Michigan basin and interrelate shifts in 
vegetation with changes in lake levels. Potzger failed to encounter 
any indication of tundra or taiga conditions during the period that 
he felt should have represented the Valders readvance. In this re- 
gard his results agree with those of Davis, Leopold, and others in 
southern New England. Unfortunately, confidence in Potzger's 
sequence is considerably undermined by his consistent failure to 
recognize such pollen zones in any of his numerous studies through- 
out eastern North America. His rock-flour samples from the inor- 
ganic sediments underlying lake gyttja from Hartford Bog indicated 
no appreciable NAP pollen sum. Elsewhere in both Europe and 
America inorganic sediments of Late-glacial age generally mark 
zones of abundant herb pollen, such as Andersen encountered at the 
George Reserve. LInless Potzger's results are confirmed, I assume 
that the rock-flour levels in Hartford Bog record a tundra ortaiga 
phase in the vegetational history of southern Michigan. 

The inconclusive results of both Andersen and Potzger provide 
poor material for attempting to locate formation boundaries during 
the Valders readvance. In extending the zone of taiga-tundra on Fig. 
3 south through southern Michigan I have assumed that the pro- 
glacial Great Lakes reenforced the periglacial climatic influence of 
the Valder's ice sheet producing a poor environment for growth of 
forest. This judgment may be only slightly less arbitrary than my 
location of the boundaries of boreal forest and temperate deciduous 
forest in this region. West of the Appalachians there is no paleo- 
ecological record definitely of Valders age to assist in locating these 


Beyond refinements in chronology and mounting evidence of a 
very close correspondence between climatic events in the New and 


Old World (Deevey and Flint, 1957), little has been added to the 
Postglacial pollen sequence summarized by Deevey in 1949. The 
Hypsithermal, also known as Thermal Maximum, Xerothermic, 
Altithermal, etc., extended with intermittent pulsations from 9,500 
to 2,000 years ago (Deevey and Flint, 1957). It is the most important 
climatic event of the period. Documentation of the classic Midwest 
Prairie Peninsula extension continues with Smith's recent valuable 
analysis of terrestrial vertebrates (1957). In addition to mapping 
relict outposts of prairie animals. Smith showed that it is possible 
to interpret anomalous and otherwise confusing splits in subspecific 
populations in terms of post-Xerothermic isolation. Instructive 
examples are found in Agkistrodon contortrix (copperhead), Natrix 
erythrogasler (copper-bellied water snake), Diadophis punctatus, and 
Opheodrys vernalis. In a bold and original interpretation Smith 
explained the history of the Pseudacris nigrita (chorus frog) complex 
in terms of invasion of P. n. feriarum, the eastern, forest-inhabiting 
race, by P. n. triseriata, a grasslands form from the west. Post- 
Xerothermic isolation left a segment of P. n. triseriata, recently de- 
scribed as P. n. kalmi, in New Jersey and the Delmarva Peninsula. 
Thus on both sides of the Appalachians separate, isolated, popula- 
tions of triseriata type chorus frogs integrate wnth feriarum. 

Postglacial pollen diagrams indicate Thermal Maximum (C-2 
pollen zone) shifts in species composition, with an increase in oak 
and hickory in southern New England and, locally, of hemlock in 
northern New England. In many diagrams a recovery of spruce 
follows in C-3. During the Thermal Maximum Whittaker (1956, p. 
60) believed that spruce and fir were pinched off the tops of certain 
mountains in the Smokies. Displacement upward of 1,000 feet or 
more is indicated by absence of these trees in presumably suitable 
sites on peaks of less than 5,500 feet elevation. 

Thermal Maximum changes, which command attention of the 
student of community composition, the evolutionist, and the bio- 
geographer, were inappreciable in terms of the plant formations 
mapped in Fig. 1. They do not justify an attempt at a separate 
vegetation map. 

Western United States, Mexico, and the Tropics 

Exclusion from Figs. 1-3 does not imply that these areas escaped 
considerable late Pleistocene climatic and environmental change. 
For the present, however, it seems impossible to express this effec- 

390 p. S. MARTIN 

tively on a Pleistocene vegetation map, unless one relies largely on 
biogeographic data as Dillon (1956) has done. Topographic com- 
plexity inevitably leads to considerable difficulties in large-scale 
mapping of vegetation. Twelve major units on Leopold's very use- 
ful vegetation map of Mexico (1950) suggest something of the 

Paleobotanical study of the Willow Creek flora of Santa Cruz 
Island, California, revealed a latitudinal shift in Pseiidotsuga, 
Cupressus, and Pinus of perhaps 440 miles, less than the 800 miles of 
zonal displacement in eastern North America (Chancy and Mason, 
1934). Studies of late Pleistocene fossil birds indicate an even less 
drastic shift. "The avifaunas of the Carpinteria asphalt and of some 
of the Pleistocene caves of northern and central California (Miller, 
1937, 1939) indicate that the boreal avifauna extended 200 miles 
farther south along the coast, at least, and 1,000 feet lower on the 
interior mountains. Possibly even more extreme extensions occurred 
in other parts of the Pleistocene" (Miller, 1951, p. 610). The latter 
comment is crucial; either the Carpinteria and other Pleistocene 
cave faunas are not of Full-glacial age or the avifaunal displacement 
is discordant with that represented by the Willow-Creek flora. 
Actually, neither deposit may represent maximum displacement of 
the coldest period. 

The same logic can be directed toward the Rancholabrean biota of 
the famous tar pits. While the living representatives of this assem- 
blage typify environments subequal to those found today in the Los 
Angeles basin (summary in Schultz, 1938), the spectacular finds of 
extinct animals stamp the assemblage as late Pleistocene. In the 
absence of C" dating or other absolute age estimate, it is futile to 
urge any bioclimatic theory relating the Rancholabrean biota to 
Pleistocene chronology. However, one suspects that certain bio- 
geographers have assumed that the fauna is of Full-glacial age and 
that it proves lack of climatic change at this latitude. Assumptions 
about the cause of large-mammal extinction in this biota, as in 
others, may be intertwined with climatic inference. In view of the 
results of isotope dating of similar late Pleistocene faunas, it seems 
we may anticipate an age postdating the Wisconsin maximum for the 
Rancholabrean fauna. 

Except for Clisby and Sears' work in New Mexico, late Pleisto- 
cene pollen studies have been confined to the Pacific Northwest and 


Alaska (Hansen, 1947, 1953; Heusser, 1953, 1955). They have de- 
veloped a sequence that parallels the Postglacial pollen zones of 
eastern North America. Hansen (1947) found a rise in grass- 
chenopod-composite pollen in south central Oregon in the Thermal 
Maximum. Apparently, grassland habitats replaced forest along the 
prairie-woodland border. Elsewhere in the west, archaeological cave 
sites and pluvial lake beds of the Great Basin promise much to the 
pollen analyst. Radiocarbon dating of lake sediments may be the 
most profitable means of correlating pluvial and glacial events, and 
radiocarbon dates of Searles Lake in southern California confirm a 
direct relationship between Great Basin pluvial lakes and the classic 
Wisconsin sequence (Flint, 1957, p. 232). To the ornithologist this 
should signify abundant and highly productive aquatic environ- 
ments at a time when glacial ice covered most of the present breed- 
ing grounds of waterfowl and scolopacid shore birds. , 

An original analysis was made by Antevs (1954) of zonal dis- 
placement in New Mexico during the Wisconsin. Snowline depres- 
sion, the hydrography of pluvial Lake Estancia, and the former 
distribution of Marmota indicate a lowering of life zones in New 
Mexico on the order of 4,000 to 4,500 feet. The yellow-bellied 
marmot is reported from Basket-maker burials at 7,000 feet in 
northeastern Arizona (Lange, 1956). This, and its distribution in 
grassland of Utah at 4,500 feet, make it a less reliable Pleistocene 
thermometer than Antevs (1954), Stearns (1942), and Murray 
(1957) have assumed. Nevertheless, the vertical displacement of 
snowline and, apparently, of treeline (Martin, 1958b) seems to 
require a major shift in montane vegetation gradients. 

Spruce (Picea) should be an ideal indicator of temperature change 
in the Southwest and should afford some biological control on the 
geological evidence of climatic change. Clisby and Sears' pollen 
study of the San Augustin plains (1956) indicated Full-glacial spread 
of spruce through central New Mexico at 7,000 feet, with a maxi- 
mum frequency of 40%, sometime before 27,000 B.P. During the 
Pleistocene, almost certainly in the Wisconsin, spruce reached the 
Valley of Mexico (Sears et al., 1955). To enter the Mexican Plateau, 
spruce, and any associated boreal animals and plants, had to descend 
to lower elevation. The lowest point on the Continental Divide be- 
tween the Rockies and the Sierra Madre lies at about 4,500 feet in 
southern New Mexico. In the adjacent Chiricahua Mountains spruce 

392 P. S. MARTIN 

is found today in narrow, northerly ravines at 8,500 feet. These 
outposts are in extremely favorable microhabitats, and vertical 
displacement from a sheltered north slope at 8,500 feet to a level 
site at 4,500 feet would require climatic change of greater magnitude 
than the temperature depression encountered between these points 
(average lapse rate of 0.6° C per 100 meters or a total drop of 7.2° C.) 

Mysteriously, spruce disappeared south of Chihuahua, Mexico, 
in Postglacial time. Subalpine conifers immediately below treeline at 
10,000 to 12,000 feet in the transverse volcanic belt of the Mexican 
Plateau include Pinus hartwegii, Abies, and Cupressus. Superficially, 
these boreal montane forests appear quite suitable for Picea, and 
more than one biologist has referred to them casually as "spruce- 

The best record on climatic change in Mexico comes from the 
sedimentary studies of Sears et al. (1955) and Hutchinson et al. 
(1956). They demonstrate important climatic fluctuations. How- 
ever, the correlation of moist climatic intervals in Mexico with 
Cordilleran glacial advances (i.e., Flint, 1957, p. 233) is considerably 
less secure than Glacio-pluvial correlations in western North Amer- 
ica. Biogeographical evidence and climatological theory raise the 
possibility that Postglacial pluvial periods in the Mexican Plateau 
are negatively correlated with minor glacial advances at high latitudes 
(Martin and Harrell, 1957). In the Thermal Maximum there is no 
sound evidence of drought in the Plateau. 

The presence of Pleistocene spruce in the Valley of Mexico, the 
biogeography of relict montane plant formations such as Cloud 
Forest (see below), glacial circ depression on A/Iexican volcanoes 
(White, 1956), Chirripo in Costa Rica (Weyl, 1955), and other 
tropical mountains above 13,000 feet makes it convenient to infer 
climatic cooling at low latitudes during the glacial period. The 
presence of an extensive North American ice sheet would, however, 
eliminate the present high-pressure system which brings summer 
cyclones to Mexico and the Southwest (J. E. McDonald, personal 
communication) and one wonders if winter Pacific storms would be 
shifted sufficiently to produce truly pluvial conditions in the Valley 
of Mexico in the Full-glacial period. Sears et al. (1955, p. 525) inter- 
preted their Mexican diagrams as climatic oscillations of moist-warm 
and dry-uncertain, the latter representing the Wisconsin glaciation. 

Within Mexico and Central America some of the strongest indi- 


cations of climatic change are found in plant-animal distribution in 
fragmented and isolated habitats such as the Cloud Forest. Griscom 
(1932, 1950) noted rather remarkable uniformity from northern 
South America to Mexico in bird life of the Subtropical Life Zone, 
which includes Cloud Forest. This habitat generally appears on 
windward slopes between 3,000 and 7,000 feet elevation. To account 
for the faunal uniformity Griscom (1932) postulated Pleistocene 
continuity of the Subtropical Zone, the result of its depression to 
sea level. It displaced the lowland tropical fauna which withdrew 

Stuart (1951, p. 32) noted that the present range of montane 
lizards and other temperate animals on either side of the Isthmus of 
Tehuan tepee (e.g., Barisia and Sceloporus malachiticiis) indicated a 
past cool corridor across the arid lowlands. But Stuart questioned 
the displacement of lowland Tropical Rainforest, which Griscom 
(1950, p. 358) located far south of its present limit in the period of 
extreme Pleistocene glaciation. "... a descent to sea level of a sub- 
tropical zone would have brought about either widespread exter- 
mination of the tropical fauna or acclimatization of that fauna to 
subtropical conditions. . . . The evidence, therefore, points to the 
presence of a [lowland] tropical environment in northern Central 
America even at the height of Pleistocene glaciation" (Stuart, 1951, 
p. 29). It seems we must have the argument both ways, altitudinal 
depression of subtropical conditions to achieve some continuity of 
Cloud Forest through Middle America from Mexico to Colombia, 
but with persistence as far north as Mexico of Arid-Tropical scrub 
and Tropical Rainforest. Actually, 3,000 feet may be too rigid a lower 
altitudinal limit for marginal populations of Cloud Forest species. 
Under extremely humid conditions subtropical animals may descend 
to 2,000 or 1,000 feet (Wetmore, 1943, p. 223). 

The nature of Cloud Forest vegetation, avifauna, and biogeog- 
raphy in tropical America is under study by B. E. Harrell (1951). 
Marshall's exemplary analysis (1957) of Mexican oak-pine wood land 
also illustrates the biogeographic advantage of studying environ- 
mental rather than political units. 

A brief summary of environmental changes in western North 
America and Central America during the late Pleistocene would 
include the following points: (1) direct correlation between glacial 
conditions in the Cordilleras and the growth of pluvial lakes in the 

394 p. S. MARTIN 

Great Basin; (2) coincidence of the Thermal Maximum in eastern 
and western North America; (3) very doubtful correlation of Glacio- 
pluvial conditions in the subtropical latitudes and a negative correla- 
tion, controlled by summer cyclones, in Post-glacial time; (4) 4,000 
to 4,500 feet displacement of biotic zones in the Southwest during 
the Full-glacial period ; (5) displacement of tropical zones by perhaps 
3,000 feet in the Pleistocene, exact time unknown, but possibly 
during the Glacial maximum. 


The foregoing cursory analysis of late Pleistocene environments 
is intended to clear the ground for a brief review of two events that 
stand foremost in Pleistocene ecology and paleontology. The im- 
portance of these events to students of modern biogeography is not 
immediately obvious and is often ignored. However, both the ar- 
rival of prehistoric man and the extinction of late Pleistocene ani- 
mals pose major biogeographic, as well as paleontological, problems. 

Man's arrival in the New World is a matter of continuing con- 
troversy. Fluted points, once associated mainly with early man in 
western North America, are appearing in many parts of the east. 
They confirm much older evidence of early man, evidence dis- 
counted during the Hrdlicka period of skepticism regarding Pleisto- 
cene man in the New World. The Schoop site in Pennsylvania 
(Witthoft, 1952), the Quad site in Alabama (Soday, 1954), fluted 
points in Michigan (Quimby, 1958), in North Carolina, and an 
apparent Late-glacial flint industry in the Manitoulin Islands (Lee, 
1957) point to the presence of early man in Late-glacial as well as 
early Postglacial time in the eastern United States. Quimby (1958) 
related the geochronology of the Lake Michigan basin to archaeologi- 
cal discoveries and infers an association of spruce-fir forest, masto- 
dons, and fluted points from about 10,000 to 7,500 B.C. Williams 
(1957) extended the latter to a more recent date, indicating no 
obligate relationship between mastodons and spruce-fir. 

The biologist who may wish to review the impressive archaeologi- 
cal record of early man will profit by consulting Wormington's 
excellent book (1957) and Sellards' equally readable account (1952). 
Early man is not invariably associated with fluted points; the old 
desert cultures such as those at Danger Cave in LTtah (Jennings, 
1957) and at Frightful Cave in Coahuila (Taylor, 1956) represent 


hunting-gathering people who did not prey on large animals. Fluted 
points may be an independent New World invention ; they have not 
been found with paleohthic sites in Siberia (Wormington, 1957). 

In South America early man had arrived at least by early Post- 
glacial time as is demonstrated by the well-known association of 
man and sloth at Palli Aiki Cave, Chile. Cruxent and Rouse (1956) 
and Rouse and Cruxent (1957) report Paleo-Indian sites in northern 

From the biological viewpoint it does not seem necessary to enter 
the Interglacial man controversy. If the Tule Spring site, Nevada, is 
correctly dated at older than 23,800 years, it clearly indicates that 
prehistoric man arrived before the Wisconsin maximum of 17,000 
years ago. Presumably this would require arrival in Alaska, at least 
by early post-Sangamon time, of a people whose economy was 
specialized for hunting large animals in treeless tundra. It seems 
easier to establish a trans-Bering population in southern Alaska 
than to understand how, during the Wisconsin glacial period, such a 
population spread south through what is mapped as glaciated 

For the ecologist and biogeographer one point remains clear. 
From the time of man's arrival we may assume a radical change in 
fire frequency. In the strict sense, theoretical climatic climax vegeta- 
tion in savanna and grassland areas (Stewart, 1951, p. 319), and 
even in parts of the Eastern Deciduous Forest, cannot postdate 
man's arrival. In addition to savannas many areas of temperate 
forest may have been greatly modified and subcHmax, consolidation, 
or even pioneer species favored at the expense of those typical 
only of climax positions in plant succession. The paleoecological 
dilemma posed by the B zone pine pollen period (Dansereau, 1953) 
may be resolved in terms of an archaeological disclimax controlled by 
early man. There is no longer much doubt about his presence in the 
East at that time. 


In the words of Darwin : " It is impossible to reflect on the changed 
state of the American continent without the deepest astonishment. 
Formerly it must have swarmed with great monsters; now we find 
mere pigmies, compared with the antecedent allied races." {Voyage 
of the Beagle, 1855, p. 222). In the hundred years since Darwin wrote, 

396 P. S. MARTIN 

discoveries in both prehistory and paleontology have enriched 
considerably our knowledge of late Pleistocene fauna. Radiocarbon 
dates (Fig. 4, Table II) confirm the fact, evident to Darwin and 
Lyell, that extinction was mainly a Postglacial event. South of 
Alaska there is abundant proof that the time of maximum glaciation 
preceded most New World extinction. 

Despite these refinements, the extinction of large mammals in 
continental North and South America and of small mammals in the 
West Indies has been a major unsolved problem, one certainly not 
inappropriate in a symposium dedicated to such matters. Until the 
cause or causes of extinction are understood, biogeographic and 
ecological interpretations based on the assumption that all fossil 
mammalian records are of paleoclimatic significance may be overly 
bold, if not entirely erroneous. Specifically, I would question paleo- 
climatic deductions based on fossil records of Marmota and Cervus 
in northeastern Mexico, Erethizon (porcupine) and Hydrochoerus 
(capybara) in the Melbourne beds of Florida, "musk-ox-like" 
genera in New Mexico and Mexico, and Tapirus in Arizona (Haury 
et al., 1950) and Pennsylvania. Strict application of the uniformi- 
tarian doctrine is to be avoided in each case ; no responsible ecologist 
would insist that modern tapir habitat, Tropical Rainforest and 
Cloud Forest, extended into southern Arizona or eastern Pennsyl- 
vania in the late Pleistocene. 

As Darwin stressed in The Origin of Species, extinction is the 
inevitable consequence of evolution and in itself will occasion no 
surprise. Through the Cenozoic equid genera disappear; Hyra- 
cotherium and others in the Eocene; Mesohippiis in the Oligocene; 
Miohippus, Parahippus, and others in the Miocene; Calippus, 
Hipparion, etc., in the Pliocene; and Nannippus and Plesippiis in 
the early Pleistocene. They represent a record of replacement by 
morphologically modified and adaptively improved types of horses. 
In the late Pleistocene the extinction of North American Equus 
and South American Equus and Hippidium is not an equivalent 
event for it constitutes extinction without replacement. For perhaps 
3,000 to 6,000 years in the Americas the horse was absent. Follow- 
ing post-Columbian reintroduction, feral horses reoccupied grass- 
land habitats with unseeming haste. Darwin (1855, p. 299) reported 
that they spread from Buenos Aires to the Straits of Magellan, 1,300 
miles, in 43 years. 



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3LE II. Radiocarbon Dates Associated with the Extinct Late Pleistocene Fauna 

in America" 





Years, B.P. 


L-290 R. 

Santa Rosa Is., 

Dwarf mam- 

Charred bone 

29, 700 ±3000 



Tule Springs, 

Bison alleni, 

Ancient occupa- 

> 23, 800 



tion site, later 



Fairbanks area, 

Bison crassi- 

Horn sheaths from 







Santa Rosa Is., 

Dwarf mam- 

Wood from base 




of mammoth- 
bearing alluvium 




''Extinct mam- 

Wood from 30- to 



mal bones" 

60-ft. depth 




Lake, Nev. 

Horse, camel 

Lowest occupa- 
tion in Fish- 
bone Cave 




Mylodon Cave, 


Dated sloth dung, 



no artifacts 




Gypsum Cave, 


Dated sloth dung 

10, 902 ±440 






Sussex Co., 


Peat associated 
with remains 



L-137 G 

Seward Penin- 


Organic material ** 

10, 200 ±800 

L-137 N 

sula, Alaska 





Bison ?antiquiis 

Snail shells from 
bone bed with 

9, 800 ±500 





Bones partly im- 

9, 700 ±600 

claim, S.D. 


pregnated with 



Lenawee Co., 


Wood immediately 
above a tusk 




Naco, Cochise 


Charcoal in clay 



Co., Ariz. 


matrix around 



Orleton Farms, 


Wood from im- 



mediately under 
skeleton; first 
two dates are of 
black carbon 

8, 460 ±400 
9, 600 ±500 



Palli Aike 

Sloth, horse, 

Burned bones. 


Cave, Chile 


with artifacts 





adiocarbon Dates . 

Associated with tl 

[le Extinct Late Pleis 

tocene Fauna 


America" — Continued 





Years, B.P. 


