PHYLOGENETIC SYSTEMATICS, BIOCHRONOLOGY, AND PALEOBIOLOGY

OF LATE NEOCENE HORSES (FAMILY EQUIDAE) OF THE GULF

COASTAL PLAIN AND THE GREAT PLAINS

By

RICHARD CHARLES HULBERT. JR.

A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN

PARTIAL FULFILLMENT OF THE REQUIREMENTS

FOR THE DEGREE OF DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA
1987

ACKNOWLEDGMENTS

The members of my supervisory committee, Drs. Bruce J. MacFadden,
S. David Webb, and Douglas S. Jones, aided the completion and
improved the content of this study in many ways. Dr. MacFadden
suggested the initial proposal, a study of the Love Site Equidae, but
has masterfully guided the project through its convoluted evolution
to its present form. He has continually gone the extra step to
provide me with support and equipment. Dr. Webb has shared with me
his considerable expertise of ungulate evolution and Florida's
prehistory. Not the least was a suggestion to take a close look at
the holotype of "Merychippus" westoni. The manuscript has greatly
benefited from their combined editorial skill. I also thank Drs.
Ronald Wolff and Jon Reiskind, who also participated in the
qualifying and final exams, and provided insightful criticism.

Without the fossil specimens, this study would not exist. The
following individuals and institutions allowed me access and
permission to study specimens in their collections during the course
of this study: R. H. Tedford, American Museum of Natural History; M.
R. Voorhies, University of Nebraska State Museum; E. L. Lundelius,
Texas Memorial Museum; G. E. Schultz, West Texas State Universtiy; J.
H. Hutchison, Universtiy of California, Berkeley; D. P. Whistler, Los

ii

Angeles County Museum; C. Smart, Academy of Natural Sciences of
Philadelphia; T. M. Bown, United States Geological Survey, Denver; W.
W. Dalquest, Midwestern State University; L. D. Martin, University of
Kansas; and J. S. Waldrop. Ron and Pat Love and John Shimfessel
graciously notified the Florida State Museum of fossils discovered on
their respective properties, and allowed museum field crews to
collect additional specimens. The following individuals donated
fossil specimens to the Florida State Museum that were used in this
study: Donald Crissinger, John Waldrop, Danny Bryant, Frank Garcia,
Larry Martin, George Heslep, Jerry Case, Howard Converse, Gale
Zelnick, James Ranson, Joe Larned, Craig Patrick, Mark Patrick,
Earlene Mitchell, Jeff Walker, Roy Burgess, Clifford Jeremiah, Eric
Kendrew, Larry Lawson, Jon Bryan and Rick Carter. The latter
individual in particular has made numerous unselfish contributions of
Bone Valley specimens in the last few years. Collectively, this
group of individuals has increased our knowledge of Bone Valley
horses manyfold.

The excellent specimen illustrations are by Wendy Zomlefer and
Gerald Masters. Dr. R. Tedford has allowed me use of unpublished
illustrations prepared by Frick personel in the 1960s. Russell
McCarty and Howard Converse prepared many of the specimens, and
sectioned numerous teeth. During the early phases of the study,
curation of the Love Site equids was aided by Diderot Gicca and Troy
Storey.

m

Dr. M. 0. Woodburne provided a copy of J. P. Quinn's Master's
thesis. Dr. Charles Smart took the time to locate the lectotype and
paratype of Protohippus supremus at a rather hectic moment during the
SVP meetings. I also benefited from discussions with Jack Wilson on
Gulf Coast biostratigraphy.

My tenure as a graduate student at Florida has been blessed with
close camaraderie with my fellow students and the museum VP staff,
and this study bears witness to their helpful support and input.
Specifically, I thank Gary Morgan, Ann Pratt, Jon Becker, Steve
Emslie, Mary Ellen Ahearn, David Wright, Roger Portell and Art Poyer
for their many and diverse contributions.

Finally, I thank my family for their support, and for offering
temporary refuge from the world of academia and fossil horse teeth.
My visits to various museums across the country, a crucial aspect of
this study, were financed by a bequest from my grandmother, Mary
Peterson. This study is what results from taking an impressionable
young child to see the dinosaurs at the Field Museum. Once again, my
companions from Richard Adams to Roger Zelazny, inclusive always
provided a necessary escape from reality when called upon.

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ■■ ^'

LI ST OF TABLES ^^' ^ ^"

LIST OF FIGURES ^"^

KEY TO ABBREVIATIONS ^^

ABSTRACT ^^''

CHAPTERS

1 INTRODUCTION 1

2 HISTORY OF PREVIOUS WORK ON GULF COASTAL PLAIN EQUIDS 5

Flon' da q

Texas

3 MATERIALS. METHODS AND TERMINOLOGY H

Material s ll

Systematic Methodology J^

Terminology

Ontogenetic and Individual Variation in Equid

Cheekteeth 21

4 DESCRIPTION OF GULF COASTAL PLAIN EQUID LOCALITIES 25

Northern Peninsular Florida 25

Southern Peninsular Florida 34

Texas Gulf Coastal Plain ^^

5 SYSTEMATIC PALEONTOLOGY ^3

Order Perissodactyla Owen, 1848

Family Equidae Grey, 1821 . .nr^n /n

Subfamily Equinae Steinmann and Dbderlein, 1890 4j

Tribe Hipparionini Quinn, 1955 ^4

V

Genus Neohipparion Gidley, 1903 46

Neohipparion affine ( Lei dy ) , 1869 48

NeohipiJarion trampasense (Edwards), 1982 57

Neohlpparfon" eurystyle (Cope), 1893 77

Genus Pseudhippan'on Anrieghi no , 1904 90

Pseudhipparlon sp. ;••:••>•••;;;; 11

Pseudhi|3|3anon curtivallum (Quinn), 1955 y^

PseudhipparTorT skinneri Webb and Hulbert, 1986 93

PseudhipparTorT sTmpsom Webb and Hulbert, 1986 94

Genus Nanmppus Matthew, 1926 ^^

Nanmppus tncki new species ^^

Nanmppus sp., cf. Nannippus fr-Jcki _....; Ij^

Nannippus westoni (bimpsonj, l^-iu new combination... ii/

Nannippus minor (Sellards). 1916 136

Genus Cor iiiohip par ion Skinner and MacFadden, 1977 156

Cormohlppanon sphenodus (Cope). 1889 159

Cormohipparion occTdentale (Leidy), 1856 164

Cormohipparion pTicatile (Leidy),

1887 new combination 1' 4

Cormohipparion ingenuum (Leidy),

1885 new combination 218

Cormohiiparion emsliei new species 238

Genus Hipparion de Christol, 1832 262

Hippanon shirleyi MacFadden, 1984 263

Hipparion tehonense (Merriam), 1916 265

Hipparion sp.. cl. H. tehonense (Merriam), 1916 267

Tribe Lquini Quinn. 1953" 276

Subtribe Protohippina Quinn. 1955 new rank ^/'

Genus Calippus Matthew and Stirton. 1930 277

Subgenus CaTTppus Matthew and Stirton. 1930 282

Cal. (Calippus) proplacidus (Osborn).

19 18 new combination 283

Cal. (Calippus) placidus (Leidy). 1869 298

"CaT. (Calippus) reguius "Johnston. 1937 304

■CaT. (Calippus) sp 319

"CaT. (Calippus) elachistus new species 320

SuEgenuTlirammohippus new subgenus 331

?Cal. (Grammohlppus; circulus (Quinn),

r955 new combinati on 334

Cal. (Grammohippus) martini Hesse. 1936 341

"CaT. (GrammohippUs) cerasinus new species 360

"CaT. (Grammohippus) hondurensis (Olson and

>lcGrew). 1941 new combination J ' '

Cal. (Grammohippus) sp.. cf. CaT_. hondurensis 383

■CaT. (Grammohippus) maccartyi new species 384

Genus Protohippus Leidy. I8bti 392

Protohippus perditus Leidy. 1858 394

Protohippus" supremus Leidy. 1869 410

Protohippus" gidieyT'new species 4^i

VI

Subtribe Equina new subtribe 436

Genus Pliohippus Marsh. 1874 438

cf. Pliohippus sp 440

Genus Astrohippus Stirton, 1940 443

Astrohippus stockii (Lance), 1950 444

Genus Dinohippus Quinn, 1955 444

Dinohippus sp. 446

DinohippuT mexicanus ( Lance ) , 1950 448

6 PHYLOGENETIC ANALYSIS AND CLASSIFICATION 449

Introduction and Historical Perspective 449

Methods 456

Results and Classification 469

Comparisons with Previous Phylogenies 515

7 BIOCHRONOLOGY, BIOSTRATIGRAPHY, AND SPECIES DYNAMICS 519

Biostratigraphy 523

Diversity and Extinction Patterns 527

8 CONCLUSIONS AND SUMMARY 532

REFERENCES CITED 551

BIOGRAPHI CAL SKETCH 570

vn

LIST OF TABLES

Page

Table 1. Moss Acres Racetrack Site faunal list 32

Table 2. Neohipparion affine upper cheekteeth statistics 53

Table 3. Neohipparion affine lower cheekteeth statistics 55

Table 4. Neohipparion trampasense upper cheekteeth statistics 65

Table 5. Neohipparion trampasense lower cheekteeth statistics 71

Table 6. Neohipparion eurystyle upper cheekteeth statistics 82

Table 7. Neohipparion eurystyle lower cheekteeth statistics 84

Table 8, Measurements of individual Nannippus cheekteeth 105

Table 9. Nannippus fricki upper cheekteeth statistics 108

Table 10. Nannippus westoni upper cheekteeth statistics 121

Table 11. Measurements of medial metapodials of Nannippus 129

Table 12. Inventory of Moss Acres skeletons of Nannippus minor 140

Table 13. Nannippus minor upper cheekteeth statistics 141

Table 14. Nannippus minor lower cheekteeth statistics 147

Table 15. Measurements of individual Cormohipparion cheekteeth 163

Table 16. Mandibular measurements of hipparionines 168

Table 17. Frequency of plications in lower cheekteeth

of Cormohipparion 169

Table 18. Cormohipparion plicatile upper cheekteeth statistics 180

Table 19. Cormohipparion plicatile and Cor. ingenuum lower

cheekteeth statistics 193

Table 20. Variation in basal tooth length in equid populations 198

vm

Table 21. Median values of Cormohipparion fossette plications 210

Table 22. Cormohipparion ingenuum upper cheekteeth statistics 223

Table 23. Cormohipparion emsliei upper cheekteeth statistics 249

Table 24. Cormohipparion emsliei lower cheekteeth statistics 250

Table 25. Measurements of medial metapodials of

Cormohipparion emsliei and other equids 257

Table 26. Comparison of unworn crown height of equids 258

Table 27. Hipparion upper cheekteeth statistics 268

Table 28. Measurements of individual cheekteeth of Hipparion 270

Table 29. Calippus proplacidus and Cal. placidus upper

cheekteeth statistics 286

Table 30. Calippus proplacidus and Cal. placidus lower

cheekteeth statistics 288

Table 31. Measurements of cheekteeth of Calippus proplacidus 290

Table 32. Calippus regulus and Calippus elachistus upper

cheekteeth statistics 310

Table 33. Calippus regulus and Calippus elachistus lower

cheekteeth statistics 312

Table 34. Measurements of cheekteeth of Calippus sp 318

Table 35. Measurements of cheekteeth of Calippus elachistus 327

Table 36. Measurements of cheekteeth of Calippus (Grammohippus) ... 338

Table 37. Calippus martini upper cheektooth statistics 348

Table 38. Calippus martini lower cheektooth statistics 350

Table 39. Calippus cerasinus upper cheektooth statistics 370

Table 40. Calippus cerasinus lower cheektooth statistics 372

Table 41. Protohippus spp. upper cheektooth statistics 399

Table 42. Protohippus spp. lower cheektooth statistics 401

IX

Table 43. Measurements of cheekteeth of Protohippus 405

Table 44. Comparison of cranial characters of Protohippus

and Pliohippus '^^^

Table 45. Measurements of cheekteeth of Florida equines 442

Table 46. Character matrix for 57 equid species 459

Table 47. Description of characters and character states 463

Table 48. Consistency indices for characters in Figure 69 479

Table 49. Classification of the Hipparionini and Equini 513

Table 50. Equid species diversity analysis 528

Table 51. Summary of late Neogene equid distributions 534

LIST OF FIGURES

Page

Figure 1. Dental nomenclature and measurements 19

Figure 2. Map of Florida with locations of major fossil sites 27

Figure 3. Neohipparion affine cheekteeth from Texas 52

Figure 4. Facial region of Neohipparion trampasense 61

Figure 5. Neohipparion trampasense toothrows 62

Figure 6. Neohipparion trampasense upper cheekteeth 64

Figure 7. Neohipparion trampasense lower cheekteeth 70

Figure 8. Neohipparion eurystyle cheekteeth from Florida 81

Figure 9. Type palate of Nannippus fricki 102

Figure 10. Nannippus fricki upper cheekteeth from Nebraska 104

Figure 11. Nannippus sp., cf. Nan, fricki cheekteeth 115

Figure 12. Nannippus westoni upper cheekteeth 123

Figure 13. Nannippus westoni lower cheekteeth 124

Figure 14. Medial metapodials of Nannippus from Florida 128

Figure 15. Late Hemphillian Nannippus minor upper cheekteeth 143

Figure 16. Late Hemphillian Nannippus minor lower cheekteeth 144

Figure 17. Outline of partial skull of Nannippus minor 151

Figure 18. Nannippus minor cheekteeth from Moss Acres 153

Figure 19. Cormohipparion sphenodus cheekteeth 162

Figure 20. Principal components analysis of Cormohipparion

occidentale and Neohipparion affine 171

Figure 21. Cormohipparion pli

Figure 22. Cormohipparion pli

Figure 23. Cormohipparion pli

Figure 24. Cormohipparion pli

Figure 25. Cormohipparion pli
Figure 26.
Figure 27.

catile maxilla 182

catile upper toothrows 183

catile upper cheekteeth 185

190

catile ramus showing diastema

catile lower toothrows 191

Cormohipparion pli catile lower cheekteeth 192

201

Histograms of Cormohipparion pli catile and Cor,
ingenuum upper premolars....

Figure 28. Histograms of Cormohipparion pli catile and Cor.

ingenuum upper molars 203

Figure 29.

Figure 30.

Figure 31.

Figure 32.

Results of discriminant analysis

Histograms of premolar fossette plications
Histograms of molar fossette plications...

205
212
214

Figure 33.

Figure 34.

Figure 35.

Figure 36.

Figure 37.

Figure 38.

Figure 39.

Figure 40.

Figure 41.

Figure 42.

Figure 43.

Histograms of fossette plications of Cormohipparion

occidentale from Nebraska 215

Cormohipparion ingenuum maxilla 225

Cormohipparion ingenuum upper toothrows 226

Cormohipparion ingenuum lower toothrows 227

Cormohipparion ingenuum lower cheekteeth 228

Cormohipparion emsliei holotype and topotypes 243

Cormohipparion emsliei upper cheekteeth 246

Cormohipparion emsliei lower cheekteeth 248

Cormohipparion emsliei metatarsal III 256

APL vs. TRW for Cormohipparion and Nannippus species... 259

Maxilla and cheekteeth of Florida Hipparion 272

Plot of equid toothrow length vs. muzzle width 281

xn

Figure 44. Calippus proplacidus cheekteeth from Texas 291

Figure 45. Calippus sp. and Calippus proplacidus from Florida 292

Figure 46. Molar BAPL vs. PRL for four species of Calippus 293

Figure 47. Molar APL vs. unworn crown height for Calippus 294

Figure 48. Calippus placidus upper cheekteeth from Texas 301

Figure 49. Calippus regulus skull and mandible 309

Figure 50. Molar BAPL for four populations of Calippus 317

Figure 51. Calippus elachistus cheekteeth from the Love Site 324

Figure 52. Calippus elachistus holotype mandible 325

Figure 53. Early Hemphillian Calippus elachistus cheekteeth 326

Figure 54. ?Calippus circulus upper cheekteeth 337

Figure 55. Calippus spp. from Florida 347

Figure 56. Molar BAPL vs. PRL for four species of Grammohippus 352

Figure 57. Calippus cerasinus holotype skull and referred jaw 365

Figure 58. Calippus cerasinus upper cheekteeth 367

Figure 59 . Calippus cerasinus lower cheekteeth 369

Figure 60. Calippus maccartyi cheekteeth from Florida 387

Figure 61. Calippus maccartyi holotype mandibular symphysis 388

Figure 62. Protohippus upper cheekteeth from Florida 404

Figure 63. Protohippus supremus upper cheekteeth from Nebraska 415

Figure 64. Protohippus gidleyi toothrows from the Love Site 428

Figure 65. Protohippus gidleyi cheekteeth from the Love Site 429

Figure 66. Timing of protocone connection and hypoconal groove

closure in upper premolars of Protohippus gidleyi 431

Figure 67. Cladograms of previous phylogenetic hypotheses

regarding the Equinae '^52

xm

f^igure 68. Forsten's cl ado gram of the Hipparionini 454

Figure 69. Computer-generated cladogram of 45 equid taxa 472

Figure 70. Computer-generated cladogram of 45 equid taxa using

only highly consistent characters 474

Figure 71. Computer-generated cladogram of genotypic species 476

Figure 72. Computer-generated cladogram of Barstovian species, 478

Figure 73. Most parsimonious cladogram of the Hipparionini 484

Figure 74. Preferred cladogram of the Hipparionini 486

Figure 75. Most parsimonious cladogram of the Equini 503

Figure 76. Preferred cladogram of the Equini 505

Figure 77. Chronologic distribution of equid species 521

Figure 78. Equid diversity patterns in the late Neogene 530

KEY TO ABBREVIATIONS
Institutional Collections

AMNH— Department of Vertebrate Paleontology, American Museum of

Natural History, New York.
ANSP— Academy of Natural Sciences. Philadelphia.
F:AM— Frick American Mammals, now housed with AMNH collection.
JWT— C. S. Johnston collection, housed in PPM.
KUVP— University of Kansas Museum of Paleontology, Lawrence.
LACM— Natural History Museum of Los Angeles County, Los Angeles.
LACM(CIT)— California Institute of Technology collection, now housed

with LACM collection.
MSU~Midwestern State Universtiy, Wichita Falls, Texas.
PPM--Panhandle-Plains Historical Museum, Canyon, Texas.
SDSM—Museum of Geology, South Dakota School of Mines and Technology,

Rapid City.
TAMU— Texas ASM University collection, now housed with TMM

collection.
TMM— Texas Memorial Museum, University of Texas, Austin.

TRO — Timberlane Research Organization, private collection of John

Waldrop, Lake Wales, Florida.
UCMP— University of California Museum of Paleontology, Berkeley.
UCR~Department of Earth Sciences, University of California,

Riverside.
UF— Florida State Museum, University of Florida, Gainesville.
UF/FGS— Florida Geological Survey collection of fossil vertebrtes,

now housed with UF collection.
UNSM—University of Nebraska State Museum, Lincoln.
USNM— National Museum of Natural History, Smithsonian Institution,

Washington, D.C.
WM— Walker Museum collection, now housed at the Field Museum of

Natural History, Chicago.
WT— West Texas State University collection, housed in PPM.

Morphological Characters and Terms

DPOF— dorsal preorbital fossa (= lacrimal or nasomaxillary fossa).

MF— malar fossa.

IOF~infraorbital foramen.

MT— metatarsal.

MC— metacarpal .

R, L— right, left.

I/i~upper/lower incisor.

C/c~upper /lower canine.

P/p— upper/lower premolar (e.g. P4 is an upper fourth premolar).
M/m--upper/lower molar (e.g. m2 is a lower second molar).
D/d— upper/lower deciduous tooth (e.g. dp2 is a deciduous lower

second premolar).
P34, p34, DP34, dp34, M12, ml2— col lecti ve terms for

indistinguishable isolated teeth (e.g. P34 refers to upper third

or fourth premolars).
HI— hypsodonty index (=maximum M12 MSCH/mean M12 BAPL)

Measurements

Those in uppercase refer to upper dentitions; lowercase to lower
dentitions. Measurements taken on oclusal surfaces of cheekteeth are
illustrated in Figure 1.
APL—maximum anteroposterior length, excluding the ectoloph and

hypocone.
BAPL— anteroposterior length at the base of the crown.
TRW— transverse width from mesostyle to lingual-most part of the

protocone.
PRL— maximum length of the protocone, excluding spur and connection

to protoselene.
PRW— maximum width of the protocone perpendicular to PRL.
MSCH— crown height measured from the occlusal surface to the base of

the crown along the mesostyle.
UTRL— upper toothrow length from the anterior-most projection of the

P2 to the posterior-most part of the M3.

XV ii

UDL~upper postcanine diastema length, measured between the alveoli

of the C and the P2 (excludes DPI if present).
ROC— radius of curvature, measured on the mesostyle (Skinner and

Taylor, 1967).
apl— maximum anteroposterior length from the paralophid to the

hypoconulid.
bapl—anteroposterior length at the base of the crown.

atw— transverse width from the protoconid to the metaconid.

ptw— transverse width from the hypoconid to the metastylid.

entl—anteroposterior length of the entoflexid.

mml--length from the anterior-most point of the metaconid to the

posterior-most point of the metastylid.
mcch— crown height measured from the occlusal surface to the base of

the crown along the metaconid.
Itrl— lower toothrow length measured from the anterior-most part of

the p2 to the posterior-most point of the m3.
ldl~lower postcanine diastema length measured between the alveoli of

the c and p2 (excluding dpi if present).

Statistical

x^~sample mean.

s_~sample standard deviation.

V— sample coefficient of variation expressed as a percentage,

1 — sample correlation coefficient.

n— sample size.

OR — observed range of a sample.

xviii

Genera

As several genera in this study start with the same letter, the use

of the usual abbreviation for a genus (the first letter) might cause

confusion in some cases. Therefore, the following abbreviations are

uniformly used throughout the study to resolve any possible

conflicts.

Pseud. "Pseudhipparion.

Pro. — Protohippus.

Plio. — Pliohippus.

Para. —Parahippus.

Cor. — Cormohipparion.

Cal." Calippus

Nan. — Nannippus.

Neo. — Neohipparion.

Miscellaneous

ma— megaanna, millions of years before present on the radioisotopic

time scale,
assoc. — associated.

l.f. —local fauna, used in the sense of Tedford (1970).
s.s. — sensu stricto.
s.l.— sensu lato.
n. sp. — new species,
n. subg. — new subgenus.
n. comb. — new combination.

CI — consistency index, used in comparing cladograms.
NB~Nebraska.
TX--Texas.
FL—Florida.

FSM VP Toe— Florida State Museum Vertebrate Paleontology collection
locality code.

XX

Abstract of Dissertation Presented to the Graduate School

of the University of Florida in Partial Fulfillment of the

Requirements for the Degree of Doctor of Philosophy

PHYLOGENETIC SYSTEMATICS, BIOCHRONOLOGY, AND PALEOBIOLOGY

OF LATE NEOCENE HORSES (FAMILY EQUIDAE) OF THE GULF

COASTAL PLAIN AND THE GREAT PLAINS

By

Richard Charles Hulbert, Jr.

May 1987

Chairman: Bruce J. MacFadden
Major Department: Zoology

Ten genera and thirty-four species of the subfamily Equinae
(Mammalia, Perissodactyla, Equidae) are described from the late
Miocene-early Pliocene (late Barstovian-latest Hemphillian) of the
Gulf Coastal Plain of Florida and Texas, including new species of
Nannippus, Cormohipparion, Protohippus and Calippus. Hippotherium
in genu urn Leidy and H. plicatile Leidy are referred to Cormohipparion,
and Merychippus westoni Simpson to Nannippus. These referrals are
based on voluminous new material from the latest Clarendonian Love
Site (Alachua County, Florida). Nine species of equids are recog-
nized at the Love Site, and are described in detail. This site plays
a major role in understanding North American equid systematics,
phylogeny and paleoecology in the late Miocene. The horses of the
following sites or faunas are also extensively reviewed: Cold
Spring, Lapara Creek, Mixson's Bone Bed, Moss Acres Racetrack,

Withlacoochee River 4A, and the Bone Valley Region, Five distinct
faunal assemblages in stratigraphic superposition are recognized from
the Bone Valley Formation, each with a diagnostic suite of equids.
Comparisons with equid faunas from the Great Plains reveals little
distinctive provinciality between these two regions in the late
Miocene, as they have many species in common. This similarity allows
a biochronologic zonation of the period between 16.5 and 4.5 million
years ago (ma) into nine biochrons based on concurrent range zones of
two or three equid species.

Phylogenetic analysis indicates that the advanced Equinae form a
monophyletic group comprised of two tribes, the Hipparionini and
Equini. The Hipparionini consists of two major clades, one with
Neohipparion and Pseudhipparion, the other with Hipparion, Cormo-
hipparion and Nannippus. Two clades are also recognized in the
Equini, one with Protohippus and Calippus, the other with Pliohippus,
Astrohippus and Equus. Species previously assigned to the paraphy-
letic grade "Merychippus" are classified in their phylogenetically
correct positions. Equid evolution is characterized by frequent
parallelisms and character reversals that complicate phylogenetic
reconstruction. Thus, computer-generated, most parsimonious
cladograms sometimes produce evolutionarily unlikely scenarios.
Hipparionines and protohippines numerically and taxonomically
dominated North American equid faunas until about 6.5 ma; then
equines predominated. Protohippines became extinct about 6.2 ma, and
hipparionines about 2.0 ma.

CHAPTER 1
INTRODUCTION

During the later part of the Miocene, between about 14 and 6 ma,
numerous lineages of equids flourished in apparent sympatry across
North America. By the middle Pliocene (at about 4 ma), only a remnant
was left of this great radiation. Living horses, represented by the
single Old World genus Equus, display little of the morphological (and
presumably ecological) diversity that once characterized the family
Equidae. Therefore, our comprehension of the rise and fall of North
American equid diversity must be based primarily on their fossilized
remains, supplemented with information derived from other components
of the biota, and from various geological disciplines. Fortunately,
the fossil record of the Equidae is relatively complete and abundant,
sometimes overwhelmingly so. This has led to a proportionally large
body of literature concerning fossil equids, yet their systematics and
phylogenetic relationships are not well understood. Most previous
studies have either dealt with equids from a limited geographic
region, often from a single site (e.g. Leidy, 1885; Merriam, 1919;
Richey, 1948; Stirton, 1955; Forsten, 1975; Edwards, 1982), or present
overviews of equid evolution at the generic level (e.g. Gidley, 1907;
Matthew, 1926; Stirton, 1940). While not impuning the importance and
value of such studies, they do not provide the detailed, compre-
hensive, integrated information necessary to fully understand the

late Miocene equid radiation and subsequent decline. Comprehensive
generic reviews of some taxa have recently appeared (MacFadden, 1984a;
Webb and Hulbert, 1986), and for the first time modern phylogenetic
systematic methods have been used with this group of horses. Rigorous
phylogenetic (cladistic) analysis is now recognized as a necessary
prerequisite to meaningful derivative studies can be attempted (Cra-
craft, 1981). Most of the present study (Chapters 5 and 6) documents
the results of this type of systematic analysis. They in turn provide
the foundation for Chapter 7, which presents the results of studies
into various aspects of the late Miocene equid radiation.

This study originated as an analysis of an equid community
recovered from a single locality in north-central Florida, the late
Clarendonian Love Site. A preliminary review by other investigators
indicated that seven types of horses were represented at this one
site, and that most were closely related to well known species (Webb
et al., 1981). Detailed study, based on more specimens, however, did
not confirm these conlusions. Eventually, I have come to recognize
nine species at this site, of which five were undescribed when I
started this project in 1981, and three that belong to previously
poorly known species (see Chapter 5 for details). During the course
of this study it became apparent that an analysis of a single site, no
matter how detailed, was too limited. Instead, lineages had to be
traced through time, to produce a much broader understanding of
changes in diversity and faunal composition. Also, this period (ca.
1981-1986) witnessed much more widespread application of phylogenetic
systematic methods in vertebrate paleontology, and a deeper

3
appreciation of the information they produce (Wiley, 1981; Cracraft,
1981). With this in mind, it became obvious that a rigorous
phylogenetic analysis of the Equinae was needed before broader
questions could be answered.

The scope of this project was therefore widened to encompass the
equids from the last of the three great Miocene chronofaunas, the
Clarendonian Chronofauna (Webb, 1977). This interval includes the
late Barstovian, Clarendonian, and early Hemphillian Land Mammal Ages,
and lasted from about 14 to 6 million years ago. I have not attempted
to study all North American equids from this extensive period in equal
detail, but have focused on particular groups and geographic regions.
Geographically, the regions analyzed in greatest detail are the Gulf
Coastal Plain and the Great Plains. Earlier in the Miocene, these two
regions differed substantially in some aspects of their vertebrate
communities (Webb, 1977, and references therein), although they had
similar equids in common. Later, by about 15 ma, these differences
ceased, and the two exhibited broad faunal continuity (Webb, 1977;
Tedford et al., in press). It will be documented in Chapter 5 that
for the next ten million years they shared many equid species. As for
taxa, principal attention is given to two groups of advanced equids,
the hipparionines and the protohippines. Together they contributed to
most of the diversity witnessed during the height of the Clarendonian
Chronofauna (Chapter 7). Equines were apparently much rarer in the
Gulf Coastal Plain than these two groups, and did not undergo
significant diversification until the middle Hemphillian. They are
treated in much less detail in Chapter 5 than the others. I have also

4
chosen to ignore the anchithen'ne (browsing) equids of this period.
They are also rare in the Gulf Coastal Plain, and are in great need of
taxonomic revision, which would be a large study in itself.

CHAPTER 2
HISTORY OF PREVIOUS WORK ON GULF COASTAL PLAIN EQUIDS

Florida

The history of vertebrate paleontology in Florida spans little more
than a century. During this period many important Neogene localities
have been discovered, along with literally thousands of specimens.
From the beginning, equids have played a major role in biochronolog-
ical correlation of Florida's vertebrate-bearing deposits with those
of the West, as well as correlation of localities within the state.
Their abundance at most terrestrial sites, wide distributions and
rapid evolution enable them to be useful biostratigraphic indicators.
Knowledge of Florida's fossil equids is quite dynamic, and shows no
sign of stopping. Indeed, since the initiation of this project in
1981, several new lower horizons in the Bone Valley Region with horse
remains were discovered, and the extremely important Moss Acres
Racetrack Site with its associated skeletons was first worked in 1984.

Joseph Leidy described the first two species of equids to be named
from Florida in 1885 and 1887. They both were based on isolated teeth
from Mixson's Bone Bed (see Chapter 4 for detailed discussions of the
geology, fauna and biochronology of this and other localities
mentioned in this chapter), the first major late Neogene site
discovered in Florida. Although based on rather inadequate material
by modern standards, and described without adequate comparison with

other North American equids, both of Leidy's species (Kippotherium
ingenuum and H. plicatile) are still valid (Chapter 5). Cope (1889)
synonymized _H. ingenuum with an older name of Leidy, H^. gratum, and
this synonymy was followed by Lucas in his posthumous collaborative
review of the Mixson l.f. with Leidy (Leidy and Lucas, 1896). Gidley
(1907) disagreed, and considered H^. ingenuum a valid species, as have
all subsequent authors.

In the first decades of the 20th Century, vertebrate fossils began
to be routinely recovered as a by-product of large-scale phosphate
mining in Florida. This occurred in both the "hard-rock" phosphate
deposits of northern peninsular Florida (e.g. Hay, 1916), and in the
southern, "land-pebble" deposits (Sellards, 1910; 1916). The latter
area, better known as the Bone Valley Region, has ever since been a
valuable source of vertebrate fossils, as its name implies. Sellards
(1915; 1916) reported on the first remains of horses recovered from
the Bone Valley Formation. He recognized three species in these
deposits, the two previously named by Leidy, ][. ingenuum and _H. pli-
catile, and a new species, the very small _H. minor. _H. minor is now
known to be the most abundant horse in the Upper Bone Valley Fauna.
Simpson (1930) later reviewed the Bone Valley Fauna, recognized the
same three species as had Sellards (1916), and established a fourth,
H. (Neohipparion) phosphorum. Sellards (1916) and Simpson (1930) both
thought that the faunas from Mixson 's, from the northern phosphate
deposits (other Alachua Formation sites), and from the Bone Valley
Formation were all roughly contemporaneous, and that they shared many
species in common (including equids). Simpson (1930) also described

7
"Merychippus" westom' from Gilchrist County, from what he thought was
the Hawthorn Formation. This geologic assignment was primarily based
on his interpretation of the morphology and stage of evolution repre-
sented by the heavily worn type specimen. Further discoveries suggest
that Simpson was incorrect in his assessment of the specimen's age and
morphology (see Chapter 5).

Following Simpson's (1930) study, little original work was done on
late Neogene equids from Florida for over 30 years. The simplest
explanation for this was a lack of major new localities. During this
interval attention was primarily focused instead on the very important
early Miocene Thomas Farm Site, and on Pleistocene localities. This
period did see the most intensive (and final) excavations at Mixson's
Bone Bed by Frick field crews. A number of equid specimens were
collected, but the F:AM sample from Mixson's was not studied until
very recently.

This drought in the study of late Neogene equids was broken by the
discovery in 1962 of the McGehee Farm Site, the first major late
Neogene locality found in north-central Florida since Mixson's.
Equids are moderately diverse at McGehee, although represented mostly
by isolated teeth. Two genera were initially identified (Calippus and
either Pliohippus or Dinohippus) by Webb (1964). These are notable as
the first nonhipparionines reported from the late Neogene of Florida.
Later, three additional equids were listed as members of the fauna
(Hirschfeld and Webb, 1968). The discovery of McGehee was quickly
followed by further new localities with late Neogene equids,
especially the Withlacoochee River sites, the Haile sites, and the

Manatee County Dam Site. The latter produced the first record of
Pseudhipparion (=Griphippus) from Florida (Webb and Tessman, 1967;
1968). Interest was also rekindled in the Bone Valley Region at this
time, with emphasis on collecting in situ material (see Webb, 1969b,
p. 274). The equids from all these sites furnished the basis for
Waldrop's (1971) unpublished thesis, but until very recently have not
appeared in the literature (MacFadden, 1984a; Webb and Hulbert, 1986).

The next major discovery, the Love Site, is certainly the most
important late Neogene vertebrate fossil locality in Florida. For the
first time, material rivaling in quantity and quality the most
productive quarries from the Great Plains was recovered from Florida.
Excavation at the Love Site began in 1974, and continued to June,
1981. Afterwards, there was an almost two year period when its
voluminous equid material was identified, curated and catalogued. The
first report of equids from the Love Site was in Jackson's (1978)
study of Deirochelys. He noted the presence of Leidy's two classic
"Alachua Clays" species, H_. plicatile and "Nannippus" ingenuus. Webb
et al. (1981) recognized at least seven taxa of equids in their
preliminary review of the fauna, but oddly did not include either of
the two species recognized by Jackson (1978). More recently. Love
Site equids were studied by Hulbert (1982), MacFadden (1984a), and
Webb and Hulbert (1986), and also provide the major basis for this
study.

In the last 10 years, a number of other studies have investigated
late Neogene Florida equids. MacFadden and Waldrop (1980) described
specimens of Nannippus "phlegon" and proposed a neotype for Nan.

9
minor. MacFadden (1982) described a new species of Hypohippus from a
lower horizon of the Bone Valley Formation, while Berta and Galiano
(1984) illustrated a tooth of "Astrohippus" martini also from the
lower Bone Valley. MacFadden (1986) referred specimens from the Upper
Bone Valley and from the newly discovered Lockwood Meadows l.f. to
Dinohippus mexicanus and Astrohippus stockii, and discussed their
biochronological significance. The most important locality discovered
subsequent to the Love Site is the Moss Acres Racetrack Site. It was
first worked in December, 1984, and excavated sporadically through at
least 1987. Unlike all the other late Neogene localities in Florida,
specimens from Moss Acres often consist of associated and/or
articulated elements. Equids are diverse at Moss Acres, and many
species are represented by more complete material than at any other
site. The Moss Acres equids are reported here for the first time.

Texas

The record of late Neogene mammals, including equids, from the
Texas Gulf Coastal Plain is less complete than that of Florida. How-
ever, they are deposited in traceable stratigraphic units, that can be
placed in direct superposition, thereby aiding correlation. The
earliest studies of Miocene equids from this region are those of Leidy
(e.g. 1869; 1873), but the described specimens are isolated finds.
They are not very important except to generally indicate the age of
the deposits. Increased geological reconnaissance of the region in
the early 1900s resulted in the discovery of several substantial
localities that contained equids (e.g. Cold Spring l.f. and Burkeville

10
l.f.). Hay (1924) described "Merychippus" francisi from the Noble
Farm Site, but did not compare it with Great Plains forms. Hesse
(1943) first reviewed the biostrati graphic relationships of the faunas
from southeastern Texas. He referred the equids from the Burkeville
and Cold Springs Faunas to "M . " francisi and Protohippus perditus.

Quinn (1955) analyzed in detail the nonhipparionine portion of the
Texas Gulf Coastal Plain equids. His study included the faunas previ-
ously known to Hay and Hesse, but also the younger and more productive
Lapara Creek Fauna. Quinn's systematic methodology was highly unorth-
odox, and his work engendered much controversy and criticism (e.g.
Webb, 1969a). The entire equid fauna (including hipparionines) was
restudied by Forsten (1975), whose approach (in terms of alpha-level
systematics) was the diametrical opposite of Quinn's. While he
divided the equids from any particular fauna into many species, she
tended to lump many of these together. In my opinion (as documented
in Chapter 5), the "real" number of species generally lies somewhere
between their two extreme viewpoints. Unlike the situation in
Florida, no major late Neogene localities have been discovered on the
Texas Gulf Coastal Plain in the last 30 years. The differences in
classification of its equids by Quinn (1955), Forsten (1975) and this
study reflect differences in interpretation, and are not based on new
material .

CHAPTER 3
MATERIALS, METHODS AND TERMINOLOGY

Material s

Equid crania, mandibles, and isolated teeth of late Barstovian
through Blancan age (excluding Equus. Blancan Nannippus, and
anchitheriines) from the Gulf Coastal Plain of Florida and Texas were
examined and measured. Specimens from major localities and faunas
(e.g. Love Site, Lapara Creek Fauna) were analyzed quantitatively with
univariate statistics. Specimens from this region are principally
housed in the UF, UF/FGS, TMM, TAMU, and F:AM collections. The USNM
and ANSP have a few historically important specimens. In general,
post-cranial elements were not studied, except in the rare instances
when they could be unambiguously assigned to a species. Types or
casts of type specimens of all species known from this period were
examined from the AMNH, ANSP, USNM, TMM, TAMU, UCMP, LACM, PPM, UF,
and UF/FGS collections. Comparative material of equids from outside
of the Gulf Coastal Plain was similarly studied, principally from the
Great Plains but also including specimens from Mexico, Nevada and
California. A primary goal was to obtain data from large quarry
samples of well known faunas, e.g. Burge, Clarendon, Minnechaduza,
Yepomera and Coffee Ranch. These provided standard ranges of
individual and ontogenetic intraspecific variation. In many cases

11

12

they also supplied additional information concerning cranial
morphology. Equid skulls are relatively much rarer in the Gulf
Coastal Plain than in the Great Plains, and those present in the
former area are usually crushed or incomplete. The comparative
material was especially useful in associating upper and lower
dentitions of the same species, and in determining character states
for the phylogenetic analysis.

Systematic Methodology

Alpha-level Systematics

The following systematic procedures were performed for each major
Gulf Coastal Plain equid fauna (i.e. the Cold Spring, Lapara Creek,
Archer and Palmetto Faunas, see Chapter 4). First, each specimen was
assigned to a morphological group. Initially, upper and lower,
juvenile and adult dentitions were all treated separately. Thus for
any fauna, there would be n, morphs for upper adult dentitions, n^
morphs for upper juvenile dentitions, n^ morphs for lower adult
dentitions, and n. morphs of lower juvenile dentitions. All the n^. 's
were not necessarily the same. Each morph was made up of teeth of
similar size and enamel pattern. The next step was to determine which
morphs merely represented different wear-classes of the same
population. These were matched using sectioned teeth, individuals in
intermediate wear-stages, and measurements of basal crown length (BAPL
and bapl) which are uncorrected with age. Once this was
accomplished, there were then x, populations represented by upper

13
adult dentitions, x„ by upper juvenile dentitions, x^ by Tower adult
dentitions, and x. by lower juvenile dentitions. In theory each of
the x.'s should now be the same. In practice, they often differed by
one or two, either because a rare taxon was not represented in all
four groups, or because some populations were still divided into more
than one morph for one or more of the groups. Juveniles were then
paired with the appropriate adult populations using size, morphology,
and, most importantly, older juvenile specimens with erupted first and
second molars. Finally, upper and lower dentitions were paired.
Criteria such as size and relative abundance were used to eliminate
most of the possible combinations. For example, a population with a
mean UTRL of 140 mm could not correspond to a group of lower
dentitions with a mean Itrl of 105 mm. Nor is it likely that a very
rare group based on maxillae would correspond to an extremely common
population based on mandibles (although this is possible in certain
taphonomic sorting regimes). Prior to the discovery of the Moss Acres
Racetrack Site, no associated upper and lower dentitions of Neogene
equids were known from Florida (one mandible from the Withlacoochee
River 4A Site is possibly associated with a maxilla, but there is no
field evidence to substantiate this). Final judgements regarding
pairings were made with associated individuals of related species from
Texas or the Great Plains, or by identifying what genus each morph
represented. For example, if in a fauna there was a group of maxillae
of genus A, and a similar-sized group of mandibles of genus A, then
they were assumed to belong to the same species.

14
After these steps, for each fauna, nx)st of the specimens could be
placed into one of these populations. A few specimens, either because
they were unworn, or very heavily worn, could not be assigned to a
population. There were also usually a few teeth whose size and
morphology did not quite fall within the range observed in any group.
It is possible that they represented very rare taxa, but unless they
closely matched a well-known species from a contemporary fauna, it was
assumed that they were rare variants of one of the well represented
taxa. It was also assumed that each of these populations from a large
quarry sample or fauna represented a "biological" species.

Once this was accomplished for all faunas, there remained the fol-
lowing systematic problems: what binomen to apply to each population;
and how to determine if populations from two faunas are conspecific or
not? Actually these are identical problems, as one can determine the
proper name of a population by determining with which topotypic sample
it is conspecific. Determining if two, similar, allopatric
populations are conspecific, or if they belong to two closely related
species, or if they only share many primitive traits and are in fact
not especially closely related is not a straightforward procedure.
This is true for modern as well as fossil populations. In my
analyses, I have assumed that geographically and/or chronologically
separated populations can differ significantly from one another, and
still be conspecific. Species boundaries were placed only at
cladogenetic events (phylogenetic branching), or, in instances with no
evidence of branching, at nonarbitrary, punctuated jumps in a chrono-
clinal lineage. This approach differs from that of Gingerich (1985)

15
and Rose and Bown (1986) who advocated arbitrary division of clinally
evolving lineages. Traditionally, species-level studies of equids
have emphasized the differences between populations, and often each
population from a major fauna has been placed in its own species (see
Dalquest, 1981 for a good example of this). As noted by Mayr (1969,
p. 187), statistically significant differences between allopatric
populations should be taken for granted, and are not justification for
splitting them into separate species. The alpha-level systematic
approach used here usually results in fewer species with much larger
geographic and chronologic ranges than in previous studies.

Phylogenetic Analysis

The phylogenetic interrelationships of equid species and genera
were determined using cladistic methodology (Hennig, 1966; Wiley,
1981). Common ancestry is determined by the distribution of derived
character states among the taxa being studied. Polarity of character
states can be assessed by several methods (Wiley, 1981), of which the
out-group method is among the most widely applied. Character polarity
assessment is a critical step in cladistic analysis, as an error in
judgement can result in a completely false tree. The out-group method
was used here to determine polarities. In this method one or more
taxa that are closely related to but not among the taxa under study
make up an "out-group." Their character states are assumed to be
plesiomorphous. At the present time there is no generally accepted
upon procedure for choosing which of the many possible cladograms best
represents the true evolutionary history of the group. One commonly

16
used criterion is parsimony (Sober, 1983; Swofford, 1985). The most
parsimonious cladogram (i.e. that with the fewest reversals and paral-
lelisms) is considered optimal by some, although slightly less parsi-
monious cladograms can be more realistic biologically or chronolog-
ically (Clark and Curran, 1986). Moreover, when parallelism among in-
group clades is great, then use of the parsimony criterion may even be
misleading (Gosliner and Ghiselin, 1984). The equid species under
study were subjected to phylogenetic analysis using both a computer
program that generates most parsimonious cladograms (PAUP; Swofford,
1985), and cladograms configured "by hand" (see Chapter 6 for further
details on methods employed in the phylogenetic analysis).

Measurements and Counts

Measurements were primarily taken on individual, adult cheekteeth.
As crania of equids are so scarce from the primary study area, no
attempt was made to take any of the large number of traditional equid
skull measurements (e.g. Osborn, 1912; Eisenmann, 1986). Only
diastema lengths, toothrow lengths and muzzle widths were routinely
measured. Metapodial measurements were taken as described by
Eisenmann (1979). All measurements were taken with dial calipers to
the nearest 0.1 mm. For purposes of quantitative analysis, cheekteeth
were sorted into six categories: P2, P3 or P4, Ml or M2, p2, p3 or
p4, and ml or m2. Third molars were usually not measured, nor were
deciduous teeth. Using the methods of Bode (1931), it is
theoretically possible to identify most isolated cheekteeth as to
exactly where they were positioned on the toothrow, given a large

17
enough sample of "knowns." However, these procedures are time-
consuming, and do not always result in an unambiguous determination
for each specimen. Moreover, it has not been shown that lumping first
and second molars (for example) in any way adversely affects the
statistical results. In fact, some studies (e.g. Forsten, 1975) have
contined the P3 through M2 into a single class. Six measurements were
taken on each upper cheektooth, and seven on each lower tooth (Figure
1). Except for the basal lengths and crown heights, all measurements
were taken on occlusal surfaces, excluding cement. Altogether about
8000 specimens were measured (5000 upper teeth and 3000 lowers). The
data were stored on CMS files on the University of Florida's (NERDC)
mainframe IBM computer. Statistical computations were done using SAS
sorting and analytical subroutines (SAS Institute Inc., 1985a; 1985b).
Counts of meristic characters were also recorded for individual cheek-
teeth, and form the basis of much of the dental descriptions given in
Chapter 5.

Terminology

Stirton (1941) is the standard reference for equid dental termin-
ology. However, the meanings of some terms have recently been changed
to conform to Old World usage. The most important of these, the
structure Stirton (1941) referred to as the protostylid, is now called
the ectostylid. The term protostylid now refers to what Stirton
(1941) called the parastylid. Dental nomenclature employed in this
study is shown in Figure 1. The rudimentary first upper and lower

Figure 1. Schematic occlusal views of upper and lower cheekteeth of
equids demonstrating nomenclature and measurements used in this
study. A. Upper left second premolar (anterior to left, labial up):
1, anterostyle (found on P2s and DP2s only); 2, hypoconal groove; 3,
hypocone; 4, parastyle; 5, mesostyle; 6, metastyle; 7, pli caballin;
8, pli hypostyle; 9, pli postfossette; 10, pli prefossette; 11, pli
protoloph; 12, postfossette; 13, prefossette; 14, prefossette loop;
15, preprotoconal groove; 16, protocone; 17, protoselene. B. Upper
right third or fourth premolar (P34) showing the four measurements
made on the occlusal surfaces of upper cheekteeth: 1, APL, maximum
anterior-posterior length, excluding the ectoloph and hypocone; 2,
TRW, transverse width from mesostyle to lingual-most part of
protocone; 3, PRL, maximum protocone length, excluding spur or
connection to protoselene (if present); 4, PRW, protocone width
perpendicular to PRL. C. Lower left molar (anterior to left, lingual
up): 1, antisthmus; 2, ectoflexid; 3, ectostylid (generally found
only on deciduous teeth in North American taxa); 4, entoconid; 5,
entoflexid; 6, hypoconid; 7, hypoconulid; 9, linguaflexid; 10,
metaconid; 11, metaflexid; 12, metastylid; 13, paralophid; 14, pli
caballinid; 15, postisthmus; 16, protoconid; 17, protostylid. D.
Lower right third or fourth premolar (p34) showing the five
measurements made on the occlusal surface of lower cheekteeth: 1,
apl, maximum anterior-posterior length, excluding protostylid; 2,
atw, anterior width from metaconid to protoconid; 3, ptw, posterior
width from metastylid to hypoconid; 4, mml , metaconid-metastylid
length; 5, entl, length of entoflexid; 8, isthmus, the contined
antisthmus and postisthmus when the ectoflexid is shallow.

19

1410 5 12

16 2 3 14 15

20

cheekteeth are referred to as the DPI and dpi (rather than PI and pi),
as they erupt with the deciduous rather than the permanent premolar
series (Skinner and Taylor, 1967).

Definitions and boundaries of North American Land Mammal Ages
follow the revisions of Tedford et al . (in press). Unless specified
otherwise, ages of Neogene faunas outside the Gulf Coastal Plain are
as determined by Tedford (1981) and Tedford et al . (in press).
Boundaries and subdivisions of Cenozoic epochs follow those of Harland
et al. (1982).

General terms used to describe different ontogenetic phases are
very early (=earliest), early, moderate or middle, and late wear-
stages. Very early wear-stage refers to the period between onset of
wear and the time the occlusal surface is fully worn and reaches its
maximum length. At the end of this stage the tooth retains about 90?
of its original crown height. Early wear-stage refers to the period
after the very early wear-stage until the tooth is worn to about 1S%
of its original crown height. Middle wear-stage refers to the period
following the early wear-stage until the tooth is worn to about 25% of
its original crown height. Teeth with less than 25% of their original
crown height are referred to as heavily worn or as being in the late
wear-stage. These arbitrary classes are useful in describing the
changes in enamel pattern associated with wear. When more precise
information is required regarding exactly when during ontogeny a given
event takes place, it will be described in terms of "with x mm of
crown height remaining" or "with x% of original crown height
remaining." The adjective persistent will be used to refer to a

21
character that appears at the onset of wear and remains visible on the
occlusal surface to at least the end of the moderate wear-stage. A
very persistent character lasts well into the late wear-stage. A
nonpersistent character disappears either during the early wear-stage
or the first half of the moderate wear-stage. When qualitative
characters vary within a population or species, a percentage may be
given to quantify each character state, or terms such as common or
rare may be used. By these I mean that if a sample was chosen
randomly from a population, a very rare character state would be
expected in less than 3% of the sample, a rare character state would
be expected in about 3 to 10? of the sample, a common character state
in about 40 to 75% of the sample, and a usual or very common character
state in about 75 to 90% of the sample.

Ontogenetic and Individual Variation in Equid Cheekteeth

For historical and practical reasons, most of the characters used
in equid systematics (especially at the species level) are those of
the cheekteeth. Historically, many of the first specimens discovered
and described were isolated cheekteeth or maxillary fragments with a
few teeth. These specimens became the name bearers with which all
subsequent material was compared. Practically, at many Tertiary
localities, equid cheekteeth and toothrow fragments are much more
common than skulls, which in many instances are unknown altogether.
Actually, paleontologists studying equids are probably only as guilty
of overemphasizing cheekteeth as many others in their profession, or
only slightly more so. Other characters commonly used in this study

22

include relative diastema lengths, muzzle width, incisor morphology,
depth of the nasal notch, and the depth and arrangement of the facial
fossae. For Gulf Coastal Plain equids, however, detailed descriptions
of cheekteeth are essential for intraspecific and intrageneric
comparisons. As size and enamel pattern of equid cheekteeth change in
a predictable manner with wear, descriptions of them must include all
ontogenetic phases.

Gidley (1901) presented a lucid discussion of both ontogenetic
(wear-related) and individual variation in Equus. He noted
significant changes in enamel complexity and occlusal dimensions as
horse cheekteeth are worn down. He further noted that toothrow length
was strongly affected by the decreasing anteroposterior lengths of the
P3-M2 with wear. Gidley (1901) also showed that intraspecific
variation in features of the enamel pattern was much greater than
previously supposed. Unfortunately, Gidley 's study was based on
specimens of domesticated horses (_E. caballus), so it did not
necessarily demonstrate natural variation. Even more unfortunately,
authors such as Merriam, Hay and Osborn continued to describe new
species of equids on isolated teeth with little or no regard for the
results of Gidley's study. It took another generation, and studies
such as those of Matthew (1924), Bode (1934) and McGrew (1944b) to
check the flood of new equid species names based on isolated finds.

A detailed account of the enamel morphology of upper and lower
cheekteeth is given for each well represented species in Chapter 5.
Descriptions are divided into groups with similar morphology, e.g. the
Ml and M2. This is because, for most species, certain groups of teeth

23
can differ not only in size and morphology, but also in the stage of
ontogeny at which a certain morphology may appear (e.g. connection of
the protocone or loss of the pli caballinid). Upper cheekteeth are
divided into three groups for descriptive purposes, P2s, P34s, and Ml-
M3s. In Chapter 5, the following are described for each group with
respect for ontogenetic and individual variation: relative shape and
orientation of the protocone; when (if at all) the protocone connects
to the protoselene; presence/absence of a pli cabal 1 in and whether or
not it is bifurcated or multiple; strength and morphology of the
styles; degree of fossette complexity (counts of plications); and
whether or not the hypoconal groove is open. Descriptions of lower
cheekteeth are generally divided into two major classes, premolars
(p2-p4) and molars (ml-m3). In Chapter 5, the following are described
for each group with respect for ontogenetic and individual variation:
presence/absence of a pli caballinid, and whether or not it is
bifurcated or multiple; presence/absence of a protostylid;
presence/absence of plications from the paralophid or isthmus; the
depth, length, and persistence of the ectoflexid, entoflexid,
linguaflexid, and metaflexid; and the relative size, shape, and degree
of separation of the metaconid and metastylid. When available, the
common morphology exhibited by deciduous upper and lower premolars is
also described, but usually in less detail than their permanent
replacements.

Unworn crown height is an important characteristic of each equid
species. It differs among tooth positions, and is subject to
individual variation as are all size characters. An estimated unworn

24
crown height (either MSCH or mcch) is given for the P2, P34, M12, p2,
p34, and ml2 for each species when available. Estimates rather than
actually measured values are given because complete, unworn but
identifiable teeth are not known for most species. When unworn, the
base of the crown is made of very thin and fragile enamel that is
often broken in otherwise well preserved specimens. Unworn teeth
extracted from crypts usually are not fully formed, and their crown
heights can underestimate the true maximum value by 5 or 10 mm. My
practice was to measure large samples of isolated cheekteeth, and
include in these samples the least worn specimens for which crown
height could be measured. If the specimens with greatest MSCH and
mcch were truely unworn, then their values are given as the estimated
unworn crown height. If, as was typically the case, these specimens
were slightly worn, than a few (two to five, depending on my sub-
jective assessment of their degree of wear) millimeters were added to
their measured crown height to estimate the unworn value. If no
slightly worn (very early wear-stage) specimens for a species are
known, then no unworn crown height is reported. Instead, a maximum
observed crown height is given. For most species, the unworn crown
height estimated for the corresponding upper and lower teeth are equal
or insignificantly different. In order to compare relative unworn
crown height between species of different sizes, a hypsodonty index
(HI) was computed. It is obtained by dividing a species' estimated
M12 unworn crown height by its mean M12 BAPL.

CHAPTER 4
DESCRIPTION OF GULF COASTAL PLAIN EQUID LOCALITIES

Northern Peninsular Florida

Neogene vertebrate fossil localities in northern peninsular Florida
consist of sinkhole and fissure fillings or channel deposits incised
into Eocene limestone. Usually they are geologically isolated from
one another, and sites in close proximity are not necessarily the same
age. The following localities produced the majority of the specimens
from this region that were examined during the course of this study.
Listed for each are its location, associated fauna, age, geology,
previous studies, and what collection (s) house the fossils produced
there. Localities mentioned in the text that are not described here
produced only a few isolated teeth. The general positions of all
these localities are indicated in Figure 2.

Ash vi lie Site. The Ashville Site (FSM VP loc. JE02) is located in
the SEl/4, sec. 1, T. 2 N, R. 6 E, Ashville Quadrangle, at an exposed
roadcut in Jefferson County. The site was first discovered in 1961
and subsequently collected in 1963. 01 sen (1964), citing state
geologist William Yon, described the fossiliferous unit as a clayey,
pebbly, poorly sorted quartz sand with clay stringers, and suggested a
bay or estuary as the environment of deposition. This was suggested
by the transported, fragmentary appearance of the land vertebrates,
and by the presence of marine vertebrates (sharks and rays) in the

25

Figure 2. Map of northern and central peninsular Florida (between
27 and 30 N) depicting approximate locations of fossil sites
mentioned in the text. Late Barstovian and early Clarendonian : A,
Phosphoria Mine, Polk Co. Early Clarendonian: A, Hookers Prairie
Mine, Polk Co. Very late Clarendonian: B, Love Site, Alachua Co.
Late Clarendonian or early Hemphillian: C, Coffrin Creek, Alachua
Co.; C, VA Hospital Site, Alachua Co.; D, Nichols Mine, Polk Co.
(other ages too); E, Peace River near Gardner, Hardee Co.; F, Cummer
Mine, Gilchrist Co. Early Hemphillian: F, Haile Sites 5B and 19A,
Alachua Co.; F, McGehee Farm Site, Alachua Co.; G, Mixson's Bone Bed,
Levy Co.; H, Moss Acres Racetrack Site, Marion Co. Late early
Hemphillian: I, Withlacoochee River Sites 4A and 4X, Marion-Citrus
county line; J, Manatee Dam Site, Manatee Co.; K, L, Dunnellon
Phosphate Mine sites, Marion and Citrus Co. Late Hemphillian: M,
Lockwood Meadows, Sarasota Co.; N, Bone Valley Region (within general
outline), Polk and adjacent counties; 0, SR64 Site, Manatee Co.; P,
Kissimmee River 6, Okeechobee Co. Late Blancan: M, Macasphalt Shell
Pit, Sarasota Co.; F, Haile 15A, Alachua Co.

27

50 KM

28

same deposit. 01 sen (1964) included the following in the fauna:
Merychippus sp., Diceratherium sp., and indeterminant large and small
artiodactyls. Based on the stage of evolution of the horse teeth,
01 sen suggested an age intermediate between those of the lower Snake
Creek and lower Valentine Faunas in Nebraska. As currently perceived,
this would be early late Barstovian (about 14 ma). Tedford and Hunter
(1984) suggested a slightly younger age (about 13 ma), and a general
correlation with the Cold Spring Fauna of Texas. Vertebrate remains
from Ashville consist primarily of isolated teeth. These are poorly
preserved and often crushed, making identifications uncertain.
Specimens are in the UF/FGS collection.

Love Site. The Love Site (or Love Bone Bed; FSM VP loc. ALOl) is
located in the NWl/4, SWl/4, NWl/4, sec. 9, T. 11 S, R. 18 E, Archer
Quadrangle, Alachua County. It was discovered as the owner of the
property, Ron Love, tilled his okra crop in 1974. Subsequent
excavations by FSM personnel revealed a complex fluvial deposit
incised to a depth of 4 m in the Eocene limestone bedrock (Webb et
al., 1981, provide a detailed discussion of the geology of the site).
Over 80 taxa of vertebrates from a variety of paleoenvironments were
recovered, and these are represented by thousands of specimens. Taxa
previously studied include pond turtles (Jackson, 1976; 1978), a heron
(Becker, 1985a), an osprey (Becker, 1985b), a vulture (Becker, 1986),
a dromomerycid (Webb, 1983), a tapir (Yarnell, 1980), canids (Baskin,
1980b), a felid (Baskin, 1981), a nimravid (Baskin, 1981), procyonids
(Baskin, 1982), a mylagaulid (Baskin, 1980a), and a cricetid rodent
(Baskin, 1986). Major elements of the fauna that are as yet unstudied

29

include the fish, tortoises, amebelodontine gomphotheres, rhino-
ceratids, camelids, tayassuids, and the remainder of the rodents.
Although many of the vertebrates are similar, even conspecific, with
those from Mixson's Bone Bed and McGehee Farm, a slightly older,
latest Clarendonian age is suggested for the Love Site (Webb et al.,
1981). The site lacks all of the early Hemphillian indicator taxa of
Tedford et al . (in press), and detailed study of traceable lineages
strongly suggest that Love Site populations display more primitive
characters than those from Mixson's or McGehee. The best correlative
of the Love Site from the Great Plains is the very late Clarendonian
Xmas-Kat Fauna of Nebraska (Skinner and Johnson, 1984). Specimens are
in the UF collection.

McGehee Farm Site. McGehee Farm (FSM VP loc. AL27) is located in
the southern half of the NEl/4, sec. 22, T. 9 S, R. 17 E, Newberry
Quadrangle, Alachua County. Hirschfeld and Webb (1968) described the
sediments as phosphatic sand and gravel deposited over the eroded
surface of the Ocala Limestone, and interpreted the environment of
deposition as estuarine. In addition to equids, the mammalian fauna
includes sloths (Hirschfeld and Webb, 1968; Webb, in press), canids
(Webb, 1969b), a mylagaulid (Webb, 1966), Synthetoceras (Patton and
Taylor, 1971), camelids, rhinos, Tapirus (Yarnell, 1980), and
amebelodontine gomphotheres. An early Hemphillian age is indicated by
the presence of sloths (Marshall et al., 1979; Tedford et al., in
press), and the stage of evolution of the canids, equids, camelids,
and rhinos. Specimens are in the UF collection.

30

Haile 19 A Site. Haile 19A (FSM VP loc. AL34) is located in the
NWl/4, SEl/4, NEl/4, sec. 26, T. 9 S, R. 17 E, Newberry Quadrangle,
Alachua County. It very possibly represents the same depositional
system as the sedimentologically similar nearby McGehee Farm Site.
The Haile 19A vertebrate fauna is predominantly comprised of sharks,
teleost fish, and Gavialosuchus. Terrestrial vertebrates are
relatively rare and consist primarily of isolated, durable elements
like teeth. The mostly unstudied mammalian fauna includes Epicyon
validus, Pliometanastes, Aphelops, Pediomeryx hamiltoni, and
Procamelus, as well as a diverse equid fauna. The fauna most closely
resembles those from McGehee and Mixson's, and indicates an early
Hemphill ian age. Several other of the Haile sites have produced late
Miocene vertebrates, but of these Haile 19A is the most productive.
Specimens are in the UP collection.

Mixson's Bone Bed. Mixson's (FSM VP loc. LV09) is located in the
NEl/4, SWl/4, sec. 29, T. 12 S, R. 19 E, Williston Quadrangle, Levy
County. The site represents a massive clay-filled sinkhole. The
vertebrate fauna was initially described by Leidy in a series of short
papers from 1884 to 1890, and summarized by Leidy and Lucas (1896).
The site was extensively excavated in the late 1930s and early 1940s
by Frick field crews, who amassed much more complete material than
earlier workers, and made several additions to the fauna. The F:AM
material has only been partially described (Webb, 1969b; 1983; in
press; MacFadden, 1984a; Harrison and Manning, 1983; Harrison, 1986),
and no up-to-date faunal list has been published. Biochronologically
important taxa present are Thinobadistes segnis (Hay, 1919; Webb, in

31

press) and Epicyon validus (Webb, 1969b; generic assignment follows
Baskin, 1980b); they both indicate an early Hemphillian age.
Specimens are in the USNM, F:AM and UF/FGS collections.

Moss Acres Racetrack Site. Moss Acres (FSM YP loc. MR12) is
located in the NWl/4, NEl/4, sec. 11, T. 14 S, R. 19 E, Morriston
Quadrangle, Marion County. It was discovered in December, 1984,
during the construction of a practice racetrack for thoroughbred
horses. Geologically and topographically it resembles the descrip-
tions for Mixson's given by Leidy and Lucas (1896). The sediments are
a massive bluish-green clay filling a depression in the limestone.
Vertebrate remains were found only in a limited region of about 50 m
by 25 m. Even within this area fossils were scarce relative to other
Florida sites. Although some isolated elements and teeth were found,
many specimens consist of associated or articulated bones. Usually
these were limbs or strings of vertebrae, although some partial
skeletons, and associated skulls and skeletons were recovered.
Preservation is typically excellent, although skulls and other fragile
elements are badly crushed. The entire vertebrate fauna as known
through April 1987 is listed in Table 1. Most common is the long-
legged rhino Aphelops, represented by about ten skulls or palates.
The fauna indicates a slightly but significantly younger age than
Mixson's or McGehee, the gomphothere, Aphelops, Pediomeryx,
Neohipparion, Nannippus and Calippus all being represented by more
progressive species. The stage of evolution of the horses suggests a
slightly older age than the Withlacoochee River 4A site. An early

32

Table 1. Preliminary list of the vertebrate fauna from the Moss
Acres Racetrack Site, Alachua Formation, Marion County, Florida
(early Hemphillian, about 7.0 to 7.5 ma).

Class Osteichthyes

Order Lepisostei formes
Family Lepsisosteidae
Lepisosteus sp.
Class Reptilia

Order Crocodilia

Family Alii gator idae

Alligator mississippiensis
Order Chelonia

Family Trionychidae

Trionyx ferox
Family Emydidae
Pseudemys sp.
Class Mammalia
Order Edentata

Family Megalonychidae

Pliometanastes protistus
Order Carnivora
Family Can idae
Osteoborus sp.
Order Perissodactyla
Family Equidae

Neohipparion eurystyle
"Wannippus minor
Cormohippanon plicatile
Cormohi|3parion ingenuum
HippariJjn sp., cf. H. tehonense
Cal i ppus~maccartyi n. sp.
Dinonippus sp.

very small equid, gen. indet.
Family Rhinoceratidae
Aphelops mutilus
Order ArtiodactyTa

Family Tayassuidae, gen. indet.
Family Camel idae
cf. Procamelus

"Hemiauchenia" sp., cf. "H." minima
Fami ly Dromomeryci dae

Pediomeryx n. sp. (?)
Family Gelocidae, gen. indet.
Order Proboscidea

Family Gomphotheriidae

Amebelodon n. sp., near A. fricki

33

Hemphillian age of about 7.0 to 7.5 ma seems to best fit the currently
available data. Specimens are in the UF collections.

Withlacoochee River Site 4A (= With 4A). With 4A (FSM VP loc.
MR02) is located in the Withlacoochee River in the NWl/4, NWl/4, sec,
30, T. 17 S, R. 20 E, Stokes Ferry Quadrangle, on the Marion-Citrus
county line. Like Mixson's and Moss Acres, this site is a massive
clay deposit filling a sinkhole (Webb, 1969b). Besides equids, the
mammalian fauna includes Indarctos (Wolff, 197ft), Machairodus,
Osteoborus (Webb, 1969b), Enhydritherium (Berta and Morgan, 1985),
Pliometanastes (Hirschfeld and Webb, 1968), Thinobadistes (Webb, in
press), and Hexameryx (Webb, 1973). Becker (1985a) reported a new
species of heron from With 4A, and reviewed the site's age (also see
Berta and Morgan, 1985). The co-occurrence of Indarctos and
Machairodus is limited to the brief late early Hemphillian interval (6
to 7 ma), according to Tedford et al. (in press). The horses also
suggest an intermediate age between the well known faunas of the
"Alachua Clays" to the north and the Upper Bone Valley Fauna to the
south. Specimens are in the UF collection.

Withlacoochee River Site 4X (= With 4X). With 4X (FSM VP loc.
MR24) is also located in the Withlacoochee River in the NEl/4, NWl/4,
sec. 30, T, 17 S, R. 20 E, Stokes Ferry Quadrangle. Depositionally
identical to With 4A, the fauna of With 4X is less diverse but does
include several well preserved horse teeth, a progressive species of
Thinobadistes (Webb, in press), and a large Aphelops. They indicate a
Hemphillian, probably late early Hemphillian age. Specimens are in
the UF collection.

34
Southern Peninsular Florida

Neogene vertebrate deposits in southern peninsular Florida are
found in more widespread geologic horizons than those in the north,
particularly in the area known as the Bone Valley Region. Numerous
ephemeral exposures created by large-scale phosphate mining in this
900 km region have long produced vertebrate fossils. Along the
southwest coast of Florida, seaward extensions of the Bone Valley
Formation are sometimes encountered and may produce vertebrate fossils
as well. The general locations of these are indicated in Figure 2.

Bone Valley Region. The Florida State Museum has specimens from
dozens of vertebrate-bearing localities from this region on file.
Early studies of the area's vertebrates (e.g. Sellards, 1910; 1916;
Simpson, 1930) usually considered them a cohesive fauna of
approximately the same age as Mixson's Bone Bed. In the 1960s, FSM
personnel began precise stratigraphic studies of the Bone Valley.
Over the last twenty years, an increasingly clearer and more complex
geologic history has emerged for the region. A definitive
biostratigraphic summary is planned (Waldrop and Webb, in prep.). For
now, at least six distinct vertebrate faunas are recognized from the
Bone Valley Formation, with ages of: early Barstovian; early late
Barstovian; late Barstovian; latest Barstovian-earliest Clarendonian ;
late Clarendonian-early Hemphillian; and very late Hemphillian
(MacFadden and Webb, 1982; Webb and Crissinger, 1983; Berta and
Morgan, 1985; MacFadden, 1986; Webb and Hulbert, 1986). In addition
to these, the underlying Hawthorn Formation has produced earliest
Barstovian vertebrates (A. E. Pratt, pers. comm. ), and the overlying

35
sand and gravel beds contain fossils of Pleistocene age. Obviously,
specimens of unknown stratigraphic provenience from the region are not
necessarily the same age. In situ vertebrate concentrations
discovered by David Webb, John Waldrop and Don Crissinger now permit
the determination of natural fauna 1 assemblages. This was impossible
with most of the older collections, as they were recovered out of
stratigraphic context and contained temporally mixed assemblages. The
faunal terms used below are not yet formally named, but were
previously used by Webb and Hulbert (1986) to collectively refer to
approximately contemporaneous small local faunas and isolated finds in
the region.

The Bradley Fauna is represented only by a few localities from the
Kingsford and Nichols Mines in Polk County southwest of Mulberry. The
age of this fauna is late, but not latest, Barstovian based on the
presence of Gomphotherium calvertensis, Procranioceras sp., cf. P^.
skinneri, and horses such as Pro, perditus and Megahippus sp.
Stratigraphically, the fauna originates from sediments underlying
those producing the Agricola Fauna in at least one section of the
Kingsford Mine (Waldrop and Webb, in prep.). The equid component of
the Bradley Fauna contains less progressive taxa than the lower
Agricola Fauna (Red Zone), and indicates general biochronological
correlation with the upper Burkeville Fauna of Texas, the Norden Dam
l.f. of Nebraska, and the Pawnee Creeks Fauna of Colorado.

The Agricola Fauna is known from a number of mines in the region,
including the Nichols, Kingsford, Hookers Prairie, Silver City,
Brewster Haynesworth, and Phosphoria mines. It is best represented

36
from the latter, where modest in situ collections were made by John
Waldrop and associates in the late 1970s, and subsequently transferred
to the UF collection. The Phosphoria section has two distinct,
stratigraphically superposed assemblages that both belong in the
Agricola Fauna. The lower unit, the Red Zone, compares most favorably
with the Cold Spring Fauna of Texas and the Devil's Gulch Fauna of
Nebraska. The overlying Grey Zone correlates best with the Lapara
Creek Fauna of Texas and the Burge Fauna of Nebraska. The suggested
age for the Agricola Fauna is thus late Barstovian through earliest
Clarendonian. As the evidence rests almost entirely on its equid
fauna, its age will be further discussed in Chapters 5 and 7.
Pliocyon robustus Berta and Galiano (1984) is also a member of this
fauna.

Unlike the other faunas, the third late Neogene terrestrial verte-
brate assemblage recognized in the Bone Valley Region is represented
by isolated elements recovered without stratigraphic context relative
to the others. The most productive source for this fauna in the Bone
Valley are regions in the Nichols Mine where Donald Crissinger
(geologist for Mobil Chemical Company) collected about 75 specimens
from a "stream matrix." These specimens are uniformly preserved (the
enamel is a light grey), and appear to represent a cohesive fauna
intermediate in age between the Agricola and Palmetto Faunas. The
equids are conspecific with those of the Love, McGehee and Mixson's
localities, and together these sites are all referred to as the Archer
Fauna (Webb and Hulbert, 1986).

37

The Palmetto or Upper Bone Valley Fauna is the most widespread and
abundant in the region. In situ collections of this fauna are known
from the Palmetto, North Palmetto, Kingsford, Nichols, Gardinier, and
Payne Creek mines. A very late Hemphillian (about 5.0 to 4.5 ma) age
is indicated by the combined presence of Megalonyx curvidens,
Hexameryx simpsoni (Webb, 1973), advanced Teleoceras, Agriotherium
schneideri (Sellards, 1916), Megantereon hesperus (Berta and Galiano,
1983), Felis rexroadensis (MacFadden and Galiano, 1981), Plesiogulo
marshal 1i (Harrison, 1981), Enhydritherium terraenovae (Berta and
Morgan, 1985), and Osteoborus dudleyi (Webb, 1969b). The equid fauna
also supports this age assignment (MacFadden, 1986; Chapter 7). The
Palmetto Fauna's vertebrates represent a diverse suite of marine,
estuarine, freshwater and terrestrial habitats (Berta and Morgan,
1985). The Upper Bone Valley Formation consists of a complex of
channel deposits, often with coarse phosphatic gravel lag deposits,
fining upwards into unconsolidated beds of sand and clay (Webb, 1981;
Webb and Crissinger, 1983). These are interpreted as deltaic-fluvial
environments that drained into estuarine and nearshore marine habitats
when sea level stood about 50 m higher than at present (MacFadden and
Webb, 1982; Webb and Crissinger, 1983). Equids are primarily
represented in the Palmetto Fauna by isolated cheekteeth, and these
durable elements make up a high percentage of the terrestrial
vertebrate specimens. Partial mandibles and post-cranial elements of
equids are uncommon; maxillae are very rare. To date, one partial
equid skull (of Nannippus minor, UF 67000) has been recovered from the
fauna. Unfortunately, it lacks the diagnostic facial region and is

38
badly crushed. However, it at least suggests a potential for further
discoveries of more complete specimens. Equids from the Palmetto
Fauna examined during the course of this study are from the UF,
UF/FGS, TRO, AMNH, F:AM, and UCMP collections.

Manatee County Dam Site. The Manatee Dam Site (FSM VP loc. MAIO)
is located in sec. 30, T. 34 S, R. 20 E, Verna Quadrangle. The
geology of the site was described by Webb and Tessman (1968), who also
presented a geologic section. Based on the site's sedimentology, they
concluded that it represents a westward extension of the Bone Valley
Formation. The mammalian fauna includes (besides equids) camelids,
Teleoceras, Tapiravus, and Rhynchotherium (Webb and Tessman, 1967;
1968). These suggest a Hemphillian age for the fauna. The low
elevation of the site implies that deposition occurred at a period
when sea level was as low as the present. This suggests an older age
than the Palmetto Fauna, which was deposited during the very early
Pliocene when sea level was substantially higher than the present
(Harland et al., 1982). The presence of Pseud, skinneri (Webb and
Hulbert, 1986) and Calippus (Chapter 5) also indicates an older age,
probably late early Hemphillian, approximately equivalent to that of
With 4A. Specimens are in the UF collection.

Lockwood Meadows Site. Lockwood Meadows (FSM VP loc. S004) is
located in the NWl/4, NWl/4, sec. 16, T. 36 S, R. 18 E, Sarasota
Quadrangle, Sarasota County. It is primarily a marine vertebrate
fauna that was recovered from a phosphatic gravel deposit.
Terrestrial vertebrates are represented by isolated, usually waterworn
or fragmentary elements. The fauna includes several equids, a

39

camelid, a rhino, a gomphothere, a mammutid, and cetaceans (MacFadden,
1986; MacFadden and Mitchell, in prep.), and has been assigned a late
Hemphillian age. Specimens are in the UF collection.

Macasphalt Shell Pit. The Macasphalt Shell Pit (FSM VP loc. S007)
is located in the SWl/4, sec. 12, T. 36 S, R. 18 E, Bee Ridge
Quadrangle, Sarasota County. The quarry has been known by at least
three names, the Warren Brothers, Macasphalt and APAC Shell Pit. Two
different horizons exposed by quarrying operations at Macasphalt
produce vertebrate fossils. Low in the quarry, marine vertebrates,
including mammals, are found in the Tamiami Formation. The other
vertebrate-bearing horizon in the quarry is a thin unit in the
overlying Pinecrest beds. It is this latter horizon. Unit 4 of Petuch
(1982), that has produced equids, and other, locally concentrated ver-
tebrate remains. When abundant, they consist primarily of Siren,
water snakes, turtles. Alligator, many species of fish, and aquatic
birds. Terrestrial mammals are relatively much rarer, but 22 taxa
identifiable to at least the family level are known (Morgan and
Ridgeway, in press). Nineteen of these have been collected in situ
from Unit 4 by FSM personnel, and appear to represent a temporally
unmixed fauna. Biochronologically important mammals recovered from
Unit 4 are Nannippus peninsulatus, advanced Equus sp. (not
Dolichohippus) , Dasypus bellus, Holmesina floridana, Megalonyx lepto-
stomus , Glossotherium chapadmalense, Neochoerus dichroplex, Sigmodon
minor, Mylohyus floridanus, and Trigon ictus sp. Co-occurrence of
these taxa indicates a late Blancan (about 3.0 to 2.0 ma), latest
Pliocene age for Unit 4 (Marshall et al., 1979; Tedford, 1981; Galusha

40
et al., 1984), postdating the formation of the Panamanian land bridge
that connected North and South America. Stanley (1986; pers. comm.),
however, dates the entire Macasphalt section as early Pliocene (>3.0
ma) based on biochronologic ranges of selected bivalve taxa.
Multidisciplinary efforts to resolve this conflict and to date this
section using micropaleontological and geochemical techniques are
currently underway by Florida State Museum personnel.

Texas Gulf Coastal Plain

Scattered vertebrate fossils have been reported from the Texas Gulf
Coastal Plain for over a century. Wilson (1956) summarized previous
geologic interpretations, and recognized three Neogene lithostrati-
graphic units (the Oakville, Fleming and Goliad Formations) that have
produced vertebrates. They outcrop in narrow bands that run roughly
parallel to the present coastline (see Quinn, 1955, Figure 5 or
Patton, 1969, Figure 1). Wilson (1956) recognized four principal
vertebrate faunas in these three formations; these are, from oldest to
youngest, the Garvin Gully, Burkeville, Cold Spring and Lapara Creek
Faunas. He used the term "fauna" to indicate a group of local faunas
of similar composition found in the same stratigraphic unit. The
Hemingfordian Garvin Gully Fauna is excluded from this study by its
early age. Estimates of the ages for the other three faunas have
varied greatly (Hesse, 1943; Stenzel et al., 1944; Quinn, 1955;
Wilson, 1956; Patton, 1969; Patton and Taylor, 1971; Forsten, 1975;
Slaughter, 1981; Tedford and Hunter, 1984; Tedford et al., in press).

41
The Burkeville Fauna of Wilson (1956) contains a number of local
faunas which date from the early Barstovian (about 16 ma) to the early
late Barstovian (about 13.5 ma), a considerable period of time during
which significant changes occurred in the equid fauna. As this study
is limited to equids from the late Barstovian through Hemphillian,
only material from the younger local faunas of the Burkeville Fauna
was studied in detail. This excludes the Point Blank, Moscow, and
Trinity River local faunas, but not the Burkeville l.f. In fact, the
equids from the Burkeville l.f. much more closely resemble those of
the Cold Spring Fauna than they do those of the older Point Blank or
Trinity River sites. The Burkeville l.f. is of early late Barstovian
age, equivalent to the Pawnee Creeks Formation sites in Colorado and
some of the lower faunas of the Valentine Formation in Nebraska
(Tedford et al., in press). This correlation is based on the presence
of Anchitheromys and Proboscidea (Tedford and Hunter, 1984; Reinhardt,
1976). The overlying Cold Spring Fauna is also comprised of a number
of local faunas. They are thought to transcend the later part of the
late Barstovian (13.5 to 12.0 ma; Tedford et al., in press). The
equids from these local faunas are generally similar, and the material
is not adequate to document detailed microevol utionary changes. The
Cold Spring Fauna is similar in age to, and contains many of the same
equids as, the Devil's Gulch Fauna of Nebraska.

The Lapara Creek Fauna is derived from more southerly exposures
that stratigraphically overlie Burkeville and Cold Spring equivalents
(Wilson, 1956). Tedford et al. (in press) divide this fauna into two
units, citing evidence of significant in situ species-level evolution

42
of the equids. Forsten (1975) found no such differences, and my
examinations also do not support such a major division. I therefore
treat the entire fauna as a single sample for purposes of quantitative
analyses. I do follow Tedford et al . (in press) in their age
assignment for the Lapara Creek Fauna (earliest Clarendonian),
intermediate between the Burge and Clarendon Faunas. Texas Gulf
Coastal Plain equids studied during the course of this project are in
the TMM, TAMU and F:AM collections.

CHAPTER 5
SYSTEMATIC PALEONTOLOGY

Order Peri ssodactyla Owen, 1848

Family Equidae Gray, 1821

Subfamily Equinae Steinmann and Doderlein, 1890

Type genus. Equus Linnaeus, 1758.

Included taxa. Archaeohippus Gidley, 1906b; Parahippus s.1 .
Leidy, 1858 (including Desmatippus Scott, 1893); "Parahippus"
leonensis Sellards, 1916; "Merychippus" gunteri Simpson, 1930;
"Merychippus" primus Osborn, 1918; Hipparionini Quinn, 1955; and
Equini Quinn, 1955.

Revised diagnosis. Equids with relatively elongated facial
regions; orbit posteriorly placed relative to toothrow (anterior
margin dorsal to M3 or entirely posterior to M3) ; labial cingulum on
permanent upper cheekteeth vestigial or absent; metaloph usually
plicated; lateral metapodials tightly bound to median metapodial, not
able to move independently; relatively elongate first medial phalanx
with strong oblique scar for ligament attachment; shaft of ulna very
reduced; fibular shaft vestigial.

Discussion. The Subfamily Equinae traditionally includes only the
horizontal grade "Merychippus" and its "descendants," the hippar-
ionines and equines (e.g. Simpson, 1945). In this arrangement,
Archaeohippus and Parahippus are placed in the Anchitheri inae. This

43

44

classification is paraphyletic, and does not represent a natural
phylogenetic grouping. Matthew (1926 and especially 1932) first
noted the number of progressive (relative to Mesohippus and anchi-
theriines) post-cranial features shared by Parahippus, Archaeohippus,
and advanced equids. He concluded that the two should be grouped
with the protohippines rather than the anchitheriines. These post-
cranial characters were further documented, and this classification
was also advocated by Sondaar (1968, pp. 63-65). The features noted
by these two authors were used to compile the revised diagnosis.

Tribe Hipparionini Quinn, 1955
Calippini Quinn, 1955, p. 27 (in part).

Type genus. Hipparion de Christol, 1832.

Included North American genera. Pseudhipparion Ameghino, 1904;
Neohipparion Gidley, 1903; Merychippus s.s. Leidy 1857; Nannippus
Matthew, 1926; Cormohipparion Skinner and MacFadden, 1977.

Revised diagnosis. Tri dactyl equids with well cemented,
subhypsodont to hypsodont cheekteeth and well formed fossettes.
Differ from equines and protohippines by having much better separated
metaconids and metastylids (except for Equus and progressive species
of Protohippus) ; protocone usually isolated from protoselene until at
least middle wear-stage; and fossette borders more persistently and
usually more complexly plicated.

Discussion. In addition to the advanced genera commonly
recognized as hipparionines (e.g. MacFadden, 1984a), I include

45
Pseudhippan'on and "Merychippus" in the tribe. Chapter 6 details the
phylogenetic relationships among hipparionine genera, and documents
synapomorphies used to support their inclusion in the tribe. Hippar-
ionines are a monophyletic group (Forsten, 1982; 1984), not a para-
phyletic assemblage (MacFadden, 1984a). Their first appearance is
late Hemingfordian (about 17 ma). Skinner et al . (1977, p. 343)
recognized two primitive populations in the Sheep Creek Fauna of
Nebraska as "Merychippus insignis tertius (Osborn)" and "Merychippus
isonesus quintus (Osborn)." Hemingfordian and Barstovian species of
hipparionines have traditionally been referred to the grade
"Merychippus." I restrict usage of this name to the population
described by Skinner and Taylor (1967) from Echo Quarry as M.
insignis. and a very limited number of species (see Chapter 6).
Evander's (1986) suggestion that the genoholotypic specimen of
Merychippus is diagnostically inadequate deserves serious consi-
deration. Unfortunately, there is no readily available replacement
name, nor did Evander suggest one for this limited monophyletic group
of Barstovian species. I therefore refer to it as Merychippus s.s.
The alpha-level systematics of North American hipparionines were
greatly clarified by MacFadden (1984a). There are some differences
between his interpretations and mine, but for the most part these are
based either on new material unvailable to him (e.g. Moss Acres); on
the Love Site material, which he purposefully did not examine in
great detail; or on previously unstudied material that I found
uncatalogued in the F:AM and UCMP collections.

46
Genus Neohi'pparion Gidley, 1903

Neohipparion GIDLEY, 1903, p. 467.
Hesperohipparion DALQUEST, 1981, p. 506

Type species. Neohipparion Whitney Gidley, 1903 (now considered a
junior synonym of Neo. affine (Leidy), 1869).

Included species. Neo. trampa sense (Edwards), 1982; Neo. leptode
Merriam, 1915a; Neo. eurystyle (Cope), 1893; Neo. gidleyi Merriam,
1915a.

Revised diagnosis. Medium to large-sized hipparionines with
poorly developed, shallow, unrimmed DPOF, or lacking DPOF.
Protocones elongate-oval or very elongated; isolated to near base of
crown except in P2. Well developed pli caballinids on p2-p4 and dp2-
dp4 (and on ml-m3 of advanced species) that often extend further
labial ly than the base of the protoconid or hypoconid; relatively
elongated and well separated metaconids and metastylids; labial
borders of protoconid and hypoconid flattened; ectostylids weakly
developed or absent on deciduous premolars. Slender metapodials.

Discussion. Gidley (1903) based Neohipparion on the superb type
skeleton of Neo. "whi tneyi " (AMNH 9815), at the time the most
completely known hipparionine individual. He included most of the
previously described North American species of "Hipparion" in his new
genus, in what was probably the first attempt to classify these
horses phylogenetically. Gidley (1903; 1907) used both facial and
dental characters to distinguish Neohipparion from Hipparion, a very
modern approach. Except for Merriam (e.g. 1915a), most other authors

47
did not recognize Neohipparion as a distinct genus until 1935.
However, it was often used as a subgenus of Hipparion, even though
the two were thought to have separate nfierychippine origins (Matthew
and Stirton, 1930, p. 356). Beginning in 1935, Stirton and McGrew
began to separate Neohipparion and Nannippus at the generic level
from Hipparion (Stirton and McGrew, 1935; McGrew, 1938; Stirton,
1940), and its generic status has seldom been questioned since
(Forsten, 1982, is an exception, but she has subsequently [1984] used
it as a valid genus).

Traditionally, two species-groups comprise Neohipparion : one
composed of the predominantly Clarendonian taxa Neo. affine (= Neo.
whitneyi), Neo. coloradense, and Neo. occidentale; and the other of
the Hemphillian species Neo. leptode, Neo. eurystyle, Neo.
phosphorum, Neo. gidleyi, and a number of Mexican species named by
Stirton (1955) and Mooser (1960; 1964). Neo. occidentale is referred
to a separate genus, Cormohipparion. based on its deep DPOF, deep
ectoflexids, rounded protoconid and hypoconid labial borders, and
strong dp ectostylids (Skinner and MacFadden, 1977). "Neo."
coloradense is here recognized as the sister-taxon to Neohipparion
and Pseudhipparion, and thus cannot be placed in either genus
(Chapter 6). Thus, of the first species-group, only the genotype is
still considered a valid member of Neohipparion. It has long been
recognized that Neo. affine is less progressive in many of its dental
features than other members of the genus (Stirton, 1940; MacFadden,
1984a). This morphologic gap led Dalquest (1981) to formally
separate the Neo. eurystyle species-group as a distinct genus.

48

Hesperohipparion. Apparently unknown to Dal quest, there then existed
an undescn'bed population of late Clarendonian and early Hemphillian
Neohi'ppan'on morphologically and chronologically intermediate between
the two species-groups. It was formally described by Edwards (1982)
as Hipparion trampasense. MacFadden (184a) transferred it to
Neohipparion and illustrated cranial material of this new species.
Thus Dalquest's Hesperohipparion is unnecessary, and its use would
render Neohipparion either paraphyletic or monotypic.

Neohipparion affine (Leidy), 1869

Hipparion affine LEIDY, 1869, p. 286; OSBORN, 1918, p. 178.

Hippotherium occidentale (Leidy), COPE, 1889, p. 434 (in part).

Neohipparion whitneyi GIDLEY, 1903, p. 467.

Neohipparion affine (Leidy), GIDLEY, 1903, p. 467; GIDLEY. 1907.

p. 887-888; STIRTON, 1940, p. 183; MACFADDEN, 1984a, p. 90.

Hipparion (Neohipparion) affine Leidy, MATTHEW and STIRTON,

1930, p. 362.

Equus laparensis QUINN, 1955, pp. 58-60 (in part).

Equus sp. or Neohipparion sp., QUINN, 1955, p. 62.

Neohipparion occidentale (Leidy), FORSTEN, 1975, pp. 65-69 (in

part).

Type specimen. USNM 584, five apparently associated upper
cheekteeth.

Type locality. Exact locality unknown, "from the Niobrara River"
region according to Leidy (1869). Skinner et al . (1977) provided

49

evidence that the type locality might be Porcupine Butte, South
Dakota.

Stratigraphic occurrence and age of type locality. Probably
Ogallala Group; Clarendonian, about 9.5 to 11.5 ma.

Distribution. Very late Barstovian to late Clarendonian of the
Great Plains; early Clarendonian of the Texas Gulf Coastal Plain;
possibly Clarendonian of Oregon.

Referred Gulf Coastal Plain specimens. Lapara Creek Fauna (see
Quinn, 1955 and Wilson, 1956). Bridge Estate Site, Bee Co., TX: TMM
31132-432 R P34; -616 R M12; Buckner Ranch Site, Bee Co., TX: TMM
30896-572 L P34; -571, -395 2 L M12; -576, -577 2 R P2; -578, -579 2
L P2; -392 L M3; -480 R mandible with p2-m3 (Quinn, 1955, Plate
14.5); -454 R p34 (Quinn, 1955, Plate 14.3); -573, -574 2 L p34; -580
R ml2.

Revised diagnosis. Larger than Neo. trampasense or Neo.
eurystyle, toothrow lengths about 135 to 150 mm. Unworn M12 MSCH
about 56 mm, thus less high crowned than all other species of
Neohipparion. Relatively simple fosettes; pli caballin single; pli
caballinid prominent only on slightly worn p2-p4 only. Shallow,
poorly developed DPOF posteriorly includes large lacrimal bone.

Description. Neohipparion affine is a large species of
Neohipparion with a distinct, shallow, unrimmed DPOF on the lacrimal,
nasal and maxillary bones (Osborn, 1918, Plate 32.1). Its upper
cheekteeth are characterized by elongate-oval, narrow protocones,
rarely with protoconal spur; relatively simple fossettes; and wide
hypoconal groove open to the base of the crown (Fig. 3A) . The upper

50
premolars have large, broad, usually single plicaballins; they are
generally smaller and less persistent in molars. Fossette plications
are simple, not bifurcated. The pli protoloph is absent or single,
except in the P2 where 39% (n=19) have two loops. The posterior half
of the prefossette usually has a long pre fossette loop, and one to
four small, simple plications. The anterior half of the postfossette
usually has only two or three plications. A pli hypostyle is
generally either absent (35? of premolars, 532 of molars) or single
(64% of premolars, 43% of nfXDlars). In earliest wear-stages, the
lower premolars have very shallow ectoflexids and well developed pli
cabal linids (Fig. 3B) ; with wear the ectoflexid rapidly deepens and
the pli caballinid gradually disappears. The latter usually occurs
near the beginning of the moderate wear-stage, much earlier in
ontogeny than in other species of Neohipparion. AMNH 9815 (holotype
of Neo. whitneyi, Osborn, 1918, Fig. 144) is an example of the usual
morphology of moderately worn lower cheekteeth. Pli cabal linids are
rare on molars, and then only found in early wear-stages and are
rather small (e.g. TMM 30896-480). A distinctive generic character
are the flattened bases of the hypoconid and protoconid, especially
evident on the premolars. The protoconid and hypoconid of the molars
may retain the primitive rounded state, or have flattened bases. In
early wear-stages, the isthmus of the lower premolars is often pli-
cated, but there are no well developed plications extending poster-
iorly from the paralophid. Ectostylids of deciduous premolars are
very reduced. Crown heights of very slightly worn teeth are 4043 mm
for P2s, 48-51 mm for P34s, 55-58 mm for M12s, and 54-56 mm for ml2s.

51
Discussion. The Lapara Creek specimens listed above are referred
to Neo. affine, rather than to one of the nxjre abundant hipparionines
in the fauna (Cor, occidentale. Nannippus sp., cf. Nan, fricki. or
Hipparion tehonense), primarily on the basis of size (Tables 2 and
3), protocone shape, relatively simple fossettes, and pli caballin
development for uppers, and flattened labial protoconid and hypoconid
borders and size for the lowers (Fig. 3B). They were originally
referred by Forsten (1975) to Cor, occidentale, and some (but not
all) could represent extremes in that variable taxon. The differ-
ences in size among the three referred populations (Tables 2 and 3)
are exaggerated by small sample sizes and differing age-class
distributions. The recognition of Neo. affine in the Lapara Creek
Fauna is not surprising. It is a consistent, although typically rare
member of many similar age faunas in northern Texas, Nebraska and
South Dakota (MacFadden, 1984a). The latest appearance of Neo.
affine is late Clarendonian, in the Xmas-Kat faunal zone of Nebraska
(Skinner and Johnson, 1984). However, it has not yet been recorded
from Florida. As the time period during which it is most common is
still poorly known in Florida, this absence could well be the
artifact of a deficient record.