A-30 to 

Lehner site, 


Dates between 6,356 ±450 and 


Cochise Co., 


12,000db450; mammoth kill 



should be older than overlying 


organic material d 
7,000 B.P. 

ated at about 



Murray Springs, 
Cochise Co., 


Sample overlies 
clay containing 




Double Adobe, 

Equus, Cants 

Charred wood, 


Cochise Co., 

dims, mam- 

Sulphur Springs 


moth. Bison 

artifacts; same 
site as C-216 



Double Adobe, 

Equus, Canis 

Mammoth lies 


Cochise Co., 

dims, mam- 

above the 


moth. Bison 





Condor, extinct 

Extinct scavan- 


Rapids, Ore. 




gers with at- 
latls, burins, 
flaked stone 



Burnet Cave, 

Extinct mam- 

Sample from the 

7, 432 ±300 

N. M. 


8- to 9-ft. level 
in the fill 



Washtenaw Co., 


Acid-soluble car- 

6, 100 ±400 


bonates from 




Cromwell, Ind. 


Associated wood-'' 

5, 300 ±400 



Kassler Quad., 

Woolly mam- 

Date on twigs 

4, 885 ±160 



under a bone, 
possibly in- 



Lagoa Funda, 
Minas Gerais, 

"Giant bear"'' 

3, 000 ±300 



St. Petersburg, 

Extinct mam- 


2, 040 ±90 

o All dates have been published in Science. Initials indicate the laboratory: L, Lamont; 
C, Chicago; M, Michigan; W, Washington; Y, Yale; A, Arizona. 

* Organic material from muck of deposits that fill valleys of minor streams, "... under- 
lain by blue-gray silt or by an older muck that contains fossil remains such as elephant, 
horse, and bison, which are conspicuously absent in the dated muck. 

" Equus excelsus, Camelops sp., Sangamona sp., Asinus conversidens, Euceratherium 
collinum, Preptoceras sinclairi, Stockoceros onusrosagris, Bison antiquus, and Rangifer? 

'' "Material from this site should date the age of the extinct Giant Bear." 

* Charcoal from newly exposed canal. "Associated with extinct Seminole Field mam- 
mals, an archaic spear point, ilint chips and burned bone." 

•^ Tusk fragments of this mastodon yielded a much older date, M-139, 12, 630 ±1000 
years {Science, 127: 1099). 
















15 • 



10 ■ 


5 ■ 












— T- 

/ (40) 


• I 

M F 



I I I 


Geological Epoch 






















15 ■ 

I I 

M P 





Fig. 5. Caption on facing page. 


Before proceeding directly into a consideration of possible causes, 
it appears essential to examine the nature of late Pleistocene extinc- 
tion more closely [cf. Simpson (1953) for a general treatment of 
phyletic extinction]. If it is no different from that of the early 
Pleistocene or Tertiary there is little point in proceeding farther. 

Extinction without Replacement 

In addition to Equus, cited above, the following North American 
genera, representing specific ecological life forms with respectable 
Tertiary lineages, disappeared in the late Pleistocene or sub-Recent 
time: the elephants and mastodons Mammuthus and Mammut, 
the camels Tanupolama and Camelops, the Old World antelope 
Saiga, the cervid deer Sangamo?ia, and Cervalces, the shrub-oxen 
Symbos, Eucemtherium, and Preptoceras, the pronghorns Breameryx 
and Stockoceros, the giant beaver Castoroides, and others. They re- 
flect abandonment of grazing and browsing habitats by roughly three- 
quarters of the mammalian herbivore fauna. In the West Indies four 
genera of ground sloths and sixteen of hystricomorph rodents, also 
herbivores, disappeared in sub-Recent time. 

The general rule that abandonment of life forms and the disap- 
pearance of genera or subfamilies without replacement occurred only 
in the late Pleistocene may have a single minor exception. Boro- 
phagus, a New World equivalent of the hyaenid life form, is unknown 
beyond the First Interglacial (Hibbard in Flint, 1957, p. 462). How- 
ever, at no time since the extermination of the Upper Cretaceous 
duck-bills and other herbivorous dinosaurs has there been un- 
balanced extinction of equal magnitude. 

Fig. 5. Generic extinction rate curves for various mammalian orders. 
The number of genera last recorded divided by estimated age for each 
epoch is shown for three Late Cenozoic epochs: M = Miocene, 17 million 
years; P = Pliocene, 11 million years; PI = Pleistocene, one million years. 
Pleistocene extinction rates rose sharply in the primates, rodents, eden- 
tates, fissipeds, notoungulates, liptoterns, proboscideans, perissodactyls, 
and artiodactyls. There was no comparable rise in extinction rates among 
the insectivores, rabbits, cetaceans, pinnipeds, and sirenians. Data on 
extinct genera were obtained from Simpson (1945) ; orders with poor late 
Cenozoic fossil records, as the bats, pangolins, and hyraxes, are not 

402 V. S. MARTIN 

Cenozoic Extinction Rates Rise in the Pleistocene 

Extinction rates in number of genera per million years for several 
mammalian orders increased greatly at the end of the Cenozoic 
during the Pleistocene (Fig. 5). The data from Simpson (1945) repre- 
sent last appearances of genera in each of twenty mammalian orders. 
To obtain extinction rates, one divides the number of genera last 
recorded in each period by the geological estimate of elapsed time, 
17 million years for the Miocene, 11 for the Pliocene, and 1 for the 

It is obvious that only certain orders exhibit a strong Pleistocene 
effect. Those include the artiodactyls, proboscideans, marsupials, 
edentates, rodents, perissodactyls, fissipeds, and primates. Certain 
groups with moderately good late Cenozoic fossil records, as the 
cetaceans and pinnipeds, appear unaffected. The extinct Pleistocene 
genera of marsupials are all Australian and include large kangaroo 
and phalangeroid herbivores. Within the primates, 8 of 14 extinct 
Pleistocene genera were lemur-like forms from Madagascar. Among 
the rodents, a rise in Pleistocene extinction rate can be attributed 
in part to the extinction of insular genera, 15 of them West Indian. 
Regarding the entire late Cenozoic record of mammals, extinction 
rates rise from 25 per million years in the Miocene, 40 in the Plio- 
cene, to 203 in the Pleistocene. From this we may believe that 
Pleistocene extinction transcends that of the rest of the Cenozoic. 
Was it caused by climatic change of the Glacial periods? 

Pleistocene Extinction Rates Rise in the Last Glacial Period 

Hibbard's valuable list (1958; also in Flint, 1957) of Pleistocene 
mammals shows a considerable measure of extinction in the First 
Interglacial, the Aftonian. However, with the single exception of 
Borophagus, there is continual replacement of generic types until 
the Wisconsin. 

Estimating the Glacial periods arbitrarily at 100,000 years each 
and the interglacials at 250,000 years we obtain for North America 
the following extinction rates, expressed as number of genera per 
100,000 years: Nebraskan, 1.0; Aftonian, 6.0; Kansan, 5.0; Yar- 
mouth, 1.2; Illinoian, 1.0; Sangamon, 0.0; Wisconsin, 31.0 (ter- 
minal records from Hibbard in Flint, 1957, with addition of Floridian 
Melbourne mammals). On this basis it is possible to conclude (1) 
that the extinction rate in the Wisconsin was considerably higher 


than earlier in the Pleistocene and (2) that extinction is not related 
to the Glacial period or to the climatic change brought on by 

In part such figures may be an artifact of paleontological sampling. 
Late Pleistocene sediments, bogs, caves, and alluvium, are better 
preserved than older deposits exposed to a longer history of geo- 
logical wear and tear. The late Pleistocene should be better known 
than a preceding fauna. Nevertheless, accepting the fossil record at 
face value, it seems that extinction was predominantly a Wisconsin 
phenomenon. The facts do not agree with the proposal that the rise 
in Pleistocene extinction rates is the result of climatic change. 

Late Pleistocene Extinction Affected Only Large Animals 

Obviously, this is not strictly true, as Eisley (1946) and Gill (1955) 
pointed out. On the one hand, cetaceans and pinnipeds were unaf- 
fected; on the other, small to medium-sized West Indian mammals, 
lizards, and birds disappeared. In tropical forests and savannas 
certain edentates survive, such as the anteaters and tree sloths. 
Their plains-dwelling relatives of subequal size, such as Nothro- 
therium and Chalmytherium, disappeared. Moose, elk, white-tailed 
deer, and probably bison survived in temperate forests while, except 
for one species of pronghorn and the mule deer, the grasslands were 
stripped of large herbivores. 

Nevertheless, the size relationship is crucially important. The 
vulnerability on most islands of relatively small animals (from the 
size of a Norway rat to that of a beaver) can be contrasted with 
that on continental areas where, aside from possible trimming of 
marginal populations, the extinction of such small animals did not 
occur at the end of the Pleistocene. I am indebted to K. C. Parkes 
for pointing out that, of the reasonably rich late Pleistocene passerine 
avifauna, there are recognized only two extinct genera, both in the 
family Icteridae and both cowbirds, Pandanaris and Pyelorhamphus 
(Wetmore, 1956). It requires no great imagination to suggest that 
they shared a commensal table with the modern cowbird genera, 
Molothrus and Tangavius, and that extinction of the large herbivores 
reduced the variety of ecological niches for both scavenger and 
cowbird life forms. The extinct scavengers are more numerous and 
include the genera Breagyps, Teratornis, Cathartornis, Neogyps, and 

404 P. S. MARTIN 

Extinction Marks the Boundary between the Pleistocene and 

In the Rocky Mountain region Hunt (1953) reported that the 
disappearance of such large mammals as elephants, camels, and 
horses coincides with a widespread unconformity in the late Quater- 
nary deposits. He correlated this break with the drought of the 
Altithermal and finds that extinction immediately predates it. 
While this relationship may be of geological utility in western North 
America, chronological detail does not bear out such a distinction 
between "Pleistocene" and "Recent" elsewhere on the continent. 
In Alaska thin gravels and clays containing remains of extinct 
mammals are at least of Late-glacial age or older. Organic material 
overlying the remains of elephant, horse, and extinct bison has been 
dated at 10,200±800 (L-137G) and 9,400±750 (L-137N) years 
B.P., (see discussion by Sigafoos and Hopkins in Broecker et al., 
1956, pp. 156-157). Horn sheaths of Bison crassicornis were dated 
at 16,400 ±2000 (M-38). 

In Mexico the Upper Becerra Peat, containing remains of the 
mammoth M. imperator is also considered as older than 10,000 
B.P. (Wormington, 1957, pp. 91-99). Hibbard (1955) considered it 
early Wisconsin. MacNeish's important and, in large part, unpub- 
lished studies in southern Tamaulipas (1950, 1955) have revealed 
leaflike points associated elsewhere with the Becerra mammoths, but 
there is no evidence of extinct animals in his radiocarbon -dated 
middens, which cover the entire Post-glacial period (personal com- 
munication). Apparently extinction in both Mexico and Alaska 
preceded that in the Rocky Mountains. 

In Florida and South America extinction postdated the Alti- 
thermal. Unquestionably this is the most controversial aspect of the 
extinction chronology, partly because it all but eliminates climatic 
change as an extinction cause. The vastly rich fauna of the Mel- 
bourne and Seminole beds of Florida was dated on archaeological 
and geochronological grounds by Rouse (1952) at 4,000 to 2,000 
years ago. A radiocarbon date, L-2N, 2,040 ±90, of charcoal from a 
newly exposed canal is "associated with extinct Seminole Field 
mammals, an 'archaic' spear point, flint chips, and burned bone . . . 
the date seems anomalously low in view of the extinct fauna" (field 
description from unidentified collector in Broecker et al, 1956, p. 
161). The fauna of the Seminole field includes the porcupine, capy- 


bara, dire wolf, short-faced bear, smilodon, ground sloths, glypto- 
donts, horses, a tapir, extinct peccaries, camels, mastodons, mam- 
moths, and various small mammals conspecific with living species 
(Cooke, 1945, pp. 308-309). Forty years of scrutiny have not re- 
solved the apparent contradiction that a rich and varied extinct 
savanna fauna survived here until a very late date, perhaps 4,000 to 
2,000 years ago, contemporaneous with archaic man (Rouse, 1952; 
Heizer and Cook, 1952). 

In South America an extinct mastodon, Ciivieronius, was found 
associated with pottery (Spillmann in Osborn, 1936, pp. 571-574). 
More recently a radiocarbon sample from Minas Gerais, 3,000 ± 
300 B.P. (M-354), "... should date the age of the extinct Giant 
Bear" (genus unspecified, collected by Evans and reported in Crane, 
1956, p. 672). The recent review of mastodon remains and radio- 
carbon dates by Williams (1957) indicates that outside Florida the 
genus endured in eastern North America until at least 6,000 years 
ago and is associated with archaic artifacts. 

One waits with keen anticipation additional study of these and 
other problem areas such as the West Indies. Tentative conclusions, 
based on the harvest of eight years of radiocarbon dates associated 
with extinct animals, follow: (1) Mexican and Alaskan large mam- 
mals were the first to be eliminated, this in Late-glacial time; 
(2) the Plains Megafauna disappeared in the early part of the Post- 
glacial period; (3) eastern temperate forest and tropical rainforests 
were the last continental refugia for large mammals; (4) the Floridian 
savanna, surrounded by forest, served as a refuge for plains her- 
bivores after they had disappeared elsewhere in western North 


An idealized descriptive model designed to illustrate probability 
of extinction within the late Pleistocene terrestrial fauna would in- 
clude many factors. Without doing violence to such a model we may 
be able to limit it to three: (1) body size, (2) habitat, and (3) total 
range of the species. Reasons for this choice and certain apparent 
exceptions to the model will become evident subsequently. 

The probability of extinction in the late Pleistocene appears to 
have been maximized by large body size, usually accompanied by 
low values of r (intrinsic rate of increase), and T (mean generation 



pericnd); by open habitat, i.e., savanna, grassland, tundra, and 
desert, and by limited range, either insular or on such ecological 
islands as Alpine meadows surrounded by forest. Conversely, sur- 
vival was enhanced by small size, forest habitat, and a large range 
for the species in question. 










Fig. 6. A Late Pleistocene extinction model for New World mammals. 
This generalized model is intended to indicate the interaction of variables 
that appear to have been important in determining probability of ex- 
tinction for any particular species or population. Points beneath the sur- 
face of the solid lie within the region of high extinction probability; those 
above the surface lie in the region of high probability of survival. 

The primary question in late Pleistocene extinction revolves 
around the herbivores (trophic level A2 in Lindeman's system). 
According to ecological and evolutionary theory it is axiomatic 
that a reduction in the number of species operating at one level will 
require reduction at higher trophic levels. Our present task is to 


describe the pattern of herbivore extinctions, with the assumption 
that extinction of certain wolf, cat, cowbird, vulture, and vampire 
life forms followed inevitably. 

Figure 6 is a diagrammatic attempt at such a descriptive model, 
showing high and low regions of extinction probability. The high 
regions lie within the shaded portion of the solid ; the low regions lie 
above in the unshaded portion. Following Dansereau (1957), habi- 
tat can be divided conveniently into the four biochores: forest, 
savanna, grassland, and desert. All terrestrial communities from the 
equator to the Arctic fall within one of these units. Animal body size 
is divided into four classes, represented respectively by (1) Norway 
rat, (2) Norway rat to beaver, (3) beaver to pronghorn, (4) prong- 
horn to mammoth. Total range of the species in square miles is 
arbitrarily listed as very small (less than 2,000), small (2,000- 
20,000), medium (20,000-200,000), and large (200,000 and more). 
Three specific examples, which were used in constructing the model, 
illustrate its predictive function : 

Case A. Upper-left-rear corner of the diagram. Small animals in a 
small area of forest, Puerto Rico. 

Extinct. Nesophontes, an insectivore; Acratoc7ius, a small ground 
sloth ; and six genera of hystricomorph rodents: Heptaxodon, Elasmo- 
dontomys, Isolobodon, and Proechimys (surviving on mainland South 
America), Heteropsomys, and Homopsomys. 

Surviving. Eleven genera of native bats; introduced Rattus and 

Extinction intensity. Heavy. 

Case B. Upper-left-front corner. Small animals in extensive 
forest, eastern North America. 

Extinct. None known. 

Range possibly reduced : Neofiber, round-tailed vawskrSit ; Erethizon, 
porcupine; Didelphis, opossum. 

Surviving. Twenty-one genera of native rodents, various other 
small terrestrial mammals and bats. 

Extinction intensity. Very light. 

Case C. Lower-center and right-front corner. Large animals in 
extensive desert, grassland, and savanna habitats, the Basin and 
Range province and western North America generally. 

Extinct. Mammuthus, mammoths of two or three species; Mam- 

408 P. S. MARTIN 

mut, mastodon; Paramylodon, Nothrotherium, and Megalonyx, 
ground sloths; Glyptotherium, glyptodont; Platygonus, peccary; 
Tanupolama, long-legged llama; Camelops, camel; Sangamona, 
extinct deer; Breameryx, tar-pit pronghorn; Stockoceros, pronghorn; 
Euceratherium and Preptoceras, shrub-oxen; Bootherium, musk-ox; 
Equus, horse and ass, various species. 

Surviving. Antilocapra, pronghorn; Odocoileus, mule deer; Bison, 
buffalo, one species only. 

Extinction intensity. Heavy. 

In addition to these three cases it is obvious that other regional 
faunas fulfill the requirements. For example, the Greater Antilles ex- 
perienced complete extinction of all beaver-sized and larger animals 
and partial survival only among the small mammals and reptiles. 
In Alaskan tundra and Mexican steppe there was a high extinction 
rate for large herbivores (pronghorn size and over) , but not for small 
or medium-sized mammals. Applying the model to South America 
we would expect heavier extinction on the pampas and campo 
cerrado savannas than in the Amazonian rainforest. 

Paleontology of the Pampean formation (Simpson, 1940) showed 
that a variety of ground sloths, glyptodonts, and other edentates, 
horses, certain camels, and the native ungulates, as the macra- 
ucheniids, toxodonts, mesotheres, and hegetotheres, disappeared 
from the plains areas. Some extinction of forest forms must have 
occurred, probably more than the scanty fossil record of mastodonts 
and bears would indicate (tropical forest Pleistocene sediments are 
all but unknown) . However, survival in the forest exceeds that on the 
plains. Peccaries, large edentates, monkeys, tapirs, capybaras, and 
various deer in the forest and forest margin contrast with the pres- 
ence of only two large native herbivores in the pampas and in Pata- 
gonia, the guanaco or wild llama and the pampas deer. 

If the model is adequate in these cases, it by no means explains 
lack of extinction under certain circumstances that call for it. The 
survival of four species of native camamelids in South America, at 
least two of them with relatively narrow ranges in the i\ndean Puna 
is mystifying, both in terms of the model and the extermination of 
the camamelids in North America. The survival of Capromys ingra- 
hami on one of the smaller Bahaman Keys and of Testudo, the giant 
tortoises of the Galapagos, introduce an additional problem that 
appears worthy of special treatment. 



Late Pleistocene and sub-Recent insular extinction throughout 
most of the world appears to have been intense. Certain oceanic 
islands exhibit the phenomenon of extermination without replace- 
ment noted in North and South America. Giant marsupials inhabited 
Australia (Gill, 1955), large flightless birds survived in New Zealand 
at least until 1300 a.d. (Deevey, 1955), and giant lemurs, tortoises, 
and large birds lived in Madagascar (Sibree, 1915). West Indian 
mammals, reptiles, and birds experienced extermination both of 
relatively medium-sized genera (tortoises and ground sloths) and of 
many smaller rodents. In this respect West Indian extinction differs 
from the continental record. Summary articles by Allen (1911) and 
Matthew (1919) have been superseded by Simpson's valuable zoo- 
geographic synthesis (1956). Allen (1942) discussed most of the ex- 
tinct mammals. Except for Cuban ground sloths (Allen, 1918; 
Aguayo, 1950) and Jamaican bats and rodents (Anthony, 1920; 
Koopman and Williams 1951; Williams, 1952b), the distribution of 
most of the extinct mammals is covered in Miller and Kellogg's 
Checklist (1955). 

The extinction chronology is rather baffling and is not simplified 
by the possibility that certain forms such as Nesophontes may yet be 
found to survive in remote mountainous districts. I am indebted to 
K. F. Koopman for pointing out that more than 300 years elapsed 
between discovery of the islands by western man and the first serious 
scientific description of their fauna. Extermination in this interval, 
perhaps at the hands of superior competitors as Rattus, or as the 
result of clearing and cultivation, will be difficult to distinguish from 
prehistoric extermination. Nesophontes, for example, appears to 
have been contemporaneous with Rattus. In contrast Testudo and 
various ground sloths almost surely were not present at the time of 
the conquest. Ground sloths may have existed into the ceramic 
period (Aguayo, 1950), and the giant rodent Quemisia was ap- 
parently known to Oviedo (Allen, 1942), but there is no certain 
evidence of other large hystricomorphs (Elasmodontomys, Clidomys, 
and Amblyrhiza) in post-Columbian middens and it is most unlikely 
that their presence would have gone unrecorded by early observers. 

Simpson listed twenty-two extinct genera of terrestrial mammals 
in the Greater Antilles. Even assuming some unnecessary splitting, 
the fossil fauna is quite impressive. By comparison, the present sur- 

410 P. S. MARTIN 

viving fauna of four genera is depauperate : Solenodon on Hispaniola 
and Cuba, Oryzomys (recently extinct?) on Jamaica, Capromys (here 
to include Geocapromys) on Cuba, the Plana Keys, Jamaica, and the 
Swan Islands, and the closely related Plagiodontia on Hispaniola. 

Considering the poverty of chiropteran remains elsewhere, the 
fossil record of the West Indian bats is remarkably good. It has been 
used to identify relative faunal ages in Jamaica (Koopman and 
Williams, 1951 ; Williams 1952b). At first glance the presence of two 
genera of fossil bats now extinct in Jamaica seems to contradict the 
principle I have noted earlier that late Pleistocene extinction did not 
affect such animals. Other than commensals and parasites of large 
herbivores, such as the cowbirds and vampires, we would predict no 
elimination of life forms among the bats and birds. In theory climatic 
change during the Wisconsin and earlier Glacial advances altered 
the ecological opportunities for various genera and changed faunal 
composition at low latitudes. However, it is my present thesis that 
generic extinction did not accompany such events. Koopman and 
Williams' studies make it clear that the local extirpation of bats 
{Tonatia and Brachyphylla) in Jamaica was accompanied by replace- 
ment by related genera in the same subfamily. Tonatia and Brachy- 
phylla survive in Central America and Hispaniola respectively. The 
Jamaican bat fauna remained rich and bears no resemblance to the 
annihilation experienced by the terrestrial herbivores. The shift in 
the species composition of bats may be attributed to climatic change. 