52

B

2cm

Figure 3. Occlusal views of cheekteeth of Neohi'pparion affine from
the Buckner Ranch Site, Bee County, Texas (early Clarendoman,
Lapara Creek Fauna). A. TMM 30896-395, L Ml, early to moderate
wear-stage. B. TMM 30896-574, L p3 or p4, early wear-stage.

Table 2. Standard univariate statistics for upper cheekteeth of
Neohipparion affine. Measurements defined in Chapter 3. The first
line for each entry gives _x, _s and n, the second line OR and _V.
Populations are LC, Lapara Creek Fauna, Bee County, Texas; CLAR,
Clarendon Fauna, Donley County, Texas; and NEB, combined sample of
Clarendonian localities from Nebraska and South Dakota.

53

FAUNA

LC

CLAR
P2

NEB

APL

28.5,0.85,3

29.2,1.73,10

29.2,0.90,5

27.5-29.1,2.99

27.0-32.4,5.93

28.8-31.1,3.02

BAPL

22.6,0.50,2

24.1,0.70,3

22.2, ~ ,1

22.2-22.9,2.20

23.6-24.9,2.91

TRW

20.3,1.48,4

22.0,1.12,9

22.1,0.52,5

18.5-21.8,7.33

19.8-23.4,5.07

21.3-22.6,2.34

PRL

7.1,0.47,4

7.4,1.06,10

8.4,0.41,5

6.5-7.5,6.57

4.9-8.4,14.37

8.1-9.1,4.86

PRW

3.8,0.47,4

4.3,0.45,10

4.3,0.52,5

3.4-4.4,12.15

3.9-5.0,10.57
P34

3.9-5.2,11.93

APL

24.3,0.78,2

24.5,1.53,22

23.9,1.32,11

23.7-24.8,3.21

21.2-27.1,6.24

22.1-25.9,5.52

BAPL

18.7,0.50,2

19.3,1.18,9

19.8,0.74,3

18.3-19.0,2.65

17.8-21.8,6.08

19.0-20.4,3.72

TRW

21.8,0.64,2

23.4.1.54,21

23.3,0.60.11

21.3-22.2,2.92

20.6-25.7,6.57

22.0-24.5,2.57

PRL

8.5,0.35,2

9.7,0.96,22

9.5,0.93,11

8.2-8.7,4.18

7.1-11.1,9.86

7.7-11.0,9.80

PRW

4.1,0.35,2

4.2,0.28,20

4.1,0.27,11

3.8-4.3,8.73

3.6-4.8.6.66

3.4-4.4,6.65

Table 2 — continued

M12

54

APL

24.3,0.38,3
24.0-24.7,1.56

22.5,1.47,18
20.0-24.5,6.56

21.9,1.49,12
20.1-24.2,6.81

BAPL

17.5, ~ ,1

18.9,1.11,4
17.6-20.3,5.84

17.7,0.69,4
17.1-18.6,3.90

TRW

20.7,2.54,3
17.9-22.8,12.26

21.9,1.23,18
20.3-25.4,5.59

21.5,1.08,12
19.2-22.9,5.02

PRL

9.8,1.20,2
8.9-10.6,12.33

9.2,0.63,18
8.3-10.4,6.85

9.3,0.80,12
8.0-10.3,8.56

PRW

3.5,0.21,3
3.3-3.7,6.00

4.0,0.38,18
3.6-5.3,9.59

3.9,0.22,12
3.5-4.3,5.68

55

Table 3. Standard univariate statistics of lower cheekteeth of
Neohipparion affine. Measurements defined in Chapter 3. Format and
samples as in Table 2. No lower second premolars measured from
Lapara Creek sample.

FAUNA LC CLAR NEB

P2

apl 25.6.1.34.10 26.2,1.46.3

23.6-28.2.5.23 25.0-27.8,5.57

bapl 19.4. — .1 22.4. ~ .1

atw 9.2,0.74,10 9.3,0.47,3

8.2-10.5,8.02 8.9-9.8.5.10

ptw 11.9.0.64.10 12.1.0.95.4

11.2-13.1,5.17 11.0-13.3.7.84

mm! 9.9.1.11.10 12.1.2.54.3

7.7-11.8.11.20 10.0-14.9.21.04

entl 11.8.0.93.10 11.7.0.89,4

10.0-13.1,7.88 10.4-12.2,7.54

p34

apl 22.8,0.71.2 25.6.0.76.17 22.3.2.03.7

22.3-23.3.3.10 24.1-27.2.2.95 19.1-24.2,9.10

bapl 20.5,0.92,2

19.8-21.1.4.50

atw 11.2.0.00.2 11.6,1.12,17 12.1,0.80,7

11.2-11.2,0.0 9.4-13.6.9.67 11.1-12.9.6.60

ptw 11.5.0.14.2 12.1.0.94.17 11.8,0.51.7

11.4-11.6,1.23 10.3-13.6,7.81 11.1-12.5,4.33

mml 11.5,0.28,2 13.9,0.89,17 13.7,0.83,7

11.3-11.7,2.46 12.4-15.1,6.39 12.6-15.0.6.06

entl 11.4,0.92,2 12.1,0.73,17 10.9,1.73.7

10.7-12.0.8.10 10.8-13.7.6.03 7.9-12.2.15.92

Table 3~continued

ml2

56

apl

22.8,0.28,2
22.6-23.0,1.24

24.8,1.26,19
21.9-26.6,5.08

20.5,1.06,6
18.9-21.7,5.20

bapl

18.7,0.07,2
18.6-18.7,0.38

18.0,0.70,4
17.1-18.8,3.88

atw

9.4,0.28,2
9.2-9.6,3.01

9.9,1.11,19
8.2-11.9,11.15

10.3,0.26,6
9.9-10.6,2.60

ptw

9.0,0.21,2
8.8-9.1,2.37

9.3,0.89.19
7.6-11.0,9.62

9.6,0.46,6
8.9-10.1,4.83

mini

12.9,0.92,2
12.2-13.5,7.15

13.6,0.85,19
11.9-15.2,6.23

12.1,0.34,6
11.5-12.5,2.81

entl

9.1,0.85,2
8.5-9.7,9.32

9.6,1.04,19
8.0-11.9,10.75

8.0,1.66,6
6.0-9.8,20.75

57

Neohippan'on trampasense (Edwards), 1982

Neo hip pari on nr. N^. eurystyle (Cope), HIRSCHFELD and WEBB, 1968,

p. 249.

Neohippan'on cf. leptode Merriam, WEBB et al., 1981, p. 526;

HULBERT, 1982, pp. 159-160 (in part).

Hipparion trampasense EDWARDS, 1982, p. 174 (in part).

Neohipparion trampasense (Edwards), MACFADDEN, 1984a, p. 97.

Type specimen. UCMP 58234, a left upper molar.

Type localtiy. UCMP V6107, Bolinger Canyon, Contra Costa Co.,
California; Kendal 1-Mal lory l.f.

Stratigraphic occurrence and age of type locality. Contra Costa
Group (undifferentiated), about 1300 feet above the top of the Neroly
Formation; late Clarendonian, about 10 ma.

Topotypic sample. As listed by Edwards (1982), except as
qualified below.

Distribution. Late Clarendonian of California; late Clarendonian
and early Hemphillian of Nebraska and Florida; early Hemphillian of
Kansas.

Referred specimens. J. Swayze Quarry, Clark Co., Kansas: F:AM
113734 L P2; 113735 R P2; 113736 R P34; 113737-113739 3 R M12; 113740
R p2; 113741 L p34; 113742-113743 2 R ml2.

Xmas-Kat Fauna, Cherry Co., NB (see Skinner and Johnson, 1984, for
discussion of the geology and location of these quarries). Xmas
Quarry: F:AM 113756 P34; 114151 R mandible with p2-m3. Machaerodus

58
Quarry: F:AM 114152 assoc. R 4 L mandibles with dp2-dp4. Line Kat
Quarry: F:AM 71854 R mandible with p2-m3. Hans Johnson Quarry:
F:AM 114154 R mandible with dp2-dp4. East Kat Quarry: F:AM 113749 R
maxilla with P4-M3. Trailside Kat Quarry: F:AM 114155 L mandible
with dp2-dp4. Leptarctus Quarry: F:AM 113752, 113753 2 assoc. R & L
mandibles with p2-m3; 113754 assoc. R & L mandibles with p2-m2;
113751 L mandible with p2-p4; 113750 R P34; 113757 R M12.

Kepler Quarry No. 1 (UNSM loc. MO- 101), Morrill Co., NB: UNSM
42449 (= AMNH 107595, cast) skull with R & L P2-M3 (MacFadden, 1984a,
Fig. 63).

McGehee Farm: UF 17211 R P34; 9607, 17132, 17134 3 R M12; 17129,
17133 2 L M12; 17135 R M3; 17136, 45594 2 L M3; 17159 assoc. R & L
mandibles with p2-m3; 45593 R mandible with p2-p3; 9500 assoc. R
ml-m3 & I p4-ml; 65177 L dp34; 45598 L p2; 17166, 17170, 45605 3 L
p34; 17141, 17143, 17171, 45601-45604, 53453 8 L ml2; 17142, 17146,
19221 3 R ml2; 9608, 9612, 45595, 45596 4 L m3; 17148, 17149, 19222,
45632 4 R m3.

Love Site: UF 32249 partial skull with R & L DP2-M1; 32291
partial skull with R A L DP2-M2; 25637 partial skull with R P4,M1,M3
& L P4-M3; 32248 assoc. maxillae with R DP2-DP4 & L DP2-M2; 32252
assoc. maxillae with R « L P2-M3; 32258 assoc. maxillae with R P3-M3
& L P2-M1,M3; 32251 R maxilla with M1-M3; 32272 L maxilla with P3-M2;
32253 L maxilla with P4-M3; 53427 L maxilla with P4-M1; 53428 L
maxilla with M2-M3; 32277 assoc. R DP2-DP4 & L DP2-DP3; 27991, 27992,
32256 3 assoc. R & L P2-M3; 32284 assoc. R P2-M1 & L P2,M2-M3;
53204/53207 assoc. R P3-P4; 32273 assoc. L P3-M2 & R Ml; 32280 assoc.

59

L M1-M3; 32159 assoc. R & L mandibles with c,p2-m3; 27317 assoc.
mandibles with R il,i3,c,p4-m3 & I p2-m3; 32148/32153 assoc. mand-
ibles with R p2-m3 & I p3-m3; 32193 assoc. mandibles with R p4-m3 & L
ml-m3; 32192 assoc. mandibles with R p2-m3 & L p2-p4; 32121 R
mandible with dp2-dp4; 32145 L mandible with dp2-dp4,ml; 32213,
32216, 32218, 32162 4 R mandibles with p2-m3; 32110, 32216, 32152 3 L
mandibles with p2-m3; 32186 L mandible with p2-p3,ml-m3; 32179 R
mandible with p2-p3,dp4,ml-m2; 32175 R manidble with p3-m2; 32127,
32184 2 L mandibles with p2-m2; 32164, 32109, 32217 3 L mandibles
with p3-m3; 32168 L mandible with p2-p3,dp4,ml-m2; 32106, 32122,
32126, 32142, 32156, 32210, 32211, 32222, 32224, 32310, 32311, 36275,
36281, 36288 14 partial R mandibles; 32131, 32149, 32166, 32188,
32246, 35899, 36273, 36273, 36274 8 partial L mandibles; 32228,
32230, 32233, 32234, 32235, 32238, 32240, 35896, 36278, 68788-68791,
13 assoc. lower dentitions; over 850 individually catalogued isolated
cheekteeth.

Revised diagnosis. Medium-sized hipparionine with toothrow
lengths between 110 and 130 mm; DPOF very shallow depression set well
anterior to lacrimal. Unworn M12 MSCH about 60 mm; higher crowned
than Neo. affine, lower crowned than Neo. eurystyle, Neo. leptode or
Neo. gidleyi. Fossettes moderately complex; pli caballin strong,
often double on premolars; metastyle present but much weaker than in
Neo. eurystyle; pli cabal linid persistently well developed on p2-p4
and dp2-dp4, on ml-m3 only in early wear-stages.

Description of Florida and Nebraska specimens. Other than
fragments, no cranial meterial was recovered with the topotypic

60

sample of Neo. trampasense (Edwards, 1982). The most complete
referable skull of Neo. trampasense is UNSM 42449 from the late
Clarendonian of Nebraska. It along with less complete cranial
material from the Love Site (UF 32251) demonstrate that Neo.
trampasense has a relatively small, very shallow DPOF developed only
on the maxillary and nasal bones, dorsal and posterior to the lOF.
It is located far anterior of the lacrimal, which is reduced in size
(Fig. 4). The malar region may have a slight depression (UF 32251,
Fig. 4), although this feature is absent in F:AM 113749 and UNSM
42449. The nasal notch is not deeply retracted, and lies over the
postcanine diastema. Mandibular and maxillary toothrow lengths in
moderate to early wear vary from 108 to 130 mm (Itrl of combined
sample from the Love Site and McGehee Farm, excluding heavily worn
individuals, has a x^ of 115.8 mm, _s=4.42, n=7). Individuals from the
Great Plains average 5 to 10? larger. Lower diastema lengths range
from 53 to 59 mm for males (x^=55.3 mm, £=2.48, n=5), while the only
measurable female had a Idl of 64.4 mm.

Upper cheekteeth of Neohipparion trampasense are generally
characterized by moderately complex fossettes, moderately elongated
protocones, deep hypoconal grooves, and well developed parastyles and
mesostyles. P2s in early wear-stages have well developed, pinched-
off anterostyles, slightly recurved parastyles, and small metastyles
(Fig. 5A). The P2 protocone is elongated, but shorter than that of
the P34, and typically connects to the protoselene during moderate
wear-stages. Complexity of fossette plications and pli caballin
development of the P2 rival or exceed slightly that of the P34.

61

DPOF

0 12 3 4 5cm

Figure 4. Lateral view of right (reversed) facial region of
Neohipparion trampasense (UF 32251) from the Love Site, Alachua
County, Florida. LAC, lacrimal bone; DPOF, dorsal preorbita fossa,
Teeth in lateral view are the M1-M3.

62

CM (O Q.

O) n3
■l-> T3

O T3 =S
•I- •!- O
S_ S_ O

U <U <U
■M ^
t. •>- <U
O) OO CD
2 O

o <u z:

i— >
o «

T3 _l <D

(O

0) +->
i_ Oi to
<U <T3 I
Q-+-> 1_
0.10(0
3 t OJ

0) ..-(

CO I

•I- C\J Li_
U- Q- =1

> i_ «

O (O Ol

-J <U 3

O) O)

■I-) I— <0

_ S_ i-

£ <a cj

o oi "a

(/J

~ rvj «

CM

•l->

03 (O

rt3

<u

<— 0)

■t->

<\)

O 5

CO

+J

1

Jx:

0) <U

i-

<u

■l-> 4-J

<o

<u

10 <T3

CD

^

1— S»

S

o

(U

>,-a

QJ

&-

i- a

+J

0)

<U E

(W

Q.

>

S~

o.

^^ <u

a;

3

■(J

-o

(+-

(0 (0
"O 1 —

O

•r-

1- «

A

to

O CM

1— )

S

1— a.

P-

0)

b-

•r—

_j

_J

>

A

>. "

*t

^—

+-> CM

t~~

<0

c rn

CO

CO

3 CM

CM

3

O lO

CO

^—

O CV1

Uf)

u

o

(0 u.

U.

o

3 =>

Z3

•

(0 CO

Q

VO

<:

aj

m

•

s-

« 0)

<D

3

0) C7)

Cn

cn+-> (13

<T3

Li_ 00 CO CO

64

E
o

CN-

o-"

65

Table 4. Standard univariate statistics for upper cheekteeth of
Neohipparion trampasense. Format as in Table 2. Populations are LOV,
Love Site, Alachua County, Florida; KM, Kendall-Mai lory l.f.. Contra
Costa County, California (type locality); NEB, Xmas-Kat Quarries
Faunal Zone, Cherry County, Nebraska; and KAN, combined sample from
the J. Swayze Quarry, Clark County, Kansas and Arens Quarry, Norton
County, Kansas.

FAUNA LOV KM NEB KAN

P2

APL 24.9. 1.28, 50 24.8, ~ .1 26.4, ~ ,1 27.7,2.11,4

22.5-27.1.5.12 26.3-30.8,7.63

BAPL 20.2,0.82.48 21.5.0.84,5

18.0-21.7.4.07 20.6-22.6,3.89

TRW 17.8,0.76,51 18.6, — ,1 19.1, — ,1 20.6,1.10,4

16.0-19.4,4.26 19.5-22.1.5.37

PRL 7.3,0.60,51 7.1. — .1 6.3. ~ .1 7.4,1.19.5

5.9-8.9,8.22 5.8-8.6,15.95

PRW 3.6,0.33,51 4.2, — ,1 3.7. ~ ,1 4.0.0.36.4

3.0-4.5.9.15 3.7-4.4.8.90

P34

APL 20.3,1.33,136 22.0,0.99,6 21.9,0.46,4 24.8,0.76,4

17.5-23.4,6.56 20.5-23.1,4.47 21.4-22.5,2.08 23.9-25.5,3.07

BAPL 16.2,0.82,124 17.9,0.97,5 17.8, ~ ,1 18.0,0.79,4

14.3-18.3,5.03 17.0-19.3,5.40 16.8-18.6,4.42

TRW 18.9,0.92,135 20.3,1.02,5 20.6,0.63,4 21.8,0.60.5

14.0-20.8,4.86 19.3-22.0,5.02 19.9-21.4,3.04 21.1-22.5,2.74

PRL 8.2,0.81,139 8.1.0.48,6 8.0,0.22,4 10.4,0.96,5

6.4-10.5,9.83 7.3-8.8,5.97 7.7-8.2,2.70 9.3-11.5,9.30

PRW 3.5,0.32.139 3.8.0.15,6 3.7.0.22.4 4.1,0.29,5

2.8-4.5,9.09 3.6-4.0,3.87 3.4-3.9,6.03 3.9-4.6,6.93

66

Table 4— continued

M12

APL

19.3,1.50,154
16.1-23.1,7.79

19.2,1.49,4
17.4-21.5,7.77

19.3,0.45,4
18.9-19.9,2.34

21.0,0.90,3
20.0-21.6,4.26

BAPL

15.2,0.71,138
13.6-16.8,4.66

16.1,0.70,2
15.4-16.8,4.35

15.8,0.29.3
15.5-16.0,1.82

TRW

17.1,0.97,152
12.8-19.4,5.56

18.6,0.46,5
18.1-19.2,2.39

19.6,0.76,4
18.7-20.5,3.90

18.5,1.15,3
17.2-19.4,6.23

PRL

7.8,0.62,158
6.5-9.4,7.97

8.3,0.58,5
7.8-9.4,7.06

8.0,0.69,4
7.4-8.9,8.62

8.8,1.62,3
7.9-10.7,18.3

PRW

3.2,0.34,155
2.4-4.1,10.38

3.6,0.26,5
3.2-3.9,7.08

3.7,0.49,4
3.1-4.2,13.52

3.6,0.21,3
3.4-3.8,5.73

67

After moderate or heavy wear, the anterostyle becomes broadly
connected with the rest of the tooth, the protocone connection also
broadens, and the parastyle becomes less distinct (Fig. 6B).
Estimated unworn P2 MSCH is about 37-40 mm, based on a large sample
of slightly worn teeth (e.g. UF 36009, 36155, 36189). The P34 (Figs.
5A, 6C) are characterized by broad, well developed styles; elongated,
obliquely oriented (anterolabial-posterolingual ) protocones isolated
until very near the base of the crown and rarely with spur; lingual
protocone borders generally concave; well developed, persistent,
often branched or double pli cabal lins; anterior half of prefossette
generally has a deep, unbranched pli protoloph, and one to three
labial accessory plications; the posterior half of the prefossette is
complexly plicated in early to moderate wear-stages, with a long,
secondarily plicated prefossette loop, and two to five pi is
prefossette of varying depth and complexity; the anterior half of the
postfossette is strikingly less complex, with a deep, only rarely
branched pli postfossette, and one to three, most often one, small
accessory plications; and the posterior half of the postfossette
general has a single, deep, unbranched pli hypostyle. The hypoconal
groove is deep and broad in early wear-stages, shallower with wear
but open to the base of the crown. The DP2-DP4 (Fig. 6A) are more
complex than their permanent counterparts, typically with multiple or
branched pli cabal lins; intricately plicated fossettes in early wear;
and more oval protocones with flat or convex lingual borders. The
DPI is very rudimentary and lost prior to the replacement of the DP2

68

by the P2 (e.g. UF 32291). Estimated unworn P34 MSCH is about 52 to
55 mm.

The upper molars are distinctly smaller than the premolars (Table
4; Figs. 5A, 6D) ; with elongate-oval, isolated protocones not so
obliquely orientated; and less pronounced styles. The lingual
borders of molar protocones are generally flat or convex, only
occassionally concave. Pli caballins are generally single, and
smaller than in the premolars. The anterior half of the prefossette
most often has a moderately deep, unbranched pli protoloph without
accessory plications. The posterior half of the prefossette has a
long prefossette loop and one to four shallow pi is prefossette. The
anterior half of the postfossette has a deep, sometimes branched pli
postfossette and up to four accessory plications. The posterior half
of the postfossette generally has a single, unbranched pli hypostyle.
About 32% of all observed molars in early and early-to-moderate wear-
stages (MSCH > 35 mm; n=93) resemble the holotype, UCMP 58234, in
having one or two accessory plications in addition the pli protoloph.
Estimated unworn M12 MSCH about 57 to 60 mm. The hypsodonty index of
the Love Site population is 3.9.

The Love Site sample of associated and isolated lower teeth is
large enough to provide numerous examples of every wear-stage (Table
5; Figs. 5B, 7). Deciduous lower premolars have very elongated
metaflexids and entoflexids; well developed pli caballinids; shallow
ectoflexids; very small or absent ectostylids (the tooth is shed
before they are exposed to wear); and less frequent isthmus
plications than on the permanent premolars (Fig. 7E). The dpi is

Oi 0) 0)

^ +-> en

+-> ro <0

^ ^ ■*-'

e <u 10
o "a I

s- Q $- •

*+- E <o o)

O) CD

I— « s <a

I— CM -M

<o E >, <o

I r- I

CO ^ s_

QJ

0.(0(0

Q-ro (o

Jj- 00

s_ <c

<u

O <D «

M- T3 CnO

O C (O «*

O) +J CM

.C s_ to CM

■P (O I <^

O) r- i.

0) o <o u.

+-> QJ 3

^ <U S

<U +J •

(1) <a >>Lij

s. s. OJ <u

OJ CI

s >

O ^-Sf ■•->
1— Q. 10

CT>

(O

O •>- O (0
S- (U

10 o CO 2
3 I— Q.

•r- Qi +J

> « (O

>, «■—

.— +J t^
(O C CO «
</) 3 LO CM
3 O O E

1— O LT)

OJ • «

i_ « (1) o
3 O) C75CM
Cn4-> (O 1^
■1- -r- +J ^

70

^ Is

=1/

E
u

CN-

O-^

1=^

ISi:

71

Table 5. Standard univariate statistics of lower cheekteeth of
Neohipparion trampasense. Format as in Table 2, sample populations as
in Table 4.

FAUNA LOV KM NEB KAN

P2

apl 21.5,1.03,67 21.9, — ,1 23.1,1.17,5 24.9,1.42,7

19.0-23.7,4.79 21.7-24.6,5.06 22.9-27.1,5.70

bapl 18.0,0.68.59 19.4, ~ ,1

16.3-20.1,3.79

atw

8.2,0.47,63
6.8-9.1,5.79

8.5,

- .1

8.3,0.47,5
7.9-9.0,5.60

9.6,0.52,7
8.8-10.4,5.35

ptw

10.2,0.77,65
7.3-11.8,7.51

9.8,

-- .1

10.0,0.78,5
8.9-11.0,7.75

11.4,0.42,6
11.1-12.0,3.65

mml

9.6,0.87,64
7.2-12.0,9.04

8.7,

- .1

9.9,0.61,5
9.0-10.6,6.19

11.7,0.67,7
10.6-12.8,5.69

entl

10.4,0.80,64
8.4-12.0,7.71

9.5.

-- .1

10.8,0.76,5
9.9-11.8.7.02

11.9,1.50,7
9.7-13.9,12.6

p34

apl 20.7,1.27,71 21.6,1.18,6 22.8,1.21,9 22.8,1.49,15

18.1-23.6,6.14 20.1-22.6,5.45 20.9-25.0,5.32 20.0-25.7,6.52

bapl 16.8,0.68,63 17.8,0.71,2 18.3,1.21,3

15.3-18.7,4.01 17.3-18.3,3.97 17.0-19.4.6.63

atw 10.2,0.61.71 10.5.0.90.6 10.1.0.80.9 11.6,0.85.15

9.0-11.9.5.94 8.7-11.2.8.58 8.8-11.4,7.95 10.3-13.3.7.34

ptw 10.2.0.63.71 10.2.1.14.6 10.3.0.98.9 11.7.0.99,15

8.5-11.6,6.19 8.1-11.1,11.24 8.8-11.4,9.50 9.7-13.9,8.45

mml 12.2,0.73,71 12.0,0.75,6 12.1, .073,9 13.6,1.13,15

10.5-14.1,5.97 10.6-12.6,6.19 10.6-12.9,6.01 11.6-15.9,8.34

entl 10.2,0.74.71 10.0.0.58.6 10.4.0.61,9 10.8,1.01,15

7.8-11.9,7.18 9.2-10.9,5.85 9.7-11.6,5.85 9.2-13.1,9.34

72

Table 5 — continued

III12

apl

20.0,1.74,68
16.9-23.9,8.69

20.2,1.58,6
18.0-22.1,7.81

22.4,1.98,8
19.3-25.1,8.85

21.7,2.27,18
17.9-26.4,10.5

bapl

15.9,0.62,67
14.4-17.8,3.96

16.2, ~ ,1

17.1,0.22,6
16.9-17.5,1.28

atw

8.7,0.67,68
6.7-10.1,7.72

9.2,0.64,4
8.3-9.7,6.93

9.0,0.66,8
8.0-10.4,5.35

9.7,0.91,17
8.1-11.5,9.35

ptw

8.2,0.81,68
5.8-9.9,9.80

8.8,0.54,6
7.8-9.3,6.15

8.6,0.88,8
7.3-9.8,10.24

9.3,0.84,18
7.9-10.6.8.67

mml

11.6,0.73,68
9.4-13.6,6.32

11.9,0.91,6
10.9-12.8,7.65

12.0,0.80,8
10.7-13.1,6.68

12.9,0.82,18
11.5-14.2,6.36

entl

8.5,1.25,68
6.0-11.2,14.72

8.4,0.65,6
7.4-9.1,7.75

9.2,1.08,8
7.6-10.8,11.84

9.0,1.30,18
6.3-11.3,13.8

73

small, rudimentary, and shed with the eruption of the p2. Lower
permanent premolars (Figs. 5B, 7A, 7B) are characterized by shallow
ectoflexids that do not penetrate the isthmus even in late wear-
stages; persistent pli caballinids; well developed protostylids;
plicated isthmuses and paralophids; expanded, subequal metaconids and
metastylids well separated throughout all wear-stages; linguaflexid
very broad, shallow, "U"-shaped in early wear (occassional ly with a
lingual plication), with wear, narrower and more "V"-shaped; labial
borders flat in early wear, with heavy wear they may take on a more
rounded appearance. Lower molar morphology changes even more
dramatically with wear. In very early wear-stages the ml and m2 are
very long, with many features similar to those observed in the
premolars, such as shallow ectoflexids and well developed pli
caballinids (Fig. 7C). Following the eruption of the m3, the ml2 APL
becomes shorter; ectoflexids deepen with gradual penetration of the
entire isthmus (Figs. 5B, 7A) ; pli caballinids fade, although in
moderate wear-stages their appearance is somewhat variable;
metaflexids and entoflexids shorten; and the labial borders of the
protoconid and hypoconid become rounder. In late wear-stages (Fig.
7D), molars lack or have only rudimentary pli caballinids; have deep,
"V"-shaped linguaflexids and ectoflexids; and have oval metasylids
and metaconids. Unworn mcch about 36 to 37 mm for p2, 48 to 51 mm
for p34, and 58 to 60 mm for ml2.

Discussion. As noted by MacFadden (1984a), Neo. trampa sense is
clearly a member of Neohipparion based on its cranial, facial and
dental features. For many characters, Neo. trampasense is

74
intermediate between those found in basal hipparionine stock or NIeo.
affine, and those in the Neo. eurystyle species-group. The topotypic
Bolinger Canyon sample of Neo. trampasense is the oldest population
referred to the species (about 10 ma, Edwards, 1982), and the least
progressive as well. When compared with the Nebraska and Florida
samples, its protocones are more oval and have flat lingual borders
(rarely concave); the lower premolars tend to lose the pli
caballinids with heavy wear (e.g. UCMP 77031); and the molars have
only rudimentary pli caballinids in moderate wear-stages (e.g. UCMP
58244). However, in many features, such as size (Tables 4, 5),
hypsodonty, fossette complexity, metastyle development, reduction of
ectoflexid depth in premolars, and flattened labial borders of lower
premolars, the Bolinger Canyon sample so closely approaches or equals
that seen in later Clarendonian and early Hemphillian samples that
they are considered the same species.

Several specimens refered by Edwards (1982) to Neo. trampasense
from the type locality clearly do not belong with that species as it
is now defined. These include UCMP 77032 (L P3-M1), UCMP 58223 (L
M1-M2, not P4-M1 as stated by Edwards, 1982, p. 174), UCMP 58225 (L
P34), UCMP 112771 (L p34) and UCMP 112154 (R & L dp2-dp4). The upper
cheekteeth of these specimens are characterized by short, oval proto-
cones with well developed spurs and convex lingual borders. In
protocone morphology, as well as size, fossette complexity, and
stylar development they match the topotypic sample of Hipparion
forcei (Richey, 1948; e.g. UCMP 94815, a L Ml). The associated lower
dentition is also probably referable to H. forcei because of its lack

75
of pli caballinids, moderately developed ectostylids, rounded labial
borders, and relatively short metaflexids and entoflexids. UCMP
112154 does not differ significantly from the large sample of decid-
uous lower premolars of _H. forcel from Black Hawk Ranch. Perhaps the
Inclusion of these Hipparlon teeth In his sample contributed to
Edwards placing his new species in Hipparlon rather than Neohip-
parlon. Finally, Edwards (1982) listed UCMP 58239 as both a L p4-ml
(p. 174) and a L m2-m3 (p. 182). The specimen Is clearly a L p3-p4
(of Neo. trampasense), as the more anterior tooth is undoubtedly a
premolar, and thus the very slightly worn posterior tooth cannot be a
molar (as the ml erupts well prior to the p4 in all equids).

MacFadden (1984a) only referred one specimen from the Xmas-Kat
Fauna of Nebraska to Neo. trampasense. Examination of previously
uncatalogued material In the F:AM collection revealed a number of
specimens referable to this species from this fauna, and from other
sites in Nebraska and Kansas. Neo. trampasense is thus more common
in the Great Plains than previously thought, and apparently Is a
useful biochronological Indicator of the late Clarendonian and early
Hemphill Ian across North America.

A number of derived dental character states found in Neo.
trampasense, some only in early wear-stages, indicate a close
relationship with later Hemphill Ian species of Neohipparion. In the
upper dentition these Include the flattened protocones, often with
concave lingual borders, and the well developed styles. Small
metastyles are much more frequent than in Neo. affine. However, it
is in the lower cheekteeth that Neo. trampasense best shows its

76
advanced features. In the premolars, the ectoflexids do not
penetrate the isthmus, even with heavy wear, nor is there reduction
of the pli caballinids. The labial borders tend to be very flat, and
the metaconids and metastylids are long and well separated. In
molars, pli caballinids are consistently found in early wear-stages,
and there is some reduction of the depth of the ectoflexids.
However, in late wear, the molars take on the primitive hipparionine
morphology (Fig. 7D). The lower dental morphology in the sequence
Neo. affine - Neo. trampa sense - Neo. eurystyle details the evolution
of a cabal loid dental pattern (sensu Forsten, 1982; 1984) from the
primitive hipparionid pattern. This pattern evolved independently
several times to varying degrees in equid lineages during the Late
Neogene. In some respects, that attained by Neohipparion was the
most advanced in the Equidae (Rensberger et al., 1984). The chrono-
logical sequence of Neo. trampasense populations demonstrates a pos-
sible mechanism (heterochrony) of how this ultimate pattern evolved.
Younger populations (early Hemphillian) of Neo. trampasense tend
to retain advanced characters such as reduced depth of the ectoflexid
and pli caballinid development in molars through later wear-stages
than do older populations (late Clarendonian) . Referred specimens of
Neo. trampasense from early Hemphillian localities in Kansas (J.
Swayze and Arens Quarries) also have significantly larger tooth
dimensions (Tables 4, 5); these combined suggest an evolutionary
trend that resulted in the western species Neo. leptode. The rela-
tively early (and most primitive) appearance of Neo. eurystyle is in
Florida (see below) from Moss Acres and With 4A. This suggests that

77

Neo. eurystyle evolved from eastern populations of Neo. trampasense,
perhaps in the Gulf Coastal Plain.

Neohipparion eurystyle (Cope), 1893

Equus eurystylus COPE, 1893, pp. 43-45.

Hipparion eury stylus (Cope), GIDLEY, 1901, p. 125.

?Hipparion eurystylus (Cope), GIDLEY, 1907, p. 918.

Neohipparion eurystyle (Cope), MERRIAM, 1915, p. 4; STIRTON,

1940; p. 183; MACFADDEN, 1984a, p. 105 (in part).

Hipparion eurystyle (Cope), OSBORN, 1918.

Hipparion phosphorum SIMPSON, 1930, p. 189.

Hipparion (Neohipparion) eurystyle (Cope), MATTHEW and STIRTON,

1930, p. 362.

Neohipparion f lore si STIRTON, 1955, p. 886.

Neohipparion arellanoi STIRTON, 1955, p. 888.

Neohipparion otomii MOOSER, 1960, p. 376; DALQUEST and MOOSER,

1980, p. 11.

Neohipparion monias MOOSER, 1964, p. 394; DALQUEST and MOOSER,

1980, p. 12.

Neohipparion cf. phosphorum (Simpson), WEBB and TESSMAN, 1968,

p. 806.

Hesperohipparion stirtoni DALQUEST, 1981, p. 510.

Type specimen. TMM 40289-1, a partial left lower molar.
Type locality. Palo Duro Canyon, Randall Co., Texas. Possibly
the Currie Ranch Site (Schultz, 1977; Dalquest, 1981).

7!

Strati graphic occurrence and age of type locality. Ogallala
Group; late Hemphillian, about 5 ma.

Distribution. Early late to latest Hemphillian of Mexico, Texas,
Oklahoma, Kansas and Nebraska. Late early through latest Hemphillian
of Florida. Possibly California.

Referred Florida specimens. Moss Acres Racetrack Site: UF 95410
assoc. R M2 « L M2-M3; 65250 R mandible with dp3-ml; 69969 R mandible
with p2-m3 and R il-iS & L il.

With 4A: UF 45518 R P2; 45520 R MS; 45546 R pd2; 17306 R p2.

With 4X: UF 53524 R P34.

Mutual Mine, near Dunnellon, Marion Co., FL: UF/FGS V-7175 L M12;
-7176 R P34; -7179 R p34; -7180 L p34; -7178 R ml2; -7177 R m3.

Manatee Dam Site: UF 11940 R P2.

Lockwood Meadows: UF 64116 R P34.

Palmetto Fauna, Bone Valley Region. Palmetto Mine: UF 17154
assoc. R ml-m3; 17114 L P2; 17115, 53529, 53534-53537, 53541 7 R P34;
53530, 53540 2 R M12; 17116, 17118, 53531, 53538 4 L M12; 53532 R M3;
17119, 53542, 53543 3 L M3; 17162 R dp3; 53479 L p2; 53509, 53496, 2
R p34; 17157 R ml2; 12501, 53500 2 L ml2; 12061, 53499 2 R m3; 17158
L m3. North Palmetto Mine: UF 18725 L M3; 18728 L m3. Payne Creek
Mine: UF 18318 assoc. R & L P4-M3; AMNH 113755 L p34. Chicora Mine:
UF 17155 R ml2. Fort Green Mine: UF 53902, 53903, 57 342, 58309 4 R
M12; 24657 L M3; 53506 R ml2. Nichols Mine: UF 24629 L P34. Agrico
Mine: UF/FGS V-5505 R P34; -1423 L M12 (holotype Neo. phosphorum) ;
-5473 L m3; AMNH 95627 R ml2. Silver City Mine: UF 65698 R M3.
Kingsford Mine: UF 17120 L P2; 53544 L M12; 17151 L p2; 53559 R ml2;

79
53560 L ml2. Mineco Mine: UF 91202 L P2; 91203 R P34. Gardinier
Mine: UF 90524-90525 2 L M12. Hookers Prairie Mine: UF 93208 L
P34. Phosphoria Mine: UF 93214 R Ml. Tiger Bay Mine: UF 25709 L
P2. Brewster Phosphate Mine: UF 65744 R M12. Specific locality
unknown: UF 53851 R M12; UCMP 130129, UF/FGS V-6605 2 L P34; UF
53545, 53852, 92930 3 L M12; UCMP 130128 L M3; UF 61502 R p34; UF
69915, UCMP 130130 2 L ml2; UF 61503, 69914 2 R ml2.

Revised diagnosis. Medium-sized hipparionine with toothrow
lengths of about 115 to 135 mm; DPOF absent; unworn M12 MSCH about 73
mm. Fossette plications moderate to very complex; pli caballin
strong on premolars; constricted mesostyle; well developed metastyle;
very elongate protocone. Pli cabal linid persistently well developed
on molars and premolars, often multiple or branched; ectoflexid
shallow.

Description of Florida specimens. Detailed dental descriptions of
referred populations of Neo. eurystyle can be found in Stirton (1955)
and Dalquest (1981). This description of Florida specimens is divi-
ded into two sections. The first describes the late Upper Bone Val-
ley sample of Neo. eurystyle (topotypic sample of Neo. phosphorum),
which is very similar to referred western populations of the species
both morphologically and chronologically. The second describes the
sample from Moss Acres, the oldest known sample of Neo. eurystyle.

The upper cheekteeth of the Bone Valley population of Neo.
eurystyle are characterized by well developed parastyles and meta-
styles (that often curve posteriorly and anteriorly, respectivley) ;
large, expanded, lingual ly constricted mesostyles; long, often

80
sinuous protocones with straight or concave borders (Figs. 8A, 8B) ;
and moderately complex fossettes (but less complex than in Cor.
emsliei n. sp.). The protocone is usually isolated except on the P2
and DP2, which can have narrowly connected protocones. One otherwise
typical P34 (UF 91203), however, has a connected protocone at a MSCH
of 35.7 mm. The pli protoloph is usually a single deep fold (rarely
absent), occassional ly with one or more rarely two much smaller
accessory plications. The long prefossette loop often extends
lingually past the base of the prefossette and is secondarily
plicated. The remainder of the posterior half of the prefossette
generally bears two to five (eight is maximum) small plications,
usually including one fairly deep fold. A deep pli hypostyle in
found in over 85^ of all upper teeth. The hypocone is notably
smaller than protocone, with its main axis oriented in a
posterolingual direction. The hypoconal groove is open to near the
base of the crown and "V"-shaped. The pli caballin is strong,
usually multiple on premolars, much smaller, occassional ly absent on
molars. Unlike most other hipparionines, the P34 are often not much
larger in occlusal dimensions than the M12, and curve posteriorly in
the anterior-posterior plane similar to molars. The P34 are
distinguished from the M12 by their larger and more complex pli
caballin, more widely opened mesostyle, and the larger, often grooved
or bifurcated parastyle. Unworn M12 MSCH exceeds 70 mm.

Lower cheekteeth (Fig. 8C) are characterized by well developed,
often branched or multiple pli caballinids that extend labially

=3 O S_
CM O)

O) I— CM

z o s:

^ C "-H C

<D jc m +->

0(0 QJ

1—1— . Dl

OO as

•a >,

(O <LI

to

CJ * "r—

C (O

3 3 -O >i

(O 1- 1—

4- Li. O S-

O M- (O

O t/J 0)

to ■•-> Ol

3 +J

> I—

i<: E

3 C +J
I— O fl

CO Ll_ OJ I^

4-> --H

S_ CU S- u_
3 I— 0) =)

oil— -a
1- <a Q •

82

Table 6. Standard univariate statistics for upper cheekteeth of
Neohipparion eurystyle. Format as in Table 2. Populations are UBV,
Palmetto Fauna, Bone Valley Region, Florida; YEP, Yepomera
localities. Chihuahua, Mexico; and CR, Coffee Ranch l.f., Hemphill
County, Texas.

FAUNA

UBV

YEP
P2

CR

APL

27.0,1.35,4
25.5-28.7,4.99

24.1,1.37,21
21.7-26.5,5.69

26.0,0.71,3
25.4-26.8.2.73

BAPL

21.5,1.46,3
20.0-22.9,6.77

20.1,1.38,15
18.1-22.3,6.83

21.5,1.20,2
20.3-22.7,5.58

TRW

19.4,0.66,4
18.6-20.0,3.73

18.6,0.94,22
17.4-21.0,5.02

19.8,1.47,3
18.1-20.9,7.46

PRL

7.8,0.56,4
7.2-8.5,7.18

7.8,0.60,22
6.9-8.9,7.66

8.5,0.49,3
8.2-9.1,5.78

PRW

3.7,0.25,4
2.4-3.9,6.62

3.8,0.26,22
3.1-4.3,6.82

P34

3.7,0.10,3
3.6-3.8,2.70

APL

21.6,1.06,10
20.1-22.8,4.92

20.6,1.10,51
18.5-22.7,5.32

20.4,1.49,10
18.0-22.8,7.30

BAPL

16.8,0.82,9
15.7-18.1,4.89

16.4,0.94,40
14.7-18.0,5.71

14.7,0.56,9
13.8-15.6,3.80

TRW

20.4,0.69,10
19.4-21.4,3.40

20.0,1.02,51
18.0-22.6,5.10

20.1,0.65,9
18.8-21.0,3.26

PRL

9.9,0.71,9
8.7-11.0,7.16

10.2,0.84,51
8.7-12.1,8.28

10.3,0.99,10
8.8-12.0,9.63

PRW

4.1,0.22,10
3.8-4.5,5.36

4.1,0.32,51
3.6-5.1,7.82

3.8,0.25,10
3.4-4.1,6.54

Table 6 — continued

M12

83

APL

20.5,0.75,15
19.0-21.5,3.65

19.6,1.08,47
17.8-23.1,5.52

20.1,1.65,21
17.0-22.7,8.20

BAPL

17.1,1.06,11
15.3-19.4,6.23

16.2,0.78,33
14.6-18.4,4.84

15.2,0.77,19
14.3-17.1,5.05

TRW

18.9,0.61,13
18.0-19.9,3.24

18.4,0.75,48
16.7-19.8,4.08

18.6,1.24,21
16.9-21.1.6.66

PRL

9.8,0.73,15
9.0-11.5,7.44

9.8,0.88,48
8.3-11.9,8.90

8.8,0.54,21
8.0-10.0,6.19

PRW

3.9,0.29,14
3.5-4.5,7.36

3.8,0.34,48
3.1-4.7,8.82

3.5,0.34,20
3.1-4.5,9.73

84

Table 7. Standard univariate statistics for lower cheekteeth of
Neohipparion eurystyle. Format as in Table 2, sample populations as

in Table

6.

FAUNA

UBV

YEP
P2

CR

apl

23.3,0.50,2
22.9-23.6,2.13

21.7,1.11,24
20.0-24.0,5.13

21.5,1.09,7
19.4-22.8,5.08

bapl

18.5, ~ ,1

17.5,0.75.10
16.3-18.6,4.26

17.0.0.21,3
16.8-17.3,1.21

atw

9.0,0.07,2
8.9-9.0,0.79

9.5,0.49,25
8.7-10.4,5.18

8.9.0.27,7
8.4-9.2,2.98

ptw

11.2,0.21,2
11.0-11.3,1.90

11.3,0.68,24
10.1-12.6,6.04

11.4,0.55.6
10.7-12.4.1.86

iTiml

13.6,0.21,2
13.4-13.7,1.57

12.0,0.94,25
10.5-14.0,7.86

11.9,1.02,7
10.6-13.3,8.56

entl

13.3,0.85,2
12.7-13.9,6.38

11.5,1.02,25
10.3-13.8,8.88

p34

11.4,0.90,7
10.1-13.1.7.86

apl

20.0,1.01,7
18.6-21.7,5.07

21.4,1.35,51
18.1-25.4,6.32

21.5.2.02,16
18.8-25.1,9,37

bapl

16.6,0.89,5
15.6-17.9,5.34

17.2,0.66,17
16.0-18.4,3.83

16.3,0.75,9
14.7-17.0.4.63

atw

10.7,0.50,7
9.8-11.2,4.68

10.9,0.70,50
8.2-12.4,6.40

10.5.0.48.13
9.4-11.2.4.56

ptw

10.5,0.59,5
9.6-11.1,5.59

11.2,0.85,50
8.4-12.8,7.56

10.8.0.66.15
9.3-11.9.6.11

mml

13.4,1.11,7
11.3-14.5,8.32

14.2,0.74,51
11.9-15.9,5.23

13.5.0.75.15
12.5-15.7,5.57

entl

10.3,0.59,7
9.4-11.5,7.63

10.8,0.79,51
9.5-13.1,7.27

10.5,1.01,15
8.8-12.0,9.63

Table 7~continued

ml2

85

apl

21.7,1.97,8
19.4-25.7,9.09

20.9,1.74,65
18.3-25.5,8.29

21.0,1.59,21
18.3-24.7,7.57

bapl

17.8,0.88,4
17.0-19.0,4.67

16.7,0.81,23
14.2-17.8,4.85

16.3,0.70,12
15.0-17.5,4.29

atw

9.6,0.99,8
8.0-11.2,10.33

9.6,0.75,65
7.6-11.1,7.86

9.5,0.74,20
8.0-10.9,7.81

ptw

8.8,0.97,6
7.3-9.7,11.08

9.2,0.86,64
6.9-11.1,9.30

9.3,0.70,22
7.9-10.5,7.50

mm!

12.7,0.97,9
10.5-13.9,7.66

12.9,0.61,65
11.9-15.9,4.69

13.6,0.87,22
11.4-15.0,6.44

entl

10.6,1.00,9
9.6-12.7,9.45

10.9,0.98,65
9.3-13.0,9.02

10.2,1.08,22
7.7-12.5,10.54

86

beyond the bases of the protoconids and hypoconids for almost the
entire crown; shallow ectoflexids not penetrating isthmuses (molars
as well as premolars); plicated isthmuses and paralophids; well
developed, posteriorly recurved protostylids, always connected to
protoconid; and large, widely flairing metaconids and metastylids.
Lower premolars broader than molars, with well developed, persistent
hypoconulids that curve anteriorly. Deciduous premolars show even
more markedly elongated features and well developed pli cabal! inids
than permanent teeth. Unworn mcch exceeds 65 mm for p34 and 75 mm
for ml2.

Description of early Hemphillian samples. Four pre-late
Hemphillian samples of Neo. eurystyle are known from Florida, Moss
Acres, With 4A, With 4X, and Mutual Mine. The latter three are all
from southwestern Marion County, and are collectively much more
similar to late Hemphillian populations. The limited Moss Acres
sample consists of the remains of three individuals. The initially
discovered mandibles were first thought to represent extremely
progressive individuals of Neo. trampasense. Recovery of upper teeth
suggest instead that they represent the oldest known sample of Neo.
eurystyle, and merely retain many primitive features. UF 95410
represents a young adult individual with a moderately wor M3. The
most striking features of UF 95410 are its relatively short
protocones. On the M2, PRL is only 7.7 mm. This is 1.3 mm less than
the shortest protocone observed from the Bone Valley Neo. eurystyle
sample, and almost three standard deviations below the mean (Table
6). The mean PRL of the Love Site Neo. trampasense sample is a

similar 7.8 mm. The lingual border of the M2 protocone of UF 95410
IS concave, and the ends of the protocone are rounded, not pointed.
On the M3, the more elongated protocone (PRL=8.7 mm) has a flattened
to slightly concave lingual border, and pointed ends. There is a
well formed, but small pli caballin on both the M2 and M3; it is
double on the M2. The fossettes are well plicated, and the
prefossette loop of the M3 extends further lingual ly than the
prefossette base. The long axis of the hypocone is directed
obliquely, posterolingually; thus the hypoconal groove is distinctly
"V"-shaped. The styles are well developed. On the M2, the parastyle
is curved posteriorly, and the metastyle is small but distictly
curved anteriorly. The mesostyle is constricted at its base.
The two individuals represented by lower cheekteeth are of
substantially different ages, thus providing more information. UF
65250 includes a well worn dp3 and dp4, and a slightly worn ml. UF
69969 is in the later half of the moderate wear-stage (ml mcch about
35 mm). They both display many of the elongated features
characteristic of advanced Neohipparion. The protostylid is strong
and slightly curved posteriorly. The pli cabal linids are all single
on UF 69969, but are much stronger on the molars than in any
comparably worn ini dividual of Neo. trampasense. The linguaflexids
of the ml2 are also broader and more "U"-shaped, at a crown height
when molars of Neo. trampasense have "V"-shaped linguaflexids. The
hypoconulids are strong and curved anteriorly; those of the premolars
remain separated from the entoconid by a deep, "U"-shaped valley.
The Itrl of UF 69969 is 128.4 mm; within the OR of Neo. trampasense

88

and Neo. eurystyle. but smaller than those of Neo. leptode. Neo.
gidleyi, or Neo. affine. UF 69969 has the incisors associated with
the cheekteeth. They have broad, cement-filled infundibula. That of
the 13 is completely enclosed, not open posteriorly as that of many
equids, including UCMP 27126, a specimen of Neo. leptode (Merriam and
Stock, 1928, Fig. 5). The incisors are not grooved (nor are they in
UCMP 27126; Forsten, 1984, has listed grooved incisors as a generic
character for Neohipparion, but I have never observed this in any
North American specimen of the genus).

Discussion. After Simpson's (1930) original description of Neo.
phosphorum, little mention was made in the literature concerning
samples from Florida of Neo. eurystyle until MacFadden (1984a). He
discussed the probable age of Simpson's type (very late Hemphillian),
and synonymized the two species. Simpson (1930) did not compare his
new species with that from the Texas Panhandle, but his sample did
not contain any lower teeth, and uppers of Neo. eurystyle were not
described until Matthew and Stirton's (1930) paper. The Bone Valley
Neohipparion compares favorably in size and morphology with the large
samples from Yepomera and Coffee Ranch (MacFadden, 1984a; Tables 6,
7). Stirton (1955) thought the proportions of Simpson's type
indicated a larger size for the Florida population. Although the
means for APL and TRW of the Bone Valley sample are larger than those
of the Coffee Ranch and Yepomera populations, the differences are not
great (usually nonsignificant), and the observed ranges overlap
considerably (Tables 6, 7). As no quantitative or qualitative
differences can be found to consistently separate the Yepomera,

89

Coffee Ranch and Bone Valley Neohipparion samples, MacFadden 's
(1984a) synonymies are followed.

All previously described populations of Neo. eurystyle have been
of late Hemphillian age, except for MacFadden 's (1984a) referral
(without discussion) of the Neohipparion from UNSM locality Ft-40, a
late early Hemphillian site from Nebraska. Neohipparion from Ft-40
and the similarly aged Oshkosh fauna are significantly larger than
Neo. eurystyle, and also lack its very derived styles. In all dental
features these equids closely resemble Neo. leptode from the early
Hemphillian of Nevada, and are referred to that species. MacFadden
(1984a) also synonymized Neo. mol le with Neo. eurystyle. Neo. mol le
was described from a single waterworn M3 (Merriam, 1915a), a specimen
that cannot be confidently distinguished from Neo. trampasense, Neo.
eurystyle. or Nan, lenticularis. It is best considered a nomen
dubium.

Unlike the Ft-40 specimens, the Moss Acres sample is not larger
than late Hemphillian individuals, and shares with Neo. eurystyle and
Neo. gidleyi derived characters like constricted mesostyles and
anteriorly curved metastyles. It shares with these two species and
Neo. leptode the obliquely oriented hypocone in molars, a "V"-shaped
hypoconal groove in molars, more persistently shallow molar ecto-
flexids, and broader molar linguaflexids. The early appearance of
Neo. eurystyle in Florida suggests a southeastern origin for the
species.

90
Genus Pseudhipparion Ameghino, 1904

Pseudhipparion AMEGHINO, 1904, p. 262,
Griphippus QUINN, 1955, p. 42.

Type species. Pseudhipparion retrusum (Cope), 1889.

Included species. Pseud, curti vallum (Quinn), 1955; Pseud, gratum
(Leidy), 1869; Pseud, hessei Webb and Hulbert, 1986; Pseud, skinneri
Webb and Hulbert, 1986; Pseud, simpsoni Webb and Hulbert, 1986.

Diagnosis. Small hipparionine with shallow, unpocketed, generally
poorly defined DPOF located far anterior to the orbit. Malar region
variably with shallow depression, true fossa absent. Muzzle region
short, but more elongated than in Calippus, with deep nasal notch
retracted to point dorsal to P2. Protocone relatively large,
elongate-oval, connects to protoselene during early or moderate wear-
stages; connects to hypocone in molars of some species. Fossettes
relatively simple for a hipparionine, pli protoloph and pli hypostyle
rarely present. Hypoconal groove closes to form fossette; completely
lost usually before late wear-stage. Ectoflexid of premolars
shallow; entoconid of molars small, unexpanded, producing relatively
broad lingual opening of entoflexid. Protostylid moderately
developed on p3-m3, not isolated from protoconid; ectostylid present
on dp2-dp4 in all but one species. [Slightly modified after Webb and
Hulbert, 1986.]

Chronologic and geographic distribution. Late Barstovian through
late Hemphillian of the Great Plains and Gulf Coastal Plain. Very

91
abundant in the latest Barstovian and Clarendonian of the Great
Plains.

Discussion. Ameghino (1904) described Pseudhipparion in a general
work of comparative odontology of mammalian herbivores. It was
overlooked until the late 1960s (Skinner et al., 1968; Webb, 1969a),
and by then an alternate name (Griphippus) had been proposed by Quinn
(1955). Webb (1969a) and Webb and Hulbert (1986) formally
synonymized the two names. Gulf Coastal Plain populations of
Pseudhipparion were described in detail in the latter study, using
identical measurements and similar terminology to those employed
here. They recognized four successive species of the genus in the
Gulf Coastal Plain: Pseud, sp.; Pseud, curti vail urn; Pseud, skinneri ;
and Pseud, simpsoni. Their work will not be duplicated in this
section; rather their diagnoses are repeated for the sake of
comparison with species of other genera, followed by brief
descriptions. Only specimens collected since completion of their
study (January, 1986), or subsequently recognized as belonging to
Pseudhipparion are listed here. A detailed and updated phylogenetic
analysis of all species of Pseudhipparion is presented in Chapter 6.

Pseudhipparion sp.

Distribution. Known only from the Bradley Fauna, lower Bone
Valley Formation, Florida; late Barstovian, about 14 ma.

Description. This sample represents a very small, low crowned

species of Pseudhipparion, that does not correspond to any named

92

species. Webb and Hulbert (1986) refrained from naming it due to the
paucity of material. No further specimens have been added to the
sample since.

Pseudhipparion curti vail urn (Quinn), 1955

Distribution. Known only from the Gulf Coastal Plain, from the
Lapara Creek Fauna of southern Texas, and the upper Agricola Fauna of
southern peninsular Florida.

Diagnosis. Moderate -si zed species of Pseudhipparion, with
toothrow lengths of about 95 mm. Estimated unworn M12 MSCH 42 mm.
Protocone remains isolated until about 50% of the crown removed;
hypoconal groove closes to form a fossette during early wear-stages,
lost only with heavy wear. Connection of protocone and hypocone much
rarer than in Pseud, retrusum, usually occurs after connection with
protoselene. Ectoflexids relatively shallow; protostylids relatively
strong.

Discussion. Webb and Hulbert (1986) referred a moderately large
sample of teeth and jaws from the Lapara Creek Fauna to Astro hi ppus
curti vail us Quinn (1955) under the new combination Pseud.
curti vallum. A smaller number of isolated teeth from Florida also
seem to represent the same species. No cranial or facial material of
Pseud, curti vallum is known. The species is possibly ancestral to
younger species of Pseudhipparion.

93

Pseudhippan'on skinneri Webb and Hulbert, 1986

Additional referred specimens. With 4A Site: UF 95374 R m2.
Manatee Dam Site: UF 95365 R P34; UF 95772 R ml2. Archer Fauna,
Bone Valley Region, Nichols Mine: UF 95776 R Ml,

Distribution. Late Clarendonian of the Great Plains. Late
Clarendonian through early Hemphillian of peninsular Florida.

Diagnosis. Small species of Pseudhipparion with average toothrow
lengths of 86 mm. Estimated unworn Ml MSCH 47 mm. Simple fossettes;
protocone connects to protoselene during moderate wear-stage, on
average earlier than in Pseud, gratum or Pseud, curti vail urn;
protocone never connects to hypocone; hypoconal groove closed in
early or moderate wear-stages, soon lost altogether. Protostylid
reduced.

Discussion. This species was typified by Webb and Hulbert (1986)
with the Pseudhipparion from the Xmas-Kat Fauna of Nebraska. They
referred specimens from a number of late Clarendonian and very early
Hemphillian faunas from Florida to the new species. They tentatively
referred a few late early Hemphillian specimens to the species as
well. Three of the specimens listed above were not previously
recognized as belonging to Pseud, skinneri . The upper premolar from
the Manatee Dam Site is waterworn and broken, but shows the following
diagnostic features: small size; simple fossettes; obliquely
orientated, elongate-oval protocone; and isolated hypoconal fossette.
These prevent it from belonging to either of the two other small
equids in the fauna. Nan. minor or Cal . elachistus. The two lower

94

molars both are small (apl of UF 95374 is approximately 13.6 mm;
atw=6.7 mm; mml=9.1 mm; all of these parameters are within the OR of
Pseud, skinneri from the Love Site); have rounded, well separated,
hipparionine metaconids and metastylids; and very small, retracted
entoconlds. In both Nan, westoni and Nan, minor, the entoconids are
large (see Figs. 13, 16, 18). In morphology and size, these two
lower molars are identical to the older referred samples of Pseud.
skinneri. UF 95374 from With 4A represents the third late early
Hemphillian locality that has produced this species. With the
increased sample of specimens of this age, it seems that a more
definite referal to Pseud, skinneri is allowable than was
conservatively put forth by Webb and Hulbert (1986) for these
populations. They also re-enforce their suggestion that the highly
advanced species Pseud, simpsoni evolved in a very short interval of
time, between about 6.5 and 5.0 ma.

The fourth specimen listed above, UF 95776, represents one of the
limited nunter of identifiable specimens from the Archer Fauna in the
Bone Valley Region. It is referred to Pseud, skinneri based on its
small size (TRW=12.6 mm), very simple fossettes, and isolated
hypostylar lake.

Pseudhipparion simpsoni Webb and Hulbert, 1986

Additional referred specimens. Palmetto Fauna, Bone Valley
Region, Gardinier Mine: UF 95775 R ml2. Bone Valley Region,

95
specific locality unknown: UF 93217 L p34; 93631 L ml2; 17572 (?) L
II; 95773 R 13; 95774 (?) L 12.

Distribution. The late Hemphillian of Florida and Kansas.

Diagnosis. Smallest and most hypsodont species of Pseudhipparion,
with incipiently hypselodont cheekteeth. Estimated total potential
M12 MSCH about 110 mm. Very simple enamel patterns; fossettes lost
in later wear-stages; large, elongated protocone connects to
protoselene in middle wear-stages; protocone does not connect to
hypocone; hypoconal groove closes on premolars, persistently open on
molars. Metaconid and metastylid very elongated and curved
lingually; protostylid reduced and present only in early wear-stages;
deciduous premolars very hypsodont and lack ectostylids.

Description. This bizarre little species was based on the large
sample of isolated cheekteeth, a few associated dentitions, two
incisors, and several metapodials from the Upper Bone Valley
(Palmetto) Fauna. The three lowers listed above add little to the
knowledge of the morphology of the species, but the Gardinier Mine
record is an additional specimen recovered in situ in the Upper Bone
Valley Formation. The incisors are more important, as they more than
double the known sample. Webb and Hulbert (1986) previously referred
to UF 57315 as an 13, but it now seems more likely to be an 12. The
occlusal shape of UF 95773 is much more like that of normal equid
I3s, with a flat medial side for occlusion with the 12, and a pointed
posterolateral side. The infundibulum is very small in UF 95773;
most of its former area is occupied by concentric rings of
replacement dentine. UF 17572, 95773, and 95774 all have narrow

96

dentine tracts running down the entire length of their lateral and
medial sides (as does UF 57315), not just on the medial side as was
reported by Webb and Hulbert (1986). The tracts widen towards the
base of the crown; this is very evident in UF 95774 which has the
enamel and dentine preserved in highly contrasting colors. UF 95774
is 29.6 mm tall (the open, growing base in well preserved), with
occlusal dimensions of 7.5 x 5.2 mm (width x depth). The hypothesis
of Webb and Hulbert (1986) that the incisors were ever-growing in
Pseud, simpsoni is not disproven by these new specimens.

Genus Nannippus Matthew. 1926

Nannippus MATTHEW. 1926. p. 165.

Type species. Nannippus phlegon (Hay). 1899 (now considered the
junior synonym of Nan, peninsulatus (Cope), 1885. see MacFadden.
1984a).

Included species. Nan, fricki n. sp.; Nan, westoni (Simpson).
1930, n. comb.; Nan, lenticular is (Cope), 1893; Nan, minor
(Sellards), 1916; Nan, bee ken sis Dalquest and Donovan. 1973.

Revised diagnosis. Very small to medium-sized, hypsodont,
hipparionine, with toothrow lengths ranging from about 85 to 117 mm.
Relatively elongated rostrum, with markedly procumbent incisors in
younger species. DPOF varies from being deep, continuously rimmed,
and pocketed in primitive species to completely absent in younger
species. DPI conical, very reduced, lacks lophs, single rooted;
possibly absent in younger species. Protocones isolated from

97

protoselene for first 80 to 90% of the crown, except for P2s which
usually have rapidly connected protocones. Hypoconal groove open to
near base of crown, does not form isolated lake. Relative to other
hipparionines, moderately developed pli cabal lin and plications on
the isthmus and fossettes (less than in Cormohipparion and advanced
Neo hip par ion; more than Pseudhipparion and Hipparion) ; pli
cabal linids poorly developed or absent except in older species.
Anterostyle of P2 and DP2, and p2 paraconid poorly developed, thus
these teeth are not especially longer than other premolars.
Metapodials relatively slender and elongated.

Discussion. Matthew (1926) originally described Nannippus as a
subgenus of Hipparion on the basis of its small size and a combin-
ation of dental and post-cranial characters. The former were very
hypsodont teeth with isolated, oval protocones, the latter were its
"...slender limbs and feet, in which the side toes are complete but
no trace remains of the fifth digit and trapezium." Central to
Matthew's concept of the genus were the Mt. Blanco specimens he and
G. G. Simpson had recently collected in 1924 (see account in Simpson,
1986). These included the first known crania and articulated feeth
of Nannippus phlegon, a species previously so poorly known that its
generic affiliation was enigmatic (Gidley, 1907; Osborn, 1918). The
new material established the species' hipparionine affinities for the
first time, but was not illustrated or described until 1968 (Sondaar,
1968; the manus) and 1980 (MacFadden and Waldrop, 1980; cranium and
teeth). Matthew (1926) did not specifically list any other species
besides the subgenotype Nan, phlegon as belonging in Nannippus, but
it can be inferred that he generally equated it with a group of

98

species he had previously informally called the Hipparion gratum
group (e.g. Matthew, 1924).

In Matthew and Stirton (1930), Nannippus was still regarded as a
subgenus of Hipparion (along with Neo hipparion and Hipparion s.s.),
but all three were considered independent lineages of "equal value"
and "...all are derivable from different species of Merychippus. .."
(p. 356). Matthew and Stirton (1930) specifically included an
additional five species in Nannippus, and repeated Matthew's (1926)
original generic characters. They also described the DPOF as "deep
but contracted" (p. 354), apparently basing this on the supposed
"neotype" skull of "Nan." lenticularis (AMNH 10584) from the Claren-
don. This specimen (and many others from the Clarendon Fauna) are
now referred to Hipparion tehonense (MacFadden, 1980; 1984a). For
unknown reasons, no mention was made of the Mt. Blanco skull of Nan.
phlegon. which lacks a DPOF (AMNH 104708; MacFadden, 1984a, Fig.
89A). Matthew and Stirton (1930, pp. 363-364) regarded the Clarendon
"Nannippus" (i.e. _H. tehonense) as ancestral to _H. ( Nan . ) lenticu-
laris of the Hemphillian. It in turn was thought to give rise to H^.
( Nan . ) phlegon. Stirton (1940; 1947) and Webb (1969) continued to
follow this phylogenetic scenerio, with other species of Nannippus
representing sidebranches. Webb (1969), however, excluded "Nan. "
retrusus and "Nan. " gratus from Nannippus, and resurrected the genus
Pseudhipparion Ameghino for them. This genus is now recognized as
being more closely related to Neo hipparion than Nannippus (Webb and
Hulbert, 1986 and Chapter 6). MacFadden (1980; 1984a) concluded that
"Nan." tehonensis and "Nan." forcei should also be removed from
Nannippus, and placed them in the Old World genus Hipparion based on

99
the configuration of the DPOF. These exclusions produced a
"Clarendonian gap" in what had once been viewed as an unparalleled
example of successional evolution (Stirton, 1947, Figs. 1 and 2).
MacFadden (1984a) recognized this problem and noted (p. 126) "...with
lack of adequate crania the origin of Nan, minor and hence the genus
remains enigmatic. It is not clear whether Nan, minor is most
related to some other hipparion or to a species within the
merychippine complex..." The recognition of a new species of
Nannippus from the Clarendonian of Nebraska, and a newly discovered
partial skull of Nan, minor permit a reevaluation of the
relationships of Nannippus with other hipparionine genera.

Nannippus fricki new species

Probably Hipparion gratum Leidy, MATTHEW, 1924, p. 175 (in
part).

Type specimen. F:AM 117046, partial palate of juvenile individual
with right DP2-M1 and left DPl-Ml. The unworn crowns of the paracone
and metacone of the Mis just erupted through the maxillary bone.
Collected in 1962 by Ted Galusha and party.

Type locality. Gallup Gulch Quarry, Cherry County, Nebraska.
Wl/2, SWl/4, SEl/4, SWl/4 sec. 24, T33N, R38W, Merriam Quadrangle.

Stratigraphic occurence and age of type locality. Lower part of
the Merritt Dam Member, Ash Hollow Formation, Ogallala Group (Skinner
and Johnson, 1984). About 10 ma, middle Clarendonian, late Miocene.

100

Topotypic sample, F:AM 117048 R maxilla with well worn P2-M2;
117049-117050 P2s; 117052-117054 P3 and P4s; 117051, 117055-117063 Ml
and M2s; 117064 M3.

Etymology. Patrynomic for Chi Ids Frick, whose efforts led to the
collection of the type material of this and many other species.

Distribution. Middle to late Clarendonian (about 10 to 11 ma) of
Nebraska. Possibly early to middle Clarendonian of Texas and Florida
Gulf Coastal Plain (see below).

Referred specimens. East Clayton Quarry, Brown County, NB: F:AM
117045 assoc. L P2-M3 (sectioned); 117066 Ml or M2.

Olcott Quarry, Sioux County, NB: F:AM 117067-117068 Ml and M2s.

Kilpatrick Quarry, Sioux County, NB: AMNH 117072 P3 or P4; AMNH
117068-117071 Ml and M2s.

Diagnosis. Relatively large species of Nannippus with estimated
TRL and trl of about 110 mm. Mean M12 TRW 17.1 mm, BAPL 14.2 mm.
Estimated unworn molar crown height about 45 mm. Elongate-oval
protocones with pointed or rounded ends, generally isolated on all
cheekteeth except P2; moderate fossette complexity; pli hypostyle
rarely absent except in heavily worn teeth; P2 anterostyle less
reduced than in other species of Nannippus; pli cabal 1 in strong,
frequently double; deep hypoconal groove. Deep, pocketed DPOF with
well defined anterior margin as in Cormohipparion . Anterior-most
point of DPOF lies dorsal to parastyle of P3 and DP3, and directly
overlies infraorbital foramen.

Description. The holotype consists of the juvenile palate of a
very young individual (Fig. 9). The posterior part of the DP4 was
not yet in wear, and the Ml had only just begun to erupt. Based on

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108

Table 9. Standard univariate statistics for upper cheekteeth of
Nannippus fricki n. sp. from the middle Clarendonian of Nebraska.
Combined sample from the Gallup Gulch, East Clayton, Olcott, and
Kil Patrick Quarries. Format as in Table 2.

P2 P34 M12

APL

22.3,1.06,2
21.5-23.0,4.77

19.8,0.98,5
18.6-21.2,4.92

18.3,0.84,14
17.0-19.9,4.59

BAPL

18.0, ~ ,1

15.4,0.81,3
14.8-16.3,5.30

14.2,0.38,13
13.7-15.0,2.70

TRW

17.8,1.42,3
16.9-19.4,7.97

19.3,1.09,6
17.6-20.5,5.66

17.1,0.84,14
15.5-18.5,4.94

PRL

5.6,1.00,3
4.8-6.7,17.99

6.0,0.96,6
4.9-7.4,16.03

6.4,0.53,14
5.3-7.3,8.17

PRW

4.5,0.42,2
4.2-4.8,9.43

3.8,0.63,6
3.1-4.6,16.59

3.3,0.36,14
2.8-4.2,11.18

109

the eruption sequence in modern Equus, it was less than one year old
at death, and most likely between 6 and 10 months old. The cranium
is undistorted and well preserved in a matrix of poorly cemented,
medium to coarse quartz sandstone. The top and rear portions of the
skull are missing. The right and left DPOF are equally incomplete:
only the ventral halves are present. The DPOF is well rimmed
ventrally and pocketed posteriorly (Fig. 9A) . It is about 44 mm in
total length, located a minimum of 31.7 mm above the labial alveolar
margin (measured at the DPS mesostyle). The fossa narrows anteri-
orly, but its anterior margin is well defined with a moderate rim.
The lacrimal bone makes up the rear portion of the DPOF, if the
feature on the right side is correctly interpreted as a suture. The
appearance of the fossa, and its relative position to the infraor-
bital foramen (lOF) is like that of Cormohipparion sphenodus (e.g.
USNM 1352, MacFadden, 1984a, Fig. 124). In a much less complete
adult specimen, F:AM 117048, the anterior-most portion of the DPOF is
also located dorsal to the IGF, and has a well defined anterior
margin. It is about 40 mm above the labial alveolar margin; in the
type juvenile specimen the anterior margin of the DPOF is about 35 mm
above the alveolar border.

In F:AM 117046, the malar ridge extends anteriorly to a point
dorsal to the DP3 metacone. The ridges are not prominently inflated
(as in Pseudhipparion). Only the portion of the facial crest made of
the maxilla is present, as most of the jugals disarticulated from the
specimen along the maxillo-jugal suture. There is no trace of a
ventral depression on the posterior cheek portion of the maxillary

110
bones. The maximum width measured across the skull on the facial
crest at the posterior-most point of the maxillae is 90.2 mm.

The teeth preserved on F:AM 117046 include the DPI on the left
side (only its alveolus on the right). This tooth is extremely small
(maximum length about 4.5 mm), and simple with only one central cusp.
It does not contain the series of lophs typically found on equid DPls
(see e.g. Osborn, 1918, Plate 12 for Cor, sphenodus or Skinner and
Taylor, 1967, Fig. 5E for "M . " insignis) and is much smaller. The
DP2 through DP4 are of the advanced equid type, with a heavy coat of
cement and fully formed fossettes (Fig. 9B). The maximum length from
the DP2 to the DP4 is 70.5 mm, very similar to that of Nan, bee ken sis
(Dalquest and Donovan, 1973, p. 40). The enamel pattern of the
DP2-DP4 show many unusual and complex features, some due to the early
wear-stage. Perhaps the most strange are the projections eminating
lingually from the parastyles, especially on the DP3 (Fig. 9B). The
fossettes are moderately complex, with prominent prefossette loops.
The protocone is round on the DP2 with a slight anterolabial spur,
oval on the DPS, and elongate-oval on the DP4. The parastyles and
pli cabal 1 ins are well developed.

The left Ml was extracted from the holotype maxilla and sectioned
about 10 mm above the unworn occlusal surface to reveal its enamel
pattern (Fig. 9C). It resembles the referred upper molars (Figs.
lOD-lOI) in its isolated, elongate-oval protocone; strong pli
caballin; persistently open, deep hypoconal groove; large, elongate
hypocone; and moderately complex fossettes. The referred P2s have
relatively unexpanded anterostyles. The protocone of the premolars
bears a spur in early wear-stages, a primitive hipparionine feature

Ill

(MacFadden, 1984a). In the P2, the spur connects the protocone with
the protoselene in early to moderate wear-stages. However, it fades
with wear on the P34 and even very heavily worn individuals retain
isolated protocones (Fig. lOA) . The protocone of the molars tends to
be longer (relatively and absolutely. Table 9) with angular ends.
Parastyles, particularly in the P34, are large and often grooved in
early wear. The hypoconal groove is almost always deep and retained
until very late wear-stages. The hypocone of the molars is not
reduced as in other species of Nannippus.

Relative to other hipparionines, the fossettes are moderately
complex in Nan, fricki. The internal fossette margins combined
usually bear between seven and ten plications (Figs. 9C, 10). These
are deep, but with less tendency to bifurcate than those of
Cormohipparion. A pli protoloph and pli hypostyle are present in the
majority of specimens (Fig. 10).

Discussion. Nanippus fricki is distinguished from its sympatric
hipparionine contemporaries Cor, occi den tale, Neo. affine. Pseud.
gratum and _H. tehonense by a combination of size, dental characters
and DPOF morpholgoy. Upper cheekteeth of Pseud, gratum are easily
distinguished by their more rapidly connected protocones, tendency to
close the hypoconal groove, and simpler fossettes (Webb, 1969).
Isolated upper cheekteeth of _H- tehonense more closely resemble those
of Nan, fricki, but are on average larger, have simpler fossettes
(greater tendency to lose pli protoloph and pli hypostyle), and more
rapidly connected protocones. Neohipparion affine is much larger
than Nan, fricki, and has simpler fossettes. Cor, occidentale is
also much larger, with more complex fossettes and without protoconal

112
spurs. All four retain larger DPls than Nan, fn'cki. Neohipparion.
Pseudhipparion and Hippan'on have shallower DPOFs without well
defined anterior margins (Webb and Hulbert, 1986; MacFadden, 1980;
1984a).

Nanippus fricki is evidently extremely rare in middle Clarendonian
faunas of the Great Plains, and is only recognized from three local-
ities in Nebraska. While Pseud, gratum is represented by hundreds of
teeth in the Snake Creek Fauna, only six specimens of Nan, fricki
were found. No lowers are referred to Nan, fricki in the type
region, because of the difficulty in unambiguously distinguishing
them from those of the similarly sized Pseud, gratum. However, some
of the mandibles from the Gallup Gulch Quarry can probably be shown
to belong to Nan, fricki with further study. As described below,
lowers from southern faunas can be referred to a very similar, if not
conspecific, species of Nannippus, because the associated species of
Pseudhipparion is much smaller than Nan, fricki. The phylogenetic
implications of the facial and dental features of Nan, fricki are
discussed in Chapter 6.

Nannippus sp., cf. Nannippus fricki

Nannippus cf. Nan, in genu urn (Leidy), FORSTEN, 1975, pp. 61-65
(in part).

Referred specimens. Lapara Creek Fauna, Bee County, TX. Farish
Ranch Site: TMM 31081-660 assoc. R P2-P3; -630 assoc. R P2,M1-M2;
-1159 assoc. L M1-M2; -319, -825 P34s; -658, -659, -1411, -1413,
-1421A M12s; -16, -27, -176, -566, -675, -735, -1511 mandibles; -1506

113
L dp2; -168, -953, -956 p34s; -1413, -1424 ml2s. Buckner Ranch Site:
TMM 30896-450 assoc. L M1-M2; -400 M12; -455 nil2. Bridge Estate
Site: TMM 31132-402 P34; -4338 M12; -306 juvenile mandible.

Agricola Fauna, Bone Valley Region. Gray Zone, Phophoria Mine:
UF 28564 P2; 28568 P34; 28569-28571 M12s; 28562-28563 M3s; 28573,
28577, 28578 ml2s; 28678 m3. Hookers Prairie Mine: UF 93207 R ml.

Description. These two populations consist of isolated cheek-
teeth, and in the case of the Texas sample, a number of mandibles.
No cranial material is known. The upper cheekteeth resemble those of
Nan, fricki from Nebraska in size (Table 8) and general enamel
morphology (Figs. UA-UD, UF-llI). This includes frequent double
pli caballins, elongate-oval protocones on molars, moderate fossette
complexity, strong parastyles, large hypocones, and deep hypoconal
grooves. The Florida sample is on average smaller than that from
Nebraska, but this is often the case for populations considered
conspecific from the two regions (Webb and Hulbert, 1986). The
Phosphoria Mine sample is also probably less high crowned. A very
slightly worn Ml has a MSCH of only 38.3 mm.

The lower cheekteeth are of the primitive hipparionid pattern
(Forsten, 1984), with well developed, rounded metastylids that remain
well isolated from the metaconids throughout ontogeny. Protostylids
are well developed on the p3-m3 and dp34 (Figs. HE, IIJ, and UK),
and sometimes project further labial ly than does the base of the
protoconid. The ectoflexid is shallow in the premolars, not
penetrating the isthmus, very deep in the molars and deciduous
premolars. The entoconid is large, and in slightly worn premolars
often has a prominent anterior plication that lies labial to the

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metastylid. Prenxjlars have small but distinct pli caballinids in
early wear-stages. They do not extend further labial ly than the base
of the hypoconid. Pli caballinids are absent or ephemeral on molars
(e.g. TMM 31081-566, n)2). Isthmus and paralophid plications are
frequent in slightly and moderately worn premolars, absent on molars.
The p2 paraconid is relatively poorly developed, such that the tooth
is rather short (Table 8).

None of the Lapara Creek mandibles preserve the entire symphyseal
region, nor do any possess incisors, but the postcanine diastema can
be estimated on TMM 31081-27 (about 52 mm) and TMM 31081-16 (about 55
mm). This is approximately half the trl . The depth of the ramus
measured between the p4 and ml is 43.0 and 46.2 mm for 31081-16 and
31081-27, respectively. The deciduous lower premolars are well
cemented and possess moderately large ectostylids.

Discussion. Forsten (1975) referred the entire Lapara Creek
sample of medium-sized hipparionines to a single taxon, "Nannippus
cf. N^. ingenuum" [sic]. The dental morphology of the topotypic and
other referred Florida samples of "Nan." in genu us are described
beolw. They have enlarged P2 anterostyles and p2 paraconids, very
complex enamel plications, more persistently isolated protocones
without spurs, and relatively broader premolars. "Nan." ingenuus
belongs in the genus Cormohipparion. For the most part, the
specimens from the Lapara Creek and Clarendon faunas that Forsten
(1975) assigned to Nan, cf. ingenuus are referable to a single
species, namely H^. tehonense (MacFadden, 1980). They differ from
those here referred to Nannippus by being (on average) larger, having

117
less complex fossettes, deeper premolar ectoflexids, fewer isthmus
and paralophid plications, more poorly developed pli caballinids
(usually absent), weak protostylids, and more poorly developed
ectostylids on dp2-dp4. As noted above, teeth of Nan, fricki and H^.
tehonense generally resemble one another, and a sizable proportion of
the Lapara Creek sample is indeterminate between the two. Most of
the associated dentitions and lesser worn teeth are referable to one
or the other, based on both size and morphology.

The Lapara Creek and Phosphoria Mine samples of Nannippus are only
provisionally referred to Nan, fricki, because they lack cranial
material, and the type locality of Nan, fricki has no referable lower
cheekteeth. Although the three samples differ slightly in size and
morphology, they are within the general accepted range of variation
for a widely distributed equid species. The relatively lower unworn
crown heights of the Florida sample probably reflect their greater
age (early, possibly very early Clarendonian).

Nannippus westoni (Simpson), 1930 new combination

Merychippus westoni SIMPSON, 1930, p. 164; STIRTON, 1940, p.
178; FORSTEN, 1975, 40.

Nannippus cf. minor (Sellards), WEBB et al., 1981, p. 526.
Nannippus minor (Sellards), MACFADDEN, 1984a, p. 123 (in part).

Type specimen. UF/FGS V-4088, right maxillary fragment with

heavily worn P3-M2.

Type locality. Phosphate mine of the Cummer Lumber Company,

located about 7 km west-northwest of Newberry, Gilchrist County,

118
Florida, Probably NWl/4 sec. 25, T9S, R16E, Waters Lake Quadrangle
(Simpson, 1930, pp. 155-156).

Stratigraphic occurence and age of the type locality. Uncertain,
but here interpreted to probably be early Hemphillian. Previously
thought to be significantly older, i.e. equivalent to the Quincy and
Midway local faunas, or late Hemingfordian.

Topotypic sample. None other than holotype, UF/FGS V-4088.

Distribution. Known only from the latest Clarendonian through the
early Hemphillian (about 8.0 to 9.5 ma) of northern peninsular
Florida.

Referred specimens. Love Site: UF 96575 assoc. L DP2-DP3; 62155
assoc. R P3-P4; 96760-96774, 96813-96816 DP2s; 96775-96809 DP34s;
60247, 60397-60400, 62151-62154 P2s; 53157, 53398, 62156-62164,
62166-62170, 62179, 62421, 95387 P34s; 50351, 50352, 62171, 62173-
62178, 62180-62194, 90265 M12s; 96308-96319 M3s; 32187 L mandible
with dp3-ml; 32130 assoc. R p2-m3 and probably assoc. L p3, p4, and
m2; 63984 p2; 59162, 63986-63989, 63989, 63992, 63993, 64920, 64921,
92978 p34s; 63994-63998, 64502, 92976, 92977 ml2s; 63999, 64000,
92970-92975 m3s; 96567-96569 dp2s; 92979-92981, 92985, 96571-96574,
96576 dp34s; 66800, 33818, 33849-33851, 33967, 33986, 34029-34034,
34036 MC III; 33411, 33432, 33448, 33609, 33631 MT III.

McGehee Farm Site: UF 95376, 95377 P34s; 17126, 95378. 95379
M12s; 95380 p34; 95381-95384 ml2s; 95385 m3.

Mixson's Bone Bed: F:AM 104871 Ml(?); 104870 p34.

Haile 5A: UF 17294 P34.

Haile 19A: UF 47324 p2.

119
Revised diagnosis. Moderate-sized species of Nannippus with esti-
mated trl of about 100 mm. Smaller than Nan, fricki. Nan, lenticu-
lar is or Nan, beckensis; larger than Nan, minor; similar in size to
Nan, peninsulatus. Mean M12 TRW 14.9 mm; mean BAPL 12.7 mm. Unworn
M12 MSCH about 43 mm. Differs from Nan, fricki in its simpler fos-
sette pattern; smaller, rarely double pli caballins; shallower hypo-
conal groove; and reduced molar hypocone. Differs from Nan, minor
and all other advanced species of Nannippus by its lower unworn crown
height; protoconal spur on P34 in early wear; simpler fossette
plications; strong protostylids on p3-m3 and dp34; well developed pli
caballinids and isthmus plications in slightly worn premolars; and
ectostylids on dp2-dp4.

Description. The P2s have oval or rounded protocones that are
connected to the protoselene in all known specimens, including the
slightly worn UF 60397 (Figs. 12D-12E). The anterostyle varies from
being only moderately reduced as in Nan, fricki (e.g. UF 62154 and
60400) to very reduced as in Nan, minor (e.g. UF 62152). The
hypoconal groove is occasionally deep but usually shallow and narrow.
Fossettes are moderately to simply plicated. Pre- and postfossettes
are frequently confluent, a common feature of equid P2s. Pli
caballin is single, not well developed. Mesostyle is strong (Fig.
12D). Unworn P2 MSCH estimated to be at least 30 mm.

The P3 and P4 are notably low-crowned relative to molars, with
unworn MSCHs of only about 35 mm. The parastyle is grooved through
much of the crown. It and the mesostyle are very strong, but the
metastyle is weak or absent. The protocone is oval to elongate-oval,
rarely rounded (UF 62166 is such an exception), with a moderate

120
anterolabial spur in early wear-stages (Fig. 12F). The pli caballin
is usually single, only occassionally bifurcated, but persists until
late wear-stages. The hypoconal groove is initially deep and wide,
shallows with wear, but remains persistently open until MSCH of about
10 mm or less. Fossette borders are relatively simple: pli proto-
loph either single (50% of Love Site sample, n=16) or absent (50%);
prefosette loop poorly developed; and pli hypostyle either single
(63%) or absent (37%). The posterior half of the prefossette
generally has only two, or more rarely three, plications in teeth
with MSCHs greater than 15 mm; the opposing face of the postfossette
usually has one, occasionally two or three, plications (Figs. 12F-
12G).

The Ml and M2 are moderately hypsodont (HI=3.4), with unworn MSCH
about 43 mm. The parastyle is weaker than that of P34, and only
grooved during earliest wear-stages. Protocones are oval or
elongate-oval, often with lenticular ends, usually isolated until
MSCH less than 13 mm; during early wear-stages, a protoconal spur is
absent or much smaller than that of premolars. The pli caballin is
single, unbifurcated, lost at MSCHs of about 20 mm. The hypocone is
usually relatively small, as in Nan, minor, but occasionally unre-
duced (e.g. UF 62189). Hypoconal groove depth varies with wear, but
remains persistently open, until latest wear-stages (MacFadden,
1984a, Fig. 96). Fossette borders resemble those of the premolars
(Figs. 12I-12J).

Lower premolars are characterized by large, rounded to oval
metaconids, metastylids and entoconids. The entoconid is closely

121

Table 10. Standard univariate statistics for upper cheekteeth of
Nannippus westoni from the Love Site, Alachua County, Florida (very
late Clarendonian). Format as in Table 2.

P2 P34 M12

APL

20.7,1.52,10
17.6-22.7,7.36

17.1,1.19,16
15.3-19.6,6.94

16.2,1.04,27
14.3-18.3,6.38

BAPL

16.7,0.80,10
15.3-17.8.4.77

12.9,0.62,16
11.6-14.1.4.78

12.7,0.55,24
11.6-13.7,4.31

TRW

16.0,0.83,10
14.9-17.4,5.20

16.1,0.85,16
14.4-17.4,5.28

14.9,1.02,25
12.5-17.1,6.85

PRL

4.5,0.54,10
4.0-5.7,12.00

5.4,0.77,17
3.9-6.7,14.34

5.3,0.59,27
4.3-6.7,11.23

PRW

3.6,0.37,10
2.9-4.2,10.48

3.3,0.45,17
2.4-4.2,13.88

3.1,0.41,25
2.3-3.9,13.13

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1cm

Figure 13. Occlusal views of lower cheekteeth of Nannippus westoni
from Florida. A. F:AM 104870, R p34, late wear-stage; Mixson's Bone
Bed, Levy County. 8-0, Love Site, Alachua County. B. UF 64921, L
p34, early wear-stage. C. UF 64501, L ml2, early wear-stage. D. UF
63997, R ml2, moderate wear-stage.

125

appressed to the metastylid, leaving only a very narrow lingual
opening for the entoflexid (Figs. 13A-13B). The p2 has a strong pli
caballinid, a small pli entoflexid and a very shallow ectoflexid.
The p2 apl is less than that of the p34 (Table 10). The ectoflexid
of the p34 is deeper and broader than that of the p2, penetrating
just up to the base but not into the isthmus. The p34 pli caballinid
varies from absent (UF 59162) to weak (UF 64921) to strong (UF
92978), and is usually present through the first two-thirds of the
crown. The p34 always have a protostylid that first appears on the
occlusal surface after the first 5 mm or so of crown wears off. The
protostylid is usually prominent, often extending further labial ly
than the base of the protoconid (Fig. 13B); sometimes curved
posteriorly; and is always connected to the protoconid except for its
initial few millimeters. Isthmus and paralophid plications are
generally restricted to the upper half of the crown. A slightly worn
p4 has a mcch of 35.8 mm (UF 32130), indicating that lower premolars
are slightly higher crowned than corresponding upper teeth.

Lower molars of Nan, westoni generally resemble those of Nan.
fricki or Cor, ingenuum in morphology, with oval metaconids and
metastylids separated by a "V"-shaped linguaflexid and a deep
ectoflexid that usually completely divides the isthmus. In early
wear-stages however, and even in a few moderately worn molars (e.g.
UF 64504), the ectoflexid depth is reduced. As in the premolars, the
protostylid is strong, attached to the protoconid, and observed on
every available specimen (Figs. 13C-13D). Isthmus and paralophid

126

plications are rare and limited to slightly worn specimens, as are
pli caballinids. Unworn mcch is about 42 or 43 mm.

The dp2 is relatively short, with an unexpanded paraconid, a
shallow ectoflexid, and a moderate pli caballinid. It thus greatly
resembles the permanent p2, except for its greater length, oval
ectostylid, and rudimentary protostylid. In the dp34, both the
protostylid and ectostylid are usually strong, the ectoflexid deeply
penetrates the isthmus, and there is a weak pli caballinid in early
wear-stages. The dp34 are less high crowned than those of Nan.
minor, with an unworn mcch of about 19.5 mm.

A number of medial metapodials from the Love Site are referred to
Nan, westoni as their size is similar to those of other species of
Nannippus (Table 11). They display a mosaic of advanced Nannippus
and primitive hipparionine features. Advanced characters include
their length (Table 11), slenderness, large unciform facets on the MC
III, and large cuboid and entocuneiform facets on the MT III.
Primitively, the MC III has two distinct facets for articualtion with
the unciform (Fig. 14; they merge in Nan, minor and Nan, penin-
sulatus), the proximal anteroposterior breadth is large relative to
the proximal width (cf. Sondaar, 1968, p. 55), and the distal width
measured across the tuberosities is usually greater (although often
by less than 1 mm) than the width measured across the distal
condyles. The MT III retains a moderate distal depression on the
anterior face of the shaft above the condyles. It is further reduced
in later species of Nannippus (Hussain, 1975). The distal width of

Figure 14. Proximal (A-D) and anterior (E-G) views of medial
metapodials of Nannippus from Florida. A. UF 57344, proximal
metacarpal III of Nan, mi nor. Palmetto Fauna, Bone Valley Region,
Polk County. B, ETUF 34029, metacarpal III of Nan. westoni. Love
Site, Alachua County. C, F. UF 69936, metacarpaTTlI of fJarT. minor.
Moss Acres Racetrack Site, Marion County. D, G. UF 69934, metatarsal
III of Nan. minor. Moss Acres Racetrack Site, Marion County.

128

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the MT III measured across the tuberosities is also greater than the
distal condylar width (Table 11). Hussain (1975, p. 207) stated that
the opposite is true for Nannippus, but most MT III of Nan, minor.
Nan. lenticularis and Nan, peninsulatus I have measured are like
those of the Love Site in this regard (Table 11).

Discussion. Simpson (1930) based Merychippus westoni on a
maxillary fragment containing four heavily worn teeth (Fig. 12A) .
Although the MSCH cannot be measured directly on any of the teeth (as
they are still housed in their alveoli), I estimate their crown
heights to be about 12 to 16 mm maximum. Simpson (1930) interpreted
the specimen's morphology to represent a primitive, low crowned
species of Merychippus; it seems more plausable to now consider the
type an old individual of a more advanced, hypsodont species. Except
for details reflecting individual variation, heavily worn Love Site
specimens perfectly match the type in size (Table 8) and all aspects
of its enamel morphology (Figs. 12B-12C). The persistently open
hypoconal groove and isolated protocone preclude assignment to
Pseudhipparion or Calippus, and the simple nature of the fossettes
stressed by Simpson (1930) is merely an artifact of the specimen's
advanced age. As far as can be determined, no other vertebrate
specimens were ever recovered from the type locality of Merychippus
westoni , and thus the geologic age of the holotype can only be
inferred from the specimen itself. The exact locality was never
recorded, and was no doubt destoyed by mining operations.

Mining in the vicintiy of the town of Newberry continues to this
day, although now the limestone itself is being quarried, rather than

134

the phosphatic pockets. Vertebrate fossil-bearing sediments, either
from filled sinkholes, or from channel deposits incised into the
limestone, are common in this region. The Florida State Museum has
collections from 41 separate localities (the Haile sites) from a
limited region only about 9 km due east of the type locality of
Merychippus westoni. Of these, six are early Hemphillian, one
Blancan, six Irvingtonian, and 28 Rancholabrean. These, and all
other Miocene vertebrate sites in the vicinity are either too young
to contain a primitive species of Merychippus (e.g. Love Site,
McGehee Farm Site), or are too old (Thomas Farm, Buda, or SB-IA). In
summary, there is neither good morphological or geological evidence
for considering the holotype of M^. westoni a primitive, late
Hemingfordian-grade merychippine as did Simpson (1930) and Stirton
(1940). Rather, the more abundant referred material indicates a
younger age and a referral to Nannippus.

Nan, westoni is principally known from isolated cheekteeth, the
two major exceptions being the worn holotype and UF 32130, a
fragmentary ramus with slightly worn teeth. Thus, none of the
phylogenetically important cranial and rostral characters of
Nannippus are known for this species, as well as the morphology of
the lower incisors and the DPI. Generic features of Nannippus that
are known for Nan, westoni are its small size (Tables 10, 11),
oval-lenticular protocones isolated throughout most of the crown,
open hypoconal grooves that do not form isolated hypoconal lakes as
in Pseudhipparion, relatively persistent pli hypostyle, and poorly
developed anterior regions on the P2 and p2. Other dental
characters, not usually considered typical of Nannippus (e.g. strong

135
protostylids) are plesiomorphous, and cannot be used to exclude the
species from the genus. Although crania are unknown, the relatively
low crowned prenwlars suggest that Nan, westoni retained the
anteriorly and ventral ly positioned DPOF found in Nan, fricki.
Metapodials of Nan, westoni also demonstrate some derived Nannippus
characters, such as large unciform and entocuneiform facets (see
above).