On the other hand, the survival of a rodent, Capromys {Geo- 
capromys) ingrahami, on the tiny Plana Keys and of C. thoracatus 
on the Swan Islands, seems a serious violation of the general rule 
that the smaller the surface the greater the vulnerability to extinc- 
tion (Fig. 6). The record of Capromys is instructive. C. ingrahami 
was described in 1891. Closely related fossil populations were sub- 
sequently found on the larger Bahaman Islands, Crooked, Eleuthera, 
Long, Great Exuma, Great and Little Abaco. In 1955 Rabb and 
Hayden (1957) revisited the Plana Keys, collected three specimens 
of the "cootie" and noted that the island had undergone little change 
since Ingraham's visit. East Plana Key is a small, rocky islet not 
more than 50 feet above the ocean, one-half mile wide, four to five 
miles long and "... entirely without fresh water except in the rainy 
season, when pools of fresh water may be found in holes in the rocks" 
(Allen, 1891). In the absence of fresh water it is doubtful that the 


Carib Indians ever maintained permanent settlement on the island; 
Rabb and Hayden note that it is uninhabited at present. This fea- 
ture may be crucial. We can attribute the remarkable survival of 
Capromys both on the Plana Keys and on the Little Swan Islands 
to lack of permanent prehistoric habitation. For the archaeologist 
this carries the corollary that the other Bahaman Islands were more 
intensively occupied. 

The foregoing account emphasizes the mammalian fossil record. 
In addition, there were "giant" late Pleistocene lizards (Hecht, 1951, 
1952) turtles (Williams, 1950, 1952a), and birds (Wetmore, 1937). 
The record of the tortoises, Testudo, is an important adjunct to the 
extinction of the large mammals. An interesting sidelight is their 
apparent extinction in the Greater Antilles before the main period 
of mammalian extinction (Williams, 1952a, p. 554). Elsewhere they 
evolved through the Tertiary and into the late Pleistocene. Species of 
relatively small size survive in northern South America. The New 
World giant tortoises remain only on the Galapagos. As in the case of 
Geocapromys on the Plana Keys, there is reason to believe that these 
islands escaped permanent occupation in prehistoric times. Heyer- 
dahl and Skjolsvold (1956) reported no archaeological evidence of 
prehistoric occupancy of the Galapagos other than temporary or 
seasonal visits, and no preceramic contact. With a long reproductive 
time lag and no special defense against man, the giant tortoises 
must have been especially vulnerable to human predation. This may 
explain their early demise compared to the rest of the fauna in Cuba 
(Williams, 1952a). The Galapagos and Plana Key exceptions to the 
generalized extinction model (Fig. 6) indicate that it will apply only 
to regions permanently inhabited by prehistoric man. 


"A hypothesis which implies that practically all the important 
fossil forms had existed until a comparatively Recent date and then 
become extinct in a geologically short period of time had seemed 
equally improbable to the writer; and yet it is to such a conclusion 
that a study of the evidence leads" (Romer, 1933). Flint (1957), 
Osborn (1936, pp. 1512-1513), and Sauer (1944) are also among 
those who indicate that prehistoric man was the principal agent of 
late Pleistocene extinction. If circumstantial evidence points to man, 
it does not reveal his methods. Sauer's fire-drive hypothesis (1944) 

412 p. S. MARTIN 

may be Important in understanding the possible hunting techniques 
of use against the large, gregarious plains herbivores. However, as 
Eisley (1946) noted, even the most ardent proponent of fire as an 
ecological force may hesitate to attribute the extinction of forest 
mastodons, the giant beaver {Castoroides) , and the West Indian 
hystricomorphs to this technique. The mysterious survival of large 
African herbivores frustrates sweeping conclusions. 

For paleoecological purposes it seems necessary to consider the 
significance of large vertebrates as climatic indicators. If prehistoric 
man is an extinction agent, how are we to interpret shifts in range in 
terms of paleoecological uniformitarianism? Tapirs and capybaras, 
today denizens of tropical forest, formerly ranged far to the north, 
respectively to Oregon and Pennsylvania and to Florida and Arizona. 
Are there compelling reasons to believe that, in the absence of man, 
these animals would not occupy the same range under the present 

The porcupine, opossum, and armadillo have notably extended 
their ranges within historic time. The opossum and armadillo moved 
northward (Guilday, 1958; Fitch et at., 1952), the porcupine south- 
ward, into Sonora (Benson, 1953). These extensions can be at- 
tributed to climatic change. They can also reflect the reoccupation 
by these species of marginal positions in their former range, from 
which they had been eliminated in prehistoric time by human preda- 
tion. The mountain top populations of Marmota flaviventris in 
southern Arizona, New Mexico, and northeastern Mexico were 
trimmed. Subalpine and boreal habitats, apparently suitable for 
marmots, persist in these areas today. 

The giant tortoises, like the tapir and capybara, are another 
group in which a complacent assumption of tropicality is read into 
their ranges, for example, by Crook and Harris (1958, p. 241). Sur- 
vival of tortoises only on remote oceanic islands seems to be at- 
tributable to the circumstance that they here escaped pre-Columbian 
extermination by man rather than to climatic change. Assumptions 
of climatic change based on the present distributions of relatives of 
the late Pleistocene fossil vertebrates are gratuitous as long as an 
alternate cause of extirpation is possible. In brief we may inquire 
whether tropical forests and remote islands constitute refugia from 
climatic change or from the hunting practices of prehistoric man. 

For sensitive indicators of climate and past environments it may 


be necessary to consider only plant distributions plus those small 
animals whose population density and reproductive capacity could 
keep pace with human predation. 

Within our present knowledge there seems little agreement on the 
problem of extinction and man's role in it. Most authors who have 
reviewed the problem reduce it to the outcome of an interaction of 
all factors that can limit animal populations — predation, competi- 
tion, parasitism, climatic change, evolutionary lag during environ- 
mental stress, and also the effect of man (Colbert, 1938; Gill, 1955; 
Hamilton, 1939; Osborn, 1906; Romer, 1945; Simpson, 1931, 1953). 
I believe this multiple hypothesis does injustice to the temporal 
and ecological record, i.e., (1) differential loss of large animals, (2) 
lack of evidence of major climatic change during the extinction 
period, (3) the narrow chronological range in which extinction oc- 
curred, and (4) the phenomenon of removal without replacement. It 
would appear that within the Cenozoic the late Pleistocene environ- 
ment had some unique features. Man is the only one clearly 


In part the viewpoints expressed grew out of seminars and less formal 
discussions on Pleistocene matters at the universities of Michigan, Yale, 
Montreal, and Arizona. In particular I would thank the following for their 
help: P. Dansereau, M. B. Davis, E. S. Deevey, J. A. Elson, R. F. Flint, 
F. K. Hare, B. E. Harrell, E. W. Haury, J. J. Hester, C. W. Hibbard, 
K. F. Koopman, J. F. Lance, A. and D. Love, C. H. Lowe, G. Lowther, 
M. Martin, J. E. McDonald, J. E. Mosimann, J. G. Ogden, G. B. Rabb, 
J. Schoenwetter, T. L. Smiley, and D. R. Whitehead. Mrs. Helen Griffin 
provided valuable clerical aid. I am indebted especially to palynologists 
F. H. Barclay, M. B. Davis, E. B. Leopold, and D. A. Livingstone, who 
forwarded advance copies of their unpublished pollen diagrams. 


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The Palaearctic Element in the New World Avifauna 

Kenneth C. Parkes 

Carnegie Museum, Pittsburgh, Pennsylvania 

In the March 1946 issue of The Wilson Bulletin, 
Ernst Mayr pubHshed an important paper entitled "History of the 
North American bird fauna," a review that represents a much- 
quoted landmark in the study of the zoogeography of North America. 
Mayr summarized the recent advances in zoogeography in general, 
with particular reference, of course, to birds, and pointed out 
especially the contributions of the palaeontologist and the tax- 
onomist. After a brief review of the geological history of North 
America, he proceeded to classify the avifaunal elements of the 
Americas on the basis of probable geographic origin. He pointed 
out that it is impossible to place many of the bird families as to 
probable major land mass of origin. In the first place, many families, 
mostly oceanic or freshwater, are now so widely distributed as to 
make speculation as to their genesis fruitless. Mayr calls these the 
"unanalyzed element." This group includes such sea birds as the 
petrels and gulls, such freshwater birds as ducks, herons, rails, 
the shore birds, and a few families of land birds, including the 
diurnal birds of prey, the woodpeckers, and the swifts. 

Another group of uncertain origin is also widespread but only, 
at present, in the tropics. Mayr calls this the "pantropical element" 
(this adjective strikes me as less awkward than "tropicopolitan," 
used by Darlington (1957) and others). This group includes aquatic 
birds like the anhingas and skimmers, and a few land birds, the 
trogons, barbets, and parrots. In the arctic and north temperate 
zones the loons, auks, and some other birds constitute still another 
group of families that is now so widely dispersed that no continent 
can be named as their original source. 

The strictly New World families, or rather the families of New 
World origin, since some of these have found their way to the 
Old World, were divided by Mayr into (1) those of probable North 


422 K. C. PARKES 

American origin, (2) those of probable South American origin, and 
(3) a Pan-American element now so widespread in both continents 
as to be of uncertain continental origin (see Darlington, 1957, pp. 
280-286, for a critique of Mayr's theories concerning these New 
World groups). 

Finally, there are the families that are generally acknowledged to 
be of Old World origin, but that now form a component of the 
avifauna of the Americas. This is the group which will be reviewed 

As Mayr pointed out, birds apparently crossed the Bering Strait 
connection between Asia and North America more or less con- 
tinuously through most of the Tertiary. This continuity of origin 
is reflected in the complete spectrum of zoogeographic and taxon- 
omic status of the Old World groups in the Americas. At one end of 
the spectrum are families the representatives of which arrived so 
early that there has been time for a major secondary radiation in 
the Americas. Such a history is exemplified by the quails, derived 
from the Old World pheasant and partridge family, and by the 
jays, which are much more diversified in the New World than in the 
Old. It should be acknowledged that factors other than the mere 
time element are involved in the extent to which these secondary 
radiations have developed; evolutionary opportunity in the form 
of available ecological niches and comparative rates of evolution 
must also be considered. But it seems safe to assume that a group 
that has reached approximately the subfamily level of difi^erentia- 
tion must have derived from a rather early invasion. 

At the opposite end of the spectrum Mayr mentions species 
which have only a slight foothold on this continent and are insep- 
arable even subspecifically from their Old World progenitors. 
These include two Alaskan birds, the Yellow Wagtail {Motacilla 
flava tschiitschensis) and the Red-spotted Blue-throat {Luscinia 
svecica svecica), and one species, the Wheatear, which has entered 
Alaska from the west (as Oenanthe oenanthe oenanthe) and the east- 
em Canadian Arctic from Greenland (as 0. o. lencorhoa). All these 
species are obviously recent immigrants but belong to two families 
(Motacillidae and Turdidae) with wide distribution in the New 
World from earlier invasions. A category even beyond this can be 
established for those Old World species that do not have a foothold 


on this continent in the sense that there is no known breeding 
population, but which occur here from time to time as so-called 
accidentals or casuals. It is here we encounter some of the "unsolved 
problems" appropriate to mention in a symposium with the general 
title, "Some Unsolved Problems in Biology, 1957." 

In discussing the so-called accidentals, particular attention will 
be paid to the Transatlantic species. Fewer Transpacific crossings 
can be expected for obvious geographic reasons, and a stray Asiatic 
bird might easily be overlooked along the Pacific Coast of North 
America, which is much less closely scrutinized by bird-watchers 
than is the Atlantic Coast. 

It is widely known that American birds occur in western Europe, 
particularly the British Isles, far more often than European birds 
appear in eastern North America. Peterson, Mountfort, and Hollom 
(1954) list 41 American species or subspecies of non-pelagic, non- 
introduced birds as accidental in western Europe. The American 
Ornithologists' Union Check-list of North American Birds (1957), 
hereafter referred to as "A.O.U. Check-list," lists 24 such species 
or subspecies from Europe as accidental in eastern North America. 
And even the comparative figure 41 versus 24 is misleading, since 
the actual number of individual occurrences of accidental birds is 
much higher in Europe than in North America. Alexander and 
Fitter (1955) listed 260 authenticated records of North American 
herons, cranes, rails, and waders alone in western Europe, and an 
additional 126 records of land birds. The figures for European 
accidentals in North America would be far fewer, particularly since a 
substantial number of these are among the ducks, gulls, and other 
families not included in the figures given by Alexander and Fitter. 

There is no great mystery here, as the prevailing winds across the 
North Atlantic are predominantly from west to east. The unsolved 
problem in this case lies with the species that do manage to get 
across to the western side of the Atlantic with some frequency. 
Six species of palaearctic water birds occur along our Atlantic 
seaboard with such regularity that a large percentage of the bird- 
watchers of Long Island and New England are familiar with them, 
and keep an eye out for them every year. Two are ducks, the 
European Green-winged Teal {Anas crecca) and the European 
Widgeon {A . penelope) ; two are sandpipers, the Curlew Sandpiper 

424 K. C. PARKES 

(Erolia ferruginea) and the Ruff {Philomachiis pugnax) ; and two 
are gulls, the Black-headed Gull {Lams ridibundus) and the Little 
Gull (L. minutus)} 

What particular attribute, if any, do these six species share to 
give them the propensity for such frequent Transatlantic crossings 
against the prevailing winds? Three of the species, the two ducks 
and the Black-headed Gull, are known to nest as far west as Iceland. 
But why, then, do not other, related, Iceland nesters make the 
same trip? Among the gulls, for instance, the Lesser Black-backed 
Gull (Larus fuscus) breeds in Iceland, but the two specimens of 
this species that have been collected in North America were both 
of the British rather than the Icelandic breeding race. Of the three 
remaining species, the Little Gull nests as far west as Denmark and 
the coast of the North Sea, the Ruff to western France, and the 
Curlew Sanrlpiper only in eastern arctic Siberia. The breeding ranges 
of all these species are more or less duplicated by those of related 
species or other birds of similar migration patterns. Why, then, do 
we see these six so much more often along our East Coast? Several 
possibilities suggest themselves. One is that other vagrant species 
are being overlooked. Readers familiar with the zeal of the bird- 
watching groups on Cape Cod or Long Island will discount that 
one immediately. It has been said that the publication of Peterson's 
Field Guide to European birds in 1954 was a real boon to many 
Massachusetts bird-watchers, who had by then worn out their 
Field Guides to the birds of western North America! 

Another possibility is some sort of innate tendency in these few 
species to go astray, so to speak; perhaps a high incidence of error 
in their "direction-finding apparatus," that mysterious organ for 
which ornithologists still search in vain. This would be exceedingly 
difficult to demonstrate, and seems rather unlikely from an evolu- 
tionary point of view, since getting lost would not appear to be a 
selectively advantageous trait. A third possibility and perhaps the 
most reasonable, at least for some of the species, is the existence of 
undiscovered breeding areas of these species much closer than any 
we know of now, perhaps even in North America itself. Certainly 

1 The list of eight European birds most regularly observed on the Atlantic Coast of 
North America presented by Lindroth (1957, p. 251), which overlaps the above list by 
four species, was based on an obsolete and incomplete reference, the 1931 edition of the 
A.O.U. Check-list. Even the 1957 edition is misleading in this respect; see Eisenmann, 
1958, for remarks on the status of certain European birds in the New York City region. 


the unexplored tundra in the New World arctic is vast enough to 
hide a small local breeding population of the Curlew Sandpiper. 
It may be less likely for some of the larger species, but certainly 
cannot be discounted. Every year many thousand Eastern Dowitch- 
ers {Limnodrormis grisens griseiis) pass on migration along our 
East Coast, but as of 1957 the A.O.U. Check-list can only say of 
this large shorebird, "Breeding range uncertain, but presumed to be 
in the interior of the Ungava Peninsula." Thus these so-called 
accidentals may yet be shown to be an established component of 
the New World avifauna. 

We turn next to those Old World groups known to be established 
in the Americas. Mayr listed approximately twenty families of New 
World birds as being of Old World origin — approximately, since 
family limits are a subject for continuing debate among ornitholo- 
gists. He divided these roughly into three groups; Early, Fairly 
Early, and Recent Immigrants. Two principal types of evidence 
are used to classify these groups. The fossil record, of the relatively 
few species for which it is at all adequate, is naturally the best 
evidence, but note the warning of Darlington (1957, p. 238) : "Birds 
are a good example of the fact that, in zoogeography, a poor fossil 
record interpreted too literally is almost worse than no record at 
all." The other type of evidence is more inferential, based on the 
relative numbers of species and genera in the New and Old Worlds, 
the degree to which the New World forms have differentiated 
taxonomically, and the distance into the Americas they have 
penetrated. Mayr's tripartite chronological division is of necessity 
arbitrary and, particularly for large families, may be misleading in 
suggesting a lesser number of invasions than has probably occurred. 
Mayr circumvented the latter difficulty by subdividing the rep- 
resentatives of some families, as the Corvidae (crows and jays) 
and the Turdidae (thrushes) into older and newer invasions. Even so, 
additional subdivision beyond Mayr's seems desirable. For instance, 
Mayr pointed out, on the basis of both fossil and Recent taxonomic 
evidence, that the typical owls, family Strigidae, though almost 
certainly of Old World origin, must have reached the New World 
very early. Fragmentary remains assigned to an allied but extinct 
family, Protostrigidae, are known from the Eocene of Wyoming, 
and a Lower Miocene species from South Dakota is identified with 
the living genus Strix (this and other data on fossil birds are chiefly 

426 K. C. PARKES 

from Wetmore, 1956). Six endemic genera of owls are currently 
recognized from the New World. On the other hand, no fewer 
than eight species, in six genera, are currently considered to be 
conspecific with Old World owls ; among these is a panarctic species 
with no races, the Snowy Owl [Nyctea scandiaca). Another species, 
the Short-eared Owl {Asio flammeus), has a highly unusual dis- 
tribution. The nominate race is found, without appreciable geo- 
graphic variation, throughout Europe and northern and central 
Asia, and in North America through about the northern half of the 
United States. There is then a distributional gap, beyond which 
the species reappears (as subspecies bogotensis) in the arid temperate 
zone of the mountains and plateaus of the northern Andes. Again, 
beyond a gap, appears the subspecies suinda, which ranges from 
southern Peru and southern Bolivia to Tierra del Fuego. There are 
isolated endemic subspecies on the Falkland Islands, the Hawaiian 
Islands, the Galapagos Islands, Hispaniola, Puerto Rico, and 
Ponape in the Carolines. Probably few living species of birds have 
had so complex a distributional history. 

A good illustration of the value of the fossil record where it is 
available to counteract misleading evidence based on modern 
distribution is furnished by the family Gruidae, the cranes. On the 
basis of the living forms only, one would probably characterize 
this family as a rather recent immigrant to the New World, for 
there are only two American species, one of which also occurs in 
eastern Siberia and both of which belong to a widespread Old 
World genus, and cranes have penetrated only as far south in the 
New World as Cuba. However, the evidence of the living species is 
misleading. Cranes of as many as three extinct genera are known 
from the Eocene of Wyoming, and one Eocene fossil is tentatively 
assigned to the living genus Grus. But lest it be thought that cranes 
became extinct in North America in, perhaps, the late Tertiary, 
with the two living species representing a rather recent second 
invasion, it should be pointed out that fossils indistinguishable from 
the living species occur as early as the Pliocene: the Whooping 
Crane in the Upper Pliocene, and the Sandhill Crane in the Lower 

Good examples of what were undoubtedly secondary New World 
radiations from an early invading Old World stock are the cuckoos, 
the pigeons, and the jays. The large and diverse Old World family 


Cuculidae is represented in the Americas by thirty species, which 
are arranged in ten genera, not a single one of which occurs in the 
Old World. In the pigeon family, Columbidae, there are nineteen 
endemic New World genera, some highly distinctive. The twentieth 
genus, which is shared with the Old World, is the eminently success- 
ful genus Coliimba, to which the domestic pigeon belongs. There are 
no fewer than eighteen New World species of Columba, of which 
seventeen are confined to the warm latitudes between the Rio 
Grande and south Florida to the north and approximately Buenos 
Aires to the south. Darlington (1957, p. 273) argued for a tropical 
New World origin of the genus Columba, with dispersal to the Old 
World through the north. To me, the facts suggest, rather, (1) an 
origin in the Old World, (2) a secondary radiation in the New World 
tropics, and (3) a quite recent northward movement by a single 
species, the Band-tailed Pigeon (C. fasciata), which now ranges 
from Central America to southwestern British Columbia. That 
Columba was originally a tropical genus is suggested not only by 
the somewhat greater number of tropical than of temperate species 
in the Old World, but by the fact that the genera currently placed 
closest to Columba (Peters, 1937) are also confined to the Old World 
topics. This would give strength to the idea that Columba is older 
in the Old World than in the New, as would the fact that a larger 
number of species has been able to become adapted to temperate 
conditions in the former area than in the latter. 

Turning now to the family Corvidae, we may note that the 
greater diversity of the jays in the New World is evidence for an 
early secondary radiation from corvid stock. It is, in fact, quite con- 
ceivable that the few jays of the Old World may represent a re- 
invasion of the Old World. One genus of jays, Perisoreus, now 
inhabits northern coniferous forests of both hemispheres, with a 
distinct but related species {"Boanerges'' internigrans) in the moun- 
tains of western China. Amadon (1944, p. 5) believed that the 
distribution of Perisoreus leaves "little doubt that it is an Old World 
genus which reached America recently, later than the other American 
jays." If the jays, as postulated above, represent a reinvasion of the 
Old World by corvid stock which had differentiated in the New 
World, then Amadon 's interpretation would require Perisoreus to 
have returned, so to speak, to the New World. This is possible, 
but a New World origin for Perisoreus itself must be considered. 