Populations here considered referable to Nan, westoni were
previously placed in Nan, minor (Waldrop, 1971; MacFadden and
Waldrop, 1980; MacFadden, 1984a), although their more primitive
nature (relative to the topotypic Upper Bone Valley sample) was
realized. The rationale for this was the belief that Florida
Nannippus populations formed a single, continually and gradually
evolving lineage through the Hemphillian, with no obvious point of
demarcation. A thorough study of the Love Site sample, by far the
largest known for Nan, westoni, and new discoveries of relatively
complete early Hemphillian Nan, minor (see below), suggest otherwise,
at least for a set of characters that can be used to distinguish the
two species.

Five localities ranging in age from very late Clarendonian to
early Hemphillian (Fig. 1) contain referable specimens of Nan.
westoni in addition to the type locality. Nan, westoni is rare at
all these sites, with the exception of the Love Site, the rarest
equid in each fauna. This is notable as Nan, minor is particularly
common in later Hemphillian faunas in Florida, and is often the most
abundantly represented equid species. Only a few records of
Nannippus from the early Hemphillian of the Great Plains exist (e.g.

136

F:AM 113744 from the J. Swayze Quarry, Kansas), and most often they
consist of one or two isolated teeth inadequate for conclusive
specific identification. Some are referable to Nan, lenticular! s
(MacFadden, 1984a; Winkler, 1985), while others might be either Nan.
fricki. Nan, westoni , or an unde scribed taxon.

Nannippus minor (Sellards), 1916

Hipparion minor SELLARDS, 1916, p. 96.

Hipparion (Nannippus) minor Sellards, SIMPSON, 1930, p. 188;

MAHHEW and STIRTON, 1930, p. 354.

Hipparion (Nannippus) in genu urn (Leidy), SIMPSON, 1930, p. 187

(in part).

Nannippus minor (Sellards), STIRTON, 1940, p. 186; WEBB and

TESSMAN, 1968, p. 807 (in part); VOORHIES, 1974, p. 110;

MACFADDEN and WALDROP, 1980, p. 31; MACFADDEN, 1984a, p. 123

(in part).

Nannippus cf. minor (Sellards), LANCE, 1950, p. 52.

Nannippus aztecus MOOSER, 1968, p. 7; DALQUEST and MOOSER, 1980;

p. 13.

Hipparion ingenuum (Leidy), WEBB and TESSMAN, 1968, p. 807 (in

part).

Type specimens. The holotype (UF/FGS 5867) and paratype (UF/FGS
1167) were lost in the 1920s. MacFadden and Waldrop (1980) selected
UF 17570 as the neotype; it consists of an associated left P3-M3 and
right M2-M3.

Neotype locality. Palmetto Mine, Polk County, Florida.

137

Stratigraphic occurence and age of the neotype locality. Upper
horizon of the Bone Valley Formation; very late Hemphillian (early
Pliocene), about 4.5 to 5.0 ma.

Distribution. Early, but not earliest, Hemphillian of Florida;
late Hemphillian of southern North America (northernmost records are
from the Texas Panhandle).

Referred Florida specimens. Moss Acres Racetrack Site: UF
69933/69934 assoc. R P3, P4, M2, M3 and L P4, M2, M3; R and L
mandibles with p2-m3; and post-cranial elements (Table 12); UF
69935/69936 assoc. R maxilla with P2-M3; premaxillae with R and L
11-13; L mandible with p2-m3; R p3; and post-cranial elements (Table
12); 92994 L P34; 95409 assoc. R m2-m3; 95404 L ml2; 69955 assoc. R
and L juvenile hindlimbs (Table 12); 97263 assoc. R and L MT III and
tarsal elements; 69954 L femur; 95465 L distal MC III; 95406 R distal
tibia.

Dunnellon Phosphate Mines: UF/FGS V-1424 M12; -1492 p34; -1429
ml2.

With 4A: UF 18311 L maxilla with P3-M2; 17202, 53522, 63645,
63646 P34s; 19618, 53520, 53521, 53523, 53546, 53547, 63649 M12s;
63647, 63650 M3s; 45512, 45513 DP34s; 17304, 95368 p2s; 95369-95373,
95375 p34s; 17307, 53488, 53489 ml2s; 45516 m3; 45584 MT III.

Manatee Dam Site: UF 11929 P4(?); 11933 DP34; 11924-11926 p34s.

Lockwood Meadows Site: UF 61459, 64117 P34s; 61460, 61462, 61463
p34s; '61457, 61458, 61461 ml2s; 61456, 61465 m3s.

Palmetto Fauna, Bone Valley Region: UF 67000 laterally crushed
rear half of skull with R M2-M3 and L M3; 57576 partial L maxilla
with L M1-M3; UF 17249. 19431-19433, 24701, 63626, 63959, 63960,

138

67980, 68976. 91206 P2s; F:AM 113760, UF/FGS V-1426, UP 14988, 17250,
17251, 17276, 19435, 47368, 55822, 55891, 57214, 57312, 58382, 63628,
63629, 63965, 63966, 63978-63980, 64156, 64157, 67982, 91211, 93224,
93252, 93253 P34s; F:AM 113761, 113763-113765, UCMP 130132-130134, UF
10313, 17252, 17253, 17264, 17267, 17279, 17281, 19434, 47362,
47364-47366, 47370-47372, 53843-53845, 53952, 53953, 55893, 55933,

57215, 58296, 58381, 58409, 61992, 62030, 63627, 63630-63633,
63961-63964, 63967, 63968, 63977, 64174, 65796, 67981, 67983, 90385,
91210, 91207, 91208, 93222, 93225, 93232, 93240, 93241 M12s; UF
10300, 12056, 17183, 17254, 17290, 19436, 25710, 32017, 40082, 47369,

57216, 57217, 57394, 58481, 62014, 63635, 63969-63976, 65717, 65794,
68994, 91209, 91212, 91214, 93209, 93233 M3s; UF 17255 DP34s; UF
65176 R mandible with p3-m3; UF 17273 R mandible with p4-ml; UF 69903
(cast of TRO 567) L mandible with p2-m3; UF 57213 L mandible with
p2-p4; UF 97360 mandibular symphysis with R and L il-i3; UF 10310,
17629, 53878, 61486, 61487. 61489, 65178. 65179. 65201 p2s; UF 13219.
17270, 17277, 24710, 28855, 28856, 52432. 52433. 53954. 61304.
61490-61495, 65180. 65182, 65192-65198, 65212, 65223, 65228-65230,
68959-68962, 68978, 69911, 91213. 93226 p34s; UF/FGS V-6608. -6610.
-6611. -6615. UF 10299. 10303, 12500, 17271, 17274, 17293, 21028,
24702, 24702, 24704, 24706, 24708, 24712, 28854, 52434, 53955, 57218,
58482, 61496, 62032, 65183-65191, 65202-65204, 65210, 65211,
65214-65219, 65227, 68977, 69912, 93234, 93235, 93254 ml2s; UF 10313,
17272, 17280, 17394, 18914, 24698, 24699, 24703, 24709, 61497, 62031,
65205-65209, 65213, 65220-65222 m3s; UF 69905, 69906 dp2s; UF 17275,
53959. 61488. 61499. 69649, 69650, 93255 dp34s; UF 53905, 53906,

139
53964, 57344, 61983 proximal MC III; UF 53926, 57395 proximal MT III;
UF 53931 distal MT III.

Revised diagnosis. Smallest species of Nannippus with trl of 82
to 95 mm; mean M12 TRW 13.7 mm; unworn M12 MSCH 51 to 53 mm. Proto-
stylids very reduced or absent on most permanent lower cheekteeth; if
present not isolated from protoconid as in Nan, lenticularis.
Ectostylids absent on dp2-dp4. Isthmus and paralophid plications
frequent. Hypoconal groove shallow, usually remains open until late
wear-stages, does not form isolated lake.

Description. The following dental description is based on the
topotypic Bone Valley sample of Nan, minor. The Yepomera and El
Ocote samples have been described by Lance (1950), Mooser (1968),
Sondaar (1968), Dalquest and Mooser (1980), and MacFadden (1984a).
The Mexican populations are similar to that from Florida (Tables 13,
14), and I follow Waldrop (1971) and MacFadden (1984a) in considering
them conspecific. Older, early Hemphillian samples (which include
associated cranial and post-cranial material) referred to Nan, minor
are described in a following section and compared to the late
Hemphillian population. Originally described based on a single tooth
(now lost). Nan, minor from the Bone Valley was poorly known through
the first half of this century. Over the past 20 years, extensive
field operations and generous donations by amateurs to the Florida
State Museum have resulted in the recovery of over 200 specimens.
Most of these are isolated cheekteeth, but a few niore complete
specimens are now known, including a partial skull (UF 67000) and one
complete lower toothrow (UF 69903). Unfortunately, UF 67000 does not
preserve any portion of the skull anterior to the orbits, and it has

140

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141

Table 13. Standard univariate statistics for upper cheekteeth of
Nannippus minor. Format as in Table 2. Populations are W4A,
Withlacoochee River Site 4A, Florida; UBV, Palmetto Fauna, Bone
Valley Region, Florida; and YEP, Yepomera localities. Chihuahua,
Mexico. No P2s are present in the Withlacoochee River 4A sample.

FAUNA

W4A

UBV
P2

YEP

APL

16.8,1.29,9
15.0-18.9,7.69

16.1,0.92,13
14.9-18.1,5.68

BAPL

13.6,0.69,6
12.7-14.5,5.05

13.2,0.63,12
12.4-14.4,4.73

TRW

13.4,0.80,9
12.3-14.6,5.94

14.8.0.64,13
13.7-15.8,4.29

PRL

4.3,0.34,9
3.8-4.9,7.90

4.4,0.46,13
3.6-5.3,10.37

PRW

3.1,0.29,9
2.8-3.6,9.41

P34

3.6,0.21,13
3.3-3.9,5.65

APL

13.9,1.49
12.0-16.0

6
,10

.73

14.9,1.22,25
11.6-17.3,8.22

14.7,1.01,35
13.1-16.8,6.86

BAPL

11.7,1.31
9.8-12.8

,4
,11

.27

11.6,0.90,20
10.1-13.4,7.74

11.8,0.41,32
10.9-12.7,3.51

TRW

14.2,1.42
12.3-15.5

,6
,10

.02

14.5.0.82,25
12.7-15.9,5.62

15.2,0.67,34
13.8-16.5.4.37

PRL

5.0,0.92
4.2-6.3,

.6
18.

45

4.4,0.50,28
3.6-5.5,11.44

5.4.0.48.35
4.6-6.4,8.96

PRW

2.9,0.41
2.4-3.4,

,6
13.

92

3.0,0.30,26
2.5-3.8.9.99

3.7.0.24,35
2.7-3.9,6.41

142

Table 13 — continued

M12

APL

13.9,2.01,10
11.7-17.8,14.48

14.7,0.94.45
12.6-16.7,6.39

14.2,1.09,39
12.1-17.0,7.71

BAPL

10.8,1.31,6
8.7-12.3,12.10

11.3,1.30,26
9.6-14.0,10.38

11.2,0.43,35
10.3-12.1,3.84

TRW

12.9,1.37,9
11.3-15.5,10.63

13.7,1.10,43
11.2-16.1,8.06

14.3,0.52,39
13.5-15.7,3.64

PRL

5.0,0.82,9
4.2-6.6,16.32

4.7,0.51,46
3.6-5.6,10.91

5.5,0.50,39
4.6-6.8,9.13

PRW

2.6,0.33,10
2.1-3.2,12.57

2.9,0.26,48
2.4-3.5,9.14

3.5,0.17,39
3.0-3.8,4.69

143

1cm

Figure 15. Occlusal views of upper cheekteeth of Nannippus minor
from the Palmetto Fauna (latest Hemphillian), Bone Valley Region,
Polk County, Florida. A. UF 63626, R P2, early wear-stage. B. UF
67980, R P2, late wear-stage. C. UF 63628, R P34, early moderate
wear-stage. D. UF 17250, R P34, moderate wear-stage. E. UF 63978,
R P34, late moderate wear-stage. F. UF 67981, R M12, early moderate
wear-stage. G. UF 47362, L M12, early moderate wear-stage. H. UF
67983, L M12, late moderate wear-stage. I. UF 90385, L M12, late
moderate wear-stage.

144

1cm

-J

Figure 16. Occlusal views of lower cheekteeth of Nannippus minor
from the Palmetto Fauna (latest Hemphillian), Bone Valley Region,
Polk County, Florida. A. UF 57213, associated L p2-p4, moderate
wear-stage. B. UF 53954, R p34, moderate wear-stage. C. UF 93235,
R ml2, early wear-stage. D. UF 65192, R ml2, moderate wear-stage.
E. UF 17275, R dp34, late wear-stage.

145

been laterally crushed and deformed. No measurements taken on the
specimen would realistically conform to its original dimensions.

The P2s of Nan, minor (Fig. 15; Table 13) have very poorly
developed anterostyles and have relatively short APLs and BAPLs. The
pseudoparastyle is prominent. The oval protocone connects to the
protoselene during very early wear-stages (Fig. 15A) ; the connection
remains tightly constricted by the pre- and postprotoconal grooves
until the tooth is heavily worn. The pli cabal lin is long, narrow,
and usually single. Fossette complexity is moderate to high, but
most plications are shallow and not bifurcated. Unworn MSCH is about
34 mm.

The P3 and P4 are characterized by round (Figs. 15C, 15E) to
slightly oval (Fig. 15D) protocones that lack spurs and remain
isolated until MSCHs of 14 mm or less; strong, grooved parastyles;
better developed metastyles than Nan, westoni ; usually single, well
developed pli caballins; open, usually shallow hypoconal grooves; and
moderate to very complicated fossettes (Figs. 15C-15E), A single pli
protoloph and pli hypostyle are usually retained until MSCHs of less
than 20 mm, and the anterior half of the prefossette may also bear
one or two additional plications in early wear. The posterior half
of the prefossette generally has three to six plications (eight
maximum) in early to moderate wear-stages, one or two in heavily worn
teeth. The anterior half of the postfossette has two to four
plications. Unworn P34 MSCH is about 45 to 47 mm. The DP34 have
small, oval protocones; strong, bifurcated parastyles; and moderately
complex fossettes.

146

The Ml and M2 are only slightly smaller than the P34 (Table 13),
with relatively longer protocones, smaller hypocones, pli caballins
often reduced or absent, and weaker metastyles (Figs. 15F-15I).
Fossette complexity varies greatly; some molars resemble the P34 and
are complex (Figs. 15G, 151), others are noticably simpler at
comparable crown heights (Figs 15F, 15H) . The pli protoloph and pli
hypostyle are often present but are absent more frequently than in
the P34. Protocones begin connecting to the protoselene at MSCHs of
about 10 mm. Unworn M12 MSCH of this species does exceed 50 mm
(contra MacFadden and Waldrop, 1980 and MacFadden, 1984a), but
complete specimens are rare (due to breakage). The tallest
measurable Bone Valley specimens are UF 93240 (MSCH=45.7 mm) and F:AM
113762 (48.1 mm); both are worn with fully formed postfossettes,
implying that unworn molars would be at least 3 to 5 mm taller. Two
specimens with wear from Yepomera, LACM (CIT) 3759 and 3784, each
have MSCHs exceeding 50 mm.

The only known specimen from the Bone Valley Region that preserves
the mandibular symphysis and lower incisors is UF 97360. Collected
in 1983 in association with typical Upper Bone Valley Fauna elements,
it is referred to Nan, minor because of its small size. The maximum
transverse width across the i3s is 43.1 mm. At its early wear-stage,
the infundibula are large and completely formed on the il and i2.
Those of the i3 are incomplete ("half infundibulum" of Bennett,
1980). The incisors plesiomorphically resemble those of other
hipparionines (e.g. Cormohipparion) rather than the extremely
procumbent lower incisors of Nan, peninsulatus and Nan, bee ken sis
(Dalquest and Donovan, 1973; MacFadden and Waldrop, 1980).

147

Table 14. Standard univariate statistics for lower cheekteeth of
Nannippus minor. Format as in Table 2. Populations are UBV,
Palmetto Fauna, Bone Valley Region, Florida; and YEP, Yepomera
localities. Chihuahua, Mexico, both of latest Hemphillian age.

FAUNA UBV YEP

P2

apl 14.9,1.05,7 14.8,0.57,11

13.1-16.3,7.08 13.6-15.4,3.87

bapl 11.8,0.23,3 11.8,0.38,10

11.7-12.1,1.95 11.3-12.6,3.25

atw 6.2,0.41,7 7.0,0.39,11

5.5-6.7,6.60 6.7-8.0,5.51

ptw 7.7,0.21,8 8.5,0.37,11

7.3-7.9,2.80 8.0-9.2,4.33

mml 7.0,0.55,10 7.7,0.46.11

5.9-7.6,7.95 7.0-8.4,5.96

entl 7.3,0.78,10 6.2,1.02,11

5.9-8.7,10.70 4.0-7.2,16.45

p34

apl 14.4,1.21,35 15.4,0.87,10

12.6-17.1,8.38 14.6-17.3,5.62

bapl 11.3,0.74,20 11.7,0.78,6

10.0-12.7,6.51 10.6-12.9.6.66

atw 8.1,0.70,32 9.3,0.84,9

6.5-9.5,8.67 8.0-10.3,9.10

ptw 7.9,1.24,32 9.0,0.39,10

6.8-13.9,15.7 8.6-9.8,4.33

mml 8.9,0.63,36 10.2,0.50,10

7.2-10.4,7.04 9.6-11.0,4.90

entl 6.7,0.99,36 6.4,1.00,10

3.5-8.1,14.74 4.5-7.6,15.74

148

Table 14 — continued

inl2

apl

15.1,1.57,40
12.3-18.4,10.44

14.7,1.63,14
12.9-18.5,11.09

bapl

10.8,0.73,15
9.4-12.0,6.71

11.0,0.58,13
9.9-11.9,5.23

atw

6.9,0.47,36
5.6-7.9,6.76

8.1,0.66,15
6.6-9.2,8.18

ptw

6.4,0.48,39
5.5-7.7,7.60

7.3,0.56,15
6.2-8.5.7.56

mml

8.6,0.52,42
7.8-9.8,5.99

9.3,0.47,15
8.4-10.1,5.06

entl

5.5,0.79,42
4.2-7.6,14.24

4.7,1.36,15
3.2-8.3,29.09

149

Lower cheekteeth of Nan, minor have large, oval, expanded
metaconids and metastylids (Table 14); shallow, broadly "V"-shaped
(occasionally "U"-shaped) linguaflexids; rounded labial borders; and
relatively simple enamel (Fig. 16). Pli caballinids are limited to
slightly worn teeth, and are much less prominent than in Neo.
eurystyle or Cor, emsliei from the same fauna. Isthmus plications
are less common than in these two species, but are more frequent than
in Nan, westoni . However, most lowers (e.g. 32 of 36 p34s) have a
plicated paralophid. The ectoflexid is shallow in premolars and very
slightly worn molars; usually the ectoflexid of the molars rapidly
penetrates the entire isthmus, but in some it remains shallow (Fig.
16D). The entoconid is smaller relative to the metastylid than in
Nan, westoni. The protostylid is variably expressed in the Bone
Valley sample, with three morphs observed: 1) those with relatively
strong protostylids running most of the length of the crown; 2) those
with very rudimentary protostylids restricted to near the base of the
crown; and 3) those with no trace of a protostylid. Of 33 Bone
Valley p3 and p4s, morph 2 is most common (n=21), while 11 are of
morph 3, and only one specimen (UF 61492) shows morph 1. A combined
sample of lower molars (ml-m3, n=56) has 5 with morph 1, 18 with
morph 2, and 33 with morph 3. Unworn mcch are similar to those of
the upper cheekteeth. For example, UF 65203, a slightly worn ml has
a mcch of 50.9 mm, and UF 12500, a worn m2, has a mcch of 50.7 mm.

The Bone Valley sample includes a number of lower deciduous
premolars (Fig. 16E). They are very high crowned, with unworn mcchs
of about 24 mm for the dp34. The dp2s have shorter apl and bapl than

150
the dp34, and bear strong pli cabal! inids. No pli cabal! inids are
observed on the dp34s. The metacom'd-metastylid complex is very
elongated, and the ectoflexid is typically shallow. A protostylid is
present on all dp34s, but it is reduced and rises to variable heights
on the crown (10 to 18 mm). None of the specimens bears an
ectostylid.

Post-cranial elements of Nan, minor are poorly represented from
the Bone Valley, and only a few broken metapodials are confidently
referred to the species. Four relatively complete metacarpals and a
metatarsal are known from the Yepomera Fauna. These elements are 20
to 30 mm shorter than those of Nan, westoni (Table 11), but have sim-
ilar proximal, midshaft and distal widths. The two unciform facets
of the MC III are merged to form one continuous surface (Fig. 14A).

Description of Early Hemphillian Nan, minor from Florida. The
sample of Nannippus from Moss Acres is intermediate in size and crown
height between Nan, westoni and the Bone Valley sample of Nan, minor
(Table 8; Figs. 14C-14D, 14F-14G, 17, 18). The approximate UTRL of
UF 69935 is 95 mm. The slightly worn P4, M2, p4 and m2 of UF 69933
indicate that the unworn crown heights for this population would have
been about 40 mm for premolars and 45 mm for molars. UF 69933 and
69935 are referred to Nan, minor (rather than Nan, westoni ) because
they display the following characters: very reduced P2 anterostyle;
lack of protoconal spur in slightly worn premolars; relatively
complex fossettes; protostylid absent or very rudimentary; and well
developed isthmus and paralophid plications. The maxillary fragment
of UF 69935 preserves some of the preorbital facial region (Fig. 17),
although it is crushed and fragmented. The lOF is small and located

151

Figure 17. Schematic lateral view showing the area of the facial
region preserved (darkened area) on UF 69935, Nannippus minor from
the Moss Acres Racetrack Site, Marion County, Florida. The specimen
is too poorly preserved to be illustrated, but does indicate the
presence of a well developed DPOF in this species. See Figure 18A
and 18F for occlusal views of the cheekteeth of this individual.

O CO

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153

154

posteriorly, dorsal to the P4 parastyle, about 27 mm above the
alveolar margin. There is no trace of a DPOF immediately dorsal to
the lOF (as in Nan_. fricki). However, part of the postero ventral
margin of the DPOF is present located about 40 mm anterior of the
orbit. It is difficult to discern how for dorsal ly the DPOF is above
the toothrow (because of the crushing), but it was probably located
much higher on the face than in Nan_. fricki. It is impossible to
judge its exact dimensions, but it was undoubtedly smaller than in
Nan, fricki.

The Moss Acres sample of Nan, minor includes three partial
associated skeletons (Table 12), and several isolated post-cranial
elements. Two of the skeletons (UF 69934 and 69936) were directly
associated with the dental and cranial elements described above, and
are therefore readily identifiable. The other specimens were
referred to Nan_. minor because of morphologic similarity to these two
individuals. A comprehensive descriptive osteology of these
specimens is beyond the scope of this review, and only a few points
of importance are noted. Just as the teeth are intermediate in size
between Nan_. westoni and late Hemphillian samples of _Nan_. minor, so
too are the metapodials (Table 11). The MC III morphologically
resemble the latter in their small proximal breadth relative to
proximal width (Fig. 14C; Table 11). The two unciform facets are
partially fused into one, especially on the right MC III. The
entocuneiform and cuboid facets are well developed on the MT III, and
the distal depression on the anterior face of the shaft is very
shallow. UF 69936 includes the wrist bones of both sides, and each

155
has a rudimentary fifth metacarpal (MC V) and trapezium. The
trapezium is an irregular, fusiform bone about 8.4 mm long, with an
articular surface bearing two facets of unequal size at the proximal
end. The larger facet, which is slightly convex, articulates with a
posterior depression on the trapezoid. The smaller facet is for
articulation with a similarly sized area on the distal face of the
scaphoid. The MC V is also fusiform, 11.1 mm long, and bears a
single, small (2.9 mm in diameter) facet for articulation with the MC
IV. Articulation of the MC V with the MC IV (instead of with the
unciform) in Nannippus resembles the condition described by Sondaar
(1968, p. 53) for Neohipparion, and differs from Dinohippus. The
absence of a MC V and trapezium have long been considered "generic
characters" of Nannippus (Matthew, 1926; Sondaar, 1968), although
these observations are based on relatively few specimens. Both
elements can be variably expressed in quarry samples of advanced
equids (Sondaar, 1968, Table 6).

The slightly younger With 4A sample of Nan, minor consists
primarily of isolated teeth. The maxilla (UF 18311) is from a very
old individual, similar to the type of Nan, westoni. Its teeth are
much smaller in occlusal dimensions than UF/FGS V-4088 (Table 13),
and the P3-M2 length is 51.5 mm. That of UF/FGS V-4088 is 58.5 mm.
The APL, TRW and BAPL of the With 4A sample have extremely high _Vs
(Table 13). These are not just due to the small sample sizes, but
truely reflect the variability of the sample. Some specimens (e.g.
UF 19619) are larger than any observed in the Bone Valley sample,
others (e.g. UF 53523) are smaller. Specimens smaller in occlusal
dimensions than average Bone Valley individuals are more abundant.

156

thus the entire sample has smaller mean values. The only major
differnce in enamel morphology between the With 4A and Bone Valley
samples is that some lower premolars have relatively strong pli
caballinids that persist until moderate wear-stages (e.g. UF 95368,
95371). Others (e.g. UF 95370) do not have pli caballinids, and
match those from Moss Acres and the Bone Valley. A heavily worn dp2.
UF 45514, is of appropriate size to represent Nan_. minor. It has a
shallow ectoflexid and lacks an ectostylid. Most (10 of 12) lower
cheekteeth of the With 4A sample either lack a protostylid, or only
have a very reduced one.

Discussion. As noted by MacFadden (1984a), Nan, minor is
referable to Nannippus based on its small size, hypsodont cheekteeth,
poorly developed P2 anterostyle and p2 paraconid, and slender
metapodials. Lower cheekteeth of Nan_. minor generally either lack
protostylids, or have rudimentary ones at the base of the crown. In
this they resemble Nan_. peninsulatus and Nan_. beckensis, as well as
in the lack of an ectostylid on the lower deciduous premolars. The
distribution of Nan_. minor is concentrated in the southern half of
North America (MacFadden, 1984a), with its northern-most records in
the Texas Panhandle, where it is exceedingly rare. Its distribution
is approximately parapatric with that of Nan_. lenticularis, the
typical Nannippus of the Great Plains.

Genus Cormohipparion Skinner and MacFadden, 1977
Cormohipparion SKINNER AND MACFADDEN, 1977, p. 917.

157
Type species. Cormohipparion occi den tale (Leidy), 1856.
Included North American species. Cor, sphenodus (Cope), 1889;
Cor. plicatile (Leidy). 1887, n. comb.; Cor. ingenuum (Leidy), 1885,
n. comb.; and Cor, emsliei n. sp.

Revised diagnosis. Medium to large-sized hipparionines with
prominent, oval or tear-drop shaped, generally deep DPOFs with well
developed, usually continuous anterior rims; other margins also well
defined; positioned far anteriorly from orbit. Advanced lineages in
both Old and New World independently reduce DPOF. Upper cheekteeth
generally with large DPI retained with adult dentition; protocone
isolated (except P2) until very late wear, usually oval or
elongate-oval in shape; P2 anterostyle well developed and P2 much
longer than other cheekteeth. In advanced species (excluding " Co£. "
goorisi), pli caballin prominent, usually bifurcated, multiple, or
both; fossettes moderately to very complicated, with persistent pi is
protoloph and hypostyle, and well developed prefossette loop; styles
strong, parastyle frequently grooved. Lower cheekteeth have large,
well separated, oval or angular metaconids and metastylids; usually
well developed protostylids (absent on p2) and plicated isthmuses;
pli cabal linids variably developed, become more prominent and
persistent in younger species. Paraconid of p2 relatively expanded.
Ectostylids prominent on dp2-dp4. [Modified after MacFadden, 1984a.]
Discussion. Skinner and MacFadden (1977) described Cormohipparion
as a new genus of hipparionine equid, and assigned both New and Old
World species to their new taxon. This led to renewed, sometimes
spirited discussions on the phylogenetic relationships of Old and New
World hipparionines that are still ongoing (e.g. MacFadden 1980;

158
1987; MacFadden and Skinner, 1981; 1982; MacFadden and Woodburne,
1982; Woodburne and Bernor, 1980; Eisenmann, 1981; Woodburne et al.,
1981; Woodburne and MacFadden, 1983; Forsten, 1982; 1983; 1984;
Bernor and Hussain, 1985; Eisenmann et al., 1987). Several
conclusions can be drawn from these works. 1) While there is no
general concensus on how many genera of hipparionines there are in
the Old World (opinions range from one to at least three and possibly
many more), there probably are several monophyletic supraspecific
groups. Opinions also vary as to whether each of these represents
independent immigration events from North America, or if some genera
evolved in the Old World from in situ ancestors. 2) Opinions on the
number of immigration events from the New World vary from one (Bernor
and Hussain, 1985) to two (MacFadden, 1980; 1984a) to three
(Woodburne and MacFadden, 1983). 3) The oldest Old World
hipparionines (Group 1 of Woodburne and Bernor, 1980 and other
authors) are probably closely related to New World species now placed
in Cormohipparion. Finally, 4) there has yet to be a cladistic
analysis of Old World species, preventing recognition of natural
monophyletic taxa. For these reasons some workers prefer not to use
generic names with certain species, as future revisions may show that
they used incorrect binomial combinations. Bernor and Hussain (1985)
placed Hippotherium primigenium (von Meyer) among the Group 1
hipparionines. Earlier, Woodburne and Bernor (1980) had cautioned
against refering this old name to any group because no cranial
material is known from its type locality. Bernor and Hussain (1985),
however, applied the name to cranial material from Howenegg, Germany.
They noted the possibility that Cormohipparion might be a junior

159
synonym of Hippotherium Kaup. although more study was needed before
such a synonymy could be formally proposed. One would prefer that
before such a step were taken, that topotypic material of H^.
primigenium would be illustrated, U should be shown that the species
name is valid (i.e. the holotype is valid for comparative purposes),
and that cranial material can be confidently referred to the species.

I propose to use Cormohipparion (at least for New World species)
until a thorough phylogenetic (i.e. cladistic) appraisal of Old World
taxa is presented. Only then can generic and subgeneric names be
rigorously delineated. "Cor." goorisi, however, must be excluded
from Cormohipparion, as it is the sister-taxon to both Nannippus and
Cormohipparion (see Chapter 6). Ironically, Forsten (1984) has taken
the opposite approach, and redefined Cormohipparion to include only
its merychippine grade elements (i.e. "Cor." goorisi), and excluded
those that are of hipparionine grade. This of course is invalid
under the rules of zoological nomenclature, as it excludes the type
species from its genus (Cor, occidentale in this case).

Cormohipparion sphenodus (Cope), 1889

Hippotherium sphenodus COPE, 1889, pp. 449-450.
Merychippus sphenodus (Cope), GIDLEY, 1907, p. 908; OSBORN,
1918, pp. 112-114; STIRTON, 1940, p. 181; GALBREATH, 1953. p.

105.

Cormohipparion sphenodus (Cope). WOODBURNE et al.. 1981. pp.

503-514; MACFADDEN. 1984a. pp. 156-162.

160

Type specimens. Lectotype, AMNH 8281, a R P2; a L P34 (also AMNH
8281) is the paratype (see discussion in Woodburne et al., 1981).

Type locality. Pawnee Buttes, Logan or Weld County, Colorado.

Stratigraphic occurrence and age of the type locality. Pawnee
Creek Formation; late Barstovian (about 13 to 14 ma).

Distribution. Late Barstovian through early Clarendonian (about
11 to 15 ma) of California, New Mexico, Colorado, South Dakota,
Nebraska, Texas and south-central Florida (revised after MacFadden,
1984a).

Referred Florida Gulf Coastal Plain specimens. Agricola Fauna,
Bone Valley Region. Red Zone, Phosphoria Mine: UF 28432, 28433 2 R
M12; 28434 L M12; 28435 L M3; 28436 L P34; 28459 L p2: 28448, 28458 2
R p34; 28460, 28475, 28476 3 L p34; 28453 R ml2; 28446, 28447 2 R m3;
Gray Zone, Phosphoria Mine: UF 28683 L P2; 28556 R P34; 28555 L P34;
28557 R M3; 28558 R Ml(?); 28567 L p34; 28568, 28569 2 R ml2; 28583 R
dp34; and Silver City Mine: UF 65706 L P34.

Revised diagnosis. Medium-sized, moderately hypsodont hippar-
ionine with a TRL of about 126 mm. Unworn MSCH of P2 about 30 to 35
mm. DPOF moderately pocketed. Protocones oval with poorly developed
anterior spur in early wear-stages. Fossettes complex, but rela-
tively simple for the genus, especially the opposing borders of the
prefossette and postfossette. Pli caballinids moderately developed
in premolars and poorly developed or absent in molars. [Slightly
modified after MacFadden (1984a, p. 156); note that his "MIMSTHT"
should read "P2MSTHT."]

Description and discussion. Both the Red and Gray Zones from the
Phosphoria Mine produced a medium-sized hipparionine referable to the

161
widely distributed Cor, sphenodus. As the sample is too limited for
statistical analysis. Table 15 presents measurements taken on
selected specimens. They compare favorably in occlusal dimensions
and crown height with data presented by Woodburne et al . (1981) for
Cor. sphenodus. Additionally, the Phosphoria Mine samples correspond
in almost every detail of enamel morphology of Cor, sphenodus as
described and illustrated by Woodburne et al . (1981) and MacFadden
(1984a). The protocone is oval or elongate-oval with a rudimentary
spur in early wear; it is isolated from the protoselene in all
specimens (Figs. 19A, 19C, 19D). The hypocone is oriented
posterolingually and has a constricted connection to the metaloph.
The posterior half of the prefossette and the anterior half of the
postfossette are moderately complex, but less so than typical younger
samples of Cormohipparion from Florida. In early wear-stages, the
lower premolars have moderately developed pli caballinids, shallow
ectoflexids, and numerous enamel plications. In later wear-stages
(e.g. UF 28460), the ectoflexid penetrates the isthmus past the level
of the base of the entoflexid. The protostylid, which comes into
wear about 10 mm below the unworn occlusal surface, is at first
isolated (Fig. 19B), but later connects with the protoconid and is a
prominent feature. This is also typical for all younger species of
Cormohipparion. The well worn deciduous lower premolar (UF 28583) is
notable for its large protostylid, ectostylid and hypostylid.
Although comparisons are limited by the small sample sizes. Cor.
sphenodus from the overlying Gray Zone is slightly more hypsodont,
complex and larger than Red Zone specimens (Table 15). Similar
observations were made by Woodburne et al . (1981) concerning

162

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164

stratigraphically superposed populations of Cor, sphenodus from the
Valentine Formation in Nebraska.

Cormohipparion occi den tale (Leidy), 1856

Hipparion occidentale LEIDY, 1856, p. 59; OSBORN, 1918, p. 176.

Hippotherium occidentale (Leidy), COPE, 1886, p. 359; COPE.

1889, p. 434 (in part).

Neohipparion occidentale (Leidy), GIDLEY, 1907, p. 877; STIRTON,

1940, p. 182; FORSTEN, 1975, p. 65 (in part).

Cormohipparion occidentale (Leidy), SKINNER and MACFADDEN, 1977,

p. 917; MACFADDEN, 1984a, p. 162.

Type species. ANSP 11287, four R and one L associated upper
cheekteeth.

Type locality. Exact locality unknown. Little White River Region,
South Dakota, see discussion in Skinner and Taylor (1967).

Strati graphic occurrence and age of type locality. Probably
Ogallala Group; middle Clarendonian, about 10 ma.

Distribution. Latest Barstovian to early Hemphillian in the Great
Plains, Clarendonian of the Texas Gulf Coastal Plain, Great Basin and
California.

Referred Gulf Coastal specimens. Lapara Creek Fauna, Farish Ranch
Site, Bee Co., TX: TMM 31081-844 crushed skull with R & L P2-M3.
Other specimens as listed by Forsten (1975, pp. 66-67), except those
referred to Neo. affine (see above).

165
Diagnosis. Largest North American species of Cormohipparion, with
toothrow lengths of 130 to 150 mm. Deep, continuously well rimmed,
keyhole-shaped DPOF. More higher crowned cheekteeth than Cor,
sphenodus. More complexly plicated fossettes than Cor, sphenodus.
Cor. plicatile and Cor. ingenuum (on average, at comparable wear-
stages). Ectostylids on dp34 oval and larger than those of other
North American species.

Description. TMM 31081-844 is notable as the only cranial
material of Cormohipparion known from the Gulf Coastal Plain
preserving the entire pre-orbital region. The DPOF (on the better
preserved right side) is teardrop-shaped, about 60 mm long, and has a
maximum dorsoventral height of about 30 mm. The anterior border is
located above the P3, and the posterior border is above the M1-M2
contact. The pocketed, well rimmed fossa is located well anterior to
the orbit with a preorbital bar length of about 57 mm (due to
crushing and reconstruction with plaster this measurement is a rough
estimate). For all important features, the facial region of TMM
31081-844 falls within the range of variation expressed by the large
Hans Johnson Quarry sample of Cor, occidentale from the late
Clarendonian of Nebraska (Skinner and MacFadden, 1977). The size and
complexity of the cheekteeth of TMM 31081-844 are equivalent to the
dental features of the Lapara Creek sample of Cor, occidentale
described in detail by Forsten (1975). MacFadden (1984a, Fig. 134)
was the first to illustrate a specimen of Cor, occidentale from the
fauna, a right maxillary fragment with P2-M1.

In the upper cheekteeth. Cor. occidentale from Lapara Creek
display the following important features that reflect their close

166
relationship with other referred samples of the species (notably
those from the Clarendon and Xmas-Kat Faunas). Premolars are
slightly longer and much wider than the molars, with well developed
styles. In early wear, the parastyles of the P34 are slightly
grooved. The fossettes are richly plicated; typically in premolars
the anterior half of the prefossette has a deep, persistent,
generally unbranched pli protoloph and zero to three smaller, less
persistent accessory plications. The posterior half of the
prefossette and the anterior half of the postfossette are of approx-
imately equal complexity, with numerous (usually four or five, up to
eight) plications apiece, several of which are usually deep and
bifurcated. The pli hypostyle is usually deep, unbranched, and per-
sistent; it is often (33% of examined specimens) accompanied by one
or two additional small plications. In the M12, the fossettes are
typically only slightly less complex, but the folds are not as deep
and have fewer bifurcations. Both the pli protoloph and pli hypo-
style are well developed, persistent, and have occassional accessory
plications. Pli caballins are prominent, often multiple (60% of
specimens examined) in P34, generally single in P2 and M1-M3. Proto-
cones are elongate-oval, usually slightly longer than twice their
width, very rarely with spur, except on P2. Protocones are isolated
until very late wear-stages, again except for the P2 which generally
connects the protocone during the moderate-stage. When compared with
the Clarendon and Xmas-Kat populations of Cor, occidentale. the
Lapara Creek sample shows slight differences in size, hypsodonty
(unworn M12 MSCH is about 50-54 mm in the Lapara Creek sample, about
60 mm in the two younger samples), and plication frequency. The

167

Xmas-Kat sample is significantly more complicated than either of the
two Texas populations. For example, pli caballins are multiple or
bifurcated in 88% of the P34s (n=66) and 55? of the M12s (n=75). In
complexity of fossette plications, the Xmas-Kat Quarries population
of Cormohipparion is exceeded among North American hipparionines only
by the late Hemphillian sample of Cor, emsliei n. sp.

In the lower cheekteeth, the Lapara Creek sample is characterized
by rounded to slightly flattened labial protoconid and hypoconid
borders (but not to the degree of Neo. affine); large, oval, subequal
metaconids and metastylids; and relatively large protostylids that
are ofen isolated from the protoconid during early wear. Pli
cabal linids are variably developed on the p2-p4; prominent in early
wear-stages, retreating with wear until disappearing during late
middle wear-stages. They are at best rudimentary on the ml-m3, and
then only appearing in very early wear-stages. Lower cheekteeth are
frequently plicated (Table 17); these are best expressed during early
and early moderate wear-stages. The ectoflexids on the premolars
generally penetrate to a level about equal to the base of the
metaflexid, although there are some with deeper and some with
shallower ectoflexids. In the molars, ectoflexids are deep and
completely divide the isthmus. Deciduous lower premolars have wider
and deeper ectoflexids than permanent premolars, rudimentary pli
caballinids, and relatively large, tall ectostylids that soon appear
on the occlusal surface after the onset of wear (e.g. TMM 31081-456,
31081-7).

Discussion. Leidy described this species on five associated upper
cheekteeth. Although of uncertain stratigraphic provenience

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169

Table 17. Frequency of occurrence (in %) of different enamel
plications in the lower cheekteeth of various populations of
Cormohipparion. Samples are: 1, Cor. occidental e, Lapara Creek
Fauna; 2. Cor, occi dental e. Claren'Hon" Fauna; 3, Cor, occidentale,
Xmas-Kat Quarries Fauna; 4, C. plicatile. Love Site; 5, Cor, plf-
catile, combined early HemphTllian sample of Florida locaTTties;
6, Cor. ingenuum. Love Site; 7, Cor. emsliei n. sp.. Upper Bone
ValTiy Fauna. FARA, posterior pTTcation on paralophid; ANTI, pli-
cation on antisthmus or anterior side of isthmus; PSTI, plication
on postisthmus or posterior half of isthmus; PLCB, pli caballinid.

SAMPLE n PARA ANTI PSTI PLCB
p3 and p4 combined

1

24

49

33

50

58

2

17

26

35

65

59

3

29

66

62

59

62

4

48

48

71

47

45

5

9

56

67

44

44

6

35

63

63

46

49

7

7

71

ml and m2

86

combined

57

100

1

16

30

63

38

12

2

18

0

28

17

0

3

30

27

63

30

3

4

68

16

76

19

4

5

16

13

56

25

13

6

44

32

70

23

0

7

16

25

69

50

31

Figure 20. Scatter diagram of standardized scores for principal
components I and II of A) individual P3 and P4s and B) individual Ml
and M2s of Cormohipparion occidentale and Neohipparion affine. Seven
characters were used in the analysis, APL, TRW, PRL, PRW (see Figure
1); width from the mesostyle to the pli cabal lin (MacFadden, 1984a);
the sum of the plications from the posterior half of the prefossette
and the anterior half of the postfossette; and the sum of the
plications the anterior half of the prefossette and the posterior
half of the postfossette. See discussion in text.

171

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' ■' USNM 584 (Holotype)
o C. oceld9ntala

* C. sphanodus

-8-6-4-2 0 2 4 6

PRINCIPAL COMPONENT I

172

(Skinner and Taylor, 1967), the holotype displays a number of charac-
ters than unites it with referred populations from the Lapara Creek,
Clarendon, and Xmas-Kat Faunas (and others listed by MacFadden,
1984a, p. 163). These include size (relatively large), elongated
protocones without spurs, well developed pli caballins that tend
toward branching on the premolars, and complex fossette plications.
However, Woodburne (pers. comm.) observed two or more cranial
morphologies among the specimens combined here into a single species.
This may indicate either the presence of more than one species with
the distinctive "Cor. occi dental e" dentition in the Clarendonian of
the Great Plains, or that the species in polymorphic for certain
cranial characters. If the former is correct, then Leidy's type
material may not be complete enough to confidently assign it to one
of the species, and the name may not be valid.

Prior to the naming of Cormohipparion by Skinner and MacFadden
(1977), the species occidental^ was routinely referred to the genus
Neohipparion (e.g. Stirton, 1940). While there are similarities
between Cor, occidentale and Neo. affine, especially in protocone
shape and overall size, there are major differences in DPOF depth and
degree of rimming, relative position of the DPOF and lacrimal bone,
fossette complexity, shape of the labial borders of the protoconid
and hypoconid, and the development of the ectostylid in deciduous
premolars (Skinner and MacFadden, 1977; Skinner et al., 1977;
MacFadden, 1984a). These serve not only to distingiush the two as
distinct species, but support a phylogenetic hypothesis that they
represent separate genera (see Chapter 6).

173
Principal component analyses of upper cheekteeth (P34s and M12s
analyzed separately; Fig. 20) generally segregated specimens of Cor.
occidentale from Neo. affine, although there was some overlap. The
first principal component (PC I) accounted for about 50% of the total
variance in both analyses. The PC I in Figure 20B contrasted molars
with longer protocones and simpler fossettes with those having
shorter protocones and more complex fossettes. In the analysis of
the P34s (Fig. 20A), PC I had large, positive coefficients for both
size and fossette variables; small (probably insignificant), negative
coefficients for PRL and PRW. This tended to place specimens of Neo.
affine. Cor, sphenodus, and moderate to heavily-worn individuals of
Cor, occidentale to the left of the graph, lesser worn individuals of
Cor, occidentale to the right. The PC II in Figure 20 A had high,
positive loadings on APL, TRW, PRL and a large negative coefficient
for the number of internal plications. This separated the smaller,
more complex Cor, sphenodus and worn Cor, occidentale individuals
from those of the larger, less complex Neo. affine. The multivariate
analyses corroborated the evidence from cranial morphology that these
populations represent two distinct species.

Although wide-spread and common throughout the western half of the
United States during the Clarendonian, Cor. occidentale is not yet
recognized from Florida. Instead, Cor, sphenodus seems to have
persisted longer in the Southeast, and was then followed by Cor.
plicatile and Cor, ingenuum, species not observed in the Great Plains
(see below).

174
Cormohipparion plicatile (Leidy). 1887 new combination

Hippotherium plicatile LEIDY, 1887, p. 310; COPE, 1889, p. 444;

LEIDY and LUCAS, 1896, p. 50; MACFADDEN, 1984a, pp. 170-174 (in

part).

Hipparion plicatile (Leidy), HAY, 1902, p. 620; GIDLEY, 1907,

p. 905; HAY, 1916, pp. 41-42; OSBORN, 1918, p. 192; SIMPSON,

1930, pp. 187-188 (in part); HIRSCHFELD and WEBB, 1968, p. 249;

WEBB and PERRIGO, 1984, pp. 243-245 (in part).

Hipparion sp., SIMPSON, 1930, p. 176.

?Hipparion plicatile (Leidy), STIRTON, 1940, p. 184.

Type specimen. USNM 3292, a R upper cheektooth, probably a P4.

Type locality. Mixson's Bone Bed, Levy County, Florida.

Stratigraphic occurrence and age of the type locality. Alachua
Formation; early Hemphillian, about 8 ma.

Topotypic sample. UF/FGS V-1428 R P2; F:AM 111730 assoc. R P2-M2
and L P3-M3; 107876 badly crushed skull with R and L DP2-M1; 113620
assoc. L P2-M2 and R Ml; 113621 assoc. R P2-P3,M2-M3 and L P3,M2-M3;
113625-113629, 113638 6 upper cheekteeth; 107874 assoc. R and L
mandibles with i3,cl,p2-p3,dp4,ml-m2 and R (only) i2; 113630 assoc. R
p2-p3 and L p2; 113634 assoc. L m2-m3; USNM 3309 R p2; F:AM 113640 L
p2; 113636 R p34; 113631, 113632 2 L p34 ; 113633, 113635 2 L ml2.

Distribution.— Very late Clarendonian through early Hemphillian
(about 6.0 to 9.0 ma) of peninsular Florida.

Referred specimens. Moss Acres Racetrack Site: UF 93000 assoc.
juvenile crushed skull with R and L DP2-M1, R and L mandibles with

175
dp2-ml, and various post-cranial elements; 69968 R M12; 96386 assoc.
R M2-M3 and L MS; 69967 assoc, R and L mandibles with il-i3,c,p2-m3.

Dunnellon Phosphate Company mine, Marion Co., FL: USNM 8265 R
maxilla with P2-P4 (Hay, 1916, Plate 2.8).

Dunnellon Phosphate Company, Plant No. 5, near Hernando, Citrus
Co.. FL: UF/FGS Y-1400 R M12.

Archer Fauna, Bone Valley Region. Nichols Mine: UF 24638 R P2;
23986 R P4; 24626, 24650, 24655 3 R dp34; 24631 R p34; 24625 R ml2;
24642 L ml2. Fort Green Mine: UF 53924 R p34. Unknown mine near
Mulberry, Polk Co., FL: AMNH 22482 mandible with p3-m3.

Peace River, near Gardner, Hardee Co., FL: UF/FGS V-4889, UF
55948 2 R M12; UF/FGS V-1482 L p34; UF 55951 R ml2; UF 55952 L ml2.

McGehee Farm: UF 17121 L P2; 17099, 17124, 17208, 17210, 19237,
45616 6 R P34; 17206, 17212, 45614, 53548 4 L P34; 9605, 9611, 17213,
45615 4 R M12; 17090, 17207, 17214, 45612 4 L M12; 7234 assoc. R
mandible with p2-m2 and L mandible with p2-p4; 9541 assoc. R dp2-dp3;
12050 R dp2; 7240 L dp34; 45619, 45620 2 R p2; 17167, 45627, 53454 3
R p34; 17196, 17197, 45623, 53452 4 L p34; 7243, 9606, 16837, 17140,
17173, 17192, 18707, 45623, 53452 9 R ml2; 17169, 17172, 17175,
17192B, 17193, 17195, 45618 8 L ml2; 45631 R m3.

Haile 5B, Alachua Co., FL: UF 17226 L P34.

Haile 19A, Alachua Co., FL: UF 47319 R M12.

Cummer Mine No. 8, Alachua Co., FL: UF/FGS V-1408 L p34.

Cofrin Creek, Alachua Co., FL: UF 17178 R p34; 55522 R ml2.

Love Site: UF 32257 partial skull with R and L 12-13, P3 and R P4;
32260 assoc. R maxilla with P4-M2 and L maxilla with P4-M3; 32250 R
maxilla with P4-M3; 32255 L maxilla with Dp2-Ml; 35891 L maxilla with

176
P4-M1; 32267 assoc. R DP2-DP4; 27993, 32262, 32263 3 assoc. R and L
P2-M3; 32283 assoc. R P2,P4-M1 and L M1-M2; 32270 assoc. R P2-M1,M3
and L M1-M3; 32265 assoc. R and L P2-M2; 32264 assoc. R P3-P4,M2-M3
and L P4-M3; 27316 assoc. R P2-M3; 36289 assoc. R M1-M2 and L P4;
32276, 32295 2 assoc. L DP2-DP4; 32285 assoc. L DP2-M1; 32266 assoc.
L P2-M2; 53284 assoc. L P3-P4; 35967. 35970, 35976-35978, 35984-
35985, 35988-35989, 35994, 36000-36002, 36005-36006, 36008, 36010,
36015, 36031-36035, 36037, 36040, 36044, 36047, 36051, 36063, 36068-
36071, 36263, 36266, 36269 37 R P2; 36143, 36147, 36151, 36153,
36156, 36158-36159, 36162, 36165-36166, 36169, 36171, 36177, 36181-
36182, 36184-36186, 36188, 36190, 36193-36194, 36201, 36205, 36209,
36211-36212, 36218-36219, 36223, 36225-36227, 36237, 36243-36244,
36247, 36250, 36253, 36255 41 L P2; 50641, 50643-50644, 53287-53289,
53291-53294, 53296, 53298-53299, 53301, 53423-53424, 62326-62350,
62438, 62447, 69810 44 R P34; 53302-53328, 53373, 53422, 62306-62324,
62381, 62384, 69809 50 L P34; 50642, 50645, 50647-50648, 53329-53332,
53334-53340, 53344-53349, 53351-53353. 53416, 53417, 62351-62365,
69811 42 R M12: 53154-53156, 53354-53360, 53362-53367, 53369-53371,
53374, 53377-53379, 53418-53421, 62367-62376. 62378-62380, 62382-
62383, 62385-62389, 62408 48 L M12; 32119 R mandible with dp2-dp3;
32157 assoc. R and L mandibles with p2-p3,dp4,ml-m2; 32180 assoc.
mandibles with R m2-m3 and L p3-m3; 27317 R mandible with p2-m3;
32104, 32174 2 R mandibles with p2-m2; 32212 R mandible with p2-ml;
32116 R mandible with p2,p4-m3; 32190 R mandible with p3-m3; 32144,
35893 2 R mandibles with p4-m3; 32107, 32199 2 L mandibles with
p2-m3; 32111, 32118, 32160 3 L mandibles with dp2-dp4; 32123, 32163 2
L mandibles with p2-m2; 32113, 32151 2 L mandibles with p2-ml; 32198,

177
32245 2 L mandibles with p3-iD3; 32165 L mandible with p4-m3; 32182,
32105, 36282, 32134, 36285, 36280 6 partial R mandibles; 32197,
32195, 32137, 36287, 35892, 32102 6 partial L mandibles; UF 35895
assoc. R dp2-dp4 and L dp3-dp4; 32286, 90154 2 assoc. R dp2-dp4;
90160 assoc. R dp2-dp3; 90155, 90156 2 assoc. R dp3-dp4; 32196 assoc.
R p2-m3 and L p2-m2; 32293 assoc. L p4,m2-m3 and R p3-p4; 32146
assoc. R p2-m3; 32225 assoc. R p2-p4; 32239 assoc. R p3-m3; 32203,
32229 2 assoc. R p4-m3; 32181, 32223 2 assoc. R ml-m3; 32232. 32221 2
assoc. R m2-m3; 90158 assoc. R dp3 and L dp2-dp4; 90159 assoc. L
dp2-dp3; 32227 assoc. L ml-m2 and R m2; 65167 assoc. L ml-m3; 90162-
90179 18 R dp2; 69813, 69814, 90121-90159 41 R dp34; 90180-90186,
90188-90197 17 L dp2; 90071-90120 50 L dp34; 50355, 50356, 50358-
50362, 50364, 50365, 50369, 64926-64927, 64929-64931, 64934-64936 19
R p2; 50370, 50372, 50374-50379, 64937, 64940-64943, 64466 14 L p2;
50461-50479, 50538, 50544, 50635, 50639, 64981-65027 70 R p34; 50447-
50455, 50460, 50458, 50640, 32226, 64944-64946, 64948-64980, 65166 50
L p34; 50420-50445, 65076-65109, 65028-65050, 69816 84 R ml2; 50400-
54019, 65112-65165, 69818, 90262 76 L ml2; 50380-50389 10 R m3;
50390-50399 10 L m3; and many more catalogued and uncatalogued
cranial fragments, isolated teeth, and post-cranial elements.

Revised diagnosis. Medium-sized hipparionine with toothrow
lengths of 125 to 140 mm in middle wear-stages. Unworn MSCH of P2
about 40 mm and M12 about 58 mm. On average, smaller than Cor.
occidentale, generally with less complicated fossettes and less
elongate protocones. More hypsodont and more complex enamel
plications than Cor, sphenodus. Larger and higher crowned than Cor.

178
ingenuum, larger than Cor. emsliei with weaker pli caballinids. Very
elongated post-canine diastema.

Description. All cranial material referable to Cor, plicatile
lacks uncrushed or complete pre-orbital regions. Four specimens (UF
32257, 32255, 35891, 32250) from the Love Site and UF 93000 from Moss
Acres preserve parts of the facial region, but none contain the
entire DPOF. The specimen with the most complete DPOF, UF 32250, is
an uncrushed, partial maxilla with well worn but diagnostic P3-M2
(Fig. 21). It contains the ventral base and rim of a deep (at least
15 mm) DPOF located 46 mm dorsal to the toothrow (Fig. 21A). The
three other Love Site specimens also preserve small portions of a
fossa. These crania differ considerably from Love Site specimens
assigned to Neo. trampasense, in which the DPOF is reduced to a
slight depression (MacFadden, 1984a, and p. 60 above). The badly
crushed skull of UF 93000 preserves only the dorsal portion of both
DPOFs. It was evidently more poorly rimmed dorsal ly than those of
Cor, occidentale, and probably shallower. Another extremely crushed
skull of Cor, plicatile, F:AM 107876 from Mixson's Bone Bed, was
noted by MacFadden (1984a) as not possessing a deep DPOF. F:AM
107876 is crushed and fragmented to such a degree that not even the
orbits are discernible. Until discovery of uncrushed, more complete
cranial material, the facial region of Cor, plicatile and the exact
morphology of its DPOF must remain poorly documented. The Love Site
and Moss Acres Racetrack Site specimens strongly suggest the presence
of a moderate to deep DPOF.

The following dental descriptions are based primarily on the
abundant Love Site sample, with added comparisons from other

179
localities. Statistics of cheektooth dimensions of Cor, plicatile
are presented in Tables 18 and 19. Upper cheekteeth of Cor.
plicatile are characterized by oval protocones with convex lingual
borders, richly plicated internal fossette borders (especially in
early wear), moderately deep hypoconal grooves open to near the base
of the crown, and strong styles. The P2 has a well developed
anterostyle, and is by far the longest tooth in the toothrow (Figs.
22A, 22B). The oval protocone of the P2 generally remains isolated
from the protoselene until mid-wear. Many P2s with MSCHs of 20 to 25
mm retain isolated protocones. Unworn MSCH of the P2 is about 38 to
42 mm. Fossette plications resemble those of the P34, except that
the anterior half of the pre fossette usually has two or three small
folds. The pli caballin is generally single, although often bifur-
cated. The P34 (Figs. 21B, 22, 238) are much larger in occlusal area
than the M12, with larger and more widely opened parastyles and
mesostyles. The parastyles are often slightly grooved, and meta-
styles are occasionally developed, but not as prominently as in Cor.
emsliei or Neohipparion eurystyle. In very early wear, the protocone
of the P34 is elongate, often with a spur, but with wear the spur
vanishes and the protocone rapidly becomes more oval. This change is
produced by an increase in protocone width, as protocone length is
uncorrelated with crown height (r.=0.05, n=132), while protocone width
has a significant negative correlation with crown height (r_=-0.64,
n=130, £<0.001). Protocone length is generally less than twice its
width, a feature useful in distinguishing Cor, plicatile from its
slightly smaller contemporary, Neohipparion trampasense. The main
axis of the protocone runs in a more direct anterior-posterior

180

Table 18. Standard univariate statistics for upper cheekteeth
of Cormohipparion plicatile from Florida. Format as in Table
2. Faunal abbreviations: LOV, Love Site, Alachua County, late
Clarendonian; HE, combined sample from various early
Hemphillian localities including McGehee Farm, Mixson's Bone
Bed, Moss Acres Racetrack Site.

FAUNA LOV HE

P2

API

26.7,1.26,55
23.5-30.6,4.73

27.1,1.36,4
25.6-29.3,5.03

BAPL

21.8,0.79,54
20.4-24.0.3.59

22.0,0.40,5
21.4-22.4,1.84

TRW

19.6,0.94,57
17.3-21.5,4.79

20.6,1.17,6
19.7-22.8,5.70

PRL

6.1,0.53,58
5.0-7.2,8.66

6.5,0.68,6
5.6-7.6,10.60

PRW

4.1,0.52,57
3.4-5.6,12.76

4.0.0.30,6
3.7-4.5,7.59

181

Table 18--continued

P34

APL

21.8,1.19.112
19.4-25.3,5.46

22.1,1.08,18
19.7-23.9,4.88

BAPL

17.6,0.98.107
15.9-20,0.5.56

17.6,0.72,14
16.6-18.8,4.09

TRW

21.0,0.99.112
18.6-24.1,4.70

21.5,0.96,19
19.8-23.4,4.46

PRL

7.4,0.80,116
5.9-9.2,10.80

6.9,0.70,19
6.1-8.5,10.04

PRW

4.1,0.47,114
3.0-5.2.11.41

3.9,0.36,19
3.4-4.9,9.23

M12

APL

20.5,1.36,115
18.2-25.4,6.61

20.5,1.51,18
17.6-23.9,7.38

BAPL

16.4,0.69,108
15.1-18.2,4.20

16.5,0.69,11
15.4-17.7,4.20

TRW

19.4,1.22,113
15.4-22.0,6.29

19.4.0.94,18
17.1-20.8,4.82

PRL

6.9,0.62,121
5.7-8.3,8.99

6.7,0.68,18
5.6-8.4,6.26

PRW

3.8,0.56,120
2.6-5.2,14.76

3.6,0.41,18
2.8-4.9,11.37

182

0 3cm

' ' ' '

Figure 21. Lateral (A) and occlusal (B) views of UF 32250,
Cormohipparion plicatile. Love Site (late Clarendonian), Alachua
County, norida": Occlusal pattern of R P3-M2 represents the late
wear-stage for this species.

183

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direction than that of Nan. trampasense. The protocone of the P34
does not connect to the protoselene until very late wear-stages (MSCH
of 15 mm or less). Fossette and pli cabal! in complexity also vary
considerably with crown height. In early wear, the well developed
pli caballin is usually multiple, branched, or both (Fig. 22A) . With
wear, it decreases in length and complexity, usually becoming single
by late mid-wear (MSCH of 15 to 30 mm), and lost or rudimentary only
in very late wear (Fig. 21B). In the Love Site sample, the anterior
half of the P34 prefossette most often is not plicated (60% of
examined specimens, n=112), or has a single, small pli protoloph
(32%; Figs. 22A, 22B). The latter condition occurs most frequently
in the less worn teeth. The posterior half of the prefossette in
early to moderate wear is richly plicated, with four to nine folds,
of which several are often deep and bifurcating. The anterior half
of the postfossette is only slightly less complex, generally with a
deep, often branched pli postfossette and two to five accessory
plications. In moderate to late wear-stages, these internal fossette
plications become shallower and less numerous (e.g. Fig. 21B),
although even very heavily worn teeth usually retain at least two or
three folds. The posterior half of the postfossette has a single
(59%, n=110), relatively shallow and small pli hypostyle, or lacks
all plications (39% of observed specimens). Early Hemphillian
samples of P34s of Cor, plicatile, while of similar proportions as
the Love Site sample (Table 18), are on average more complexly
plicated (Figs. 23B, 23D). For example, of 16 observed P34s, seven
(44%) had a single pli protoloph, eight (50%) had a pli protoloph

187

plus one or two accessory plications, and only one lacked all
plications on the anterior half of the prefossette (the character
state found in the majority of the Love Site sample). Unworn P34
MSCH varies from 50 to 55 mm.

In mid-wear, M12 of Cor. plicatile have nearly square occlusal
surfaces, with length slightly exceeding width on average (Table 18).
However, since length is positively correlated with crown height
(r=0.77, n=124), and width is negatively correlated with crown height
(r^=-0.50, n=123), the ratio of length to width changes greatly
through ontogeny. The M12 protocone is slightly smaller than that of
the P34 (Table 18), but similar in morphology and degree of isolation
from the protoselene. The pli caballin is only rarely double (6% of
observed Love Site specimens, n=121), but it persists until late
wear, when it gradually disappears in extremely worn teeth (almost
always after MSCH is less than 20 mm). In the Love Site sample, the
anterior half of the prefossette of the M12 generally lack plications
(81«, n=120). A single, relatively shallow pli protoloph is
occasionally found in early wear-stages, and it rarely has accessory
plications. The posterior half of the prefossette most often has
from three to five, rarely bifurcated plications, and a well
developed prefossette loop. The anterior half of the postfossette
generally has between two and four plications (862 of Love Site
sample, n=121), usually consisting of a relatively deep, unbifurcated
pli postfossette and several labial accessory plications. The
posterior half of the postfossette in early wear often has a single
pli hypostyle; it is usually lost by mid-wear. As with the P34, M12
of Cor, plicatile from the early Hemphillian localities (Mixson's,

188
McGehee, Moss Acres) are on average more complicated than the Love
Site population (Figs. 23A, 23C), although of the same general size
(Table 18) and degree of hypsodonty. For example, a third of the
pooled sample of M12 from the younger sites have multiple pli
caballins (Figs. 23A, 23F). Also, fossette plications are more
numerous and tend to persist longer throughout wear. Unworn MSCH of
M12 are about 56 to 59 mm.

Deciduous upper premolars of Cor, plicatile have very large
parastyles, generally multiple pli caballins, and oval protocones.
The degree of fossette complexity is intermediate between that of the
P34 and the M12. Protoconal spurs are not uncommon, and the
hypoconal groove frequently has a pli dihypostyle. No specimens are
available to indicate the relative size of the DPI, but it was
apparently lost in some mature individuals (e.g. USNM 8265).

The referred Love Site sample includes numerous associated lower
dentitions and partial mandibles of Cor, plicatile (as well as
several hundred isolated lower cheekteeth), but none are complete;
i.e. there are no mandibles that include symphysial regions, and only
one with an ascending ramus. However, UF 69967, from Moss Acres, has
a relatively complete symphysis (Fig. 24). In this adult male
individual (ml mcch=35.3 mm), the incisors form a normal rounded
equine arcade about 55 mm in width (across the i3s) and are slightly
procumbent. The ils have only small traces of the infundibula
remaining, and the i3s do not have enclosed infundibula. The
symphysial region is extremely elongated, with a Idl of about 88 mm
(Fig. 24). Another relatively complete symphysis is found on F:AM
107874 fromMixson's Bone Bed (MacFadden, 1984a, Fig. 143). This

189
immature specimen has a Idl of only about 66 mm. Whether the
difference in diastema length between F:AM 107874 and UF 69967 is due
to ontogeny, or if they just represent the extremes in a normal
distribution, can only be judged with further samples.

Adequate samples of associated lower dentitions of Cor, plicatile
are available to allow comparisons with other Miocene hipparionines
(Table 16). While smaller than Cor, occidentale. Cor, plicatile was
the largest hipparionine present at the Love, McGehee and Mixson's
localities. The lower premolars of Cor, plicatile are very wide
relative to length, as contrasted with the molars, or with the
premolars of Neo. trampasense. The p2-p4 have large, oval
metaconids, metastylids and entoconids (Figs. 25, 26B, 26D). In very
early wear-stages, the ectoflexid is very shallow, the isthmus is
often plicated, and a pli caballinid is variably developed (Fig.
26B). If present, the pli caballinid reduces in size with wear until
it gradually vanishes, usually by moderate wear-stages. Plications
from the isthmus and paralophid are common (Table 17), and generally
persist until at least mid-wear. The protostylid first comes into
wear after the first 12 to 15 mm of the crown are worn away, and is
at first isolated from the protoconid (e.g. the p3 in Figs. 25A,
25B). It quickly becomes attached, and is a prominent feature. The
labial borders of the protoconid and hypoconid are rounded or only
very slightly flattened. Ectoflexid depth varies, but most commonly
only penetrates the isthmus to about the level of the base of the
entoflexid, or slightly deeper, even in heavily worn teeth (Fig.
26D). Unworn mcch of p2 is about 40 mm, and 51 to 54 mm for the p34.

190

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B

2cm

Figure 26, Occlusal views of lower cheekteeth of Cormohipparion
plicatile from Florida. A. F:AM 113635, L ml2, Mixson's Bone Bed
(early Hemphillian), Levy County. B.C. Love Site (late Claren-
donian), Alachua County. B. UF 50639, slightly worn p34. C. UF
90154, slightly worn assoc. R dp2-dp4. D. UF 7234, heavily worn
assoc. L p2-p4, McGehee Farm Site (very early Hemphillian), Alachua
County.

193

Table 19. Standard univariate statistics for lower cheekteeth of
Cormohipparion plicatile (CP) and Cor, ingenuum (CI) from Florida.
Format as in lable 2. Populations as in Tables 18 and 22.

TAXON CP CP CI CI

FAUNA LOV HE LOV HE

P2

apl 23.7,1.14,39 23.8,1.11,4 21.5,0.96,19 22.0, - ,1
22.0-27.1,4.83 22.7-24.9,4.67 20.2-24.1,4.48

bapl

19.9,0.92,37
18.0-21.3,4.62

19.3, - ,1

18.0,0.65,19
16.9-19.6,3.64

atw

9.3,0.74,39
7.5-10.4,7.97

8.8,0.52.4
8.5-9.6,5.88

8.6,0.66,21
7.7-9.9,7.70

8.

4,

-- .1

ptw

11.5,0.91,41
9.6-13.3,7.91

11.5,1.03,4
10.3-12.5,8.95

10.6,0.86,21
9.0-12.6,8.13

9

6,

-- .1

mml

10.2,1.13,41
7.0-12.5,11.03

10.2,0.74,4
9.2-10.8,7.20

9.1,0.99,21
7.5-11.7,10.87

8

0,

-- .1

entl

9.8,1.34,41

9.8,1.63,4

8.7,1.37,21

10

.1.

-- .1

6.1-12.0,13.62 7.6-11.5,16.64 5.5-10.6,15.85

194

Table 19~continued

apl

22.8,1.34,48
19.2-25.6,5.87

21

19

bapl

18.7,0.71,49
17.0-20.6,3.82

17
17

atw

12.0,0.98,48
8.4-14.0,8.14

12

11

ptw

12.0,1.01,48
9.1-14.2,8.45

12
10

mml

13.1,1.07,48
9.9-15.3,8.14

12
11

entl

10.4,1.02,48
6.1-12.1,9.88

10
8

apl

22.2,2.03,68
18.6-26.3,9.15

21

18

bapl

17.4,0.90,64
15.4-20.2,5.15

17
16

atw

10.2,1.08,68
8.1-12.6,10.52

10
8

ptw

9.3,1.07,68
6.4-11.4,11.49

9
7

mml

12.2,0.83,68
10.5-14.3,6.78

12
10

entl

8.0,1.21,68
5.5-10.1,14.08

7
5

p34

4,1.34,9 19.

4-24.1,6.28 17.

8,0.37,4 16,

3-18.2,2.08 14.

3,0.74,8 10,

1-13.4,5.97 9.

.0,0.78.8 10,

,9-13.5,6.53 8,

,9,0.68,9 11,

,9-14.0,5.24 10,

,1,0.95,9 9,

,0-11.2,9.35 6,

ml2

,3,1.90,15 19

,4-24.4,8.91 17

.8,0.88,8 15

.9-19.4,4.94 13

.7,1.72,16 9

.1-13.4,16.14 6

.5,1.50,16 8

.1-12.1,15.78 6

.1,1.34,16 10

.1-14.2,11.10 9

.4,1.21,16 6

.5-9.8,16.29 4

,5,1.13,35
,6-22.1,5.81

,1,0.74,32
,4-17.8,4.60

,9,0.82.34
,5-12.5,7.50

,6,0.61,35
.9-11.8,5.77

.3,0.59,35
.0-12.6.5.23

.1,1.03,35
.1-10.8,11.35

,5,1.63,43
.0-23.5,8.39

.3,0.89,41
.2-17.1,5.79

.1,1.07,44
.2-11.9,11.81

.4,0.84.44
.5-10.0.9.96

.7,0.65.44
.0-12.1.6.03

.8.1.08,44
.5-9.0,15.80

19.7,0.76.3
19.2-20.6,3.84

16.2.0.71,2
15.7-16.7.4.36

11.1.0.21.3
10.9-11.3.1.88

11.2,0.46,3
10.8-11.7,4.09

12.1,0.85,3
11.5-13.1,7.03

9.1,1.50,3
7.6-10.6,16.5

18.2,1.82.4
16.2-20.4.10.0

15.6. ~ ,1

9.9,0.70,5
9.4-11.1,7.03

9.0,0.42.5
8.6-9.7,4.65

11.1,0.69,5
10.3-11.8,6.18

6.5.1.62.5
4.3-7.2.24.97

195

The lower molars of Cor, plicatile (Figs. 25, 26A, Table 19),
although smaller, closely resemble those of Cor, occi den tale in
overall enamel morphology. Although initially shallow, the
ectoflexid deepens rapidly with wear, so that even molars with crown
heights exceeding 50 mm have completely divided isthmuses. The
metaconid and metastylid are well separated from each other by the
deep ectoflexid and a broad, 'U'-shaped linguaflexid. The metaconid
is generally oval, while the metastylid is typically more angular
(Figs. 25B, 25C). The bases of the metaflexids and entoflexids are
not flat, due to rounded lingual projections from the protoconid and
hypoconid. Pli cabal! inids are rare in molars, always small, and
confined to very early wear-stages (e.g. the m2 of F:AM 107874).
Rudimentary thickenings of the enamel at the position in the ecto-
flexid from where pli cabal 1 inids would originate are not infrequent
in early and moderate wear-stages, however. The antisthmus generally
has a single plication in early wear-stages (Fig. 25), but plications
are less common from the paralophid and postisthmus than in the
premolars (Table 17). Slightly worn to unworn mcch of ml2 varies
between 56 and 60 mm, while that of the m3 is about 53 to 56 mm.

Lower deciduous premolars of Cor. plicatile (Fig. 26C) have more
elongated metaconids and metastylids than do the p2-p4, large
protostylids on the dp34, and somewhat variable ectoflexid depths.
The ectoflexids may be shallow, especially in early wear-stages, and
sometimes do not penetrate the isthmus; but generally they deepen
with wear on the dp34. The dp2 ectoflexid tends to remain shallow.
As is typical for the genus, ectostylids are well developed,

196
especially on the dp3. This structure extends 8 to 17 mm above the
base of the tooth, producing an isolated, dentine-filled lake on the
occlusal surface when the tooth is sufficiently worn (Fig. 26C). Pli
caballinids are either absent, or, in early wear-stages, rudimentary.
Metaconid crown height of unworn dp34s is about 26 mm.

Discussion. Leidy (1887, p. 309) noted that the holotype of Cor.
plicatile (USNM 3292; see MacFadden 1984a, Fig. 140) was found at the
same locality (i.e. Mixson's Bone Bed) as other fossils sent to him
by local collectors. It is clear from his earlier writings (Leidy,
1884; 1885; 1887) that he considered the type locality of
"Hippotherium" in genu urn, "H^." plicatile, "Rhinoceros" proterus,
"Auchenia" major, and other newly described taxa all to be Mixson's
Bone Bed. It was later revealed that some specimens sent to him had
been collected at additional localities in the vicinity of the town
of Archer (Leidy and Lucas, 1896, pp. ix and xi ) . However, there is
no evidence that Mixson's is not the type locality of both Cor,
plicatile and Cor. in genu urn (e.g. based on preservation), and
additional specimens referable to both were collected there by Frick
field crews in the 1930s and 1940s.

Ever since its initial description, USNM 3292 has been described
as a "molar" (Leidy, 1887, 310; Osborn, 1918, p. 192; MacFadden,
1984a, p. 170). Leidy, however, used the term to refer to both true
molars and premolars. Leidy and Lucas (1896, p. 50) described USNM
3292 as a molar, "...probably the third...", apparently a reference
to a P4. There are several features of the specimen that indicate
that it is indeed a premolar, and not a molar. These include the
relatively large and widely-open parastyle and mesostyle, and the

197

complex pli cabal! in. Most importantly, the mesostyle angles
anteriorly in labial view when the occlusal surface is face down, a
distinguishing characteristic of P34s and not M12s (Bode, 1931).

That the holotype of Cor, plicatile is a premolar is important,
because (as will be detailed below) the only feature that clearly
distinguishes worn upper cheekteeth of Cor, plicatile from those of
Cor. in genu urn is size. Is the size difference between the hoi o types
of Cor. plicatile and Cor, in genu urn merely a reflection of the
typical significant size differences between P34s and M12s of
Cormohipparion? For both Cor, plicatile and Cor, in genu urn to be
valid, distinct species, it is necessary to show: 1) that two
different sized populations of Cormohipparion exist at Mixson's Bone
Bed and other nearby localities; 2) that the holotype of Cor, pli-
catile matches upper premolars of the larger-sized population in size
and morphology; and 3) that the holotype of Cor, in genu urn matches
upper molars of the smaller-sized population. If any of these condi-
tions is not met, then Cor, plicatile must be considered a junior
synonym of Cor, ingenuum. The range in size and V^ of the combined
sample are greater than that observed in other single-species quarry
or faunal populations (Table 20), indicating the presence of more
than a single species. Frequency distributions of occlusal and basal
crown dimensions (Figs. 27, 28) are bimodal, but do indicate appre-
ciable overlap between the two populations. The apparent greater
overlap in APL is lessened when the data are adjusted for crown
height. The holotype of Cor, ingenuum clearly clusters with the
molars of the smaller-sized population both in univariate and multi-
variate analyses (Tables 15 and 22; Figs. 27-29), indicating that the

198

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length (BAPL) for combined Florida samples of upper third and fourth
premolars (P34) of Cormohipparion ingenuum (A, C and E) and Cor.
plicatile (B, D and F). Analyzed samples exclude very slightly worn
and very heavily worn individuals. A,B. P34 APL; n=53 for Cor.
ingenuum. n=121 for Cor, plicatile (similarly, the first value given
in the following for sample size is that of Cor. ingenuum, the second
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Distributions are interpreted as being primarily bimodal with varying
degrees of overlap between the two species. All measurements in mm.

201

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Figure 28. Histograms of the distribution of occlusal antero-
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length (BAPL) for combined Florida samples of first and second molars
(M12) of Cormohipparion ingenuum (A, C and E) and Cor, plicatile (B,
D and F). Analyzed samples exclude very slightly worn and very
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being primarily bimodal with varying degrees of overlap between the
two species. All measurements in mm.

203

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206

smaller sample should be referred to by the older name. The holotype
of Cor, plicatile, while only within the range of the larger-sized
population for TRW and BAPL (Table 15; Figs. 27D and 27F), has a
relatively small APL (19.7 mm) that is within the observed range of
both populations (Tables 15. 18, 22; Fig. 27B). Linear discriminant
analysis separates the two with very little overlap, and places USNM
3292 with the larger sample (Fig. 29). Thus, the link between USNM
3292 and the larger-sized population, while somewhat more uncertain
than that of the type of Cor, ingenuum and the smaller-sized popu-
lation, is reasonable. The best matches for the peculiar fossette
morphology of USNM 3292 are found in the larger-sized population
(e.g. UF 17210, Fig. 23B). The Mahalanobis distances between the two
populations are significantly different (at £<0.01) for both of the
separately analyzed samples of P34 and M12. That the two do in fact
represent distinct species is further emphasized by the differences
in the DPOF, the p2 morphology (described below), and in unworn crown
height. The conditions for validation of both Cor, plicatile and
Cor. ingenuum set forth above are thus apparently met, although the
holotype of Cor, plicatile is atypical for certain characters
relative to the majority of specimens referred to the species. These
are judged to reflect individual variation rather than species-level
differences.

Leidy's (1887), and later Cope's (1889), referral of plicatile to
the genus Hippotherium reflected no particular phylogenetic
significance. At this period, all hipparionine and many merychippine
species were placed in Hippotherium, a name then considered valid for

207

all Eurasian and North American forms previously recognized as
Hipparion. Starting about 1900, Hipparion replaced Hippotherium as
the commonly used genus for hipparionine equids, and plicatile was
routinely transferred to Hipparion during this period (e.g. Hay,
1902). Gidley's (1907) use of "Hipparion" plicatile did have
phylo genetic significance, however, as he felt that "H." plicatile
(along with "H^." ingenuum and H. venustum) "...belong to an American
branch of the Hipparion group of the Old World" (Gidley, 1907, p.
906). Gidley's separation of hipparionines into two genera,
Neohipparion (for New World species) and Hipparion (primarily for Old
World species), was not accepted by his contemporaries Matthew and
Osborn (see e.g. Osborn, 1918, p. 173), who continued to refer all
hipparionines to a single genus. Matthew (1924) concluded that the
Miocene hipparionines from Florida and South Carolina (including "H."
plicatile) were not especially related to Old World species, a view
also endorsed by Simpson (1930). Stirton (1940) separated North
American Hipparion s.l. into three genera, Hipparion s.s., Nannippus
and Neohipparion, and, by his assignment of "?Hipparion plicatile",
again raised the possibility that it was more closely related to Old
World taxa than most North American hipparionines (which he assigned
to either Neohipparion or Nannippus). More recently, "H_." plicatile
has appeared in some faunal lists (e.g. Hirschfeld and Webb, 1968;
Webb and Perrigo, 1984), but it was not again analyzed
phylogenetically until MacFadden (1984a). MacFadden (1984a, pp.
170-174) concluded that the species, while valid, was generically
indeterminant. The major problem with all prior studies of the
generic affinities of "Hippotherium" plicatile was the limited amount

208
of available topotypic and referable material. This obstacle has
been eliminated by the samples from McGehee Farm, Moss Acres, and
especially the Love Site.

Quantitative and qualitative analyses of the dental material
listed above indicate that "H^. " plicatile is more closely related to
Cor. sphenodus and Cor, occidentale than to any other hipparionine
taxa from North America, and that it can be referred to Cor mo -
hipparion sensu MacFadden (1984a). Cormohipparion plicatile shares
the following features with Cor. sphenodus and Cor. occidentale which
in combination serve to distinguish them from other North American
hipparionine genera: high, well developed ectostylids on deciduous
lower premolars; lower permanent premolars with moderately reduced
ectoflexid depth and moderate pli caballinids in early wear-stages;
high frequency of plicated isthmuses; p2 and P2 much longer than p34
and P34 with expanded paraconids and anterostyles, respectively; oval
or elongate-oval protocones isolated until late wear-stages; and
highly complex and intricately plicated fossettes and pli caballins
until at least middle wear-stages. While some of these character
states evolved independently in other hipparionine genera, in combi-
nation they support the referral of plicatile to Cormohipparion.
This assignment can be tested with the discovery of more complete
material, especially well preserved skulls. This referral to Cormo-
hipparion in part vindicates the theories of Gidley (1907), Osborn
(1918, p. 192) and Stirton (1940) concerning possible relationships
with Old World taxa. However, both Cor. plicatile and Cor. ingenuum
are too young to be directly ancestral to Old World hipparionines.

209
Leidy's name "plicatile" suggested that the species had excep-
tionally complex fossette borders (as indeed is shown by the somewhat
atypical holotype). This has been further emphasized by MacFadden
(1984a, pp. 170-171). However, these observations were based on
small sample sizes, and, in some cases, included specimens I would
refer to Cor, ingenuum. Cormohipparion plicatile in fact has fewer
fossette plications on average than any other advanced species of
North American Cormohipparion (Table 21; Figs. 30, 31). It might
also be noted that the complexity of the holotype of Cor, plicatile
results more from extreme bifurcating of plications, and a not
unusually high number of total plications (12) for the species.
Although the median differences (Table 21) are slight. Figures 30 and
31 reveal a quite different pattern of fossette plications between
Cor. plicatile and Cor. occi dental e. The multimodal distribution for
Cor. occidentale is not the result of combining samples from
different localities. Similar multimodal distributions were produced
using a sample drawn from a restricted geographic and chronologic
population (Fig. 32). Much of the difference between Cor, plicatile
and Cor. occidentale results from variation of plications on the
anterior half of the prefossette. Slightly worn uppers of Cor.
occidentale typically have four to six plications on the anterior
half of the prefossette. More moderately worn teeth most often have
only one or two. The decrease does not proceed linearly with wear,
but tends to follow a step-wise pattern. This, combined with a
perhaps more linear decrease in plications on other regions of the
fossette s, produces the multimodal distributions in Figures 30A, 31 A
and 32. There are three distinct peaks in fossette complexity within

210

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Figure 30. Histograms of total number of fossette plications on the
P3 and P4 of four species of Cormohipparion. A. Cor, occidentale,
combined sample from Clarendonian and early Hemphillian of Texas and
Nebraska, n=44. B. Cor, plicatile, combined sample from Florida
sites, n=62. C. Cor. ingenuum, combined sample from Florida sites,
n=33. D. Cor. errisTTei, combined sample from Bone Valley and
Macasphalt "STiell Pit sites, n=23. Samples include only specimens
with MSCH between 50 and 90? of unworn crown height for each
particular species.

212

A CORMOHIPPARION P3 AND P4

II I I I I I I I I I I I I ' I ' I ' I ' I —

6 8 10 12 14 16 18 20 22

B

I I ■ I ' 1 ' I ' I ' I ' I — I ' I ' I — I I

10 12 14 16 18 20 22

I I I r
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10 12 14 16 18 20 22

10 —

5 —

J^=i:

I I I I I II 1 1 1 1 1 1 1 1 1 1 r

6 8 10 12 14 16 18 20 22

TOTAL FOSSETTE PLICATIONS

Figure 31. Histograms of total number of fossette plications on the
Ml and M2 of four species of Cormohipparion. A. Cor, occi den tale,
combined sample from Clarendonian and early Hemphillian of Texas and
Nebraska, n=39. B. Cor, plicatile, combined sample from Florida
sites, n=85. C. Cor, ingenuum, combined sample from Florida sites,
n=41. D. Cor, emsliei, combined sample from Bone Valley and
Macasphalt Shell Pit sites, n=29. Samples include only specimens
with MSCH between 50 and 90% of unworn crown height for each
particular species.

214

CORMOHIPPARION M1 AND M2

I ' I ' I ' I ' I ' I ' I ' I ' I ' I — I — I I ' I I ■ I

6 8 10 12 14 16 18 20 22

B

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I ' I ' I 1 T"

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t' ' I ' I ' I ' I I I I
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6 8 10 12 14 16 18 20 22

I ' I ' I ' I ' I ' I ' I ' I ' I ' I 1 ' I ■ I

8 10 12 14 16 18 20

— r
22

TOTAL FOSSETTE PLICATIONS

215

TOTAL FOSSETTE PLICATIONS
Cormohipparion qccidentale

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^-^

^ 1 T 1

10 12 14 16 18 20

22

Figure 32. Histograms of total number of fossette plications of A,
the P3 and P4 {n=43); and B, the Ml and M2 (n=40) of Cormohipparion
occi dental e from the Xmas-Kat Quarries Fauna, Cherry County,
Nebraska (late Clarendonian) . Sample analyzed as those in Figures
30 and 31, but the Xmas-Kat sample consists primarily of skulls.
Therefore, crown height cannot be directly measured on most of these
specimens. To make the sample comparable to those in Figures 30 and
31, values of APL were used to exclude slightly worn or excessively
worn specimens. The Xmas-Kat specimens, although slightly more
complex on average, display the same multimodal pattern as the
combined sample of Cor, occidentale in Figures 30 and 31.

216

the wear-stages under consideration. These are an early phase with a
mode of 18, 19 or 20 (here termed fossette-group A); an intermediate
group (B) with a mode of 15 to 17; and a final group (C) with a mode
of 11 to 13. In Cor, plicatile, three important differences are
observed: 1) the number of plications on the anterior half of the
prefossette is much less variable, being almost always 0, 1, or more
rarely 2; 2) the modal values are less (by 2 or 3); and 3) group C is
reached much earlier in ontogeny, such that groups A and B are either
not observed (group A for molars. Fig. 31B) or are very rare.
Generally, the first two fossette-groups are ephemeral ly expressed
during earliest wear-stages, in the first 10% of the crown. The
result is a distribution that appears more normal than that of Cor.
occidentale, and only slightly skewed to the left. The pattern in
Cor. plicatile is judged to represent the primitive condition, as the
general trend in the genus is to increase plication number and
duration, and because Cor, sphenodus appears to have a similar
pattern (although limited available sample sizes prevent further
analysis of that species). The fossette border morphology of Cor.
occidentale could have evolved from an ancestor with Cor. plicatile-
like fossettes by slightly increasing the median plication number
(per fo set te -group), and, more importantly, substantially delaying
the average crown height at which fossette-group A transforms into B,
and likewise B into C.

Cormohipparion plicatile is known from at least thirteen
localities in Florida (see referred specimens list and Fig. 2) that
range in age from latest Clarendonian (Love Site, about 9.0 ma)

217
through the later part of the early HemphilHan (about 6.0 ma). The
youngest specimens referred to Cor, plicatile are probably those
derived from the Dunnellon phosphate-mining region. In this area.
Cor. plicatile is found together with Cor. ingenuum. Nan, minor and
Neo. eury style. The period of overlap between these four is the late
early Hemphillian (about 6.0 to 7.0 ma; Tedford et al., in press).
The otherwise best represented fauna of this interval in Florida, the
With 4A site (Webb, 1969b; Becker, 1985a), lacks Cor^. plicatile.
however. Ana genetic microevol ution is observed when younger and
older samples are compared, especially in terms of plication
complexity. Another relatively young referred sample is that from
the Moss Acres Racetrack Site (Figs. 23A, 24, 250. The upper molars
from Moss Acres (UF 69968, 93000 and 96386) are much more complex
than average Love Site specimens, with multiple pli protolophs and
pli cabal 1 ins. The lower molars of UF 69967 and UF 93000 have
stronger and more persistent pli cabal! inids than any specimen from
the numerous Love Site sample. The Moss Acres sample does not appear
to differ from older populations in terms of size or hypsodonty. The
observed magnitude of intraspecific evolution is similar to that
found in other equid chronospecies over similar intervals of time
(e.g. Neohipparion trampasense) .

Equid populations from outside of Florida have only occasionally
been referred to Cor. plicatile. Webb (1969a) listed "H^." plicatile
in the Clarendon Fauna, but gave no references or specimen numbers.
Apparently he was referring to the same population later placed by
MacFadden (1980; 1984a) in H^. tehonense. Webb and Perrigo (1984)
recently referred to "H." plicatile a sample of about 50 cheekteeth

21i
from the Gracias Formation of Honduras. While morphologically
similar to Cor. plicatile, the smaller occlusal dimensions of this
sample clearly indicate a referral to Cor, ingenuum, and they will be
more fully discussed with that taxon. Examination of equid specimens
from the following major faunas or localities (in the F:AM, AMNH,
UNSM and UCMP collections) of late Clarendonian or early Hemphillian
age has failed to indicate the presence of Cor, plicatile in western
North America: Xmas-Kat Channels, Cole Highway Pit, Pratt Pit I, J.
Swayze Quarry, Port of Entry Pit, Box T Quarry, Higgins Fauna and the
Cambridge Fauna. Most of these instead contain a large, advanced
form of Cor, occidentale. Thus, at the present time, there are no
known referable samples of Cor, plicatile outside of central Florida.

Cormohipparion ingenuum (Leidy), 1885 new combination

Hippotherium ingenuum LEIDY, 1885, p. 33.

Hippotherium gratum (Leidy), COPE, 1889, p. 445 (in part); LEIDY

and LUCAS, 1896, pp. 49-50 (in part).

Hipparion ingenuum (Leidy), GIDLEY, 1907, p. 902; SELLARDS,

1916, pp. 94, 97 (in part); OSBORN, 1918, p. 191.

Hipparion (Nannippus) ingenuum (Leidy), SIMPSON, 1930,

pp. 187-188 (in part).

Nannippus ingenuus (Leidy), STIRTON, 1940, p. 186; QUINN, 1955,

p. 75 (in part); MACFADDEN, 1984a, pp. 126-133 (in part).

Hipparion plicatile (Leidy), SIMPSON, 1930, pp. 187-188 (in

part); WEBB and PERRIGO, 1984, pp. 243-245 (in part).

"Hippotherium" plicatile (Leidy), MACFADDEN, 1984a, pp. 170-174

219

(in part).

Cormohipparion n. sp., BECKER, 1985a, p. 30.

Not Nanm'ppus cf. Nan, ingenuum (Leidy), FORSTEN, 1975,

pp. 61-65.

Not Hipparion ingenuum (Leidy), WEBB and TESSMAN, 1968. p. 807.

Type specimen. USNM 3306, a L upper molar, probably a Ml (Osborn,
1918, Fig. 154 or MacFadden, 1984a, Fig. 97).

Type locality. Mixson's Bone Bed, Levy County, Florida.

Stratigraphic occurrence and age of type locality. Alachua
Formation; early Hemphillian, about 8 ma.

Topotypic sample. USNM 3305 L M3; F:AM 107875 assoc. R P2,P4-M3
and L P2-M3; F:AM 113623, 113624, 113638 3 L M12; F:AM 104870 L p34.

Distribution. Very late Clarendonian through early Hemphillian
(about 6.0 to 9.0 ma) of central Florida. Early Hemphillian of
Honduras.

Referred Gulf Coastal Plain specimens. McGehee Farm: UF 17209 R
P34; 7246, 17215 2 L P34; 9557, 45613 2 L M12; 17219. 53549 2 R M3;
11825 L dp34; 17165 L p2; 19482 R p34; 17194, 45626 2 R ml2; 9775,
17101 2 L ml2.

Haile 19A; UF 65727 L M12; 47323 R p2; 64751 R p34.

Cofrin Creek, Alachua Co., FL: UF 57107 R ml2; 17223 R m3.

YA Hospital Site, Alachua Co., FL: UF 17224 L M12; 53562 R M12;

With 4A: UF 17204 L maxilla with P2-M3; 45517, 53518, 53519 3 L
P2; 17200, 53516 R P34; 45530 R M12; 19622. 53512 2 L M3; 53459,
53482, 53492 3 L p34.

With 4X: UF 18329 L P34.

220
Moss Acres Racetrack Site: UF 97259 female R and L mandibles with

il-i3, p2-m3.

Dunnellon Phosphate Mining Region, Marion Co., FL: UF/FGS V-1479
R M12; -1483, -1485 2 L M12.

Archer Fauna, Nichols Mine: UF 24624 L M2; 24632 L p2.

Peace River, near Gardner, Hardee Co., FL: UF 55950 R ml2.