428 K. C. PARKES 

At any rate, members of the family Corvidae other than the jays 
have continued to enter the New World, some so recently that the 
American populations are barely separable subspecifically from 
their Old World relatives (the family thus paralleling the owls in 
this respect). The Magpie {Pica pica) now exists in North America 
in two well-marked forms: the Black-billed [P. p. hudsonia), very 
similar to Old World races, and the Yellow-billed, usually considered 
a full species (P. nuttalli). Only the latter is known from fossil 
(late Pleistocene) remains in North America, from within or close 
to its present range in California. The magpies of North America 
may well represent a double invasion by the same Old World 
species (see Lanius, beyond). Again, within this family, the genus 
Corvus has entered the New World at least twice, and probably 
more often. A cluster of closely related species of this genus in the 
southern United States, West Indies, and Mexico probably represents 
a rather early invasion, since these species at present have no clear 
affinities with any Old World crows. On the other hand, the southern- 
most penetration of this genus in the Americas is that of the Raven 
(C. cor ax), which has reached Nicaragua. Pleistocene fossils of the 
Raven are known from as far south as Nuevo Leon, Mexico, yet 
all New World Ravens are only subspecifically different from those 
of the Old World, and the northernmost populations are barely 

The weakness of the fossil record is nowhere better demon- 
strated than in the large order Passeriformes, the perching birds, 
to which half our living species belong. Wetmore (1956) listed from 
North America (including the West Indies) only 51 species of 
passeriform birds known from fossil (for one species Recent cave) 
remains. Of these 51, no fewer than 44, or 86%, are Pleistocene 
fossils of living species. A single species, for which the family 
Palaeospizidae has been erected, is known from the Upper Miocene 
or Oligocene; one extinct genus of finch is known from the Middle 
Pliocene ; two extinct genera of blackbirds are known from the late 
Pleistocene, and one of these may prove to be of Recent origin; 
and two extinct species of living genera are known from the late 
Pleistocene. All the extinct species of living passeriform families 
belong to families of New World origin. Thus we have none of the 
sort of evidence quoted earlier for the cranes to show that deductions 
on the basis of the living forms only may be highly misleading. 


Evidence from other than fossil sources can, of course, be so over- 
whelming as to be tantamount to proof of origin of some of these 
passeriform families. The larks (Alaudidae), for instance, comprise 
a diverse and widespread Old World family, which extends from the 
arctic to the tropics. It is represented in the New World by a single 
species, the Horned Lark {Eremophila alpestris), which, although it 
has penetrated the Americas as far as the vicinity of Bogota, 
Colombia, remains no more than subspecifically different from the 
palaearctic forms. 

The distributional history of other passeriform families in the 
New World is far more obscure. The waxwings (Bombycillidae) 
are a good example. Mayr, following Lonnberg, listed this family 
without comment as being of North American origin. The evidence 
from the three living species is anything but unequivocal. One 
species {Bombycilla garrulus) is distributed across the northern 
Palaearctic, from Scandinavia to Siberia, and also in northwestern 
North America, and breeds about as far southeast into the continent 
as Glacier Park, Montana. Another species, the Cedar Waxwing 
{B. cedrorum), is found virtually throughout North America, from 
southern Alaska and Newfoundland south to the upper southern 
states. The third species {B. japonica) breeds only in a relatively 
small area of eastern Siberia in the Amur River basin. There is 
little here upon which to base conclusions as to origin, but I would 
say that the balance might be tipped in favor of the Old World. 
The next step would be to examine the families considered most 
closely related to the waxwings. Their nearest allies appear to be 
two other American groups which are, by some "lumpers," even 
placed as subfamilies of the Bombycillidae. These are the Ptilo- 
gonatidae of the southwestern United States and Central America, 
and the Dulidae, a monotypic family known only from Hispaniola. 
This would seem to argue for an American origin for the \\ax\\ ings. 
On the other hand, recent investigations indicate that the odd 
genus Hypocoliiis from the Persian Gulf region is closely related to 
the waxwings. Such are the difficulties encountered in trying to 
work out a distributional history for a small family of birds with no 
significant fossil record and of uncertain near relationships. 

One of the most plausible indications of double invasion of the 
New W^orld by a palaearctic stock is furnished by the shrikes 
(Laniidae). It seems clear that the two North American species 

430 K. C. PARKES 

have been derived from two incursions of the same stock. The de- 
tails of these invasions may be inferred to have been as follows. 
The first immigration took place prior to the Pleistocene glaciation 
by birds belonging to the widespread Old World species that we now 
call Laniiis excubitor. With the advent of glaciation this species 
moved south. It is highly adaptable, as shown by its Old World 
range, which extends from northern Scandinavia to India and 
Arabia. Therefore, with the retreat of the glacier, populations of 
this shrike were able to remain as far south as southern Mexico, 
while northern populations reoccupied an area extending to central 
Canada. At some uncertain time the species again crossed the 
Bering Strait and quickly spread through the boreal portion of 
North America. This second wave is currently regarded as con- 
specific with and closely related to the Old World races through 
the Siberian population, while the descendants of the first invasion 
are given specific rank (L. liidovicianus) . Certain well-marked 
differences that have evolved in these earlier and more southern 
populations are invoked as specific characters. However, members 
of this so-called species, the Loggerhead Shrike, resemble some of 
the ecologically parallel populations of the Old World species 
(Olivier, 1944, p. 43), Judging from published maps and range 
descriptions, the Northern and Loggerhead shrikes nowhere come 
into actual contact during the breeding season in North America. 
There is thus no available natural testing site for the criterion 
of reproductive isolation. We have here an interesting problem of 
deciding what to call the two North American shrikes; although 
they have almost always been listed as full species, there are argu- 
ments and precedents for the opposite view. The problem they 
illustrate is an interesting, although perhaps uncommon one: 
the question of the taxonomic treatment of obvious derivatives, 
from two well-separated invasions of the same stock, that are now 
separated spatially, so that no evidence as to reproductive iso- 
lation is forthcoming. 

Perhaps the most intriguing problem connected with the palae- 
arctic element in the New World avifauna, and the one least likely 
to be solved, deals with the related questions "which?" and "why?" 
— which groups made the trip, and why these and not others? 
Undoubtedly the most striking aspect of this problem is the apparent 
one-way traffic between the two continents; Darlington (1957, 


p. 279) reminded us that this pattern is also true of mammals and of 
cold-blooded vertebrates. Lindroth (1957) listed twenty-four 
species of passeriform birds as occurring in both Eurasia and North 
America. After deducting the swallows and the waxwing, of uncertain 
origin, and two species no longer considered conspecific with their 
overseas counterparts {Pants atricapillus with P. borealis; Sitta 
canadensis with S. corea, kruperi, villosa, and whiteheadi), we are 
left with nineteen species in common. Of these, no fewer than 
sixteen, of nine families, are regarded as of Old World origin and as 
invaders of the New World, while only three species, of two families, 
are treated as immigrants from the opposite direction. Two of 
these species, the Lapland Longspur (Calcarius lapponicus) and the 
Snow Bunting {Plectrophenax nivalis), are panarctic birds that have 
developed a few weakly characterized subspecies. The third species, 
on the contrary, is the highly polytypic wren Troglodytes troglodytes. 
The A.O.U. Check-list (1957), which probably oversplits them, 
recognizes no fewer than twelve North American races, while the 
situation in Eurasia may be judged by Vaurie's recent paper (1955), 
in which he reduced to eight a total of twenty-one proposed races 
from eastern Asia alone. The question, of course, is why} Why has 
this single passeriform species been so obviously successful? Why 
was it one of the very few that has been able to "swim against the 
tide," and what caused the "tide" in the first place? Why are the 
palaearctic-derived siskins, pipits, and thrushes found all through 
South i\merica in suitable habitats, whereas only a single group 
of New World passeriform birds, the emberizine finches, has radiated 
at all in the Old World? Such are the unsolved problems of this 
corner of zoogeography, and most are likely to remain chiefly 
intellectual exercises, since the likelihood of securing tangible 
evidence with which to solve them appears small. 


Alexander, W. B., and R. S. R. Fitter. 1955. American land birds in west- 
ern Europe. British Birds, 48: 1-14. 

Amadon, Dean. 1944. The genera of Corvidae and their relationships. 
Am. Museum Novitates, No. 1251: 1-21. 

American Ornithologists' Union. 1957. Check-list of North American 
Birds, 5th edition. Published by the Union. 

Darlington, Philip J., Jr. 1957. Zoogeography. John Wiley & Sons, New 

432 K. C. PARKES 

Eisenmann, Eugene. 1958. The new A.O.U. Check-list. Linnaean News- 
letter (Linnaean Society of New York), 11, No. 7-8: [1-3]. 
Lindroth, Carl H. 1957. The Faunal Connections between Europe and North 

America. John Wiley & Sons, New York. 
Mayr, Ernst. 1946. History of the North American bird fauna. Wilson 

Bull. 58: 1-41. 
Olivier, Georges. 1944. Monographie des Pies-Grieches du genre Lanius. 

Lecerf, Rouen. 
Peters, James L. 1937. Check-List of Birds of the World, Vol. 3. Harvard 

University Press, Cambridge, Mass. 
Peterson, R. T., Guy Mountfort, and P. A. D. Hollom. 1954. A Field 

Guide to the Birds of Britain and Europe. Houghton, Mifflin, Boston, 

Vaurie, Charles. 1955. Systematic notes on palearctic birds. No. 16. 

Troglodytinae, Cinclidae, and Prunellidae. Am. Museum Novitates, 

No. 1751: 1-25. 
Wetmore, Alexander. 1956. A check-list of the fossil and prehistoric 

birds of North America and the West Indies. Smithsonian Misc. 

Collections, 131, No. 5. 

Distributional Patterns of Vertebrates in the 
Southern United States in Relation to 
Past and Present Environments 

W, Frank Blair 

Department of Zoology, The University of Texas, 
A iistin 

1 he thesis of this discussion is that the present 
distributions of vertebrates in the southern United States, on the 
Gulf and Atlantic coastal plains in particular, can be explained only 
on the hypothesis of drastic ecological changes in the deep south in 
the Pleistocene. The germ of this concept was stated by Adams 
(1902). More recently, Deevey (1949) expressed the hypothesis 
clearly and reviewed some of the supporting evidence in his general 
discussion of Pleistocene biogeography. The argument is essentially 
that at peaks of glacial advance into the northern United States 
climatic and ecological changes in the southern United States were 
so great as to drive warmth-adapted species into separate refuges in 
Florida and Mexico. Blair (1951) referred to additional evidence 
from the vertebrates. 

Braun (1955 and other papers) has been particularly vigorous in 
opposition to this hypothesis and has argued that the conditions 
that produced the Pleistocene glaciations had little effect in the 
southern United States. 

I now reopen the question, reviewing some of the evidence cited 
by previous workers and introducing additional material. The evi- 
dence is concerned primarily with past and present distributions of 
tetrapod vertebrates, other than birds. One item in the past distribu- 
tion of fishes is cited, but the present distribution of this group is 
excluded from consideration. Similarly, no treatment of birds is 
attempted, because of the author's relative unfamiliarity with this 

The area to which the discussion will be largely limited is the Gulf 


434 W. F. BLAIR 

coastal plain and the bordering grasslands to the west, although the 
argument applies equally to other species in eastern North America 
not today limited to the coastal plain. Two major biotic formations 
are involved. The Austroriparian forest extends with only minor 
variance in climate, ecological dominants, and general aspect from 
eastern Texas to the Atlantic coast. The southern grasslands border 
the forest of the west. These grasslands, with beginnings in the late 
Miocene and great development in the Pliocene (Clements and 
Chaney, 1937) stand today as a barrier to the westward distribution 
of many forest animals. 

I consider three major questions: 

1. What is the evidence in regard to Pleistocene climates in the 
southern United States? Were the climatic changes sufficiently 
drastic as to force the withdrawal of warmth-adapted coastal plain 
animals into separate eastern (Floridian) and western (Mexican) 

2. How effective were the grasslands as a Pleistocene barrier to 
the southwestward withdrawal of warmth-adapted species into 

3. How do present distributions fit the hypothesized Pleistocene 

climatic changes? 


Evidence from various sources indicates major ecological changes 
on the coastal plain in the Pleistocene, including far southward 
shifting of northern plants and animals during stages of glaciation 
in the north. Climatic implications from these shifts must rest on 
the assumption that ecological requirements of living species and 
genera do not differ significantly from those of their Pleistocene 
progenitors. When single taxa are involved, this assumption some- 
times may be of doubtful validity. When whole faunal or floral 
assemblages are represented, little or no basis seems to remain for 
questioning its validity. 

Plant Fossils 

Most of the scanty but highly significant evidence from plant 
fossils has been reviewed by Deevey (1949, 1950). On the western 
coastal plain, spruce {Picea) and fir {Abies) pollens have been found 
at the base of bog deposits in Lee, Milam, and Robertson counties. 


Texas (Potzger and Tharp, 1947, 1954). The determination that 
spruce and fir pollens total 11% of the pollen in the lowermost foot 
level in the Gause bog in Milam County was interpreted by the 
authors as "adding to the accumulating evidence of a widespread 
cool-moist climate, and migration of boreal genera far to the south 
of the actual borders of the continental ice caps." On the eastern 
coastal plain, Frey (1951) reported spruce and hemlock (Tsuga) 
pollens from a profile from Singletary Lake, North Carolina, and 
found a pine-spruce maximum at a zone of approximately 10,000 
years age, determined by radiocarbon dating. Below this zone an 
amelioration of climate is indicated, and above it successive changes 
to warm, moist and to warm, dry are indicated. Spruce and fir 
pollens have been reported from northern Florida, in Pleistocene 
peats hypothesized as of late Wisconsin age (Davis, 1946). 

Pleistocene macrofossils of northern types have been recorded 
from a few southern localities. Larch (Larix) has been reported 
from northern Georgia (Berry, 1907). Remains of larch, spruce, 
and arbor vitae (Thuja) have been found along Little Bayou Sara in 
southern Louisiana (Brown, 1938). Braun (1955) attempted to 
rationalize these southern records of northern plants with her argu- 
ment against general displacement southward of climatic zones in 
the Pleistocene. The hypothesis that frost pockets existed near the 
coast and that cold, foggy climates prevailed there was suggested as 
the explanation of the past occurrence of northern species on the 
southern Atlantic coastal plain. She further suggested that ecologi- 
cal requirements of the northern indicator species may have been 
at one extreme of the tolerance range as manifested today. On the 
contrary, the past occurrence of species that now live in the region 
of the Little Bayou Sara deposits with the northern invaders can 
more plausibly be explained by the assumption that they then 
existed there at the limits of their cold tolerance, rather than that 
the northern species were there with them because of their own 
warmth tolerance. It seems quite unreasonable to attribute the 
appearance of the presently cold-adapted species near the present 
Gulf shores to any circumstance other than climatic change, and it 
seems only reasonable on Dr. Braun 's own argument to attribute 
their coexistence with present warmth-adapted species to the ability 
of the latter to exist under conditions bordering the limits of their 
cold tolerance. 

436 W. F. BLAIR 

Vertebrate Fossils 

Pleistocene fossils from the coastal plain itself are few, except in 
Florida, which is postulated as a glacial-stage refuge. Records from 
other areas, however, are strongly indicative of major southward 
shifts of climatic zones. The evidence comes from individual species 
with northern distributions today and from relatively large faunal 
assemblages with similar distributions. 

Southernmost records of the Pleistocene muskox Symbos (Hay, 
1923, 1924) lie far south of the present distribution of the living 
genus Ovibos (Fig. 1). These records show that this muskox ranged 
at least as far south as LeFlore County, Oklahoma, and Natchez, 
Mississippi. If it is assumed that Symbos even approached Ovibos in 
its ecological requirements, and it is plausible to do so, these records 
indicate much colder conditions than those of the present. The 
Oklahoma and Mississippi records are far south of the glacial border 
at the time of maximum advances. 

The walrus (Odobenus) is known from several Pleistocene fossils 
collected in the vicinity of Charleston, South Carolina (Hay, 1923), 
but in historic times it has occurred only as far south as Maine 
(Allen, 1930). 

The moose (Alces) is known from the Pleistocene as far south as 
Charleston, South Carolina, and Bigbone Lick, Kentucky (Hay, 
1923), but within historic times has occurred only as far south as 
northern New York (Miller and Kellogg, 1955). 

Among small mammals, a shrew (Sorex cinereus) is known from 
several Pleistocene localities far south of its present range (Fig. 2). 
The southernmost of these is the San Josecito cave in southern 
Nuevo Leon (Findley, 1953). This species is also listed in the Conard 
Fissure fauna of northwestern Arkansas (Hay, 1924), and Hibbard 
(1949) reported it from the Cudahy fauna, regarded as Kansan in 
age, and from the Jones Ranch fauna, regarded as late Wisconsin, 
of southwestern Kansas. 

The marmot (Marmota) likewise lived south of its present southern 
limits during parts of the Pleistocene. The southernmost record is 
from San Josecito cave in southern Nuevo Leon (Cushing, 1945). 
This rodent has also been recorded from Pleistocene cave deposits in 
southern Arizona and New Mexico (Skinner, 1942; Stearns, 1942; 
Murray, 1957). The present southern limit of Marmota fiaviventris 
is in northern New Mexico, at elevations above 11,000 feet. 



'TO l«0 140 100 eO 40 30 

Fig. 1. Present distribution of the muskox, Ovibos (shaded) and 
southernmost records of the Pleistocene muskox, Symbos. 

438 W. F. BLAIR 

The climatic implications of the bog lemming {Synaptomys cooperi) 
in the San Josecito cave fauna (Gushing, 1945) have been discussed 
by Hibbard (1955a). The present southern limits of this species are 
in northeastern Kansas, except for relictual populations in small 
bogs in southwestern Kansas. 

The most complete picture of the southward shift of northern 
faunas comes from the work of Hibbard in southwestern Kansas and 
northwestern Oklahoma. Four cool faunas are recognized and ten- 
tatively identified with the four major glaciations of the Pleistocene 
(Hibbard, 1953). Two warm faunas are attributed to the Second 
and Third Interglacials, and only the First Interglacial is unrepre- 
sented. Mammalian components of several of these faunas are listed 
by Hibbard (1949). The Cudahy fauna, regarded as representing the 
closing phase of a Glacial age (Kansan), has the following small 
mammals of northern afifinity: 

Sorex cinereus, present distribution (Fig. 2). 
Sorex cudahyensis, extinct. 

Sorex (Neosorex) lacustris, extinct; most closely related species 
today mostly in Ganada, south in Rocky Mountains to northern 
New Mexico. 

Microsorex pratensis, extinct; most closely related species today 
mostly in Ganada and Alaska, south to northern Iowa. 
Synaptomys borealis, now north of Ganadian border. 
Microtus paraoperarius, extinct ; related species operarius now in 
northwestern Ganada and Alaska. 
Microtus llanensis, extinct. 
Pitymys meadensis, extinct. 

Phenacomys sp., genus now mostly in Ganada, but south in Rocky 
Mountains to northern New Mexico. 

The assemblage contains a few cricetine rodents and a few species 
of little climatic significance. The great preponderance of microtine 
rodents and shrews, however, leaves no doubt that there was a shift 
of a boreal fauna at least as far southward as southwestern Kansas. 
There is no reason to assume that Hibbard 's work in this area was 
done at the periphery of the range of this northern fauna, but the 
evidence has yet to be accumulated to show how much farther south 
it extended. 

The Jones fauna (Hibbard, 1949), regarded as late Wisconsin in 
age, includes the northern species Sorex cinereus, Citellus richardsoni, 



Fig. 2. Present distribution of the masked shrew, Sorex cinereus, 
(stippled) and Pleistocene records of this species (dots). 

440 W. F. BLAIR 

and Microtus pennsylvanicus , along with various species and genera 
that occur in southwestern Kansas today and some highly euryther- 
mal forms. 

Another fauna from the same general area is of extreme interest 
because it includes a number of fishes (Smith, 1954). This fauna, 
from Beaver County, Oklahoma, is regarded as Illinoian in age. 
Along with species of presently wide distribution, it includes such 
northern species as the muskellunge {Esox miisquinongy) and yellow 
perch {Perca flavescens) , both of which have southern limits today 
several hundred miles to the northeast. Spruce, fir, and pine pollens 
were found in the deposits from which the fossils were taken. Mam- 
mals listed in this fauna include the northern species Sorex cinereus 
and Microtus pennsylvanicus and a few types that occur in the 
region today. 

Other faunas from this same region are regarded as Interglacial, 
and are dominated by mammals of generally southern affinities 
(Hibbard, 1949, 1955b). When considered along with the cool- 
climate faunas, they indicate recurrent major climatic shifts in 
the region. 

The Conard Fissure fauna of northwestern Arkansas (described 
by Barnum Brown and listed by Hay (1924), who regarded it as 
possibly Illinoian in age) includes a number of mammals that occur 
today considerably farther north, or have their closest relatives 
there. These are: the red squirrel {Sciurus hudsonicus), which now 
ranges south to southern Iowa; the porcupine {Erethizon dorsatum), 
which now ranges south to central Wisconsin in the central states, 
but is widely distributed in mountains of the west; the snowshoe 
hare {Lepus americanus), which now reaches a present southern 
limit in the central United States similar to that of the porcupine; 
the masked shrew {Sorex cinereus) and the pigmy shrew {Micro- 
sorex), which now range south to northern Iowa; the fisher (Martes 
pennanti) , which now occurs north of the Great Lakes ; and the least 
weasel (Mustela erminea), which now ranges south to southern 
Nebraska. The extinct muskox (Symbos) is also represented. 

Another cave fauna from much farther south includes a similar 
representation of cold-adapted mammals. This is the Burnet Cave 
fauna of the Guadalupe Mountains, New Mexico. As listed by Mur- 
ray (1957) this assemblage includes various species that occur in the 
region today and several of presently more northern distribution. 


The latter are: the hoary marmot {Marmota flaviventris) , a microtine 
{Microtiis longicaudus), the hoary packrat {Neotoma cinerea), the 
white-tailed jackrabbit {Lepus townseudi), and the red fox (Vidpes 
fulva). These species are associated today with yellow pine and 
spruce-fir forests and with the exception of the microtine reach 
their southern limits about 250 miles to the north at high elevations 
in the mountains. An extinct caribou-like species, Rangifer fricki, 
and an extinct bovid, Eiiceratheriimi collinum, of debated ecological 
significance, are also listed. 