Love Site: UF 32300 partial skull with L 13, R and L C,P2-M3;
32254 assoc. R maxilla with P2,P4-M3 and L maxilla with P2-M3; 53409
assoc. R and L M2; 53410 assoc. R and L Ml; 35966, 35971-35973,
35975, 35979-35980, 35990, 35996, 36011, 36017-36023, 36026-36027,
36029-36030, 36039. 36042-36043, 36045-36046. 36050, 36052, 36055,
36058, 36061-36062. 36067. 36261-36262, 36264-36265. 36267-36268.
60396 39 R P2; 36138-36142. 36148, 36150, 36154, 36160-36161, 36163-
36164, 36167, 36170, 36172, 36175, 36178-36179, 36187, 36191, 36196-
36198, 36203-36204, 36207-36208, 36215-36216, 36224, 36230-36231,
36234. 36240, 36242. 36245-36246, 36252, 36259, 36271, 69808 43 L P2;
53350. 53392, 53393, 53397, 53399-53404, 62433-62437, 62439-62446,
62418, 62426. 62297 26 R P34; 53176, 53406-53408, 62325, 62377,
62449-62453, 62455, 62457-62459, 62461-62464, 62466-62470 24 L P34;
53333, 53341, 53343, 53386-53391, 53394-53396, 53426, 62304, 62414-
62417. 62419-62425. 62427-62432 31 R M12; 53375. 53380-53385, 62390-
62407, 62409-62413 30 L M12; 32120, 32133 2 R mandibles with dp2-dp4;
32150 L mandible with dp2-dp4; 32191 assoc. R mandible with p2-m3 and
L mandible with p3-m3; 32172, 36286 2 R mandibles with p2-m3; 32169 R
mandible with p2-m2; 32155, 32189 2 R mandibles with p3-m3; 32101,
32154, 32297 3 L mandibles with p2-m3; 32198 L mandible with p3-m3;
32171, 32132, 60395, 32124, 32241, 32138, 36284, 32289, 32181, 36280,

221
32117 11 partial R mandibles; 32103. 32112. 32128. 32115. 32158 5
partial L mandibles; 90199, 90200 2 assoc. R dp2-dp3; 90198 assoc. L
dp2-dp3; 32294 assoc. L dp2-dp4; 32200. 36286 2 assoc. R p2-m3; 35894
assoc. R ml-m3; 90201-90209 9 R dp2; 90210-90214 5 L dp2; 90236-90261
26 R dp34; 90215-90235 21 L dp34; 50357. 50363. 50366. 50367. 64807-
64842. 64923-64925, 64932. 64933. 92968 16 R p2; 50371. 64800. 64801.
64803-64806. 64922, 64938, 64939, 69817, 92967 12 L p2; 50542. 64752-
64778 28 R p34; 50457, 50459, 50519, 50526, 64779-64799 25 L p34;
64814-64859, 65174, 65175 48 R ml2; 64860-64901, 65169-65173 47 L
ml2; and many more catalogued and uncatalogued isolated teeth and
post-cranial elements.

Revised diagnosis. Medium-sized hipparionine with toothrow
lengths of 112 to 120 mm in middle wear-stages. Unworn MSCH of P2
about 37 mm and M12 about 49 mm. Smaller than Cor, sphenodus. Cor.
occidentale or Cor, plicatile. Less unworn crown height than Cor.
occidentale. Cor. plicatile, or Cor. emsliei. Ventral border of DPOF
less distinctly rimmed than Cor. occidentale or Cor, plicatile, but
fossa better developed than in Cor, emsliei. Lower permanent and
deciduous second premolars with an enamel fold projecting from the
metaconid (or less frequently the paraconid) that in late wear-stages
usually closes off the metaflexid into an isolated fossettid.

Description. Cranial material completely exhibiting the gener-
ically diagnostic facial region is unknown for Cor, ingenuum. Only
two referable specimens (UF 32300 from the Love Site and UP 17204
from the With 4A locality) preserve portions of the face, each
including only the ventral-most part of the DPOF. On the more
complete specimen (UF 17204, Fig. 33A), the ventral portion of the

222
DPOF consists of a moderately deep impression (at least 11 mm) with
an unrimmed, sloping ventral border located about 33 mm above the
alveolar border of the P4. The border is located just posterior to
the infraorbital foramen. On UF 32300, the ventral -most part of the
DPOF is located about 37 mm dorsal to the alveolar border of the P3.
Summary statistics of measurements on upper and lower cheekteeth
are listed in Tables 19 and 22. As is typical for Cormohipparion,
the P2 is the longest upper cheektooth, with a well developed
anterostyle (Fig. 34A). Upper premolars are characterized by
elongate-oval protocones, often with straight or concave lingual
borders, that are isolated until late wear (except P2), grooved
parastyles for the upper third of the crown, well developed pli
caballins and complex fossette borders (Figs. 33B, 34A, 34B). In the
Love Site sample, half (26 of 52 observed specimens) of all P34s
contain bifurcated or multiple pli caballins; this includes almost
all specimens in early and moderate wear-stages. Most (75%, n=51) of
the P34s have a single, deep, unbranched pli protoloph on the
anterior half of the prefossette; the remainder have an additional
one to three smaller plications labial to it. The pli protoloph is
lost only in very late wear-stages. The posterior half of the
prefossette is richly plicated, the large prefossette loop is
secondarily plicated with deep folds in early wear, and there are
usually four to six total infoldings of varying depth and complexity.
The anterior half of the postfossette is somewhat less complex,
generally with between two and five folds (96% of observed
specimens); the pli postfossette is usually bifurcated, as are one or
two of the other plications in early wear-stages. A single.

223

Table 22. Standard univariate statistics for upper cheekteeth
of Cornphipparion ingenuum from Florida. Format as in Table 2.
Faunal abbreviations: LOV, Love Site, Alachua County, late
Clarendonian; HE, combined sample from various early
Hemphllllan localities including McGehee Farm, Mixson's Bone
Bed, and Withlacoochee River 4A and 4X.

FAUNA LOV HE

P2

APL

24.5,1.24,43
22.1-26.9,5.06

25.2,0.42,2
24.9-25.5,1.68

BAPL

19.8,0.91,42
18.0-21.2,4.60

20.6, — ,1

TRW

17.3,0.74,44
14.9-18.8,4.27

17.8,0.44,3
17.5-18.3,2.45

PRL

5.9,0.55,43
4.6-7.5,9.37

6.9,0.61,3
6.4-7.6,8.81

PRW

3.6,0.32,42
3.0-4.8,8.87

3.4,0.23,3
3.3-3.7,6.73

224

Table 22— continued

P34

APL

19.2,0.73,49
17.8-21.5,3.82

18.8,1.58,9
15.0-20.5,8.44

BAPL

15.5,0.70,46
13.9-16.6,4.52

15.8,1.12,4
14.2-16.7,7.07

TRW

18.5,0.85,49
16.9-20.7,4.58

17.4,2.02,9
14.0-19.5,11.6

PRL

6.7,0.69,50
5.0-8.7,10.24

6.4,0.92,9
4.8-7.5,14.49

PRW

3.6,0.37,49
3.1-4.7,10.17

3.5,0.30,9
2.9-3.8,8.53

M12

APL

18.3,1.28,54
15.6-20.8,7.00

18.6,1.27,12
16.8-21.1,6.85

BAPL

14.6,0.57,47
13.5-15.8,3.90

14.9,0.70,8
14.1-15.9,4.67

TRW

16.7,0.94,54
13.8-18.9,5.65

17.0,0.86,12
15.6-18.1,5.03

PRL

6.5,0.58,55
5.2-7.5,8.84

6.3,0.83,12
4.7-7.4,13.33

PRW

3.4,0.39,54
2.3-4.3,11.45

3.3,0.27,12
2.9-3.7,8.11

225

Figure 33. Lateral and occlusal views of Cormohipparion ingenuum
from the Withlacoochee River Site 4A (late early Hemphi Mian),
Marion-Citrus county line, Florida. A. UF 17204, lateral view of
right maxilla showing poorly defined anterior ventral margin of
dorsal preorbital fossa. B. UF 17204, occlusal view of R P3-M3
(reversed).

226

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2cm

Figure 36. Occlusal views of lower cheekteeth of Cormohipparion
ingenuum from Florida. A,B. Love Site (late Clarendonian), Alachua
County. A. UF 32294, moderately worn assoc. L dp2-dp4. B. UF
32171, slightly worn assoc. R p2-p4. C. UF 24632, L p2, Nichols
Mine (late Clarendonian or early Hemphillian), Polk County.

229

unbranched pli hypostyle is found on most of the P34 (92%, n=50); it
is rarely absent or with accessory folds. The hypoconal groove
remains open throughout wear. Unworn or slightly worn MSCH of P2s
range from 36 to 38 mm; examples of unworn or slightly worn P34s are
rare, but their MSCHs are about 45 mm.

Upper molars are noticeably smaller in occlusal area than P34
(Table 22), with less well developed styles and generally with
shorter, more oval protocones (Fig. 34A) . The lingual border of the
protocone is usually convex; occasionally concave or straight,
especially in early wear-stages. Pli cabal 1 ins, while well
developed, are more likely to be single (76?, n=55. Love Site sample)
than branched or multiple (18%), but are retained until very late
wear-stages. The anterior half of the prefossette most often has a
single pli protoloph (56%, n=55), while 27% also have small accessory
plications. The posterior half of the prefossette consists of only a
moderately developed (relative to that of the P34) prefossette loop
and generally four to six plications. These are smaller and
shallower than their counterparts on the P34, and have a greater
tendency to disappear with wear. The anterior half of the
postfossette most often has between three and five plications, and
the pli postfossette is often bifurcated in early and moderate wear.
The posterior half of the postfossette generally (84%, n=50) has a
single, shallow pli hypostyle. Unworn MSCH of M12 is about 47 to 51
mm.

Lower cheekteeth of Cor, in genu urn are principally known only from
the Love Site, and demonstrate many phylogenetically important

230

features. They generally resemble lower dentitions of other species
of Cormohipparion, except for their smaller size (Tables 16, 17, 19).
The lower premolars are characterized by: rounded labial borders;
large metaconids and metastylids equal in size and well separated
from each other, especially by an anterol ingual extension of the
entoflexid (Figs. 35, 36B); ectoflexids that generally partially
penetrate the isthmus; and well developed protostylids. In early
wear-stages (Fig. 36B), isthmus and paralophid plications are common,
and a small pli cabal linid is usually present (Table 17). With wear,
the ectoflexid deepens, and the plications and pli caballinid fade
(Fig. 35B). Protostylids are slightly less prominent than in Cor.
plicatile. As is usual in Cormohipparion, they first appear as
isolated structures, but quickly connect to the protoconid. On most
p2s (and dp2s), there is an anterolabial plication that emanates from
the metaconid (Fig. 35A). Infrequently, the plication originates
instead from the paraconid, and projects posteriorly, or both
plications can be present (e.g. Fig. 36B). The plication first
appears on the occlusal surface during early to middle wear-stages,
although the crown height at which it becomes exposed varies. In
later wear-stages, it commonly connects the metaconid and paraconid,
isolating a portion of the metaflexid as a fossettid (Figs. 35 B, 36 A,
360 . While similar plications are occasionally found on p2s of
other species of Cormohipparion and other genera, in no other sample
is its appearance so frequent (except for Cor, emsliei ). Unworn mcch
of p2 is about 35 mm, and 43 to 47 mm for the p34.

The lower molars of Cor, ingenuum are similar in morphology to
those previously described for Cor. plicatile, but have shorter

231
unworn crown heights and are much smaller (Table 19; Fig. 35). Pli
cabanim'ds are very rare in the Love Site sample, and if present
occur only in slightly worn individuals. The Moss Acres specimen (UF
97259) retains small but distinct pli caballins on its deeply worn
molars. Plications on the isthmus and paralophid are common (Table
17), especially in slightly worn teeth. Unworn or slightly worn ml2
mcch is about 50 mm.

Lower deciduous premolars of Cor, ingenuum have relatively shallow
ectoflexids, elongated metaconids, metastylids and entoconids, and
moderately developed pli caballinids in early wear. With wear,
however, the ectoflexids deepen, the metaconids and metastylids
become more oval, and the pli caballinids are lost or become
rudimentary. In late wear-stages, small, generally elongate-oval
ectostylids appear on the occlusal surface (Fig. 36A). They are not
as prominent as in Cor, emsliei. Cor. occidentale or Cor, plicatile.
and are especially rudimentary on the dp2. Unworn dp34 mcch is about
21 to 23 mm.

Discussion. To an even greater degree than Cor, plicatile, the
generic affinities of "Hippotherium" ingenuum have remained enigmatic
due to the paucity of topotypic material. This has led to a number
of equid populations from the western United States being incorrectly
considered conspecific with it. The numerous Love Site sample for
the first time gives an accurate representation of the size and
variation of its upper and lower cheekteeth, and at least a partial
indication of its facial morphology. These combine to suggest a new
generic assignment for "H^." ingenuum and to falsify all previous
hypotheses.

232
As was shown in the discussion section of Cor, plicatile, late
Clarendonian and early Hemphillian faunas of central Florida contain
two very similar equid populations distinguished primarily on the
basis of size and hypsodonty. The smaller of these two populations
agrees with the holotype of "H^." ingenuum both in size (Figs. 28, 29)
and enamel morphology, and can confidently be referred to that
species. It is this population that has been described in the
proceeding section. Two important questions remain to be discussed:
1) are any equid populations or species other than those from
north-central Florida so similar in hypsodonty, dental and cranial
morphology, and size that they can be referred to "H^. " ingenuum (or,
if based on an older name, is "H^. " ingenuum a junior synonym of
another species)? and 2) with what species is "H^." ingenuum most
closely related, i.e. in what genus does it belong?

In his descriptions of "H." ingenuum and "H." plicatile, Leidy
(1885; 1887) made no attempt to compare them with other taxa, except
for "H." venustum, an inadequately known species from South Carolina.
The holotype of the latter is lost and it is a no men dubium
(MacFadden, 1984a, p. 126). Cope (1889) synonymized "H." ingenuum
with "H." gratum without comment, and Lucas (in Leidy and Lucas,
1896) followed this synonymy. Pseudhipparion gratum is now known to
differ greatly from "][. " ingenuum in size, facial morphology, and
enamel pattern (Webb, 1969a; Webb and Hulbert, 1986). Later workers
(e.g. Gidley, 1907) resurrected Leidy's species, and it has subse-
quently been considered valid. Stirton (1940) listed it with Nan-
nippus, but did not state any reasons for his referral. Quinn (1955,
p. 73) listed both Nan, tehonensis and Nan, ingenuum as occurring in

233
the Lapara Creek Fauna. Forsten (1975) referred the entire sample of
medium-sized hipparionines from both the Lapara Creek and Clarendon
Faunas to Nannippus cf. ingenuum. She gave no specific reasons for
her referral, and presented no comparisons with material from
Florida. MacFadden (1980; 1984a) later referred the same population
from the Clarendon Fauna to H_. tehonense, and a portion of the Lapara
Creek sample is also referable to this species of Hipparion, and not
to "Nan." ingenuum. Other specimens from the Lapara Creek Fauna
included in "Nannippus cf. ingenuum" by Forsten (1975) are referable
to Nannippus sp., cf. Nan, fricki (see pp. 112-117).

More recently, MacFadden (1984a, p. 132) synonymized "Nannippus"
ingenuus and Nan, lenticular is (a late Hemphillian species
particularly well known from the Coffee Ranch, Edson, and Uptegrove
localities of the Great Plains) "...based on overall similarity in
size, crown height, and dental pattern...". Examination of large
numbers of individuals of both taxa fails to substantiate the
validity of MacFadden 's synonymy. While of similar size ("H^. "
ingenuum is slightly larger on average, but observed ranges of tooth
length and width overlap), there are numerous important differences
between the two. In Nan, lenticularis, the posterior cheek region
does not contain a fossa, but there is a small fossa located anterior
to the infraorbital foramen. This observation of MacFadden (1984a,
p. 130) is based on a single specimen, F:AM 113731. I believe that
this feature may be an artifact of, or greatly accentuated by, the
preservation and/or preparation of this particular specimen. In "H^. "
ingenuum. a moderately developed DPOF is located posterior to the

234
infraorbital foramen. Significant dental differences between the two
taxa are:

1. Unworn crown height of upper and lower third and fourth
premolars of "H^." in genu urn is about 45 mm, of first and second
molars about 50 mm. In Nan, lenticularis, unworn premolar
crown height is about 50 mm, and 57 mm for molars.

2. In "H." ingenuum, the P2 and p2 are much longer than the
other premolars, with well developed anterostyles and
paraconids, respectively. In Nan, lenticularis, they are
relatively short, with poorly developed anterostyles and
paraconids. The former is characteristic of Cormohipparion and
Neohipparion. the latter condition is found in Nannippus and H^.
tehonense. As shown in Chapter 6, a reduced antero style is a
derived character state for hipparionines.

3. In "H^. " ingenuum, pli cabal 1 ins are well developed,
frequently bifurcated or multiple, and persistent throughout
wear. In Nan, lenticularis, pli cabal 1 ins are at best
moderately developed, not branched or multiple, and are often
absent or lost with wear (e.g. F:AM 111731, MacFadden, 1984a,
Fig. 98D).

4. In "H." ingenuum, fossette plications are very complex,
often deep and bifurcating. In Nan, lenticularis, fossette
plications are shallow and usually simple, with a much greater
tendency for the pli hypostyle to be absent.

5. In "H_." ingenuum, the lingual border of the protocone is
often straight or concave, especially in premolars. In Nan,
lenticularis, it is nearly always convex. The protocone also

235

tends to connect to the protoselene much earlier in the
premolars of Nan, lenticularis, at MSCHs as high as 25 mm.

6. In "H^. " ingenuum, the protostylid is prominent and is
isolated from the protoconid only for a short period of wear.
In Nan, lenticularis, the protostylid is small, remains
isolated from the protoconid until very late wear-stages, and
is occasionally absent (see also Dalquest, 1983).

7. In "H." ingenuum, the metaconid of the p2 and dp2 have an
anterolabial plication that closes off the metaflexid. In
samples of Nan, lenticularis, such structures are absent or
very rare.

There are additional, more minor, differences between the
cheekteeth of the two taxa, but the seven listed above (plus the
differing facial morphologies) suffice to prove that two separate
species and genera are represented by these populations. The
differences are greater than those observed between early and late
populations of other equid species with long, well documented
chronologic ranges (e.g. chronoclinal variation observed in Neo.
trampasense or Cor, occidentale). Typically in those cases, the
younger population shows advanced features that are observed in more
rudimentary form in the older population. Samples of intermediate
age are of intermediate grade. With regards to "H^. " ingenuum and
Nan, lenticularis, some of the features of the younger taxon (those
numbered 3, 4, 5 and 7) are more primitive than those of the older.
Others (2 and 6), which are derived in the younger population, are
not observed in any rudimentary or incipient form in the older
samples. Nan. lenticularis is best considered a distinct, valid

236

species. Although its inclusion in Nannippus has been questioned
(Sondaar, 1968), it shares a number of derived features with other
species of Nannippus and should be retained in that genus.

Leidy's (1885) "H^. " in genu urn can be referred to Cormohipparion
based on the same suite of characters previously used (p. 217) with
Cor, plicatile. As is the case with the latter species, recovery of
well preserved cranial material will test this phylogenetic
hypothesis.

Fossette plications in Cor, in genu urn more resemble those of Cor.
plicatile than Cor, occidentale in frequency distributions (Figs. 30,
31), although it has slightly more fossette plications on average
than does Cor, plicatile (Table 21). The distribution of total
fossette plications for the P3 and P4 (Fig. 30C) is obscured by the
small sample size, and no obvious modal value for fossette-group C
(see p. 216) is apparent. It could be either 10, 12, or 13. How-
ever, the distribution of fossette plications of the Ml and M2 is
more revealing (Fig. 31C). Two modes are apparent, that of group C
at 9, and group B at 15. Like Cor, plicatile. Cor. ingenuum repre-
sents the primitive Cormohipparion pattern for ontogenetic variation
in fossette complexity (see p. 216 for further discussion).

Webb and Perrigo (1984) referred a sample of teeth from the
Gracias Formation of Honduras to "Hipparion" plicatile. As they
noted, in many respects this sample does compare favorably with Cor.
plicatile as defined in this study. However, the size of the
specimens, as listed by Webb and Perrigo (1984, p. 244), clearly
indicates a referral to the smaller Cor, ingenuum. The north-central
Florida and Central American samples are remarkably similar.

237
considering the geographic distance separating them. The major
difference is a better developed pli caballinid in the Honduran
sample. It is more persistent on the p2-p4 than in the Love Site
sample, and even occurs on some molars. It is not so well developed
as in Cor, emsliei, however, nor does the Honduran sample have the
extreme fossette complexity observed in the Pliocene species. The
relatively advanced nature of the Honduran sample of Cor, in genu urn
emphasizes Webb and Perrigo's (1984) conclusion that the age of the
Gracias Fauna is early Hemphillian rather than late Clarendonian.
As noted by Simpson (1930), Cor, in genu urn is commonly found in
Florida, however typically it is less abundant than its congener.
Cor. plicatile. Its biostratigraphic range in Florida as here
recognized extends from the latest Clarendonian (Love Site) to the
late early Hemphillian (With 4A and Dunnellon sites). Simpson (1930,
Fig. 20C) illustrated a molar of Nannippus minor as Cor, ingenuum
(UF/FGS V-1426). The specimen is actually less complete than
represented in the figure, and slightly smaller. The slightly worn
molar he figured as Cor. plicatile (Simpson, 1930, Fig. 20B) is
referable to Cor, ingenuum, instead. Diagnostic features of this
specimen (UF/FGS V-1485) are its narrow protocone with a flattened
lingual border and its small TRW. Cormohipparion ingenuum has often
been recognized from the Bone Valley Formation (Sellards, 1916;
Simpson, 1930; Webb and Tessman, 1968; Webb, 1969b), either as
"Hipparion" ingenuum or "Nan." ingenuus. Most of these records are
referable to the more advanced species. Cor, emsliei . Others,
particularly those from the Manatee Dam Site (Webb and Tessman,
1968), are either generically indeterminant or referable to Nan.

23!
minor. Both Cor. plicatile and Cor, ingenuum are recognized from the
Bone Valley Formation (especially from the Nichols Mine, see referred
specimens listing and Figure 36C), but are interpreted as being
derived from an older horizon than that which produces Cor, emsliei .
Based on the joint occurrence with Pseud, skinneri (Webb and Hulbert,
1986), these records are either late Clarendonian or early
Hemphillian.

Cormohipparion emsliei new species

Hipparion ingenuum (Leidy), SELLARDS, 1916, p. 97 (in part); not

WEBB and TESSMAN, 1968, p. 807, Figure 5.

Hipparion (Nannippus) ingenuum (Leidy), SIMPSON, 1930, pp.

187-188 (in part, not Figure 20C).

Hipparion plicatile (Leidy). SIMPSON, 1930, pp. 187-188 (in

part).

Nannippus phlegon (Hay), ROBERTSON, 1976, pp. 158-159 (in part).

Figure 15; MACFADDEN and WALDROP, 1980, p. 7 (in part).

"Hippotherium" plicatile-like form, MACFADDEN, 1986, p. 471.

Type specimen. The holotype is UF 94700, a partial skull
consisting of nxjst of the right maxilla with DPI, P2-M3; right and
left premaxillae with 11-13; and an edentulous fragment of the left
maxilla with alveoli for the DPI and P2. The premaxillae were
collected about 15 cm from the maxillae, and there is no direct
contact between them. They are judged to belong to the same indi-
vidual based on their close association in the field, similar stages

239
of tooth wear, identical preservation, and on the overall rarity of
mammalian remains at the type locality. Collected 13 June 1986.

Type locality. Macasphalt Shell Pit, 3 km north of Fruitville,
Sarasota County, Florida.

Stratigraphic occurrence and age of the type locality. Unit 4 (of
Petuch, 1982), Pinecrest Member, Tamiami Formation. Age based the
associated mammalian fauna is Upper Pliocene (late Blancan), about
2.0 to 3.0 ma.

Topotypic sample. UF 94634, R M12; 94696, R p2; 94697, L p34;
94698, L ml2; 94699, L dp4; 94635, R metatarsal III; 94636, R
ec toe unciform; 94637, proximal phalanx of lateral digit.

Etymology. For Steven D. Emslie, Department of Zoology,
University of Florida, who collected the hoi o type and several of the
topotypes, and in recognition of his contributions to vertebrate
paleontology of the Pliocene and Pleistocene of Florida.

Distribution. Known only from the Pliocene (about 5.0 to 2.0) of
peninsular Florida.

Referred specimens. Palmetto Fauna, Bone Valley Region. Palmetto
Mine: UF 17184, 63636, 63983 3 R P2; 63640 R P34; 12503,
17185-17186. 63637-63639, 63956 7 L P34 ; 17187, 63641-63642, 63952 4
R M12; 63643, 63951, 63955 3 L M12; 17189. 63952, 63957 3 R M3; 10306
L DP34; 17163 R partial mandible with dp2-dp3 and partial dp4; 53493
L mandibular fragment with dp2 (possibly same individual as UF
17163); 17190 R partial mandible with ml-m2; 69909 R dp34; 93497 L
dp4; 17152, 69908 2 R p2; 17153, 53495, 69910 3 R p34; 19438-19439.
53494, 53498, 53501, 63644 6 R ml2; 19437, 53502, 53505 3 L ml2.
North Palmetto Mine: UF 63982 R M12; 63981 R M3. TRO Quarry, Payne

240
Creek Mine: UF 24705 R P34; 24713 R M12; 24865 L partial mandible
with clp2-dp4. Payne Creek Mine: UF 53983, L M12. Fort Green Mine:
UF 55821, 57219 2 R P2; 61981, 55901, 52431, 58410 4 R P34; 23995,
57220, 65665 3 L M12; 55823 R M3; 58380, 58411 2 L M3; 58396 L p34.
Nichols Mine: UF 24637 R P34; 28836 L P34; 53563 L mandible with ml-
m3; 24631 R p34. Phosphoria Mine: UF 53557 R M12; 93215 L M12;
53555 R ml2; 53556 L m3. Kingsford Mine: UF 53891 L P34; 13215 R
p34; 17227 L ml2. Gardinier Mine: UF 58295 R P2; 67976 L P34. C.
F. Industries Mine: UF 40083 L P2. Chicora Mine: UF 65226 R ml2.
Brewster Mine: UF 93213 R M3. Agrico Pierce Mine: UF/FGS V-5503 L
p34. Amax Mine: UF 93236 L m 12. Specific mine or locality
unknown: UF/FGS Y-6614, UF 53841-53842 3 L P2; 53551, 53853, 58333,
55900 4 L P34; 53533 R M12; 47384, 53552 2 L M12; 61476 R p2; 61484 L
p2; 53846, 61480-61481, 64158 4 R p34; 61482-61483 2 L p34; 61474 R
ml2; 61477-61479 3 L ml2; 61485 R m3.

Haile 15A, Alachua Co., FL: UF 17484 L P34.

Diagnosis. Medium-sized (mean M12 APL=19.2 mm, BAPL=15.7 mm)
species of Cormohipparion, differs from "Mer . " goorisi by greater
size and much greater unworn crown height; from Cor, occidentale and
Cor, plicatile by smaller size (by about 102 and S% on average,
respecitively); and from all North American species of Cormohipparion
by its extremely complex fossette plications and better developed,
more persistent pli caballinids. MSCH of unworn molars about 57 mm,
15% taller than those of Cor, ingenuum. Metaconid and metastylid of
dp2-dp4 and p2-p4 with unique lingual groove in early wear-stages.
DPOF reduced anteriorly. Grooved incisors.

241
Description. The only known cranial material of Cor, emsliei is
the holotype, UF 94700, a young but mature individual (Figs. 37A,
37B, 37C). The preserved portion of the facial region (Fig. 37A)
reveals a very prominent malar crest that extends anteriorly to above
the mesostyle of the P4. The infraorbital foramen (lOF) is located
about 58 mm dorsal to the alveolar margin, midway between the
parastyle and mesostyle of the P3 (Fig. 37A). The region immediately
dorsal and posterior to the lOF is preserved; it does not contain the
usual Cormohipparion DPOF (e.g. MacFadden, 1984a, Fig. 8A), but
rather a moderate depression whose long axis of maximum depth (ca. 5
nm) runs posterodorsal-anteroventrally at about a 45 angle from the
occlusal surface of the toothrow. Whether or not this depression
deepened posteriorly and was rimmed can not be determined from the
holotype. Portions of the typical equine buccinator fossa are
located anterior to the P2.

The incisors of UF 94700 form a semicircle (Fig. 37C) with a
diameter of 65.1 mm (maximum width measured at the occlusal surface
of the I3s). The lis have a single, broad, labial groove; the I2s
have two shallower labial grooves, giving the enamel surface a
slightly undulatory appearance (Fig. 37C). Both the II and 12 have
elongate, completely enclosed infundibula, and the outer enamel has
pinched-off, horn-like structures on the sides. These would have
persisted until about an additional 9 mm of crown had worn away. The
I3s are slightly worn, and their infundibula are open posteriorly.
The 13 labial surface has many shallow grooves and an irregular
texture. The dimensions of the incisors of UF 94700 (maximum
occlusal length x width, in mm) are: II, 16.8 x 9.4; 12, 19.0 x 8.7;

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Table 23. Standard univariate statistics of upper cheekteeth of
Cormohipparion emsliei n. sp. from the Palmetto Fauna, Bone Valley
Region, Polk and adjacent counties, Florida. Format as in Table 2.

P2 P34 M12

APL

23.7,2.14,5
21.8-27.3,9.00

18.9,1.40,23
17.0-22.1,7.39

19.2,1.09,24
17.5-21.5,5.66

BAPL

20.2,2.21,4
17.6-22.7,10.95

15.5,1.01,15
14.2-17.9,6.53

15.7,1.01,17
13.9-17.1,6.41

TRW

18.1,1.39,8
16.5-19.8,7.70

18.2,1.29,24
16.2-20.9,7.06

17.2,1.18,22
15.3-20.1,6.87

PRL

5.7,0.55,11
4.9-6.5,9.71

6.0,0.80,24
4.8-8.8,13.33

6.4,0.64,23
5.2-7.5,9.96

PRW

3.3,0.32,10
2.8-3.7,9.83

3.3.0.29,22
2.8-3.9,8.73

3.2,0.31,23
2.4-3.7,9.72

250

Table 24. Standard univariate statistics for lower cheekteeth of

Cormohipparion emsliei n. sp. from the Palmetto Fauna, Bone Valley

Region, Polk and adjacent counties, Florida. Format as in Table 2,

p2 p34 ml2

apl 19.4,1.46,3 19.3,1.36,9 19.1,1.62.18

18.1-21.0,7.55 17.5-21.4,7.08 15.9-22.0,8.50

bapl 16.2,0.57,2 16.1,1.07,5 15.5,1.04,8

15.8-16.6,3.49 14.9-17.3,6.69 14.1-16.5,6.71

atw 7.7,0.78,2 9.9,0.74,9 8.3,0.65.19

7.1-8.2,10.10 8.6-11.1,7.50 7.3-9.5,7.80

ptw 9.2,0.57,2 9.5,0.76,10 8.1,0.81,18

8.8-9.6,6.15 8.6-10.9,8.00 6.7-9.5,10.01

mm! 8.6,0.32,3 10.7,0.95,10 10.4,1.04,19

8.4-9.0,3.72 9.2-11.5,8.92 8.7-12.0,9.92

entl 8.8,1.54,3 9.3,0.77,10 7.4,0.89.18

7.0-9.8,17.54 8.1-10.6,8.23 5.8-8.4,12.04

251

13, 17.6 X 7.3. The lengths would decrease substantially with
attritional wear.

Upper cheekteeth characterized by: grooved parastyle in the upper
portion of the crown in both premolars and molars (Figs. 37B, 38C,
38G); strong mesostyles that are occasionally also grooved;
metastyles present and often relatively strong (but not to the degree
of Neohipparion eurystyle); P2 with well developed, large anterostyle
(Fig. 38A). The relatively large (in UF 94700, length=9.2 mm),
single rooted DPI is located almost completely anterior to the P2,
and is readily visible in lateral view (Fig. 37A). It bears wear
facets from occlusion with the p2 paraconid. The protocone of the
P3-M3 is relatively small, elongate-oval, with a variably shaped
lingual border. In early to moderate wear it is usually concave
(Fig. 37B) or straight; becoming more rounded (convex) with heavy
wear. The P2 protocone is shorter, more oval, and of all the
cheekteeth, the only one with a tendency to connect with the
protoselene prior to extremely late wear-stages. Compared to other
species of Cormohipparion, however, the P2 protocone is much more
frequently isolated in Cor, emsliei at comparable wear-stages. For
example, the percentage of isolated protocones in moderately worn P2s
(MSCH between 20 and 30 mm) is 63% for Cor. plicatile (n=24), 6U for
Cor. ingenuum (n=28) and 100? for Cor. emsliei (n=5). The hypoconal
groove of all cheekteeth is widely opened until very late wear-
stages, but shallow when heavily worn (Figs. 38B, 38F). Pli cabal-
lins are strong, persistent, and frequently double in both premolars
and molars (Figs. 38C, 38D, 38G). A very diagnostic feature of Cor.

252

emsliei upper cheekteeth is their extremely complex fossette plica-
tions (Figs. 37B, 37D, 38). Premolars are, on average, slightly more
complex than molars. The anterior half of the pre fossette of P2-P4
always has at least one, to a maximum of five, plications. The pli
protoloph is always deep and occasionally bifurcated; accessory
labial plications are also present on 21 of 33 examined specimens.
The posterior half of the prefossette generally (91% of observed P34;
n=23) has from six to eight plications, several of which are branched
and deep. The prefossette loop has several secondary folds; these
not infrequently merge to isolate portions of the distal section of
the loop from the prefossette (Figs. 380, 38F). The anterior half of
the postfossette is less complex, generally with three to five
plications. The pli hypostyle is deep, never absent, and often
accompanied by one or two accessory plications. The fossette
plications of the M1-M3 are only slightly less complex and persistent
(Figs. 37B, 37D, 38F, 38G). The anterior half of the prefossette in
early wear-stages also has a deep pli protoloph and numerous (usually
two or three, up to five) smaller plications. In later wear-stages,
the accessory plications are lost or become rudimentary, and the pli
protoloph is much shallower. The posterior half of the prefossette
and the anterior half of the postfossette have (in general) four to
eight and three to five plications, respectively. Those of the
prefossette have a greater tendency to bifurcate. The pli hypostyle
is again deep and often (40% of observed M12, n=20) accompanied by
one or two accessory plications. The only known upper deciduous
premolar (UF 10306) resembles its permanent counterparts with its
small, oval protocone, double pli caballin, complex fossettes, and

253
grooved parastyle. Unworn to slightly worn MSCHs for P34 are
estimated to be about 48 to 53 mm, and about 56 to 58 mm for the M12.

Lower cheekteeth exhibit the basic Cormohipparion pattern, but
with a greater tendency to flatten the labial borders of the
protoconid and hypoconid, and better developed pli caballinids (Figs.
37E, 37F, 37G, 39). Lower second premolars have large paraconids,
and in early wear-stages, a prominent anterior extension of the
entoconid that projects labial to the metastylid (Fig. 398). As in
Cor. ingenuum, there is a plication from either the metaconid or the
paraconid that eventually connects with the opposing structure,
isolating the metaflexid as a fossettid (Fig. 39A) . The ectoflexid
is shallow in all known p2s, not penetrating the isthmus, even in
relatively late wear-stages (e.g., UF 61484, mcch=13.4 mm). Lower
third and fourth premolars are also characterized by reduced
ectoflexid depth. In early wear-stages, a long pli caballinid
extends labially past the borders of the hypoconid (Figs. 37E, 398,
390 . The isthmus, paralophid and entoconid are frequently plicated,
and the metaconid and metastylid have angular lingual borders. A
strong protostylid appears on the occlusal surface after the
upper-most 10 to 15 mm of the crown wears off on the p34; it is
sometimes recurved as in Neo. eurystyle. The plications and pli
caballinids are reduced in later wear-stages, but are usually still
evident. In early wear-stages of the p34 and the dp2-dp4, the
metaconid and metastylid have prominent lingual grooves; these
persist until moderate wear on the metastylid of the dps (Fig. 37G),
but are rapidly worn off the permanent teeth. Unworn to very

254
slightly worn molars also have nonpersi stent lingual grooves, usually
just on the metaconid (e.g. UF 93236).

The enamel morphology of the lower molars is variable. Some
patterns are nearly identical to those of Cor, ingenuum (e.g. UF
53563, Fig. 39F), but most are more advanced, with moderately
developed pli caballinids and angular metastylids (Figs. 37F, 39E,
39G). Labial borders of the hypoconid and protoconid are flattened
in early wear-stages, rounded in later ones. The ectoflexids often
only partially penetrate the isthmus (Fig. 37F) in early wear-stages;
but in later stages they typically penetrate very deeply (Fig. 39G).
Estimated unworn mcch are about 35 mm for the p2, about 52 for the
p34, and about 57 for the ml2.

Lower deciduous premolars of Cor, emsliei are unusual among
hipparionines in having both well developed pli caballinids and
ectostylids (Figs. 37G, 39H). The dp34 also have large protostylids.
The metaflexid of the dp2 is isolated into a fossettid in moderate
wear-stages by a plication between the metaconid and paraconid.
Unworn mcch of the dp34 is about 27 mm.

UF 94635, a right MT III, is referred to Cor, emsliei based on its
moderate size, intermediate between that of Nannippus and Equus
simplicidens (Table 25), and morphology (Fig. 40). Although only
slightly longer than those of average-sized individuals of Nan.
peninsulatus or Nan, bee ken sis, it is notably more massive. The
cuboid and mesoentocuneiform facets on the proximal articular surface
are relatively small (Fig. 40 A; Table 25); while the facets for
articulation with MT II and IV are robust. The opposite is true of
Nannippus metatarsals. The posterior (plantar) surface (Fig. 40C)

Figure 40. Proximal (A), anterior (B) and posterior (C) views of
UF 94635, right metatarsal III of Cormohipparion emsliei n. sp. from
Macasphalt Shell Pit, Sarasota County, Florida (late Blancan).

256

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258

Table 26. Comparisons of unworn mesostyle crown height (MSCH) and
relative hypsodonty of first and second molars of late Miocene and
Pliocene hipparionine equids. Unworn crown height is estimated
from unworn and very slightly worn upper molars for each species;
basal crown length (BAPL) is a mean value, either of a single
sample, or a combination of populations. Hypsodonty index (HI) is
calculated as the ratio of unworn crown height to mean BAPL. The
grade of hypsodonty of Cormohipparion emsliei is more like that of
Clarendonian equids, is much less than its late Hemphillian-
Blancan contemporaries, and reflects relative stasis in this
character compared to contemporary equid genera.

FAUNA{S)

Clarendonian-early Hemphillian equids

Cormohipparion occi dental e XMAS-KAT,

LAPARA CREEK

Cormohipparion plicatile LOVE

Cormohipparion ingenuum LOVE

Hipparion tehonense CLARENDON

Pseudhipparion hessei CLARENDON

Neohipparion trampasense LOVE

Nannippus westoni LOVE

Late Hemphillian-Blancan equids

Cormohipparion emsliei n. sp. BONE VALLEY

MSCH BAPL{n)

Neohipparion eurystyle
Nannippus lenticular is
Nannippus minor
Pseudhipparion simpsoni
Nannippus peninsulatus

YEPOMERA

COFFEE RANCH

BONE VALLEY

BONE VALLEY

MT. BLANCO,

SAN PEDRO VALLEY

60

59
50
50
48
60
43

57
73
57
51
110
75

16.4(108)
14.6(47)
15.4(9)
13.1(53)
15.2(138)
12.7(24)

15.7(17)
16.2(33)
13.1(29)
11.5(26)
8.1(8)
12.5(15)

HI

17.3(13) 3.5

3.6
3.4
3.2
3.7
3.9
3.4

3.6
4.5
4.3
4.6
13.6
6.0

259

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Figure 41. Bivariate plot of occlusal anteroposterior length (APL)
versus transverse width (TRW) of upper first and second molars. A-F
represent species means, with lines indicating plus and minus one
standard deviation from the mean. A, Cormohipparion emsliei n. sp.,
upper Bone Valley sample only (n=27); B, Cor. ingenuum. Love Site,
Alachua County, Florida (n=54); C, Cor. pTTcatile. Love Site,
Alachua County, Florida (n=113); D,Tor.~occi den tale, Xmas-Kat
Quarries Fauna, Cherry County, Nebrasl<a" (n=75); E, Nannippus minor,
upper Bone Valley Fauna, Polk County, Florida (n=28); F, Nanmppus
peninsulatus, combined sample from Florida, Texas, and Mew Mexico
(n=15). CTFcles represent individuals of Cor. emsliei from the Bone
Valley; squares individuals from MacasphalTThell Pit. The latter
appear to resemble more those of Cor. plicatile, but they are in
early wear-stages and overlap similarly worn Bone Valley specimens.
Slightly worn Cor, plicatile molars are much larger, on average.

260

bears two highly roughened areas for the attachment of the inter-
osseus lateral metatarsal ligaments; these extend down about 70% of
the length of the shaft. Posterior to the large distal supra-
articular tuberosities on the lateral and medial surfaces of the
shaft are additional roughened areas for ligament attachment. On the
anterior (dorsal) surface between the tuberosities is a moderate
depression; a feature characteristic of tridactyl equids (Hussain,
1975). There is a deep groove for passage of the great metatarsal
artery on the posterolateral side of UF 94635, another feature of
tridactyl equids (Webb, 1969a, p. 125). The median sagittal ridge
(keel) that separates the distal articular condyles runs along the
entire length of the articular surface. It is notably less well
developed (lower and less sharp) on the anterior surface than it is
posteriorly. The lower part of the shaft is curved slightly
posteriorly, more so than in Nannippus. Similar-sized metapodials
(e.g. UF 58397) have been recovered from the Bone Valley Region, but
as that fauna contains several medium-sized equids, they are not yet
conclusively referred to Cor, emsliei . Increased sample sizes of
Bone Valley equid post-cranial elements are needed for rigorous
biometrical analysis and comparisons with the numerous late Miocene
specimens from Florida (e.g. the Love Site sample).

Two other post-cranial elements from Macasphalt appear to
represent Cor, emsliei , an ectocuneiform and a lateral phalanx. The
proportions of the ectocuneiform conform to those of the proximal
articular surface of the MT III. The two bones articulate reasonably
well, although they evidently are from different individuals, as the

261

fit is not perfect. The proximal surface of the ectocuneiform is
composed mainly of the navicular facet, with limited area for
nonarticular regions for attachment of intertarsal ligaments. The
ectocuneiform more nearly resembles that of Hipparion figured by
Hussain (1975, Fig. 8C) than that of Equus simplicidens (Hussain,
1975, Fig. 8B). The proximal phalanx of the lateral digit is long
and slender. Its maximum length is 36.1 mm. The concave proximal
articular surface is 14.6 mm (A-P depth) by 10.1 mm (transverse
width). Its large size indicates an animal with functional lateral
digits, as do many characters of the MT III.

Discussion. The only population of Cor, emsliei well enough
represented to allow statistical evaluation is that from the late
Hemphillian Bone Valley Region (Tables 23 and 24). Cheekteeth in
this sample have very similar occlusal dimensions to those of Cor.
ingenuum (Fig. 41), and are larger than those of Nannippus. The
topotypic sample from the Macasphalt Shell Pit has mean dimensions
slightly larger than those of the older population, and more elong-
ated protocones (Tables 15, 23, 24; Fig. 41). Much of the apparent
size difference, however, is due to the relatively early wear-stages
of the Macasphalt teeth. For example, UF 94634, which just falls
within the OR of the Bone Valley sample in occlusal length and width
(Table 23), would have a length of only about 18 mm when worn to a
MSCH of 25 mm. The upper premolars of the type specimen appear
especially large due to their early wear-stages, as almost all of the
premolars from the Bone Valley are from individuals with moderate to
heavily worn teeth. The only very slightly worn P34, UF 58333, has
an APL of 22.1 mm, which is similar to those of type. The enamel

262
patterns of the teeth from Macasphalt, except for the relatively more
elongated protocones, are identical to those from the Bone Valley.

The third occurrence of Cor, emsliei is a very heavily worn P4 (?)
from Haile 15A, UF 17484 (Robertson, 1976, Fig. 5). Its MSCH is only
about 9 mm; even so it retains a large, elongated, isolated proto-
cone. Previously this specimen was referred to Nan, "phlegon"
(Robertson, 1976; MacFadden and Waldrop, 1980), but it is too large
for that species (Table 15). A P34 of Nan, peninsulatus in the same
very late wear-stage as UF 17484, UF 22634, has an APL of only 13.8
mm, a TRW of 15.2 mm, and a connected protocone. The occlusal dimen-
sions of UF 17484 fall within the OR of the Bone Valley sample of
Cor, emsliei, and its occlusal area (APL x TRW) is 502 greater than
that of UF 22634. Thus, despite its late wear-stage, UF 17484 is
confidently referred to Cor, emsliei. The remainder of the material
listed by Robertson (1976, p. 158) does appear to represent Nan.
peninsulatus.

Genus Hipparion de Christol. 1832

Type species. Hipparion prostylum Gervais, 1849.

Included North American species. H. shirleyi MacFadden, 1984; H.
tehonense (Merriam), 1916; H. forcei Richey, 1948.

Chronologic and geographic distribution in North America. Late
Barstovian through early Hemphillian in the Gulf Coastal Plain;
Clarendonian through early Hemphillian in the Great Plains;
Clarendonian of the West Coast.

263
Diagnosis. Small to medium-sized hipparionine with relatively
deep nasal notch. Moderately deep DPOF located well forward of
orbit, usually anterior to lacrimal; poorly defined anteriorly, well
defined posteriorly with continuous rim and variably developed
pocket. Cheekteeth moderately complex for a hipparionine; protocone
often connects relatively early in ontogeny; hypoconal groove open to
near base of crown. Protostylid moderate to poorly developed, weaker
than in Cormohipparion. [Modified after MacFadden, 1980.]

Discussion. North American Hipparion sensu MacFadden (1980;
1984a) consists of three species, making it the least diverse group
of hipparionines on the continent. Their cheektooth morphology is
not very distinctive for hipparionines, but the facial and cranial
morphology suggests phylogenetic alliance with Old World Hipparion
s.s. Bernor and Hussain (1985) argued that this is a product of
parallelism. However, in this study, I continue to follow the
hypothesis of MacFadden (1980) that the resemblance is not
coincidental.

Hipparion shirleyi MacFadden, 1984

Type specimen. F:AM 73950, a nearly complete female individual
consisting of the skull, mandibles and post-cranial elements.

Type locality. Wright Farm, Polk County, Texas.

Stratigraphic occurrence and age of type locality. Fleming
Formation, Cold Spring Fauna; late Barstovian, about 13 ma.

Distribution. Known only from the Cold Spring Fauna of the Texas
Gulf Coastal Plain.

264

Referred specimens. In addition to those listed by MacFadden
(1984a) from the Wright Farm and McMurry Pit sites, the following
specimens from Cold Spring Fauna sites appear to be referable to H^.
shirleyi. Noble Farm l.f.. Grimes Co., TX: TAMU 3035 R M12; 3036 R
p2; 3037 L dp34. Goodrich l.f., Polk Co., TX: TMM 31183-11 L
maxilla with P4-M1; -22 L mandible with p3-m3. Cold Spring l.f., San
Jacinto Co., TX: TAMU 3031 L maxilla with M1-M2; TMM 31219-145 L
maxilla with DP1-P4; -67, -133 2 R P2; -342, -388 2 L P2; -24, -343,
-345, TAMU 3033 4 R P34; TMM 31219-346, -347 2 L P34; -350-353 4 R
M12; -28, -243, -354, -355 4 L M12; -356, -357, TAMU 3032 3 R M3; TMM
31219-176, -358-362 6 L M3; -363, -364 2 R p34; -365 L p34; -9, -366,
-367 3 R ml2; -32, -368 2 L ml2; -82, -369, -370 3 R m3; -371 R
mandible with p3-m3.

Diagnosis. Small, low crowned species of Hipparion, with toothrow
lengths of about 100-105 mm, and unworn molar crown heights of 30-35
mm. Protocone oval or elongate-oval with large spur; deep hypoconal
groove; hypocone elongate, with constricted connection to metaloph;
fossettes moderately complex; pli hypostyle deep and usually directed
labially, not anteriorly.