As listed by Sherman (1952), the Pleistocene mammalian fauna of 
Florida, which is commonly regarded as a refuge for warmth-re- 
quiring species during the glacial stages, contains virtually no mam- 
mals of boreal affinity. Possible exceptions are an elk (Cerviis sp.) 
and a bog lemming {Synaptomys australis). The latter, however, is 
associated with a presumably Sangamon (Third Interglacial) fauna 
in Kansas (Hibbard, 1955b). 

The evidence from plant fossils on the coastal plain, from pollen 
profiles that show spruce, fir, and other northern species of plants as 
far south as southeastern Texas and northern Florida, and from the 
numerous Pleistocene occurrences of vertebrates and vertebrate 
faunas far south of their present distributions, leads to the conclu- 
sion that there were great ecological changes in the southern United 
States in the Pleistocene. It is the thesis of the present discussion 
that these changes, particularly those accompanying the glacial 
stages, were sufficiently drastic to fragment the ranges of warmth- 
adapted coastal plain species and to force their southeastward and 
south westward withdrawal, respectively into Florida and Mexico. 


It has been argued that the southern grasslands have existed as a 
barrier to the interchange of forest biota between the eastern United 
States and Mexico since the development of the grasslands under in- 
creasing aridity in the Pliocene. Separation since pre- Pliocene times 
and slow rates of evolution are explanations given for the strong 
floral resemblance between the humid forests along the escarpment 
of the Mexican Plateau and the eastern forests (Braun, 1955). 
Martin and Harrell (1957) discussed this theory in the light of some 
vertebrate distributions and suggested that "few temperate-forest 
animals were able to cross the arid Texas barrier in the Pleistocene. 

442 W. F. BLAIR 

They probably did so along a cool savanna or open woodland 

The question of past conditions in the area occupied by the south- 
ern grasslands is highly germane to the problem of Pleistocene dis- 
junctions in the southern United States. Most of the evidence 
pertinent to this problem has never been summarized. It involves 
Pleistocene fossils and present relictual distributions. The specific 
question is one of how permanent has been the arid grassland 

Invasion from South America 

Several South American groups of mammals crossed the supposed 
grassland barrier and the coastal plain in the Pleistocene. Their 
arrival in North America must have followed the development of 
the Central American land bridge in the late Pliocene and early 
Pleistocene, and their dispersal around the Gulf of Mexico and east- 
ward across the coastal plain must have occurred after the develop- 
ment of the presumed grassland barrier. The known Pleistocene 
faunas of Florida include several representatives of this element, 
including: the common porcupine (Erethizon dorsatum), capybaras 
(two genera, Hydrochoerus and Neochoeriis), glyptodonts {Boreo- 
stracon), armadillos {Daspyus, Holmesina), and ground sloths 
{Megatherium, Megalonyx, Paraniylodon, Thinobadistes) , as listed by 
Sherman (1952). Of these, the porcupine and ground sloths must 
have required trees for their dispersal, and others, the capybaras, at 
least, would have required much greater moisture than is available 
at present in the southern grasslands. 

Fossil Evidence of Interglacial Conditions 

Various Pleistocene fossils from the region of the present grass- 
lands represent groups that probably could not exist there under 
present conditions and that probably required greater moisture or 
forest. One of the most striking of these is the water rat (Neofiber). 
At present this rodent is limited to bog situations in peninsular 
Florida (Fig. 3). In what was probably the Third Interglacial 
(Sangamon) this water rat occurred in the Texas panhandle and in 
central Kansas (Meade, 1952; Hibbard, 1943). This rodent is also 
known from the Pleistocene of Pennsylvania (Hibbard, 1955c), 
where it presumably lived during an Interglacial interval. Another 



444 W. F. BLAIR 

significant distribution is that of an extinct bog lemming {Synap- 
tomys australis), which is known from the Pleistocene of Florida 
(Sherman, 1952) and from the Jinglebob fauna (Sangamon) of 
southwestern Kansas (Hibbard, 1955b). 

Ground sloths, which presumably depended on trees for browsing, 
have been recorded from various localities in the present grasslands. 
Paramylodon is known from the Jinglebob (Sangamon) fauna of 
southwestern Kansas, where its fossils are associated with pine 
(Pinus) and Osage orange (Madura) pollens (Hibbard, 1955b). This 
sloth is also known from various localities in Colorado, Nebraska, 
and Texas in the area of the present grasslands, and Nothrotheriiim 
is known from such presently arid grasslands as the Big Bend region 
and panhandle of Texas (Hay, 1924). 

Tapirs {Tapir us) are even more indicative of forests than ground 
sloths. These have been recorded from the present grasslands in 
north central Oklahoma and as far west as El Paso, Texas (Hay, 
1924) and southwestern Oklahoma (Hibbard, 1957). A mandible in 
the Centennial Museum, Texas Western College, from a cave in the 
Hueco Mountains, Texas, is not permineralized and possibly repre- 
sents a late occurrence of the tapir in this presently arid and treeless 
region (W. S. Strain, oral communication). 

The preceding evidence implies that vastly different conditions pre- 
vailed at times during the Pleistocene, where grasslands exist today. 
It seems reasonable to hypothesize that under the vast shifts of 
climatic regimes that characterized the Pleistocene a wide spectrum 
of conditions from moist to arid might be expected to have existed 
in the present grasslands in various combinations with temperature 

Relations of the Floridian Vertebrates 

The present Floridian fauna includes various animals that have 
been there for a long time, including some that have their nearest 
living relatives in eastern Asia, but this circumstance is not perti- 
nent to the present discussion except as it indicates the long-con- 
tinued existence in the Southeast of a faunal center of distribution 
and dispersal. The Floridian fauna also includes a considerable ele- 
ment of species that belong to groups with centers of distribution in 
the Southwest, where they are generally adapted to more xeric 
conditions than exist today on the coastal plain. The presence of 


this western element in Florida suggests past climatic fluctuations 
on the coastal plain that favored eastward spread. This element 
includes: Scaphiopus holbrooki, Bufo woodhousei, Microhyla caro- 
linensis, Sceloporiis undidatus, Cnemidophorus sexlineatus, Crotalus 
adamanteus, Speotyto cimicularia, Aphelocoma coerulescens, Pero- 
myscus polionotus, P. gossypinns, Reithrodontomys humulis, R. 
fulvescens, Geoniys pinetis, and Neotoma Jloridana. Some of these 
(e.g., Microhyla carolinensis and Peromyscus gossypinus) have 
become adapted to high-moisture situations of the coastal plain. 
Others have tended to retain their xeric adaptations and exist today 
in the most xeric situations available. The most extreme examples 
of the latter group include Scaphiopus, Cnemidophorus, Aphelocoma, 
and Peromyscus poliojiotus. 

Relictual Distributions in the Southern Grasslands 

Present relictual occurrences of forest plants and animals argue 
against the past stability of the grasslands. The isolated populations 
are reasonably assumed to be remnants of the widespread popula- 
tions of post-Wisconsin time and indicate greater, or at least more 
effective, moisture in the not distant past than prevails in the grass- 
land today. The sugar maple group {Acer saccharum and others) is 
an important example because it is representative of a group with 
Mexican disjuncts that was regarded by Braun (1955) as having 
been separated since pre-Pliocene times. Martin and Harrell (1957) 
showed the occurrences of Acer skulchii in Mexico and Guatemala 
and the general distribution of the saccharum group in the eastern 
United States, but they overlooked a highly' significant group of 
relictual populations in Texas and western Oklahoma, These are 
shown in Fig. 4 along with an approximation of the western limits 
of this group in the eastern forest and the approximate eastern limits 
of the representative of this group (A . grandidentatum) in the south- 
ern Rocky Mountain chain. In Oklahoma, these relicts occur in the 
Wichita Mountains in the southwestern part of the state and in 
Caddo Canyon, Caddo County. In Texas, there are relict popula- 
tions along the southern escarpment of the Edwards Plateau (Sar- 
gent, 1922). Sugar maples (identified as A. grandidentatum) occur in 
moist ravines in the higher mountains of trans- Pecos Texas (Sargent, 
1922, and author's observations). It does not seem possible that the 
Oklahoma and Texas populations are relicts of a pre-Pliocene dis- 



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tribution. They are taken, instead, to indicate a Wisconsin or 
post-Wisconsin distribution that could have connected the Mexican 
and eastern populations of sugar maples. 

The bald cypress {Taxodium distichum) occurs as far west in 
Texas as the Devil's River (Sargent, 1922). Isolated palmetto 
(Sabal minor) plants are found on the Edwards Plateau west of 
Austin, Texas. One of these was found on the floodplain of Bear 
Creek, Hays County, when we went to in\'estigate the locality at 
which an isolated specimen of Microhyla carolinensis had been 
collected far west of the continuous range of this eastern species of 
frog. The loblolly pine {Pinus taeda) grows on sandy soil over an 
extensive disjunct area in Bastrop County, Texas. A disjunct 
population of the greenfrog {Rana clamitans) lives along Alum Creek 
in this same area. A western montane species, the pinon pine {Pinus 
ediilis) has disjunct growths as far eastward as Kerr County on the 
Edwards Plateau. 

The piiion mouse {Peromyscus nasutus), which is distributed in 
the pinon belt and above in the southern Rocky Mountain chain, 
is represented by a disjunct sibling species {P. comanche) in the 
cedar {Jiiniperus) forests of the Palo Duro Canyon and other 
canyons along the escarpment of the High Plains in the Texas pan- 
handle. The two are separated today by more than 100 miles of arid 
grassland (Blair, 1943). The brush mouse {Peromyscus boylei), 
which is associated with montane forests in the west, has relictual 
populations (Fig. 5) much farther east than the preceding species. 
The most eastern of these is in the Ozarks and Ouachita Mountains 
of Oklahoma, Arkansas, and Missouri and is so little differentiated 
that it has been treated as the same subspecies as in western Texas, 
An eastern forest species that shows relictual populations deep 
into the present grasslands is the pine vole {Pitymys pinetorum) 
which has a close relative {P. quasialer) in eastern Mexico. The map 
of the distribution of these voles drawn by Martin and Harrell 
(1957) gives an erroneous impression of the relation of the eastern 
species to the grasslands, because the range of this species is drawn 
to include these relicts. Actually (Fig. 6), the westward distribution 
of the main body of the population of this species ends at or inside 
the border of the eastern forest in eastern Texas and Oklahoma. The 
relictual populations near Kerrville on the Edwards Plateau of Texas 
(Bryant, 1941) and in the Wichita Mountains, Oklahoma (Blair, 





Fig. 6. Present distribution of pine voles, Pitymys: P. parvulus in 
southeast; P. pinetorum in eastern United States, with reUcts in Texas 
and Oklahoma; and relict P. qiiasiater in Mexico. 

450 W. F. BLAIR 

1939) live about 200 miles farther west. This species is closely asso- 
ciated with forests throughout its range, and the relicts in Texas 
and Oklahoma as well as the Mexican relicts must have reached 
their present locations by way of forests. 

The neotenic salamanders of the genus Eurycea on the Edwards 
Plateau of Texas appear to be closely related to similarly adapted 
E. tynerensis of the Ozarks and thus indicate a southward as well as 
westward shift of conditions favorable for this group. The two groups 
are separated today by a distance of over 400 miles. In both areas, 
these salamanders are restricted to cool springs in forested regions. 
Another plethodontid genus (Plethodon) shows an interesting but 
more complex pattern of relictual distribution (Fig. 7). A population 
of P. glutinosus on the Edwards Plateau is disjunct from the main 
distribution of this eastern species, which reaches into eastern Texas. 
On the Edwards Plateau this species is found in relatively moist 
ravines and around springs or entrances to caves. Plethodon ouachitae 
of Rich Mountain in southwestern Arkansas appears to be a relict 
of an Appalachian group (Dunn and Heinze, 1933). x'\nother species 
of this genus (P. neomexicanus) occurs in spruce-fir forests of the 
Jemez Mountains of northern New Mexico (Stebbins and Riemer, 
1950). This species is described as "close to Plethodon cinereus of 
eastern United States and Canada." There are disjunct populations 
of P. cinereus in the Ozarks and in eastern Missouri, but the main 
body of the population is east of the Mississippi River. Stebbins 
and Riemer surmised that southward dispersal through the Rocky 
Mountains accounted for the New Mexico population, but dispersal 
directly across Oklahoma in the Wisconsin seems a more plausible 
explanation. The genus occurs along the Pacific Coast from northern 
California to British Columbia, and there is a relict species in north- 
ern Idaho. Another plethodontid genus with wide disjunctions is 
Amides. One species lives in the Appalachian region of the eastern 
United States, one in the Sacramento Mountains of southern New 
Mexico, and three along the Pacific Coast. Lowe (1950) hypothesizes 
geographical separation of the New Mexico species {A . hardyi) dur- 
ing early Pliocene. We suggest alternatively that a connection 
between it and the eastern population could have existed as re- 
cently as the late Pleistocene. 

An area on the floodplain of the San Marcos River in Gonzales 
County, Texas, has an assemblage of eastern coastal plain plants 



452 W. F. BLAIR 

and animals that are disjunct from their main populations. The 
palmetto {Sabal minor), burr oak {Quercus macrocarpa) , wax myrtle 
(Myrica cerifera) and ash {Fraxinus) are representative of a rather 
large number of plants in this category. The vertebrates include 
the canebrake rattlesnake {Crotaliis horridus), banded watersnake 
(Natrix sipedon), and narrow-mouth frog (Microhyla carolmensis) . 


The vertebrate groups of the coastal plain under consideration are 
characterized with few exceptions by a relative scarcity of closely 
related sympatric species and by a rather large number of allopatric 
species or populations that show evidence of relatively recent dis- 
junction. Among the 40 genera of mammals, only seven include 
species that are sympatric on the coastal plain. The best represented 
genus is Peromyscus, with five species that represent three subgenera. 
The lizard fauna is sparse, with only eight genera, of which three, 
Sceloperus, Eumeces, and Ophisaiirus, include species that are 
sympatric there. On the coastal plain, there are 25 genera of snakes 
of which nine there include sympatric species, with the largest 
representation in the genus Natrix. Four of the 13 genera of turtles 
include species that are sympatric on the coastal plain. Five of the 
seven genera of anurans include species that are sympatric on the 
coastal plain, but only Ra?ia and Ilyla, which have their United 
States center of distribution on the plain, include several species 
that are broadly sympatric there. Six of the 12 genera of urodeles 
include species that are sympatric on the coastal plain. 

If the urodeles are excluded from the tabulation the some 40 
cases of allopatry, secondary interbreeding, or narrow sympatry 
indicative of past separation into east and west populations out- 
number the cases indicative of north-south disjunction in a ratio of 
more than seven to one. These east-west disjunctions follow a few 
general patterns. One pattern involves present limitation of the 
disjunct populations to forests. One example is that of Pitymys 
(Fig. 6), which was mentioned earlier. Another example is furnished 
by the flying squirrel (Glaucomys volans), which ranges west to the 
border of the eastern deciduous forest and has a disjunct subspecies 
in the mountains from Chihuahua to Honduras (Martin and Harrell, 
1957). The opossum {Didelphis marsupialis) shows evidence of 
secondary interbreeding of previously disjunct populations in 


southern Texas (Blair, 1952). Peromyscus gossypinus of the coastal 
l^lain and P. leucopiis overlap in a generally narrow zone along the 
border of the coastal plain and along the deciduous forest border in 
eastern Texas and Oklahoma (Osgood. 1909; McCarley, 1954). The 
present distribution of this species pair can be explained as a result 
of the westward and northward spread of the coastal-plain-adapted 
gossypinus from a refuge in Florida and the northward and eastward 
spread of leucopus from a Mexican refuge, where it would have been 
adapted to less mesic upland forests. The remarkable call "races" 
of the gray treefrog {Hyla versicolor) described by Blair (1958) 
imply the splitting of this species into three populations along north- 
south axes, with subsequent spread to bring about the present 

Other examples of forest-restricted isolates, discussed by Martin 
and Harrell (1957), include: (1) the red-bellied snake {Storeria 
occipitomaculata) , which is widely distributed in the eastern forest 
with relicts in the central grasslands and in Mexico, (2) the yellow- 
lipped snakes, which comprise Rhadinea flavilata to the east on the 
coastal plain and a closely related species, R. laureata, disjunct in 
Mexico, and (3) the barred owl (Strix varia), which has a Mexican- 
Central American disjunct. 

The largest group providing evidence of past or present disjunc- 
tion into eastern and western populations is the one in which the 
eastern population inhabits forests and the western population is 
adapted to, or tolerant of, grasslands. The members of some of 
these species pairs meet or approach at or near the forest boundary 
in eastern Texas and Oklahoma. Two hylid frogs, Pseitdacris nigrila 
and P. clarki, which are interfertile in the laboratory, overlap nar- 
rowly along this boundary, where they show a complex set of isola- 
tion mechanisms (Lindsay, 1958). Two narrow-mouth frogs, 
Microhyla carolinensis and M. olivacea, overlap narrowly in this 
same area, where they hybridize to a limited extent and where 
their isolation mechanisms are apparently being reinforced (Blair, 
1955). Two populations of toads referred to by some (as by A. P. 
Blair, 1941) as an eastern species, Bufofowleri, and a western species, 
B. woodhousei, meet and freely interbreed, secondarily, in this same 
area (Meacham, 1958). The eastern pine snake {Pituophis melano- 
leucus) and the western bullsnake (P. catenifer) either approach 
range or interbreed in southeastern Texas (Smith and Kennedy, 

454 \V. F. BLAIR 

1951). The pigmy rattlesnakes comprise an eastern, forest species, 
Sistruriis miliarius, a grasslands species, 5. catenates, and a disjunct 
species, 5. raviis, in eastern Mexico (Smith and Taylor, 1945). The 
eastern box turtle {Terrapene Carolina) and western box turtle (7". 
ornata) overlap narrowly along the forest border. Two harvest mice, 
the eastern Reithrodontomys humulis and the western R. montanus, 
approach one another but apparently do not meet along the forest 
border. The ranges of two packrats, the eastern Neotoma floridana 
and the western N. micropus, Interdigitate in the broad forest-grass- 
land ecotone. Two skinks, the eastern Eumeccs anthracmus and the 
western E. septentionalis, overlap in eastern Oklahoma and Kansas. 
An eastern newt, Diemictylus viridescens, ranges west to the edge of 
the forest and is separated by a grassland gap from the related 
species D. meridionalis of southern Texas and northeastern Mexico. 
The group of species pairs discussed above interpret as having 
reached their present distributional relationships through post- 
Wisconsin spread to the margin of their respective environments, 
where they have attained contact or near contact with their sibling 
species. Another sizable group of species pairs shows a quite different 
pattern in that the Mississippi Embayment, deep within the 
Austroriparian forest, is involved in their separation. The species 
pairs in this group have mostly remained widely disjunct. Two pairs 
appear to be limited by soil types. An eastern pocket gopher, Geomys 
pinetis, occurs on sandy soil of the coastal plain to the east of the 
embayment, and a western species, G. bursarius, occurs on sands to 
the west of it. The alluvial soils of the embayment appear to be the 
ecological factor separating the present ranges of these allopatric 
species. Two species of spadefoots (Scaphiopus) have essentially 
similar distributions. The eastern 5. holbrooki and western S. hurteri 
have been shown to be interfertile in the laboratory (Wasserman, 
1956). A broader hiatus, of forested land, separates two chorus 
frogs, Pseudacris streckeri and P. ornata (Fig. 8). P. streckeri occurs 
west of the forest border, which imposes a limit to its eastward 
distribution. P. ornata ranges west on the coastal plain to the Mis- 
sissippi Embayment. There is little differentiation between the two 
in mating call or morphology. Hybrids between them have been 
produced, but one attempted backcross of a male hybrid to streckeri 
failed (Mecham, 1957). Two species of Rana have a rather similar 
distribution: The eastern gopher frog {R. capito) ranges west on the 



coastal plain to the Pearl River; the western crawfish frog (R. 
areolata) is abundant on the coastal prairie in eastern Texas and 
ranges northeastward in the grasslands but is limited in its eastward 
distribution by the forest. 

6-OHuoi w«ii «oo 

Fig. 8. Present distributions of two closely related, allopatric species 
of chorus frogs. 

Both forest and grassland occur in the hiatus between the eastern 
and western populations of the indigo snake {Drymarchon corais). 
The eastern population occurs on the coastal plain east of the 
Mississippi Embayment; the western population ranges from the 
area of Corpus Christi in Texas southward into northern South 
America. The eastern black-headed snake (Tantilla coronata) occurs 
east of the embayment, and its western counterpart, T. gracilis, 
lives west of the forest border. Eastern and western populations of 
Amphiuma, distinguished by a difference in the number of toes, 
meet at the Mississippi Embayment where they may act as species 













(see Baker, 1947) or at most secondarily interbreed. A very wide 
disjunction exists between an eastern treefrog, Hyla femoralis, 
and the apparently related //. arenicolor of the west (Fig. 9) : H. 
femoralis occurs on the coastal plain west to the embayment and 
H. arenicolor ranges westward from trans-Pecos Texas, which means 
there is a gap of some 700 miles between the ranges. 

Another disjunction involving the Mississippi Embayment and a 
forest gap is that of the diamondback rattlesnakes. The eastern 
diamondback (C adamanteus) is limited on the west by the embay- 
ment; the western diamondback (C. atrox), with a wide range in 
northern Mexico and the southwestern United States has its east- 
ward distril)ution limited at the forest border. An apparently 
isolated (relict) population of this species is known from the vicinity 
of Tehuan tepee, Oaxaca, Mexico (Stebbins, 1954). A third isolate, 
C. ruber, in southern California and Baja California, possibly stems 
from a Pleistocene isolate in Baja California fsee Gloyd, 1940). 

The gopher turtles (Gopherus) also comprise three isolates (Fig. 
10). The eastern species, G. polyphemus, ranges on the coastal plain 
west to the vicinity of the Mississippi Embayment. Another, G. 
berlandieri, occurs in northeastern Mexico and southern Texas and is 
separated from the eastern species by a gap involving both grassland 
and forest. The third disjunct. G. agassizi, ranges from northern 
Sonora through western Arizona and southeastern California to 
southern Nevada. 

The cricketfrogs (Acris) have overlapping ranges that involve the 
Mississippi Embayment and the margin of the coastal plain. The 
eastern coastal plain species, A. grylliis, is limited westward by the 
embayment. The western species, A. crepitans, overlaps the range of 
the eastern species just east of the embayment and along the Fall 
Line (see Blair, 1958). The distributional relationships of these 
frogs are comparable to those of the Peroniyscus leucopus group ex- 
cept for the limitation of the eastern population by the embayment, 
and they are interpreted similarly as the result of post- Pleistocene 
spread from Floridian and IVlexican refuges. 

The distributional pattern of the Bujo americaniis group of toads 
is a more complex variation of the same general pattern (Blair, 
1958). The eastern coastal plain form, B. terrestris, is limited west- 
ward by the Mississippi Embayment. A population to the north of 
the Fall Line, B. americanus, is interpreted as having spread from a 




southwestern refuge, leaving a relict, B. houstonensis , on the eastern 
Texas coast. 

The Mississippi Embayment also limits the westward distribution 
of five species of anurans that have no western counterparts. These 
are the oak toad {Bujo quercicus), bird-voiced treefrog {Hyla phaeo- 
crypta), barking treefrog {H. gratiosa), little grass frog (//. ocularis), 
and river frog {Rana heckscheri) . 

The Peromyscus maniculatus group of mice, with one of the most 
complex distributional patterns of any North American vertebrate 
(Fig. 11), shows east-west speciation on the coastal plain (Blair, 
1950). The beach mouse (P. polionotus), which occurs on the coastal 
plain east of Mobile Bay, on morphological evidence is derived 
from the grassland-adapted ecotype of the deer-mouse (P. manicula- 
tus), which today ranges southward into south-central Texas (Fig. 
11). The beach mouse presumably originated through an eastward 
dispersal along Gulf Coast beaches and subsequent isolation in 
Florida. The forest-adapted ecotype of the deer-mouse living today 
in the southern Appalachians presumably moved south during 
glacial stages into the area that is today a gap between the range of 
the beach mouse and that of its Texas progenitor. 

The brown water snake {Matrix taxispilota) , which ranges from 
Florida into Mexico, has a disjunct population in southern Mexico 
(Smith and Taylor, 1945). The rat snake (Elaphe obsoleta) shows 
evidence of secondary interbreeding on the Edwards Plateau in 
Texas. Turtles of the genus Graptemys are of dubious value here be- 
cause of lack of agreement among specialists on the group. As 
mapped by Carr (1952) the range of G. pseudogeographica is mostly 
west of the Mississippi River, and that of G. geographica mostly east 
of it. The mud turtles, Ki?tosterno7t, are represented by two species 
in the eastern forest and three to the west of it (Cagle, 1957). 

The bats have been omitted from the preceding discussion, but 
they too show east-west disjuncts across the coastal plain. Examples 
are found in the genera Tadarida, Eumops, Cory?iorhinus, Pipistrel- 
lus, Dasypterus, and Lasiurus. In Lasiurus, the pattern of distribu- 
tion is comparable to that of the Peromyscus leucopus group: the 
western L. borealis overlaps the coastal plain L. seminolus along the 
forest border in the west and along the Fall Line. 

Some species of vertebrates, showing no evidence of previous dis- 
junction, range today completely across the Gulf Coast, and conse- 



bution of the Peromyscus maniculatus species group of 

Fig. 11. Distri^^.,-.. 
mice (from Blair, 1950) 

quently across the central area from which warmth-adapted species 
are indicated to have been driven. Such species as the cotton rat 
{Sigmodon hispidus) , cottontail {Sylvilagus floridanus) , coachwhip 
{Masticophis flagellum), and green treefrog {Hyla cinerea) are 
representative. Their wide distribution can be explained as having 
been attained by spread from an eastern or western refuge or by 
such a rapid spread from both refuges that contact of populations 
and interbreeding were reestablished before marked differentiation 


had occurred. Their existence does not controvert the evidence 
presented above of extensive east-west fragmentation of ranges 
among warmth-adapted coastal plain vertebrates in the Pleistocene. 

Instances of north-south fragmentation of ranges involving 
coastal plain species, exclusive of the urodeles, are contrastingly 
scarce. The southern rough green snake {Opheodrys aestivus) and 
northern smooth green snake (0. vernalis) constitute one example. 
However, relicts of the northern species in central and southeastern 
Texas (Davis, 1949) indicate a very different past distribution and 
suggest the possibility that the present distribution is derived from 
an east-west disjunction comparable to that postulated for the 
Peromysciis leucopus group. In the common water snake {Matrix 
sipedon) a freshwater ecotype shows secondary interbreeding with a 
salt-marsh ecotype around the Gulf Coast. Pettus (1956j hypothe- 
sized continuous distribution of the salt-marsh type in the Pleisto- 
cene and a southern refuge or refuges for the freshwater type. Hyla 
andersoni of the New Jersey pine barrens is an apparent relict of a 
formerly more northern extension of H. cifierea on the xA.tlantic 
coastal plain (see Blair, in press). 

The Pseiidacris nigrita group, with the most complex distribution 
pattern of any group of North American anurans, does show evi- 
dence of north-south speciation in the eastern United States. A 
small group of relicts of grasslands-adapted mammals in Mexico 
and on the Texas coast (Blair, 1954) is consistent with the thesis of 
southward displacement of cold climates and of the Arcto-Tertiary 
forest. In the east there are a few such relicts of groups that occur 
today in the northern United States. The spotted turtle {Clemmys 
guttata) occurs as a relict in northern Florida. A northern species of 
frog, Rana sylvatica, has left relict populations in northwestern 
Arkansas and in the Flint Hills of Kansas (Smith, 1950). 

The distributional patterns of warmth-adapted vertebrates on the 
coastal plain as discussed above are overwhelmingly indicative of 
east-west fragmentation of ranges as the initial agent of geographic 
speciation in this fauna. The variations in distributional patterns 
shown by allopatric populations undoubtedly reflect differences in 
ability to reoccupy territory after the initial disjunction, differences 
in the time that has elapsed since the initial separation, and other 
more subtle factors. It might be argued that the east-west speciation 
simply reflects adaptation to forest and grassland environments. 

462 W. F. BLAIR 

However, evidence inconsistent with such an explanation is pro- 
\'ideci by the numerous hiatuses between eastern and western 
populations that involve segments of one or the other environments 
or segments of both. 

Sympatric distributions of coastal plain groups may trace back to 
the same kind of east- west disjunction exhibited by the allopatric 
populations, but such history is difficult to demonstrate. McConkey 
(1954) has theorized that the three species of legless lizards (Ophi- 
saurus) of the coastal plain originated through east-west splitting 
in the Third Glacial (Illinoian) and through subsequent isolation of 
the third population on Florida islands in the Third Interglacial 


A comparison of the distributional patterns of anuran and urodele 
amphibians in the eastern United States illustrates as clearly as any 
possible documentation the postulated Pleistocene history of the 
coastal plain biota. The anurans are mostly a warmth-adapted 
group, with more species on the coastal plain than anywhere else in 
the United States. Ten of the 24 coastal plain species or species 
groups show evidence of past or present disjunction into eastern and 
western populations, as discussed in the preceding section. Seven of 
the 10 have their eastern population limited to the coastal plain. 
The other three, Biifo woodhousei, Pseudacris nigrita, and Hyla 
versicolor, range widely in the eastern United States. Six of the 
remaining 14 species are limited to the coastal plain east of the 
Mississippi Embayment and are presumed to have spread to their 
present limits from a Pleistocene refuge in Florida. Of the eight 
remaining species, only three are limited to the coastal plain. Two 
of these, Hyla cinerea and H. squirella, range across the coastal plain 
from the Atlantic to Texas, and the range of the third, Rana grylio, 
stops short of the forest border in eastern Texas. The five remaining 
species, Hyla crucifer, Rana pipiens, R. palustris, R. clamitans, and 
R. catesbeiana, all range northward into Canada, and on the basis 
of their present distribution it seems likely that they could have 
existed continuously across the coastal plain under Pleistocene 
Glacial-stage conditions. North-south speciation in the anurans is 
limited to the splitting off of Hyla andersoni and the speciation in 
the Pseudacris nigrita complex discussed earlier. 


The urodeles, by contrast with anurans, are typically a cool- or 
cold-adapted group. The center of distribution of the large family 
Plethodontidae, which includes a majority of the urodeles of the 
eastern United States, is in the Appalachian highlands in remnants of 
the Arcto-Tertiary forest, which the evidence shows to have shifted 
southward in the Glacial stages of the Pleistocene. As might be 
expected, there is for this group no strong pattern of east- west dis- 
junction comparable to that of the warmth-adapted anurans. Of 
some 56 species and species groups of urodeles in the eastern United 
States, only 23 occur on the coastal plain, and only 11 are restricted 
there. Only two of the coastal plain group, Diemictylus and Amphi- 
uma, show evidence of east-west disjunction, as earlier mentioned. 
The most obvious disjunctions in the eastern urodeles are ones that 
are attributable to the southward and westward spread of the Arcto- 
Tertiary forest and its urodele fauna under Glacial-stage climates 
and to the isolation of relictual populations under locally tolerable 
conditions, as the environment became warmer and dryer. This 
would explain the relict populations of Plethodon, Hemidactylium, 
and Eurycea in the Ozarks, of Plethodon and Eurycea on the Edwards 
Plateau, and of Aneides and Plethodon in the mountains of New 
Mexico. The absence of plethodontid relicts from the cloud forests 
of Mexico, discussed by Martin and Harrell (1957), would be ex- 
pected if these animals stayed with the Arcto-Tertiary forest in the 
southern United States. The difference in the pattern of distribution 
of anurans and urodeles results, then, from the fact that the urodeles 
would have moved with the invading environment that fragmented 
anuran ranges. Amelioration of the environment that permitted 
reoccupation of the coastal plain by warmth-adapted anurans would 
have led to the observed disjunctions in urodele ranges. Unlike the 
situation in the anurans, there are numerous instances of north- 
south or unoriented speciation in the urodeles of the eastern United 


A large body of paleontological and zoogeographical data support 
the thesis that present distributional patterns of the warmth- 
adapted vertebrates of the Gulf of Mexico and southern Atlantic 
coastal plains reflect Pleistocene splitting of this faunal group into 
eastern and western populations. The agency of this splitting, as 

464 W. F. BLAIR 

hypothesized by previous workers, is considered to be the southward 
shifting of cHmatic belts during the Glacial stages of the Pleistocene 
and the resultant enforced withdrawal of the warmth-adapted biota 
into separate refuges in Florida and Mexico. 

The evidence from fossil pollens and from plant macrofossils 
indicates that at times in the Pleistocene northern species of trees 
such as spruce, hemlock, fir, larch, and arbor vitae extended onto 
the Gulf and southern Atlantic coastal plains. Boreal mammals and 
a few fishes of northern affinity are known from Pleistocene deposits 
far south of their present distributions and as far south as southern 
Nuevo Leon in Mexico. Both the plant and animal fossils are indica- 
tive, then, of major ecological changes in the southern United 
States in the Pleistocene. 

Evidence from various sources indicates that the southern grass- 
lands have not acted as a continuous barrier to the exchange of 
forest biotas between the eastern United States and the Mexican 
highlands since their origins in the late Miocene and early Pliocene. 
The Pleistocene mammalian fauna of Florida includes various groups 
of South American origin, some of them forest types, that must have 
crossed the area of the present grasslands barrier, as their enti-y into 
North America would necessarily have followed the emergence of the 
Central American land bridge in the late Pliocene. Various Pleisto- 
cene fossils from the area of the present grasslands are indicative of 
greater moisture and of forests at times in this area in the Pleisto- 
cene. These include such indicators of extreme departure from 
present ecological conditions in the area as Neofiber in the Texas 
panhandle and Tapirus in trans-Pecos Texas. An impressive number 
of present day relicts of forest-adapted species in the grasslands 
also argues against past continuity of grassland in the area. 

Present distributional patterns of coastal plain vertebrates indi- 
cate many east-west and very few north-south disjunctions. Some 
of these involve eastern, forest-adapted and western, grasslands- 
adapted populations, with the forest-grasslands boundary important 
in their present distributional relationships. Other patterns involve 
the Mississippi Embayment as a distributional boundary, and in 
this group the hiatus between eastern and western populations may 
include either forest or grassland, or both. Still other patterns in- 
volve eastern and western forest-adapted types, some of which have 
their western populations as relicts in the Mexican highlands. 


The fossil evidence of ecological change in the southern United 
States during the Pleistocene and the evidence derived from the 
existing distributional patterns of vertebrates are consistent in 
indicating that the east-west splitting of the warm-adapted biota 
by the southward shift of colder climates and of the cold-adapted 
biotas has been the chief agency initiating speciation in this area. 
The urodeles of the eastern United States show very different dis- 
tributional patterns from the anurans, because the conditions that 
fragmented the ranges of the warmth-adapted anurans promoted 
the southward and westward spread of the urodeles. Then, the condi- 
tions that permitted reoccupation of the coastal plain by the anurans 
would have forced northward and eastward the retreat of the 


Base map for figures used with permission of University of Chicago. 
Base map for Figs. 1, 2, and 6, copyright 1937 by the University of 
Chicago. Base map used for Figs. 3, 4, 5, 7, 9, and 10, copyright 1938 by 
the University of Chicago. 


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466 W. F. BLAIR 

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General Conclusions 

Carl L. Hubbs 

Scripps Institution oj Oceanography, University of 
California, La Jolla 

1 he fourteen papers from the symposium on 
The Origins and Affinities of the Land and Freshwater Fauna of 
Western North America, plus the three richly supplementing contri- 
butions from the symposium on Geographic Distribution of Con- 
temporary Orgafiisms, constitute a vast storehouse of information on 
zoogeography, on companion fields, and on various sciences that 
provide the background that is necessary for a full understanding of 
zoogeography. The seventeen contributions deal not only with the 
actual distribution of many but of course not all groups of land and 
freshwater animals, along with some aspects of phytogeography, but 
also with various biogeographical topics, and with the background 
material. Most of the contributors deal largely with western North 
America, but a few cover all of North America, and one even 
straddles the whole New World. 

The contributions are diverse not only in respect to the groups of 
organisms, the areas covered, and the topics stressed, but also in the 
angle of approach, in the length and completeness of review, in the 
amount of original material, in the thoroughness (or lack) of docu- 
mentation, and in the abundance, paucity, or lack of illustrations. 
The separate articles vary from abstracts (two) and mere thoughtful 
commentaries, on some phase of the general subject, to long, scholarly 
studies that give us, for the first time, the summary of a distinguished 
author's long-continued and intensive research. 

The whole volume has both the strength and the weakness that 
goes with diversity. It is strong in the variety of viewpoints and 
specialties, in the high competence of each invited participant in 
some aspect of zoogeography or in one of the basically related 
sciences, and in the potential synthesis that is favored by the close 
association of the diverse contributions. It is weak in the fragmenta- 


470 C. L. HUBBS 

tion of the subject, due to the increasing specialization of scientists, 
in the lack of attention to some groups and topics (an unavoidable 
defect in the age of specialization), and in the limited detail and 
documentation in some of the papers. 

The diversity of treatment calls at the outset for an organized 
indication (Table I) of the coverage of the various papers, in terms 
of geographic, evolutionary, systematic, and background considera- 

The individual papers are referred to in the table (and in the fol- 
lowing text) by number as given in the Contents. In the table, 
degree of emphasis (in the papers as printed) is roughly approxi- 
mated by the type: roman for least emphasis, italics, for more 
thorough treatment, and boldface for most exhaustive coverage. 

The emphasis on background considerations and on evolutionary 
and systematic correlatives, brought to focus in the table, is a strong 
indication of a healthy rebound from the course of overspecializa- 
tion. The trend toward interdisciplinary research is exemplified in 
several of the contributions, and is perhaps best illustrated, as well 
as stated, in Martin's contribution (15) on Pleistocene ecology. The 
same happy trend is glowingly evident in several of the other papers, 
notably, for example, those by MacGinitie (2) and by Blair (17). 

The overall treatment further indicates a shift from the classical, 
purely descriptive biogeography to a kinetic approach, which is 
more concerned with processes and explanations than with the 
classification of the earth into a hierarchy of biogeographical regions. 
Attention is focused on floral and faunal elements of diverse origin, 
which may be mixed in any one area, and on the past and present 
dispersions of these biotic elements. This concept of biotic elements, 
which was advanced particularly by Ernst Mayr (followed herein 
by Parkes, 16), penetrates into the limited regional classifications 
of faunas in these symposia. Linsley (13), for example, maps the 
same area of the central California coast as a diluted part of both the 
Vancouveran and Californian faunas, and Rehn (12) apportions the 
western North American orthopteran fauna according to regions 
of origin. 

Past and continuing shifts in biota receive considerable attention, 
in line with the more kinetic approach that is fortunately coming 
into vogue. The background for such biotic dispersals is elucidated 
in several of the papers, notably by King's (1) sweep through the 


grand history of changes in the face of the earth over western 
North America, by MacGinitie's (2) analysis of climatic trends and 
fluctuations in this region since Cretaceous time, and by the excellent 
reviews by Martin (15) and by Blair (17) on the dramatic events of 
the Pleistocene and their consequences. 

Some new, refined approaches in biogeographical analysis are 
emphasized. One of these is the quantitative reconstruction of past 
vertebrate biocoenoses through the study of all identifiable material 
obtained by soil washing — a truly revolutionary (and long overdue) 
development, as D. E. Savage (4) indicates. Another major refine- 
ment is the more precise and penetrating systematic analysis, such as 
is indicated in most of the reports, notably those by Peabody and 
J. M. Savage (8), R. R. ^filler (9), and Parkes (16). Another cir- 
cumstance favoring sound biogeographical conclusions is the life-long 
devoted specialization on single groups, throughout their range, that 
is obvious in the contributions by several of the authors, notably 
A. H. Miller (6), R. R. Miller (9), and the entomologists: Ross (11), 
Rehn (12), Linsley (13), and Hovanitz (14). Radiocarbon dating 
becomes a tool of research in blogeography, as in other areas (Mar- 
tin, 15). Quantitative studies, including pollen analysis, are helping 
to displace inference with data. And, most effective of all as a lead 
toward a fuller understanding of the events and processes in bio- 
geography is the recourse to interdisciplinary and multidisciplinary 

The fabric of this symposium has been woven of threads that vary 
so much in color, size, and strength as to make it difficult to pick 
out these threads to reweave a simple review and conclusion. On 
some basic lines, however, there is sufficient consensus to permit 
some generalization. 

One initial thought that seems justified is that blogeography is 
still a propitious field of inquiry. Certainly, many of the defects of 
the past are attributable to excessive inference on the basis of Inade- 
quate data. Through more intensive research, sharpened by new 
techniques and enriched by Interdisciplinary approach, sound data 
are certain to result, and broader and more reliable interpretations 
are bound to develop. Through the symposium there is to be found 
much justification for this optimism. 

A notable feature of the whole series of papers is that there is 
hardly a mention of the transoceanic land bridges that blogeog- 

472 C. L. HUBBS 

raphers not long ago threw around with abandon. King (1) assures 
us that geologists hold to the theory of the essential permanence of 
the ocean basins, and the biologists seem to have proceeded on this 
assumption. The verified intercontinental connections across the 
Isthmus of Panama and especially across the Bering Strait region 
are duly treated. The intimate relationships between the Palearctic 
and Nearctic faunas are pointed out by Parkes (16) and other 
authors, and are rightly assumed to indicate a past continuity, but, 
as Burt (5), Rehn (12), and Hovanitz (14) point out with admirable 
reserve, there is, as yet, usually little basis for postulating the region 
of origin and the direction of dispersal. In some groups there may 
have been a complex interchange. 

In general, it is admitted, or apparently assumed, that the recon- 
struction of the past history of a group, whether of origin or dis- 
persal, cannot ordinarily be postulated with assurance on the sole 
basis of the present distributional pattern. Considerable variance in 
reserve or reliance, however, is displayed in such reconstructions. 
Bartholomew (3) and Burt (5) go so far as to say there are no 
separate "origins," because there has been a continuum of life, but 
are they not playing with semantics? In terms of given natural 
groups or stages of evolution there is an origin, in both time and 

The criteria of center of origin, or of differentiation, as some would 
prefer to say, are definitely discussed by only two of the authors, 
D. E. Savage (4) and Burt (5). Savage's criteria are the more impres- 
sive because they emphasize the fossil record. His first criterion of 
area of origin is the region from which the oldest fossil is known. 
This is fine for groups with a well-known fossil record, but for groups 
with few known fossils may, as Parkes (16) notes, be even more 
treacherous than criteria based on present distributions. Savage's 
second criterion is an earlier record of progenitors (the sort of 
evidence that puts man's origin securely in the Old World) — again 
good, if the data are adequate. His third criterion is the area of 
greatest taxonomic diversity. This criterion may usually hold, but 
certainly not always. It seems not to apply, for example, to the 
origin of the catostomid fishes, which are almost restricted to North 
America, but which R. R. Miller (9) and I believe, on scanty but 
pertinent distributional and fossil evidence, to have originated in 
Asia, though they seem to have undergone most of their difi^erentia- 


tion in North America. Savage argues wisely that phyletic age, 
relict occurrence, and vagility must be taken into account, but he 
doesn't indicate just how. Other frequently expounded criteria are 
just mentioned, along with Mathew's hypothesis that primitive 
forms are peripheral. 

Savage sharply criticizes the location of the major center of 
origin in the Old World tropics, on the basis of the evidence that the 
present Holarctica is temperate to boreal. As both he and Mac- 
Ginitie (2) point out, the northern lands were subtropical through 
much of Cenozoic time. Obviously, much of evolutionary history is 
still hidden in a fog of ignorance. The task of the historians of life 
has barely begun. And until we know the past, we cannot fully 
understand the present nor guess the future. 

Several of the authors hold to the view long championed by 
Chaney and by Axelrod, and here expounded by MacGinitie (2), 
that world climate became progressively more arid and cooler 
through Tertiary time, while increased relief and other factors 
caused greater local diversity. It seems that there was a general 
northward shift in the climatic zones. All this caused a great trans- 
location of the geo-floras, and, presumably, of the accompanying 
animal communities. Some zoologists, for example Peabody and 
J. M. Savage (8), have been bold enough to reconstruct origins and 
dispersals of certain animals on the basis of the history of the geo- 
floras with which they infer these animals were associated. Are they 
treading on firm ground or on quicksand? 

It seems to be the general consensus that the vast uniformity of 
life that characterized the early Cenozoic, in both space and time, 
gradually changed to diversity throughout Tertiary time, in a grand 
crescendo that reached ecstatic proportions in the Pleistocene. 
Martin (15) and Blair (17) have compiled impressive evidence favor- 
ing the view, which seems to me to be well justified, that the Ice 
Ages were periods of intense cold, during which climatic belts were 
displaced far southward (and far downward on the mountains), and 
during which even the tropics were very considerably cooled. Dur- 
ing the Wisconsin period the temperate biota of eastern North 
America seems to have been forced into refugia in Florida and 
Mexico (Blair, 17), while in the West (Miller, 9) there was extensive 
extermination of the freshwater fauna in the north and a vast 
development of lakes in the Great Basin and southward. 



Table I. Index to Subject Coverage in Symposia on Zoogeography 

Numbers in parenthesis refer to the separate papers by the stated 
authors. Degree of emphasis is roughly approximated by type — roman 
for least emphasis, italics for more thorough treatment, boldface for 
most exhaustive coverage. 

Evolutionary and 
Systematic Considerations 




CRITERIA (on Centers 
of Origin or Differ- 
entiation) : D. E. 
Savage (4), Burt 
(5), Rehn (12), 
Hovanitz (14), 
Parkes (16) 


Of Primitive Man : 

Martin {15) 
Of Modern Man: 

Pennak (10) 



Entire New World: 
Hovanitz (14) 

Nearctica: D. E. 
Savage (4), Mar- 
tin (15), Parkes 
(16), R. R. Miller 
(9), Linsley (13) 

Southeastern United 
States: Blair (17) 

Western North 

America: King (1), 
MacGinitie (2), 
D. E. Savage (4), 
Burt (5), Peabody 
and J. M. Savage 
(8), R. R. Miller, 
(9), Rehn (12), 
Pennak (10), 
Ross (11), Lins- 
ley (13) 

ground: Bartholomew 
(3), Hovanitz (14) 


General: King (1), 

MacGinitie (2), 
Peabody and J. 
M. Savage (8) 

Hydrographic His- 
tory: R. R. Miller 
(9), King (1) 

Pleistocene Events: 
Martin (15), King 
(1), MacGinitie 
(2), Blair (17) 

Physiographic Re- 
lations: King (1), 
Peabody and J. M. 
Savage (8), R. R. 
Miller (9) , MacGinitie 
(2), Hovanitz (14), 
Blair (17) 


Plantes: MacGinitie 
(2), Linsley (13), 
Martin (15), 
Blair (17) 

Insecta: Linsley (13), 
Ross (11), Rehn 
(12), Martin (15) 

Pisces: R. R. Miller 
(9), Blair (17) 


Savage (4), Burt (5), 
R. R. Miller (9), 
Ross (11) 


Martin (15), D. E. 
Savage (4), Ross 


and J. M. Savage 

(S),A. H. Miller 

(6), Pennak (10), 

Hovanitz (14), 

Martin (15), Parkes 

(16), Blair (17) 



Plantes :MacGinitie 

(2), Martin (15), 
Linsley (13), 
Blair (17) 
Pennak (10) 

Dermaptera and 

Rehn (12) 
Northern and 



Koss (11) 

Linsley (13) 



Table I. Index to Subject Coverage in Symposia on Zoogeography 

— Continued 


Relations with Asia: 
Burt (5), 
Parkes (16), 

MacGinitie (2), 
D. E. Savage (4), 
A. H. Miller (6), 
R. R. Miller (9), 
Ross (11), Rehn 
(12), Linsley (13), 
Hovanitz (14) 
Relations with 
South America: 
Hovanitz (14), 
D. E. Savage 
(4), Burt (5), R. R. 
Miller (9), Lins- 
ley (13), Blair 

Relations of East- 
ern to Western 
North America: 
Blair (17), Pennak 
(10), Burt (5), 
A. H. Miller (6), 
R. R. Miller (9), 
Ross (11), Lins- 
ley (13), Hovanitz 
(14), Martin (15) 


Amphibia and 
Reptilia: Peahody 
and J. M. Savage 

Aves: Parkes (16) 
Mammalia: D. E. 

Savage (4), 

Martin {15), Blair 


Cretaceous : 

MacGinitie (2) 

MacGinitie (2), 
King (1), Peabody 
and J. M. Savage 
(8), Linsley (13), 
Blair (17) 

Pleistocene: Martin 
(15), Blair (17), 
MacGinitie {2), 
King (1), Stebbins 
(7), Hovanitz (14) 


MacGinitie (2), 
Blair (17), 

Martin {15), D. E. 
Savage (4), Burt (5) 

GROUND : Martin 
(15), Pennak {10), 
Linsley {13), 
Hovanitz {14), 
Blair {17), R. R. 
Miller (9), Ross (11) 

Evolutionary and 
Systematic Considerations 


Hovanitz (14) 
Pisces: R. R. Miller 

(9), Blair (17) 
Amphibia and 

Reptilia : Peabody 

and J. M. Savage 

{8), Stebbins (7), 

Martin (15), 

Blair (17) 
Aves : Parkes (16), 

A. H. Miller (6) 
Mammalia: D. E. 
Savage (4), 
Burt (5), 

Martin {15), 

Blair (17) 
Man: Martin {15) 

476 C. L. HUBBS 

Despite the evidence of extreme climatic change at the close of 
Wisconsin time and during the Postpleistocene millenia, Martin (15) 
holds to the view that the extinction of the large Pleistocene mam- 
mals is attributable not to climatic change, but to man. I favor the 
theory of a combination of factors. 

After the recurrent restoration of humidity in the Pleistocene, 
the trend toward aridity seems to have continued in the West. The 
deserts seem to have marched northward and to have spread out 
like a vast desiccating fan toward the Pacific Coast and onto the 
Great Plains. This trend is just mentioned in the abstract by 
Stebbins (7), and it is considered, but I believe probably set too far 
back in Cenozoic time, by Peabody and J. M. Savage (8). Desicca- 
tion is plausibly held by R. R. Miller (9) and by Pennak (10) to have 
been largely responsible for the impoverished freshwater fauna of the 
West and for the high incidence of local endemism. A. H. Miller 
(6) attributes the high ratio of endemism among the birds of the 
Californian fauna to the isolation of this fauna by deserts. 

In some groups, as the Orthoptera (Rehn, 12) and Reptilia, in 
contrast, the intensification and spread of the Sonoran region seems 
to have been a potent evolutionary stimulus. 

Redispersals following the vast displacements of the Pleistocene 
are held to have induced some very interesting speciational situa- 
tions. Blair (17) postulates the genetic responses, during Recent 
sympatry, of cognates that had been isolated in the Floridan and 
Mexican refugia. Hovanitz (14) similarly treats the consequences of 
cohabitation of butterflies previously segregated by the Wisconsin 
ice sheet. One pair, he states, has, by hybridization, thus produced a 
third species. 

Geologically recent topographic changes are held to have condi- 
tioned other significant speciational events. Hovanitz (14) attributes 
the high incidence of endemism of butterflies in the Andes to the 
new environments suddenly furnished by the rapid uplift of the 
Cordillera, and he regards this type of response as of general signifi- 
cance. Peabody and Savage (8) explain speciational relations among 
amphibians and reptiles in California on the basis of the establish- 
ment of a Coast Range Corridor. They cite evidence that the Sierra 
Nevada and Coast Ranges were long separated on the south by a 
marine barrier, so that the forms on the two ranges became sub- 
specifically difi"erentiated, though intergrading where their ranges 


converged in the north. They postulate that when the corridor be- 
came estabhshed the cognates met, but, because of the degree of 
separation, remained distinct in cohabitation, behaving here as full 
species at the respective ends of an otherwise specific continuum 
(in other words, forming "open circles"). 

In a slightly Chauvanistic vein, these authors close their paper 
with this exultation: "We may confidently reaffirm and echo A. B. 
Howell's assertion of thirty years ago that the fauna of the Pacific 
Coast is of unusual interest and presents many fascinating problems. 
Californians have a land-bridge laboratory in their own back yard!" 
But, as is suggested by the references just made to Hovanitz and to 
Blair, similarly fascinating situations exist outside the Golden West. 
Zoogeographical gold is where you find it! 

Author Index. 

Adams, C. C, 433, 465 
Aguayo, C. G., 409, 413 
Allee, W. C, 85, 94, 97, 127 
Alexander, W. B., 423, 431 
Allen, G. M., 409, 413, 436, 465 
Allen, J. A., 410, 414 
Allen, V. T., 40, 57 
Amadon, D., 427, 431 
Andersen, S. T., 377, 386, 414 
Anderson, F. M., 19, 57 
Andrewartha, H. B., 82, 93 
Antevs, E., 72, 77, 382, 391, 414 
Anthony, B., 219 
Anthony, H. E., 409, 414 
Atkinson, W. S., 209 
Atwood, W. W., 28, 31, 33-35, 57 
Atwood, W. W., Jr., 28, 31, 33-35, 

Axelrod, D. I., 34, 41-43, 57, 69, 

77, 100, 114, 126, 166-168, 170, 

185, 303-306, 318, 473 

Bailey, R. M., 198, 219 
Baker, A. A., 14, 57 
Baker, C. L., 457, 465 
Baldwin, A. H., 198 
Barclay, F. H., 413 
Barendsen, G. W., 387, 414 
Barnes, W., 365 
Bartholomew, G. A., 85, 86, 88- 

90, 472, 474 
Bates, M., 365 
Bell, R. Y., 59 
Bell, W. A., 112, 127 
Benson, R. B., 233, 252 
Benson, S. B., 412, 414 
Bentley, P. J., 89, 94 
Berg, L. S., 197, 205, 219 
Berry, E. W., 112, 127, 435, 465 
Birch, L. C., 82, 93 
Blackwelder, E., 213, 219 
Blackwelder, R. E., 318 
Blair, A. P., 453, 465 

Blair, W. F., 433, 447, 453, 457, 
459, 461, 465, 466, 470, 471, 

Blaxter, K. L., 87, 94 

Bogert, C. M., 85, 94 

Bogolepov, K. v., 66, 77 

Bowman, K., 365 

Boyce, S. G., 381, 419 

Bradley, J. C., 318 

Bradley, W. H., 27, 28, 33, 57 

Brame, A. H., 179, 186 

Brattstrom, B. H., 160, 185 

Braun, E. L., 375, 377, 382, 414, 
433, 435, 441, 445, 466 

Breyer, A., 365 

Brock, V. E., 214 

Broecker, W. S., 404, 414 

Brooks, C. E. P., 64, 71, 77 

Brooks, G. S., 366 

Brown, A. L., 210 

Brown, B., 440 

Brown, C. A., 72, 77, 435, 466 

Brown, F. M., 366 

Bryan, K., 36, 57 

Bryant, M. D., 447, 466 

Bullock, T. H., 88, 94 

Burbank, W. S., 14, 23, 57 

Burt, W. H., 153, 472, 474, 475 

Cabrera, A., 136, 137, 153 
Cade, T. J., 86, 88, 93 
Cagle, F. R., 459, 466 
Cain, S. A., 134, 153, 383, 414 
Camp, C. L., 160, 163, 164, 185 
Carpenter, F. M., 233, 252 
Carpenter, G. D. H., 366 
Carr, A., 459, 466 
Chandler, M. E. J., 65, 79 
Chaney, R. W., 46, 57, 64, 66, 67, 
69, 78, 100, 127, 129, 168, 185, 
390, 414, 434, 466, 473 
Chu, Y. T., 220 
Clark, A. H., 366 




Clark, J., 129 
Clark, J. G. D., 375, 414 
Chatfield, P. O., 88, 94 
Clements, F. E., 434, 466 
Clisby, K. H., 380, 390, 391, 414, 

Cockerell, T. D. A., 259, 318 
Cohen, N. W., 85, 94 
Colbert, E. H., 120, 127, 129,413, 

Comstock, J. A., 366 
Comstock, W. P., 366 
Condit, C, 185 
Cook, H. J., 104, 127 
Cook, S. P., 405, 416 
Cooke, C. W., 405, 414 
Cooper, W. S., 313, 318 
Cope, E. D., 192, 194, 220 
Core, E. L., 382, 414 
Courtemanche, A., 385, 418 
Cowles, R. B., 85, 94 
Craig, R. A., 71, 77, 78 
Crampton, G. C, 289 
Crane, H. R., 405, 414 
Crook, W. W., 412, 414 
Cross, W., 30, 58 
Crowell, J. C, 52. 58 
Cruxent, J. M., 395, 414, 418 
Curtis, G. C, 58 
Gushing, J. E., Jr., 436, 438, 466 

Dane, C. H., 57 

Dansereau, P., 378, 379, 395, 

407, 413, 414 
Darlington, H. C, 382, 387, 414 
Darlington, P. J., Jr., 101, 102, 

127, 134, 142, 153, 190, 199, 

220, 318, 421, 422, 425, 427, 

430, 431 
Darwin, C, 97, 104, 127, 395, 396, 

Davenport, D., 366 
Davis, A. C, 318 
Davis, J. H., Jr., 72, 78, 415, 

435, 466 

Davis, M. B., 377, 381, 387, 

388, 413, 415 
Davis, W. B., 461, 466 
Davis, W. M., 38, 58 
Dawson, W. R., 85, 86, 90, 93 
Deevey, E. S., Jr., 141, 153, 375, 

377, 382, 384, 386, 387. 389, 

409, 413, 414, 417, 433, 434, 

Denny, C. S., 377, 415 
Denton, S. P., 202 
Dibblee, T. W., Jr., 52, 58, 114, 

Dietz, R. S., 53, 59 
Dillon, L. S., 366, 375, 390, 415 
Dorf, E., 62, 63, 78, 318 
Dosh, E. P., 382, 419 
Drury, W. H., 377, 378, 382, 383, 

Dumas, P. C, 90, 94 
Dunbar, C. O., 57 
Dunkle. D. H., 106, 127 
Dunn, E. R., 450, 466 
Durham, J. W., 63, 65, 68, 78, 

114, 127, 249, 252 
Durham, W., 168, 185 
Dyar, H. G., 366 
Dylik, J., 381, 415 

Eager, G., 206 

Eardley, A. J., 10, 12, 57, 58, 

164, 165, 185 
Eastman, C. R., 220 
Eaton, T. H., Jr., 203, 220 
Edwards, R. S., 58 
Edwards, W. H., 366 
Eisenmann, E., 424, 432 
Eisley, L. C, 403, 412, 415 
Elias, M. K., 69, 78 
Ellerman, J. R., 136, 137, 153 
Elrod, M. J., 366 
Elson, J. A., 413 
Elwes, H. J., 366 
Emerson, A. E., 99, 102, 127 
Emiliani, C, 63, 72, 78, 141, 153, 

249, 252, 376, 415 



Epstein, S., 249, 252 
Erdbrink, D. P., 137, 145, 153 
Estes, R., 161 
Evermann, B. W., 198, 200, 202, 

205, 207-209, 220 
Evernden, J. F., 18, 58 
Ewing, M., 8, 16, 58 

Fall, H. C, 318 

Fenneman, N. M., 57 

Ferguson, H. G., 18, 58, 59 

Field, W. D., 366 

Findley, J. S., 372, 436, 466 

Fiske, W. F., 366 

Fitch, H. S., 412, 415 

Fitter, R. S. R., 423, 431 

Flint, R. F., 72, 74, 77, 78, 122, 

127, 375, 377, 378, 382, 389, 

391, 392, 401, 402, 411, 413, 

Forbes, W. T. M., 366 
Foreman, F., 419 
Fox, R. M., 366 
Frenzel, B., 375, 415 
Frey, D. G., 378, 379, 381, 386, 

387, 415, 435, 466 
Fries, C. C., 106, 127 
Frye, J. C., 70, 78 

Garnett, R. T., 318 
Garth, J. S., 366 
Gay, H., 366 
Gazin, C. L., 106, 127 
Gibson, A., 367 
Gilbert, C. H., 210, 220 
Gill, E. D., 403, 409, 413, 415 
Gilluly, J., 53, 58, 59 
Gloyd, H. K., 457, 466 
Godman, F. D., 367 
Goldsmith, J. W., 59 
Goodlett, J. C., 381, 416 
Goodrum, P., 415 
Gralenski, L. J., 414 
Grant, M., 107, 127 
Gressitt, J. L., 318 
Griffin, H., 413 

Grinnell, F., Jr., 367 
Grinnell, J., 367 
Griscom, L., 393, 416 
Grossbeck, J. A., 367 
Guilday, J. E., 412, 416 

Hack, J. T., 381, 382, 416 
Hall, E. R., 135, 153 
Hamilton, J., 318 
Hamilton, W. J., 89, 94, 413, 416 
Handlirsch, A., 303, 318 
Hansen, H. P., 391, 416 
Hardy, G. H., 318 
Hardy, R., 142, 153 
Hare, F. K., 378, 413, 416 
Harrell, B. E., 392, 393, 413, 416, 

417, 441, 445, 447, 452, 453, 

463, 467 
Harris, R. K., 412, 414 
Harriss, T. F., 18, 60 
Haury, E. W., 396, 413, 416 
Hay, O. P., 436, 440, 444, 466 
Hayden, E. B., 410, 411, 418 
Hayward, K. J., 367 
Hecht, M. K., 411, 416 
Heinze, A. A., 450, 466 
Heizer, R. F., 405, 416 
Herre, A. W. C. T., 214, 220 
Hesse, R., 85, 94, 97, 127 
Hester, J. J., 413 
Heusser, C. J., 391, 416 
Heyerdahl, T., 411, 416 
Hibbard, C. W., 106, 122, 123, 

127, 376, 401, 402, 404, 413, 

416, 436, 438, 440-442, 444, 

Hill, M. L., 52, 58 
Hock, R. J., 88, 94, 95 
Hodge, E. T., 47, 48, 58 
Hoffmann, C. C., 367 
Hollister, J. S., 51, 53, 59 
HoUom, P. A. D., 423, 432 
Horn, G. H., 318, 319 
Hospers, J., 76, 78 
Hotz, P. E., 59 
Houpt, T. R., 95 



Hovanitz, W., 367, 471, 472, 474- 

Howard, A. D., 36, 58 
Howell, A. B., 159, 185, 477 
Howell, T. R., 92, 93 
Hoy, H. E., 215, 220 
Hubbell, T. H., 284 
Hubbs, C. L., 37, 42, 43, 58, 

193, 203, 206-210, 212-214, 

216, 217, 219-221 
Hulten, E., 319 
Hunt, C. B., 30, 35, 36, 58, 404, 

Hussakof, L., 193, 220 
Hustich, I., 378, 416 
Hutchinson, G. E., 91, 94, 392, 


Irving, L., 86, 94, 95 
Irwin, J. H., 19, 31, 58, 59 
Iversen, J., 417 

Jameson, D. J., 59 

Jarnum, S. A., 95 

Jenness, D., 418 

Jennings, J. D., 417 

Jepsen, G. L., 120, 127, 129 

Johnson, P., 95 

Johnson, H. R., 58 

Johnson, W. D., 31, 58 

Jordan, D. S., 198, 200, 202, 205, 

208, 209, 220 
Jordan, K., 367 
Jorgensen, P., 367 

Kay, M., 9, 58 

Kaye, W. J., 367 

Kayser, C., 88, 94 

Kellogg, R., 136, 137, 153, 409, 

418, 436, 467 
Kennedy, J. P., 453, 468 
Ketner, K. B., 59 
Khalaf, K., 245, 252 
King, P. B., 36, 58, 470, 472, 474, 

Kitts, D. B., 384, 417 

Klebs, R., 303, 319 

Knowlton, F. H., 65, 78, 112, 

Koopman, K. P., 409, 410, 413, 

417, 420 
Krog, H., 94 
Kulp, J. L., 414 

Lack, D., 83, 94 

Lance, J. P., 59, 221,413 

Landry, S. O., Jr., 100, 127 

Lange, A. L., 391, 417 

Langston, W., Jr., 101, 127 

Larsen, E. S., 30, 59 

LeConte, J. L., 319 

Lee, A. K., 89, 94 

Lee, T. E., 394, 417 

Lee, W. T., 36, 59 

Leighton, B. V., 367 

Leonard, A. B., 70, 78 

Leopold, A. S., 390, 417 

Leopold, E. B., 413 

Leopold, L. B., 72, 78 

Leopold, S. B., 377, 387, 388, 417 

Lewis, C. B., 366 

Li, Hui-Lin, 69, 78 

Lindroth, C. H., 424, 431, 432 

Lindsay, H. L., 453, 467 

Lindsey, C. C., 187, 198, 211, 

217, 218, 220 
Linsley, E. G., 104, 128, 302, 315, 

319, 470, 471, 474, 475 
Lipson, J. I., 58 
Livingstone, B. G. R., 377, 384, 

385, 387, 417 
Livingstone, D. A., 377, 384, 385, 

387, 413,417 
Longstaff, G. B., 367 
Longwell, C. R., 10, 36, 39, 56, 

59, 221 
Lonnberg, E., 429 
Lonsdale, J. T., 129 
Louderback, G. D., 59 
Love, A., 413 
Love, D., 413 
Lovering, T. S., 14, 23, 57 



Lowe, C. H., Jr., 74, 78, 179, 

186, 413, 450, 467 
Lowenstam, H. A., 249, 252 
Lowther, G., 413 
Lucas, F. A., 194, 221 
Lydekker, R., 97 
Lyman, C. P., 88, 94 

McAlpine, W. S., 367 
McCarley, W. H., 453, 467 
McConkey, E. H., 462, 467 
MacCurdy, G. G., 414 
McDonald, J. E., 413, 492 
MacDonald, J. R., 67, 78 
McDunnough, J. J., 365 
MacGinitie, H. D., 65, 67, 69, 

79, 301, 304, 319, 470, 471, 

McGrew, P. O., 107, 128 
McKee, E. D., 19, 59 
McKenna, M., 161 
McKenna, M. C., 106, HI, 119, 

MacLachlan, J. C, 59 
MacLachlan, M. E., 59 
MacNeish, R. S., 404, 417 

Mackin, J. H., 25, 31, 34, 56, 59 

Macy, R. W., 367 

Main, A. R., 89, 94 

Malin, J. C., 74, 79 

Manley, G., 71, 79, 386, 417 

Mannerheim, G. C. G., 319 

Manning, T. H., 384, 417 

Marshall, J. T., 393, 417 

Martin, J. O., 319 

Martin, M., 413 

Martin, P. S., 377, 380, 382, 387, 

391, 392, 417, 441, 445, 447, 

452, 453, 463, 467, 470, 471, 

Martynov, A. V., 254 
Mason, H. L., 61, 79, 304, 325, 

319, 390, 414 
Matthew, W. D., 97, 101, 102, 

104, 127, 134,409,417,475 

Maxwell, R. A., 129 

Mayr, E., 100, 102, 104, 128, 421, 

422, 425, 429, 432, 470 
Meacham, W. R., 453, 467 
Meade, G. E., 442, 467 
Mecham, J. S., 454, 467 
Meek, S. E., 214, 221 
Menard, H. W., 53, 59 
Mercer, J. H., 384, 417 
Merriam, C. H., 137, 141, 153, 

311, 313, 314, 319 
Michener, C. D., 315, 319 
Miller, A. H., 92, 94, 390, 417, 

471, 474-476 
Miller, G. S., Jr., 136, 137, 153, 

409, 418, 436, 467 
Miller, R. R., 37, 43, 58, 193, 207- 

210, 212-217, 220-222, 471-476 
Mitono, T., 319 
Monson, M., 94 
Moore, T. E., 243, 244, 252 
Moreau, R. E., 375, 418 
Morrison-Scott, T. C. S., 136, 

137, 153 
Mosely, M. E., 232, 252 
Mosimann, J. E., 413 
Mountford, G., 423, 432 
Muller, S. W., 18, 58 
Murray, K. F., 73, 79, 391, 418, 

436, 440, 467 
Myers, G. S., 102, 128, 191, 221 

Nelson, E. M., 199, 201, 221 
Newman, C, 415 
Nikiforofif, C. C., 382, 418 
Noble, L. P., 52, 59 
Nolan, T. B., 12, 38, 59 
Norris, K. S., 85, 92, 94 

Officer, C. B., 58 
Ogden, J. G., 413 
Olivier, G., 430, 432 
Olson, E. C., 107, 128 

Opik, E. J., 77, 79 
Oriel, S. S., 59 



Osborn, H. F., 97, 128, 405, 411, 

413, 418 
Osgood, W. H., 135, 153, 154, 453, 


Parkes, K. C, 403, 470-472, 474, 

Patrick, R., 417 
Patterson, B., 106, 120, 128 
Peabody, F. E., 161, 180, 185, 186, 

471, 473-477 
Pearson, O. P., 85, 86, 95 
Peltier, L. C, 377, 418 
Pennak, R. W., 474-476 
Peters, J. L., 432 
Peterson, R. T., 423, 424, 427, 432 
Pettus, D., 461, 468 
Plass, G. N., 75, 77, 79 
Pongracz, A., 303, 319 
Potzger, J. E., 72, 79, 381, 385, 

387, 388, 418, 420, 435, 468 
Powell, J. W., 59 
Press, F., 8, 58 
Pruitt, W. O., Jr., 142, 154 

Quimby, G. I., 394, 418 
Quinn, J. H., 129 

Rabb, G. B., 410, 411, 413, 418 
Ramaswami, L. S., 203, 221 
Rand, A. L., 384, 418 
Rasmussen, W. C., 382, 418 
Reed, C. F., 160, 186 
Reed, E. C., 367 
Reed, R. D., 51, 53, 59 
Reeside, J. B., Jr., 57. 129 
Regan, C. T., 199, 205, 221 
Rehn, J. A. G., 470-472, 474-476 
Reid, E. M., 65, 79 
Repenning, C. A., 31, 37, 59, 193, 

Riemer, W. J., 450, 468 
Roberts, R. J., 12, 59 
Robins, C. R., 210, 222 
Robinson, G. D., 56 

Romer, A. S., 101, 128, 411, 413, 

Rosenthal, G. M., 171, 186 
Ross, H. H., 234-236, 238, 239, 

241-244, 251, 252, 471, 474, 475 
Rostlund, E., 197, 198, 222 
Rothschild, W., 367 
Rouse, I., 395, 404, 405, 414, 418 
Rouse, J. T., 30, 59 
Rousseau, J., 378, 418 
Russell, L. S., 106, 128 

Salvin, O., 367 

Sargent, C. S., 445, 447, 468 

Sauer, C. O., 411, 418 

Savage, D. E., 471-475 

Savage, J. M., 179, 186, 471, 

Sawyer, W. H., 85, 95 
Schaeffer, B., 102, 128 
Schaeffer, C., 320 
Scharff, R. F., 376, 418 
Schmid, F., 235, 252 
Schmidt, K. P., 85, 94, 97, 101, 

127, 128 
Schmidt-Nielsen, B., 87, 95 
Schmidt-Nielsen, K., 87, 95 
Schoenwetter, J., 413 
Scholander, P. F., 86, 95 
Schultz, J. R., 390, 419 
Schultz, L. P., 196, 219, 222 
Schwade, I. T., 114, 128 
Sclater, P. L., 97 
Scott, W. B., 132, 141, 154 
Scudder, S. H., 320, 368 
Sears, P. B., 380, 390-392, 414, 

Seitz, A., 323, 368 
Sellards, E. H., 394, 419 
Seward, A. C., 64, 79 
Shapley, H., 415 
Sharp, A. J., 74, 79 
Sharpe, C. F. S., 382, 419 
Shepard, H. H., 367 
Sherman, H. B., 441, 442, 444, 468 



Shotwell, J. A., 108, 128 

Sibree, J.,409, 419 

Simpson, G. G., 97, 104, 106, 109, 
110, 112, 120, 121, 123, 128, 
136, 139-141, 143, 154, 401, 
402, 408, 409, 413, 419 

Skinner, M. F., 436, 468 

Skjolsvold. A., 411, 416 

Smiley, T. L., 413 

Smith, C. L., 440, 468 

Smith, H. M., 453, 454, 459, 461, 

Smith, P. W., 74, 79,389,419 

Snyder, J. O., 210, 211, 222 

Soday, F. J., 394, 419 

Spieker, E. M., 20, 59 

Statz, G., 303, 320 

Stearns, C. E., 391, 419, 436, 468 

Stebbins, G. L., Jr., 100, 101, 128 

Stebbins, R. C, 160, 162, 171, 
178, 179, 186, 450, 457, 468, 
475, 476 

Stewart, O. C, 395, 419 

Stille, H., 54, 59 

Stirton, R. A., 194, 222, 301 

Stock, C., 129 

Stovall, J. W., 106, 129 

Strain, W. S., 444 

Stuart, L. C., 393, 417 

Swanson, V. W., 59 

Taliaferro, N. L., 17, 18, 53, 60, 

164, 186 
Taylor, E. H., 454, 459, 468 
Taylor, W. W., 394, 419 
Tharp, B. C., 72, 79, 381, 418, 

435, 468 
Theobald, N., 259 
Thomas, E. W., 376, 419 
Thorson, T. B., 86, 89, 95 
Tillyard, R. J., 254, 259 
Troll, C., 375, 415 
Tucek, C. S., 414 

Ulmer, G., 232, 252 
Underwood, E. J., 88, 95 

Ureta, E., 368 
Urey, H. C., 72, 79 
Usinger, R. L., 104, 128 
Uyeno, T., 215, 221 

Van Dyke, E. C, 309, 313, 320 
Van Frank, R., 160, 162, 186 
Van Houten, F. B., 25, 27, 28, 40, 

41, 43, 60, 109, 112, 129 
Vaurie, C., 431, 432 
Vogt, G. B., 320 

Wadia, D. N., 74, 79 
Walker, E. M., 289 
Wallace, A. R., 97, 307, 320 
Wallace, R. E., 53, 60 
Wallgren, H., 86, 95 
Walters, V., 95, 198, 203, 222 
Warren, B. C. S., 368 
Wasserman, A. O., 454, 468 
Waters, A. C., 46-48, 60 
Wells, B. W., 381, 419 
Wetmore, A., 393, 403, 411, 419, 

426, 428, 432 
Weyl, R., 392, 419 
White, S. E., 392, 420 
Whitehead, D. R., 378, 383, 413 
Whittaker, R. H., 382, 389, 420 
Wickham, H. F., 320 
WiUmovsky, N. J., 196 
Wilke, F., 90, 94 
Willett, H. C., 71, 74, 76-79 
Williams, E. E., 409-411, 417, 420 
Williams, S., 394, 405, 420 
Wilson, J. A., 106, 129 
Wilson, L. R., 378, 381, 420 
Witthoft, J., 394, 420 
Wodehouse, R. P., 66-79 
Wolfe, P. E., 382, 420 
Wood, H. E., 106, 129 
Woodford, A. O., 18, 56, 60 
Woodring, W. P., 16, 60 
Wormington, H. M., 394, 395, 

404, 420 
Wright, W. G., 368 


Wynne-Edwards, V. C, 201, 204, Zeuner, F. E., 62, 79, 259, 282, 

222 285, 289 

Yehle, L. A., 381, 382, 420 Zumberge, J. H., 387, 388, 420 

Yepes, J., 136, 137, 153 Zweifel, R. G., 160, 180, 186 

Index of Scientific Names- 

Abies, 304, 305, 392, 434 
Abramidinae, 203 
Acacia, 265 
Acantherus, 21 S 
Acanthocinus, 306 
Acanthoderes, 313 
Acer, 67, 304, 305 

grandidentatiim, 445, 446 

saccharum, 445, 446 

skutchii, 445 
Acheta, 287 

assimilis, 287 
Achiridae, 189 
Achryson surinamuni, 307 
Achurum, 274, 275 
Acipenseridae, 188 
Acmaeops pratensis, 306 
Acratocnus, 407 
Acreinae, 344, 345 
Acrididae, 259-277 
Acridinae, 273-277 
Acridoidea, 256-277 
Acris, 457 

crepitans, 457 

gryllus, 457 
Acrodectes, 282 
Acrolophitus, 274 
Actinote, 344, 345 
Adelpha, 348, 351, 352 
Adenostoma, 261 
Aeoloplides, 268 
Aeria, 337 
Aerochoreiites, 272 
Aeropedelliis, 273, 274 
Aeropus, 273 
Aesculus, 376 

octandra, 376 
Agallisus, 307 
Agapetus, 239 
^gaz'e, 376 

Ageneotettix, 274, 275 
Ageronia, 348, 351 
Agkistrodon, 377, 389 

contortrix, 377, 389 

Aglaothorax, 281, 282 
Agosia chrysogaster, 215 

klamathensis , 211 

nubila, 211 
ylgrm5, 349, 360 
^gm, 351 
Agroecotettix, 268 
Agymnastus, 270 
Aidemona, 268 
Ailanthiis, 67, 305 
Alaudidae, 429 
^Zce, 124 
>lZce5, 137, 149, 436 

a/ce5, 137 
Alesa, 353 
Alnus, 304 
yl/o/>g.v, 124, 137, 148 

la go pus, 137 
Amauronematus, 243 
Amblycorypha, 278 
Amblygonia, 354 
Amblyrhiza, 409 
Amblytropidia, 274 
Ambrosia, 377, 378 
Ambystomidae, 161 
Amelanchier , 304 
Amelinae, 292 
Amiidae, 218 
Ammobaenetes , 284 
Amphibia, 85, 475 
Amphidecta, 338, 339 
Amphipoda, 227, 228 
Amphitornus, 274 
Amphiunia, 455, 463 
^wyzow, 193, 202 
Anabrus, 280, 281 
^«am, 349, 351 
Anagapetus, 237, 238 

bernea, 238 

chandleri, 238 

debilis, 238 

hoodi, 238 
Anaglyptini, 308 
Anaptomorphidae, 110 




Anartia, 346 
Anas crecca, 423 

penelope, 423 
Anaxipha, 288 
Anconia, 272 
Ancylocera, 307 
Ancylusis, 353 
Andina, 332, 334, 359 
Andrias scheuchzeri, 101 
Anechiirella, 255 

t;ara, 255 
Anefltis, 313 
Aneides, 450, 463 

hardyi, 450 

lugubris, 171, 172, 183 
Anepsyra, 313 
Anisolabis, 254 
Anniella pulchra, 172 
Anoplodera, 302, 306 
Anoplodusa, 281 
Anostraca, 227 
^w/eo5, 331, 333 
Anthocharis, 332, 334 
Antilocapra, 124, 139, 149, 408 
Antilocapridae, 121, 122, 133, 152 
Antirrhaea, 337, 338 
Antrozoiis, 125 
Aphelocoma, 445 

coeriilescens, 445 
Aphredoderidae, 193, 197, 198 
Aplodonfia, 125, 149 
Aplodontidae, 121, 122, 146 
Apodemia, 352, 354 
^/>ote, 281 
Appalachia, 266 
Appias, 331, 357 
Aprotopos, 336 
Arbutus, 305 
Archidermaptera, 254 
Archodontes, 307 
Archonias, 331 
Archoplites, 199, 219 

interruptus, 200 
Arctocyonidae, 110 
Arctostaphylos, 261, 306 
Arenivaga, 297 

Arethaea, 277, 278 

Argiacris, 267 

^rg3'«m"5, 346, 350, 364, 365 

Argyrophorus, 341, 343 

Argytes, 284 

Arhopalus, 306 

rusticus, 306 
Ariidae, 188 
Artemesia, 37, 313 
Artiodactyla, 116, 117, 119 
Ascia, 331, 333 
Aseminae, 306 
Asemoplus, 269 
A senium , 306 

striatum, 306 
Asinus, 399 

conversidens, 399 
Asio flammeus, 426 

fiammeus bogotensis, 426 

flammeus suinda, 426 
Astacinae, 227 
Asterocampa, 348, 351 
Astraeodes, 354 
Astyanax fasciatus, 195 
Ataxia, 313 
Atelopus, 281, 282 
Atherinidae, 189, 195 
A thesis, 332, 335 
Athripsodes, 245 

cancellatus, 225 

tarsipunctatus, 245 
Athyrtis, 336 
Atimia helenae, 311 

maritima, 316 
Atlanticus, 280, 282, 290, 297 
^//a, 296 
Attaphila, 296 
Attaphilinae, 296 
Atyidae, 225 
Aulocara, 274 
^z;g5, 472 
Aztecacris, 268 

Baeotis, 354 
Baiomys, 124, 149 
Balboneura, 347, 351, 352, 360 



Barbicornis, 353 
Barisia, 393 

Baronia, 328, 330, 343, 358 
Barytettix, 268 
Basilarchia, 348, 351 
Bassariscidae, 150 
Bassarisais, 125, 148 
Batesia, 348, 352, 360 
Bathyyiella, 225 
Batrachideinae, 259 
Batrachoseps, 161, 179, 181, 183, 

attenuatus, 179, 180, 184 

leucopHs, 179 

major, 179 

pacificus, 179, 180, 184 

wrighti, 179 
5a/3;/g, 313 
Bellamira, 309 
fig/z</a, 304, 305 
5ia, 345 
Bison, 124, 149, 398, 399, 404, 408 

alleni, 398 

antiqmis, 398, 399 

crassicornis, 398, 404 
Blarina, 125, 148 
Blasticotoma, 233 
fi/a//a, 294 
Blattella, 294 
Blattoidea, 294-298 
''Boanerges'' internigrans , 427 
Bomhycilla cedrorum, 429 

garrulus, 429 

japonica, 429 
Bombycillidae, 429 
Boopedon, 274 
Bootettix, 275 
Bootheriiim, 408 
Boreostracon, 442 
Borophagus, 401, 402 
Bothidac, 188 
Bovidae, 121, 122, 147 
Brachyinsara, 277 
Brachyphylla, 410 
Brachystola, 262, 263 
Bradynotes, 268, 269 

Brassolidae, 322, 324, 325, 344, 

345, 357-359, 362 
Brassolis, 345 
Breagyps, 403 
Breameryx, 401, 408 
Brephidium, 355, 356, 360 
Brothylus, 311 
Brunneria, 270, 274, 276, 293 

borealis, 293 
Bryodema, 212 
Bryozoa, 226, 228 
Buckellacris, 268, 269 
Bm/o americamis, 457 

boreas, 170 

fowleri, 453 

hoiistonensis, 459 

microscaphus, 170, 173 

querciciis, 459 

terrestris, 457 

woodhousei, 445, 453, 462 
Biimelia, 305 

Cactaceae, 313 
Cadomastax, 261 
Caelifera, 256-277 
Caenophlebia, 360 
Calcarius lapponicus, 431 
Caligo, 344, 345 
Calippus, 396 
Ca//iVo, 341, 343 
Callicore, 348, 351 
Callidiellum ciipressi, 311 

rtifipenne, 311 

villosulum, 311 
Callidini, 311 
Callidinm, 306 

senipervirens, 311, 312 

seqttoiae, 311 

vandykei, 311, 312 
Callimellum, 309, 311 
Callimoxys, 302 
Callitaera, 337, 338 
Callithea, 348, 351, 360 
Callithemia, 336 
Callizona, 347 
Calloleria, 336 



Callorhinus ursinus, 89 
Calydna, 354 
Cambarinae, 227 
Camelidae, 133 
Camelops, 399, 401, 408 
Camelus dromedarius, 87 
Camnula, 270 
Campo stoma, 204 

ornatum, 214 
Camptocercus, 226 
Campylacantha, 267 
Canidae, 121, 122, 145 
Canis, 108, 124, 137, 148, 399 

dims, 399 

lupus, 137 
Capnobotes, 281, 282 
Capromys, 408, 410, 411 

ingrahami, 408, 410 

thoracatus, 410 
Carinifex, 227 
Carnivora, 110, 116-118 
Carpinus, 305 
Carpiodes, 202 
Carpodaptes aulacodon, 110 
Carpolestidae, 110 
Carya, 303, 305 
Castanea, 305 
Castanopsis, 67, 304 
Ca5/or, 120, 124, 049 
Castoridae, 120-122, 146 
Castor oides, 401, 412 
Catagramma, 348 
Catargynnis, 342 
Catastica, 331, 333, 357 
Cathartornis, 403 
Catonephele, 347 
Catostomidae, 188, 193, 195, 201- 

203, 205, 212, 219 
Catostominae, 201 
Catostomini, 201, 202 
Catostomus, 201, 202, 214, 215 

ardens, 212 

bernardini, 215 

catostomus, 199, 203, 212, 218 

columbianus, 212 

rimiculus, 211 

snyderi, 210 

warnerensis, 216 

wigginsi, 214 
Ceanothus, 302, 306 
Ce(/re/a, 69, 70 
Celastrus, 67 
Celtis, 305 
Centrarchidae, 188, 193, 195, 199, 

Centropomidae, 188 
Centropomus, 214 
Cerambycidae, 299-320, 474 
Cerambycinae, 306, 307 
Ceratinia, 336 
Cercidiphyllum, 305 
Cercyonis, 341, 343 
Cerocarpus, 306 
Cervalces, 400 
Cervidae, 121, 122, 147 
Cem/5, 149, 396, 441 
Ceuthophilini, 284-285 
Ceuthophilus, 284-285 
Chalmytherium, 403 
Chamaecyparis , 304, 311 

obtusa, 311 

villosulum, 301 
Chamaelimonas, 353 
Characidae, 195 
Charts, 352, 354 
Charisalia, 309 
Chasmistes, 202, 212, 213 
Cheimas, 342 
Cheleutoptera, 289, 290 
Chelisoches, 254 
Chimarocephala, 270 
Chimarra, 235 
Chion, 307 

Chiroptera, 103, 116-118 
Chirostoma, 195 
Chloealtis, 273 
Chlorippe, 348, 351 
Chloroplus, 268 
Chlosyne, 346, 351 
Choeronycteris, 125 
Chorisoneurinae, 296 
Chorisoneura texensis, 296 



Chorthippus, 273 

longicornis, 273 
Chortophaga, 270 
Chriacus sp., 110 
Chrysochraon, 273 
Chrysophanus, 355, 356 
Chrysothamnus, 313, 317 
Cibolacris, 271 
Cichlidae, 188, 195, 205 
Cichlasoma beani, 205, 214 

cyanoguttatum, 195 
Cincindelidae, 316 
CircoteUix, 272 
Citellus, 108, 125, 137, 146, 148,384 

richardsoni, 438 

iindtilatus , 137 

undulatus parryi, 384 
Cladocera, 226, 228 
Clematodes, 265 
Clemmys guttata, 461 
C/e/Z^m, 305 
Clethrionomys, 124, 137, 149, 384 

rutilus, 137, 384 
Clidomys, 409 
Clinopleura, 282 
Clothilda, 344, 346, 360 
Clothildinae, 344, 346 
Clupeidae, 188 
Clytanthus, 308 
Clytoleptus, 309 
Clytus, 306 

blaisdelli, 312 

clitellarius, 312 

planifrons, 312 
Cnemidophorus, 445 

sexlineatus, 445 
Cnemotettix, 283 
Coelenterata, 228 
Coenonympha, 340, 343 
Coenophlebia, 349, 352 
Coenopus, 313 
Coerois, 337, 338 
Colaenis, 344, 345 
Colias, 331, 333, 361-365 

6e/in, 363 

eurytheme, 361-363 

hecla, 363 

interior, 362, 363 

nastes, 363 

palaeno, 363 

philodice, 362 
Columba, 427 

fasciata, 427 
Columbia, 197, 219 

transmontana, 198, 211 
Columbidae, 427 
Compositae, 68, 313 
Compsodes, 296 
Conalcaea, 268 
Concho straca, 227 
Condylarthra, 110, 116-118 
Condyliira, 125, 148 
Conepatus, 124, 145, 148