Description and discussion. Forsten (1975) described as the most
common equid species in the Cold Spring Fauna a sample she called
"Merychippus sp. nr. Hipparion." My examination of this material
indicates that she included at least two and probably three species
in this taxon. A portion are clearly referable to H_. shirleyi
MacFadden, based on their small size, distinctive fossette
morphology, deep premolar ectoflexids, and relatively poorly expanded
metaconids and metastylids. In most uppers, the pli hypostyle does

265

not project anteriorly in the postfossette (as is typical in advanced
equids), but instead deeply penetrates the fossette labial ly (see
MacFadden, 1984a, Figs. 28 and 31). This appears to be the primitive
hipparionine condition, and it is also found in "Cor mo hi ppar ion"
goorisi and "Merychippus insignis" (MacFadden, 1984a; Skinner and
Taylor, 1967). Neither of the two partial skulls described by
Forsten (1975, p. 39) are referable to H. shirleyi. TMM 31219-224
has a very shal lowly retracted nasal notch and a shallow, indistinct
DPOF. Its dentition is worn beyond generic or specific recognition.
TMM 31219-189 has less worn teeth, but only the ventral part of the
face is preserved. It does not have the fossette pattern typical of
H^. shirleyi. The generic affinities of these two specimens are
unclear. A third hipparionine in the fauna, represented by slightly
larger and on average more complex cheekteeth than H^. shirleyi,
belongs in either Cormohipparion or Nannippus.

Hipparion tehonense (Merriam), 1916

Neohipparion gratum tehonense MERRIAM. 1916, p. 119.

Hipparion gratum tehonense (Merriam), OSBORN, 1918, p. 189.

Nannippus tehonensis (Merriam). STIRTON, 1939, p. 347; STIRTON,

1940, p. 186; QUINN, 1955, p. 73; WEBB, 1969a, p. 130.

Nannippus cf. N^. ingenuum (Leidy), FORSTEN, 1975, p. 61 (in

part).

Hipparion tehonense (Merriam), MACFADDEN, 1980, p. 623.

266

Type specimen. UCMP 21780, R M12.

Type locality. Exact locality unknown. South Tejon Hills,
southern end of San Joaquin Valley, California.

Statigraphic occurrence and age of type locality. Chanac
Formation; early Clarendonian, about 11 ma.

Distribution. Clarendonian of California, Great Basin, Great
Plains, and Texas Gulf Coastal Plain. Possibly Clarendonian and
early Hemphillian of Florida (see below).

Referred Texas Gulf Coastal Plain specimens. Lapara Creek Fauna.
Buckner Ranch Site, Bee Co., TX: TMM 30896-537 assoc. R P4,M3 & I
M1-M3. Farish Ranch Site, Bee Co., TX: TMM 31081-162 R maxilla with
DP3-DP4,M1; -705, -1440, -1482 3 L P2; -822, -1397B 2 R P34; -1033,
-1159A 2 L P34; -823, -952, -1463, -1240, -1375A, -1397A 6 R M12;
-50, -341B, -1375B, -1397C, -1421C 5 L M12; -627, -1222 2 R M3;
-168A, -862, -917 3 R dp34; -168 assoc. R p3-ml; -1072 R p2; -397 L
p2; -95 R p34; -643, -1071 2 L p34; -1117 R ml2. Medio Creek, Site
No. 19, Bee Co., TX: TMM 31170-92A, -90G, 2 R P34; -90F L P34; -90E,
-92E, -92H 3 R M12; -92M, -920, -90A, -lllC 4 L M12; -92G, -92F 2 L
M3; -49 R mandible with dp2-dp4. Bridge Estate Site, Bee Co., TX:
TMM 31132-22A,C assoc. L M1-M2; -307B, -94A 2 R P2; -169 L P2; -22B L
P34; -440A, -440B 2 L M12; -266A R p2; -386 L dp2; -287B L p34; -192
L ml2. Of the specimens Forsten (1975) referred to Nannippus cf.
Nan, ingenuum, these are confidently referred to H^. tehonense.
Others are referred instead to Nannippus cf. Nan, fricki, while the
remainder are indeterminant.

Diagnosis. Medium-sized hipparionine with toothrow lengths
between 110 and 130 mm. OPOF well developed posteriorly, poorly

267

defined anteriorly, located well anterior of the orbit. Nasal notch
usually retracted dorsal to P2. Estimated unworn M12 MSCH about 45
mm. Differs from _H. forcei in smaller size, and more poorly
developed P2 anterostyle. Isthmus plications rare; ectoflexids
generally deep. [Modified after MacFadden, 1984a.]

Description and discussion. MacFadden (1980; 1984a) described the
cranial and dental morphology of this medium-sized hipparionine, and
discussed its systematic relationships. Forsten (1975) described the
Lapara Creek sample of H^. tehonense as Nannippus cf. Nan, ingenuum,
but noted its resemblance to "Nan." te hone sis (p. 64). Comparisons
of the populations of H. tehonense from Tejon Hills, California, the
Clarendon Fauna of northern Texas, and the Lapara Creek Fauna
indicate close resemblances in size (Table 27) and enamel morphology.
In particular, the Lapara Creek sample has rounded to oval protocones
that connect to the protoselene at about the start of the late wear-
stage, and that have well developed spurs in early wear-stages. Pli
cabal 1 ins are well developed but rarely complex. Fossettes are
moderately complex, with nonbifurcating plications. Lower cheekteeth
have deep ectoflexids and few isthmus plications. These all suggest
referral to H^. tehonense.

Hipparion sp., cf. H. tehonense (Merriam), 1916

Referred specimens.— Hookers Prairie Mine, Polk Co, FL: UF 93203
R p34.

Love Site: UF 53405 R P34; 53375, 62165 2 L P34; 32108, 32125,
32170 3 L mandibles; 96526 R p34; 64917, 64918 2 R ml2; 96527 L m3.

268

Table 27. Standard univariate statistics for upper cheekteeth of
Hipparion from Texas and California. Populations are TJH, _H.
tenonense" from the Tejon Hills, San Joaquin Valley, California
(topotypic sample); CLAR, H. tehonense from the Clarendon Fauna,
Donley County. Texas; and BHR. H. forcei from the Black Hawk Ranch
l.f.. Contra Costa County, CaliTornia (topotypic sample). Format as
in Table 2.

FAUNA

TJH

CLAR
P2

BHR

APL

22.3,0.14,2
22.2-22.4,0.63

24.9,1.20,14
22.9-27.0,4.80

29.5,2.23.5
26.2-32.2,7.55

BAPL

20.8,1.04,4
19.3-21.6,5.01

23.0,1.22,5
22.1-25.1.5.30

TRW

18.3,0.42,2
18.0-18.6,2.32

19.0,1.25.14
17.1-21.3.6.59

19.7,0.99,6
18.7-21.1,5.03

PRL

6.2,0.21,2
6.0-6.3,3.45

5.6,0.50,14
5.0-6.8,8.83

5.8,0.35,6
5.2-6.2,6.10

PRW

4.2,0.14,2
4.1-4.3,3.37

4.0,0.39,14
3.5-4.7,9.71

P34

4.1,0.53,6
3.2-4.7,12.86

APL

19.1,0.74.5
18.1-19.9.3.89

20.7,1.06,27
18.5-23.2,5.11

22.7,1.82,11
19.7-25.5,8.03

BAPL

17.1,0.97,6
15.3-18.1,5.70

19.0,0.05,7
17.2-20.5,5.52

TRW

19.0,0.85.5
17.9-19.9,4.45

21.2,1.39,27
17.9-24.1,6.55

21.6,1.23.11
20.5-23.9.5.68

PRL

6.7,0.37,5
6.4-7.3,5.54

6.7,0.69,27
5.5-8.0,10.31

6.4.0.45.11
5.7-7.1.7.07

PRW

3.8,0.17,5
3.7-4.1,4.36

3.7,0.26,27
3.4-4.3,7.04

4.1.0.27.11
3.5-4.6.6.55

269

Table 27 — continued

M12

APL

18.6,2.27,8
16.2-22.4,12.22

19.3,1.40,32
16.8-22.3.7.25

21.6,1.92,5
19.7-24.6.8.87

BAPL

16.0, — ,1

15.4,1.31.9
14.0-17.1,8.47

17.7.0.74.5
16.9-18.8,4.18

TRW

17.9,0.95,8
16.5-19.5,5.32

19.2,0.99,32
17.7-21.7,5.13

20.1,0.95,6
18.9-21.7,4.72

PRL

6.2,0.37,8
5.8-6.9,6.00

6.4,0.85,32
4.9-7.9,13.21

6.3.0.52.5
5.8-7.0,8.27

PRW

3.6,0.28,8
3.1-3.9,7.66

3.4,0.25,31
3.0-4.1,7.23

3.9,0.41,6
3.5-4.6,6.55

270

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Figure 42. Hipparion sp., cf. H. tehonense from Florida. A. UF
93203, R p34. Hookers Prairie MTne (?early Clarendonian), Polk
County. B-E. Withlacoochee River Site 4A (late early Hemphillian),
Marion-Citrus county line, Florida. B. UF 17205, left maxilla in
lateral view. C. UF 17205, occlusal view of L P2-M1 and assoc. R
(reversed) M2-M3. D. UF 21027, occlusal view of L p2-m3. E. UF
21027, lateral view of L mandible. UF 17205 and 21027 probably
represent a single individual.

272

273

Moss Acres Racetrack Site: UF 95388 L nil2; 95396 R M3.

With 4A: UF 17205 assoc. L maxilla with P2-M1 and R P2-M3; 53414
assoc. L P3-P4; 53517 R P2; 17198 L P2; 53510, 53515 2 R M12; 17201,
19620 2 L M12; 17203, 53511 2 R M3; 19621, 53513 2 L M3; 17300 assoc.
R and L mandibles with p2-m3; 20868 L mandible with p2-m3; 21027 L
mandible with p2-m3 (probably same individual as UF 17205); 17305 R
p2; 53464, 53484-53486 4 R p34; 53483 L p34; 53470-53472, 53474 4 R
ml2; 53466-53469 4 L ml2; 53475 R m3.

Description and discussion. UF 93203 (Fig. 42A) is referred to
Hipparion rather than Cormohipparion based on its poorly developed
protostylid, lack of isthmus or paralophid plications and pli
caballinid, and moderate size. Its size (Table 28) is within the OR
for H. tehonense lower premolars, and it closely resembles referred
specimens of that taxon (e.g. MacFadden, 1984a, Figs. 38-39). UF
93203 was recovered from mining spoil piles, and thus its original
stratigraphic position is unknown. Terrestrial vertebrates older
than late Hemphillian are relatively common in phosphatic sediments
being processed in the region of the Hookers Prairie Mine and
adjacent mines, including the early Clarendonian Gray Zone fauna from
the Phosphoria Mine. This is the most likely source for UF 93203.
If this specimen has been correctly identified, the absence of
Hipparion from deposits in the Phosphoria Mine, that have produced
about 75 early Clarendonian equid teeth, is puzzling.

The With 4A sample is referred to Hipparion based on the presence
of a moderately deep DPOF (Fig. 42B); upper cheekteeth with rounded
to slightly oval protocones with anterior spurs in early wear-stages

274
and that connect to the protoselene relatively early in ontogeny,
fossettes with relatively simple and shallow plications, relatively
poorly developed pli caballins (especially on molars), hypoconal
grooves open to the base of the crown, and broad, unconstricted
connections of the hypocone and the metaloph (Fig. 42C) ; and lower
cheekteeth with relatively deep ectoflexids, poorly developed
protostylids, and weak plications (Fig. 42D). This combination of
dental and facial characters excludes the population from all
hipparionine genera except Hipparion.

When compared to the two recognized advanced species of Hipparion,
H^. tehonense and H^. forcei (MacFadden, 1984a), the With 4A sample
compares more favorably in size with H.- tehonense (Tables 27, 28).
On average, H. forcei , is about 15% larger than H. tehonense,
including the early Hemphillian populations referred to by MacFadden
(1984a). The With 4A sample also compares favorably with H.
tehonense in the location and depth of the DPOF, and in many dental
features. For example, the anterostyle of the P2 is poorly developed
and not well separated from the rest of the tooth (Fig. 42C). The
major differences are that the With 4A sample is slightly smaller,
lacks retention of the DPI with the permanent dentition, has on
average more complex and persistent fossette plications, has slightly
higher unworn crown heights (by about 5 to 7 mm), and, on average,
better developed plications on the lower cheekteeth. These are not
considered sufficient to designate a new species. Rather, they are
trends typically observed in evolving equid chronospecies. Early
Hemphillian H. forcei from Nebraska shows several of the same
differences when compared with Clarendonian populations from

275
California, and the magnitude of change is comparable to that in
other species with long chronologic ranges (e.g. Cor, occidentale) .
Therefore, the With 4A sample is tentatively referred to H^.
tehonense.

The lower molar from Moss Acres is very similar to slightly worn
molars from With 4A, especially the m2 of UF 20868. The protostylid
is weak and the metaconid-metastylid complex is poorly expanded, much
less so than in contemporary populations of Cormohipparion.
Therefore, it too is referred to Hipparion sp., cf. H^. tehonense.

A limited sample of mandibles and isolated teeth from the Love
Site is also tentatively referred to H^. tehonense. Observed
differences with the more common and similarly sized Cor, ingenuum
are much simpler fossettes, shorter protocones, weaker protostylids,
fewer and less persistent isthmus plications, and a shorter diastema.

These records greatly extend the known geographic range of
Hipparion in North America. The With 4A and Moss Acres populations
are significantly younger than others with H^. tehonense (MacFadden,
1984a, Table 12). If correctly indentified from these two sites, H.
tehonense would become one of only a few equid species known to have
ranged entirely across North America.

276
Tribe Equini Quinn, 1955

Equini QUINN, 1955, p. 43 (in part).
Calippini QUINN, 1955, p. 27 (in part).
Protohippini QUINN, 1955, p. 13 (in part).

Type genus. Equus Linnaeus, 1758.

Included subtribes. Protohippina Quinn, 1955 new rank; Equina new
subtribe.

Revised diagnosis. Advanced tridactyl or monodactyl equids with
well cemented, subhypsodont or hypsodont cheekteeth and well formed
fossettes. Differ from hipparionines by have more poorly separated
metaconids and metastylids on the lower cheekteeth (Equus and some
other progressive species of equines independently acquire this trait
in the late Miocene); lower molars have the metaconid placed notably
more linguad than the metastylid; protocone usually connected to the
protoselene in moderate and early wear-stages; fossette plications
relatively simple, or absent altogether (except advanced Equus which
can have complex fossettes).

Discussion. The earliest recognized member of the Equini is
"Merychippus" carrizoensis, which is well known from the late Heming-
fordian of California (Dougherty, 1940; Munthe, 1979; Quinn, 1984).
Thus the tribe's first appearance in the fossil record coincides with
that of its sister-taxon, the Hipparionini . Two monophyletic
subtribes comprise the Equini, the Protohippina and the Equina.

277

Subtn'be Protohippina Quinn, 1955 new rank

Protohippim" QUINN, 1955, p. 13 (in part).
Calippini QUINN, 1955, p. 27 (in part).

Type genus. Protohippus Leidy, 1958.

Included genus. Calippus Matthew and Stirton, 1930.

Revised diagnosis. Advanced nonhipparionine equids that differ
from equine genera by their relatively short diastemae and relatively
broad muzzles. Ectoflexid depth of the lower premolars shallow.
Malar fossa absent; DPOF depth shallow. Lateral digits with no
tendency towards reduction.

Discussion. Protohippus and Calippus are hypothesized to form a
monophyletic group based on the common possession of shortened
diastemae and broad muzzles. They both have more elongated
protocones and metaconid-metastylid complexes than primitive equines,
but these were independently acquired in many equid lineages through
the Miocene. Protohippus and Calippus are both restricted to faunas
east of the continental divide, but species of each range widely
through the Great Plains to the Gulf Coastal Plain. Protohippine
diversity was at a maximum during the Clarendonian, and both genera
went extinct at the end of the early Hemphillian.

Genus Calippus Matthew and Stirton, 1930

Protohippus (Calippus) MATTHEW and STIRTON, 1930, p. 354.
Call i pus Matthew and Stirton, STIRTON, 1940, p. 188.

278

Type species. Cal. (Calippus) placidus (Leidy), 1858.

Included subgenera. Cal. (Calippus) Matthew and Stirton, 1930;
Cal. (Grammohippus) n. subgen.

Revised diagnosis. Very small to medium-sized, tri dactyl equids,
with toothrow lengths less than 140 mm; DPOF long, relatively
shallow, not pocketed; or absent; MF absent; muzzle region greatly
expanded (width 452 or greater than UTRL), with relatively large
I12/il2; first and second incisors positioned in a straight row of
four teeth, with the I3/i3 angled sharply posteriorly; postcanine
diastema relatively short. Cheekteeth moderate to extremely
hypsodont. Upper cheekteeth with elongate or oval protocones broadly
connected to protoselene (very rarely isolated in early wear); simple
fossettes with plications absent or limited to early wear-stages;
single, unbranched pli caballins that fade with wear and are
typically much stronger on premolars than molars. Lower cheekteeth
typically with relatively nonpersistent lingual flexids; shallow
premolar ectoflexids; lacking plications (except for pli entoflexids
in early wear-stages) including pli cabal linids. Deciduous lower
premolars lack ectostylids.

Chronologic and geographic distribution. Early late Barstovian
through late early Hemphill ian (about 14.5 to 6.0 ma), although most
abundant and diverse during the Clarendonian. Widespread in North
America east of the Rocky Mountains, ranging from Florida to Texas,

279
north through the Great Plains to South Dakota, and south to
Honduras.

Discussion. The genus Calippus is here recognized by its unique,
highly derived muzzle morphology (Fig. 43, see also Fig. 49), which
along with other cranial and dental characters distinguish it from
all other equid genera. The failure of prior studies (e.g. Stir ton,
1940) to recognize this can be attributed to the rarity of complete
specimens, i.e. associated premaxillae and maxillae, or mandibles
with symphyses. Only the Frick Collection contains a sufficient
number of relatively complete crania of most of the species of
Calippus to allow recognition of the systematic importance of the
anterior skull region.

Two monophyletic species-groups of Calippus are recognized; the
smaller-sized taxa that traditionally comprise the genus, and a
number of medium-sized species classically referred to Astrohippus or
Pliohippus. Both groups lack malar fossae, a derived feature present
in Pliohippus (MacFadden, 1984b, pp. 275-277), Astrohippus (Matthew
and Stir ton, 1930, p. 361; MacFadden, 1984b, p. 277), and primitive
equines like "Merychippus" stylodontus (Quinn, 1984). These taxa
have normal (i.e. primitive) equid diastema lengths, incisor
morphologies, and muzzle widths relative to their body size (Fig.
43). The two species groups of Calippus are here formally recognized
as subgenera, Cal. (Calippus) and Cal . (Grammohippus) new subgenus.

Figure 43. Relationship between upper toothrow length and muzzle
width for various equid species. A-0 are taxa judged to have normal
(i.e. unexpanded) muzzles and are plotted to indicate baseline values
for muzzle width relative to body size (here represented by toothrow
length). A, Mesohippus barbouri; B, "Merychippus" primus; C,
Merychippus insignis; D. Cormohipparion sphenodus; E, Cor, occi-
dentale;T7 "Merychippus" republicanus; G, Neohipparion affine; H ,
Pseudhipparion retrusum; I, Pseud, gratum; J, "Merychippus" isonesus;
K, Pliohippus mirabilis; L, Plio. permx; M, Dinohippus leidyanus; N,
D. interpolatus; 0. Equus grevyi. The least squares regression line
Titted to these 15 points has an equation of y = 0.362x + 0.457, with
a correlation coefficient of 0.967. The remaining eight points (1-8)
are of taxa with relatively expanded muzzles: 1, Protohippus
perditus; 2, Protohippus supremus; 3, Calippus (Grammohippus)
martini ; 4, Cal. (G.) maccartyi (muzzle width estimated from
mandibular symphysTs); 5, CaTT~(G.) sp. from the Hemphillian of the
Great Plains; 6, Cal . (Cal.) pro"placidus; 7, Cal . (Cal .) placidus;
and 8, Cal . (Cal.) regulus. Of these, the most primitive is Pro.
perditus whose muzzle width falls within the observed range of normal
equids. However, it is relatively expanded when compared to contem-
porary equines such as Pliohippus mirabilis (K). All points are mean
values for each species, taken on mature (but not extremely heavily
worn) individuals, and when available on equal numbers of each sex.
Muzzle width measured across I3s, toothrow length from P2 to M3.

281

70 -

E

60

B

X

50

D

^

U

40

J

N

N

D

30

S

20-

O y

^

' HC" ^
/ F

T 1 1 1 1 1 1 1 \ 1 1 1 r

70 90 110 130 150 170

P2-M3 LENGTH (mm)

282

Subgenus Calippus Matthew and Stirton, 1930

Type species. Calippus (Cal.) placidus (Leidy), 1858.

Included species. Cal. (Cal.) proplacidus (Osborn), 1918, n.
coiTfc.; CaT_. (Ca]_.) regulus Johnston, 1937; CaT_. ( CaT_. ) elachistus n.
sp.

Revised diagnosis. Relatively very small, hypsodont equids with
UTRL and Itrl less than 105 mm. Elongated, elliptical protocones
that connect immediately to the protoselene at onset of wear. Pli
caballin single, relatively small or absent; absent or only present
in very early wear-stages of molars; usually present through middle
wear-stages of premolars. Upper cheekteeth relatively straight, with
reduced styles. Hypoconal groove shallow, closed by a hypostylar
fold in early or middle wear-stages; lost or persists as an isolated
fossette in advanced wear-stages. Protostylids present on p3-m3 and
dp3-dp4. Muzzle width relatively very broad, exceeds 50% of UTRL.

Discussion. Cal. (Calippus) includes all species traditionally
placed in Calippus (e.g. Stirton, 1940; Quinn, 1955; Webb, 1969a).
They are among the smallest of advanced, hypsodont equids; being
matched in size only by some species of Pseudhipparion (Webb and
Hulbert, 1986) and smaller individuals of Nan, minor. The phylogeny
of this group is therefore of interest, as decreases in body size are
uncommon among equid lineages (Romer, 1949; MacFadden, 1987). In
addition to size, members of Cal. (Calippus) generally differ from
those of Cal. (Grammohippus) n. subgen. in their straighter upper
cheekteeth, generally simpler fossettes, pli caballins and styles.

283
and the presence of well developed protostylids on lower cheekteeth
(except p2).

Cal, (Calippus) proplacidus (Osborn) 1918, new combination

Protohippus proplacidus OSBORN, 1918, pp. 139-141 (in part).

Merychippus francisi HAY. 1924, p. 9; STIRTON, 1940, p. 181;

HESSE, 1943, pp. 168-169, 171.

Merychippus proplacidus (Osborn), STIRTON, 1940, p. 182;

GALBREATH, 1953, p. 105.

Calippus francisi (Hay), QUINN, 1955, pp. 27-30; WEBB, 1969a, p.

82; FORSTEN, 1975, pp. 41-44.

Type specimen. AMNH 9115B, palate with L DP1-DP2 and R DP1-DP4,
Ml (unerupted) and associated L and R rami with dp2-dp4 (Osborn,
1918, Fig. 112).

Type locality. Sand Canyon Fauna, Logan Co., Colorado.

Strati graphic occurrence and age of type locality. Upper Pawnee
Creek Formation; late Barstovian, about 12 to 13 ma.

Topotypic sample. AMNH 9038, dp3 (one of three paratypes listed
by Osborn, 1918, p. 140).

Revised distribution. Late Barstovian of northeastern Colorado,
Nebraska, and the Gulf Coastal Plain of Texas and Florida.

Referred specimens. Devils Gulch Horse Quarry, Brown Co., NB
(Skinner and Johnson, 1984, p. 282): F:AM 60443, 60439. 60437 3
skulls; 60438 assoc. skull and mandible; 60442, 60444, 60445, 60446 4
maxillae; 114088 assoc. R and L mandibles with deciduous dentition.

284

Cold Spring Fauna. Noble Farm l.f.. Grimes Co., TX: TAMU 3013 R
DP34; 3014-3015 2 L P34; 2390 (holotype, Cal. francisi). 3016-3017 3
L M12; 3018 L M3. Cold Spring l.f., San Jacinto Co., TX: TMM
31219-143. -165 2 R P2; -307, -308 2 R P34; -309-313 5 L P34; -25,
-314-318 6 R M12; -53, -67, -91. -319-323 8 L M12; -324, -325 2 L M3;
-286 R mandible with ml-m3; -240 L mandible with p4-m3; -10 L
mandible with p3,dp4.ml; -110 assoc. R m2-m3; TAMU 3005 R dp2; TMM
31219-290. -291 2 R p2; -283. -292-294 4 L p2; -202, -296 2 R p34;
-52, -295, TAMU 3004 3 L p34; TMM 31219-11, -63, -95, -297-299 6 R
ml2; -122, -162, -300-302 5 L ml2; -114, -196, -305, -306 4 R m3;
-106, -303, -304 3 L m3. Sam Houston l.f., San Jacinto Co., TX: TMM
31191-12, -29 2 L M12. Goodrich l.f., Polk Co., TX: TMM 31183-63
and -49 assoc. palate with R and L DP1-M3 and R mandible with p2-m3.
Chapel Hill Site, Washington Co., TX: TMM 31272-35 R M12.

Agricola Fauna, Bone Valley Region. Red Zone, Phosphoria Mine:
UF 28442, 28443. 28467. 28469-28471, 28474 2 deciduous and 5
permanent upper cheekteeth; 28452 L ml2. TRO locality F7201,
Kingsford Mine: UF 55938 L P34.

Ashville Site: UF/FGS V-6101, -6125 2 L P34; -6064 R M12; -6117 L
M12; -6061 L ml2.

Revised diagnosis. Small equid with toothrow lengths of about 95
to 102 mm and unworn molar crown heights about 40 mm. Larger than
Cal. regulus or Cal . elachistus, and with better developed styles and
fossette plications. Less hypsodont, shallower linguaflexids, and
less elongated metaconids and metastylids than Cal . placidus.

285
Description. Calippus proplacidus has many distinctive characters
that it shares with other members of the subgenus, including
relatively small size (Figs. 44, 46, 47; Tables 29-31). weak pli
caballin, simple fossettes, lack of a MF, protostylids on lower
cheekteeth, and ectostylids absent on dp2-dp4. The maximum length of
the unworn DPI of AMNH 9115B is 8.0 mm. Three specimens from the
Devil's Gulch Horse Quarry have DPI lengths of 8.1, 8.2 and 9.0 mm
(F:AM 60439, 60443 and 60442, respectively), and a Cold Spring
specimen (TMM 31183-63) has a DPI length of 8.8 mm. The lower
toothrow length (dp2-dp4) of the holotype is 59.8 mm. F:AM 114088,
from the Devil's Gulch Horse Quarry, that is in the same very early
wear-stage as AMNH 9115B, has a length of 59.1 mm. Toothrow lengths
of juvenile rami of Cal. regulus are smaller; F:AM 114178 and F:AM
60428 from MacAdams Quarry, Clarendon Fauna, measure 52.3 and 52.9
mm, and F:AM 60495 and F:AM 60496, from Lucht Quarry, Surge Fauna,
55.9 and 56.1 mm.

The series of skulls from the Devil's Gulch Horse Quarry allows
description of the facial morphology of Cal. proplacidus. The DPOF
is usually large and shallow, with a moderate posterior rim. The
fossa blends into the surrounding facial region anteriorly and
ventrally. The preorbital bar is relatively narrow. The ventral
portion of the face lacks a MF. F:AM 60437 has a shallower DPOF
located more anteriorly than other mentiers of the population, but is
similar in size and dental morphology.

The cheekteeth of Cal. proplacidus (Tables 29-31; Fig. 44) were
previously described by Quinn (1955) and Forsten (1975, pp. 42-43)

286

Table 29. Standard univariate statistics for upper cheekteeth of
Calippus proplacidus from the Devil's Gulch Member, Valentine Form-
ation. Brown County Nebraska (late Barstovian) and from the Cold
Spring Fauna, Fleming Formation, San Jacinto and Grimes Counties,
Texas (late Barstovian), and for Cal . placidus from the Minnechaduza
Fauna, Ash Hollow Formation, Brown and Cherry Counties, Nebraska and
Todd County, South Dakota (Clarendonian) and from the Clarendon Fauna,
Donley County, Texas (middle Clarendonian). Format as in Table 2.

TAXON proplacidus proplacidus placidus placidus

FAUNA DEVIL'S GULCH COLD SPRING MINNECHADUZA CLARENDON

P2

APL 19.8,0.35,4 18.4,0.64,2 20.5,1.34,11 20.3,1.18,4

19.4-20.2,1.77 17.9-18.8,3.47 17.6-22.7,6.56 18.7-21.3,5.83

BAPL 15.8, ~ ,1 16.2,1.12,5

15.2-18.1,6.92

TRW 15.9,1.27,4 14.7,0.42,2 16.2,1.23.12 16.5,1.32,4

14.1-17.0,7.98 14.4-15.0,2.89 14.1-18.1,7.57 14.9-18.1,7.98

PRL 4.7,0.47.4 4.9,0.28,2 5.2,0.62,12 5.1,0.36,4

4.2-5.3,9.94 4.7-5.1,5.77 4.4-6.4,11.83 4.8-5.6,7.01

PRW 3.6,0.38,4 2.9,0.14,2 3.6,0.30,12 3.6,0.27,4

3.1-4.0,10.41 2.8-3.0,4.88 3.1-4.0,8.16 3.4-4.0.7.52

P34

APL 17.5,1.17,15 16.4,0.67,9 17.1,1.06,18 16.7,0.57,10

16.0-19.4,6.72 15.4-17.5,4.08 15.3-19.0,6.21 15.9-17.8,3.42

BAPL 14.3, — ,1 13.1,0.49,6 12.4,1.12,4

12.3-13.7,3.75 10.9-13.6,9.00

TRW 17.9,0.67,15 16.6,0.74,9 17.8,0.87,18 18.2,1.22,9

16.3-18.7,3.73 15.0-17.8,4.47 16.5-19.8,4.89 16.7-19.9,6.73

PRL 6.0,0.84,15 6.1,0.75,9 6.2,0.54,18 6.3.0.65.10

4.8-7.7.13.99 5.2-7.1.12.31 5.1-7.2,8.74 5.5-7.5,10.36

PRW 3.5.0.34,15 3.3,0.30,9 3.9,0.40,18 3.8,0.30,10

3.1-4.1,9.84 3.0-4.0,9.12 3.4-4.8,10.21 3.2-4.1,7.91

287

Table 29 — continued

M12

APL

16.3,1.13,14
14.9-18.6,6.90

16.1,1.08,14
14.8-18.2,6.67

16.5,1.08,17
14.9-18.3,6.56

15.8,1.02,10
13.8-17.1,6.45

BAPL

12.2,0.36,10
11.5-12.8,2.98

11.9,0.89,4
11.2-13.2,7.42

TRW

16.1,0.87,14
13.9-17.0,5.42

15.2,0.72,13
13.5-16.1,4.72

15.6,1.48,18
11.7-16.9,9.48

16.3,1.35,11
14.2-18.3,8.23

PRL

6.1,0.63,14
5.1-7.2,10.38

5.9,0.42,17
5.0-6.7,7.15

6.1,0.62,18
4.9-7.4,10.17

6.4,0.80,11
5.5-7.9,12.34

PRW

3.2,0.29,14
2.8-3.6,8.76

3.1,0.30,17
2.5-3.6,9.61

3.3,0.24,17
3.0-3.7,7.36

3.5,0.22,11
3.0-3.8,6.23

288

Table 30. Standard univariate statistics for lower cheekteeth of
Calippus proplacidus from the Devil's Gulch Member, Valentine
Formation, Brown County, Nebraska (late Barstovian) and from the Cold
Spring Fauna, Fleming Formation, Grimes and San Jacinto Counties,
Texas (late Barstovian), and for Cal. placidus from the Clarendon
Fauna, Donley County, Texas (middle Clarendoman). Format as in
Table 2.

SPECIES

proplacidus

proplacidus

placidus

FAUNA

DEVIL'S GULCH

COLD SPRING
P2

CLARENDON

apl

17.2,0.34,4
16.7-17.5,1.98

16.2,1.16,6
14.5-17.6,7.19

16.8,1.15,5
14.9-17.9,6.84

bapl

13.3,0.87,4
12.4-14.4,6.54

atw

7.3,0.17,4
7.1-7.5,2.39

6.2,0.29,6
5.7-6.5,4.72

7.3,0.54,5
6.5-7.8,7.36

ptw

9.5,0.34,5
9.1-10.0,3.57

8.4,0.33,5
8.0-8.6,3.93

9.1,0.66,5
8.0-9.6,7.28

mml

5.1,0.62,4
4.4-5.9,12.07

4.4,0.76,6
4.0-5.7,17.23

6.1,0.34,5
5.7-6.4,5.59

entl

6.8,0.96,5
5.3-7.8,13.97

5.6,0.78,6
4.8-6.7,13.97

p34

8.0,0.60,5
7.4-8.8.7.54

apl

17.3,1.31,12
15.7-19.6,7.56

16.7,0.45,7
16.1-17.3,2.71

17.4.0.90,9
15.4-18.8,5.20

bapl

13.9,0.50,4
13.3-14.5,3.61

atw

10.0,0.68,12
9.3-11.1,6.79

8.8,0.63,7
8.1-9.9,7.12

9.6,1.26,9
7.7-11.1.13.16

ptw

10.1,0.70,12
8.7-11.0,6.96

9.3,0.93,7
8.0-10.3,9.98

9.3.0.83.9
8.1-10,6.8.91

mml

8.6,0.68,12
7.6-9.7,7.91

7.8,0.45,7
7.1-8.5,5.71

8.7.0.39,9
8.0-9.2,4.47

entl

6.7,0.87,12
5.2-7.9,12.97

7.0,0.31.7
6.5-7.4,4.40

8.0,0.75,9
6.3-9.0,9.47

289

Table 30~continued

nil2

apl

16.7,1.53,14
14.7-19.9,9.16

16.2,1.43,10
14.3-18.4,8.79

16.7,1.34,10
14.7-18.7,8.03

bapl

12.6,0.61,7
11.5-13.3,4.81

atw

8.1,0.34,14
7.5-8.6,4.18

7.0,0.52,10
6.0-7.6,7.41

8.6.0.62,10
7.7-9.5,7.19

ptw

6.6,0.35,14
6.2-7.4,5.34

6.2,0.23,11
5.7-6.5,3.63

7.2,0.60,10
6.3-8.0,8.29

mm!

7.3,0.42,14

6.7,0.49,10

7.5,0.65,10

6.5-7.9,5.72

6.2-7.4,7.38

6.7-8.6,8.65

enti

4.2,1.16,14
2.2-6.4,27.42

4.0,0.73,11
2.8-4.8,18.24

6.8,1.33,10
4.1-8.2,19.40

290

31. Measurements of specimens of Calippus proplacidus from
horizons of the Bone Valley Formation, hoik county, Morida.

Table

lower

An "a" before a value indicates that it is an approximation from a

broken or waterworn specimen.

ToothSi

de

APL

TRW

PRL

UF 28469
UF 55938
UF 28442
UF 28471

P34
P34
M12
M12

R
L
R
R

15.0
14.6
15.4
15.4

14.9
13.9
14.8
12.9

4.9
4.6
5.8
5.6

apl

atw

ptw

UF 28452

ml2

L

16.0

6.9

6.4

PRW

3.1
3.4
3.1
3.1

mml

6.9

BAPL MSCH

10.8 32.4

10.5 a31

11.4 33.0

10.1 a33

entl
6.0

bapl

mcch
32.3

291

B

2cm

Figure 44. Occlusal views of cheekteeth of Cal . (Calippus) propla-
cidus from the Cold Spring Fauna, Texas (late Barstovian). A-B.
TIBFTe" Farm Site, Grimes County. A. TAMU 2390. L M12, holotype of
Cal. francisi (Hay). B. TAMU 3016, L M12. C-E. Cold Spring local
TaUna. San Jacinto County. C. TMM 31219-309, L P34. 0. TMM
31219-95, R ml2. E. TMM 31219-302, L ml2.

292

Figure 45, Occlusal views ftf ^ Cheekteeth. of Cal^, (Cajippuslfron]
lower horizons of the Bone Val ley Formation,-tVlk Ceuntjr, "Ion da.

A-B. Cal. proplacidus. Red Zone, Phosphoria Mine. A. UP 28469, R

P34. BT'UF 28442, R M12. C-F. Calippus sp. C. UF 61343, L p34,

Kingsford Mine. D. UF 28421, R P2, Red Zone, Phosphoria Mine. E. UF

28680, L M12, Gray Zone, Phosphoria Mine. F. UF 93201, R P34. Gray

Zone, Phosphoria Mine.

293

7-

E
E

X

H 6
CD
Z
LU

LU

Z

o
o
o

I-

o

cc

Q.

5-

4-

C.placidus

C. elachlstus

C. proplacidus

C, regulus

—[ —
10

— r—
12

9 10 11 12 13

BASAL CROWN LENGTH (mm)

— r-
14

Figure 46. Bivariate plot of basal crown length (BAPL) versus
protocone length (PRL) of combined samples of Mis and M2s for four
species of Cal . (Calippus). One standard deviation is plotted on
both sides o7~the mean value for the following populations: Cal .
proplacidus. Cold Spring Fauna; Cal. placidus, Minnechaduza Fauna;
Cal. reguTTTs, Clarendon Fauna; CaTT elachistus. Archer Fauna
(primarily the Love Site).

294

55-

50-

45-

LU

it

H

Z O
D DC 40
_ O

35-

C. placldus

C. regulus

C. elachistus

C. proplacldus

— 1 —
12

11 12 13 14 15 16 17

MOLAR ANTEROPOSTERIOR LENGTH (mm)

Figure 47. Bivariate plot of the occlusal anteroposterior length
(APL) of Mis and M2s versus the estimated unworn molar crown height
for the same four populations as in Figure 46. One standard
deviation is plotted to the right and left of the mean for APL,
while the unworn crown height is plotted plus and minus 2 mm to
estimate the observed range of variation of this character.

295

as Cal. francisi for the Cold Spring sample. Specimens from Florida
(Figs. 45A, 45B) and Nebraska generally conform to their
observations. However, Forsten (1975, p. 43) noted that her sample
included teeth with up to 14 fossette plications, about twice the
maximum I observed. Probably her sample was heterogeneous and
included specimens of the similarly sized, but more complex,
Hipparion shirleyi. Based on F:AM 60442, TMM 31183-63 and 31183-91,
unworn or slightly worn MSCHs of Cal . proplacidus are about 29 mm for
P2 and 35 to 40 mm for P3-M2. Cal. proplacidus is significantly much
larger in occlusal dimensions than Cal . regulus or Cal . elachistus,
but about the same size as Cal. placidus (Figs. 46, 47; Tables
29-30). Upper cheekteeth are characterized by relatively strong (for
the subgenus) styles, including small metastyles on some individuals
(Figs. 448, 44C, 45A, 45B). The protocone is usually connected to
the protoselene at the onset of wear, although very slightly worn
P34s may have isolated protocones with large spurs (e.g. UF 28443,
F:AM 60445). The long axis of the protocone is slightly
anterolabial-pcsterolingually orientated. The protocone occasionally
connects to the hypocone in well worn molars. As described by
Forsten (1975), the hypoconal groove is closed by a hypostylar fold,
generally in the upper quarter of the crown, but may remain as an
isolated lake until late wear before disappearing (Figs. 44A, 44B).
A few specimens (e.g. UF 28469) retain the primitive condition of an
open hypoconal groove until moderate to late wear-stages. Fossette
plications are relatively complex for a Calippus. with a single,
small pli protoloph (that rapidly disappears with wear) and a

296
somewhat more persistent single pli hypostyle. The internal fossette
margins usually have one or two shallow plications that disappear by
middle wear-stages.

Lower cheekteeth of Cal. proplacidus (Table 30) generally resemble
others of the subgenus. The lingual flexids, especially the
linguaflexid, are more poorly developed and less persistent than
those of Cal . placidus. but somewhat more advanced than those of Cal .
regulus (Figs. 44D, 44E; Quinn, 1955, Plate 4, Fig. 6). A strong pli
entoflexid is observed in early wear-stages. Protostylids appear on
the occlusal surface shortly after the onset of wear on the p3-m3.

Discussion. Osborn (1918) based "M . " proplacidus on a nearly
unworn, associated upper and lower juvenile dentition, and listed it
as a member of his Sand Canyon Fauna. Galbreath (1953) and Tedford
et al. (in press) have discussed the biostratigraphy of Miocene
deposits in northeastern Colorado. Tedford et al . (in press)
concluded that the Sand Canyon Fauna includes both the Vim-Peetz and
Kennesaw local faunas of Galbreath (1953), and that it dates from
about 13 to 12 ma. They list among its chronologic equivalents local
faunas in the Crookston Bridge and Devil's Gulch Members of the
Valentine Formation in Nebraska, and the Cold Spring Fauna of
southeastern Texas. As noted by Galbreath (1953), Stirton (1940, p.
182) proposed that Cal. proplacidus was a member of an older fauna in
the Pawnee Creek Formation. Referral of morphologic equivalents from
the Crookston Bridge Member (Webb, 1969a, p. 82), Devil's Gulch
Member and the Cold Spring Fauna to Cal . proplacidus would appear to
invalidate Stirton 's suggestion. Osborn (1918, p. 140) listed three

297
paratypes for "M . " prop1acidus> AMNH 9036, 9037 and 9038, and gave
their locality data as "...also probably from Sand Canyon...". Of
the three, only AMNH 9038 probably belongs with Cal. proplacidus. It
is an unworn dp34 of similar size (apl = 21.6 mm) and morphology as
the holotype (e.g. lacks an ectostylid, strong protostylid) . AMNH
9036 is a partial associated, heavily worn upper and lower dentition
that is referable to Pseudhipparion, cf. Pseud, retrusum, because
despite the late wear-stage the specimen retains traces of pli
caballins, the fossettes still bear some plications, and the
linguaflexids are still moderately deep. AMNH 9037, an assemblage of
seven associated right and left lower cheekteeth (plus incisors and
fragments), while referable to Calippus. is too snfiall to be included
in Cal. proplacidus, but resembles primitive, late Barstovian
representatives of Cal. regulus from the Burge Fauna in size and
morphology.

Merychippus francisi was described from an isolated upper molar
(TAMU 2390, Fig. 44A) by Hay (1924) and subsequently referred to
Calippus by Quinn (1955). The fauna from the type locality (Noble
Farm, Grimes Co., Texas) includes Gomphotherium (Hesse, 1943); thus
its age is no older than late Barstovian (Tedford et al., in press).
Other specimens referred and figured by Hay (1924) as M. francisi ,
including a P2 and a m3, probably do not represent the same species
as the type. Hesse (1943), Quinn (1955), and Forsten (1975)
described additional material of Cal . francisi from other sites in
the Cold Spring Fauna, including some relatively complete dentitions.
The Cold Spring population is morphologically indistinguishable from

29!
Great Plains samples of Cal . proplacidus. but on average slightly
smaller (Tables 29, 30). Thus, Cal. proplacidus must be regarded as
the senior synonym of Cal. francisi. Forsten (1975, pp. 41-42) also
referred a few isolated teeth from older (early late Barstovian)
sites in the Texas Gulf Coastal Plains sequence to Cal. proplacidus.
These are more primitive than referred Cold Spring or Devil's Gulch
specimens; e.g. a slightly worn Ml (TMM 40070-26) has a MSCH of only
32.4 mm. The older material is inadequate to document specific
identity with Cal. proplacidus, but is referable to Cal. (Calippus)
and indicates that the two subgenera of Calippus had diverged at
least by 14 ma.

Specimens from Florida referable to Cal. proplacidus (Figs. 45A,
45B; Table 31) have been collected in situ from the Red Zone of the
Agricola Fauna in the Phosphoria Mine. The dimensions of the Red
Zone specimens (Table 31) are similar to, or slightly smaller than,
those from the Cold Spring Fauna, but are otherwise indistinguish-
able. A few isolated teeth from the Ashville local fauna (01 sen,
1964) are also apparently referable to Cal. proplacidus. Although
poorly preserved, they appear to have better developed styles and are
larger than Cal. regulus.

Cal. (Calippus) placidus (Leidy). 1869

Protohippus placidus LEIDY. 1869. pp. 277-279 (in part); GIDLEY.
1906a, pp. 140-142 (in part); GIDLEY, 1907, p. 887 (in part);
OSBORN, 1918, pp. 133-136.

299
Protohippus (Calippus) placidus Leidy, MATTHEW and STIRTON,
1930, p. 354.

Calippus placidus (Leidy). STIRTON, 1940, p. 188; QUINN. 1955,
pp. 39-40; WEBB, 1969a, pp. 79-82 (in part).
Calippus optimus QUINN, 1955, pp. 35-38.
Astrohippus curtivallis QUINN, 1955, pp. 40-42 (in part).
Pliohippus (Astrohippus) martini (Hesse), GREEN, 1956, p. 161
(in part).
Calippus anatinus Quinn, WEBB, 1969a, p. 82 (in part).

Lectotype specimen. USNM 621, L P2 (Osborn, 1918, Fig. 106).
Selected from the type series by Gidley (1907).

Type locality. Exact locality unknown, collected from deposits
along "the Niobrara River" (Leidy, 1869, p. 277).

Stratigraphic occurrence and age of the type locality. Presumably
Minnechaduza Fauna (Ash Hollow Formation) of northern Nebraska (see
Webb, 1969a and below).

Distribution. Clarendonian (about 11.5 to 9.5 ma) of the northern
and southern Great Plains, and Texas Gulf Coastal Plain.

Referred Gulf Coastal Plain specimens. Lapara Creek Fauna.
Buckner Ranch Site, Bee Co., TX: TMM 30896-528, -530 assoc. palate
with R and L P2-M3 and R mandible with p3-m3 (type, Cal. optimus
Quinn); -200 assoc. R P4-M2; -187 DP2-M1; -479 R mandible with
dp2-ml; -419 assoc. R DP2-DP4. George West Site, Live Oak Co., TX:
TMM 30936-160 L P34; -353 L P34; -80 R P34. Bridge Estate Site, Bee
Co., TX: TMM 31132-105 assoc. L P3-M2; -617 R M12. Farish Ranch
Site, Bee Co., TX: TMM 31081-75 R P2; -1375 R M12; -1139 R M3.

300
Revised diagnosis. Small equid with toothrow lengths of about 95
to 105 mm; unworn M12 MSCH about 51 mm; DPOF long, oval and
relatively deep (for Calippus). Higher crowned teeth than Cal.
proplacidus. Larger than Cal. regulus and Cal. elachistus, with more
complex fossettes, deeper linguaflexids, and a larger, moderate-sized
DPI.

Description. Cal. placidus lacks a true MF, as do all members of
the genus, although a shallow depression on the malar bone is
occasionally observed. Incisor morphology is typical for the genus,
112 and il2 in straight rows across a broad, squared-off muzzle. The
width of the muzzle (measured across the I3s) is about 552 of the
UTRL (Fig. 43).

Upper cheekteeth of Cal. placidus (Table 29) have, in early
wear-stages, relatively large pli cabal! ins on the premolars, but
they are absent or small on the molars. Protocones are elongate, and
connected to the protoselene (Fig. 48). The hypoconal groove remains
open, or is present as an isolated lake through at least two-thirds
of the total crown height. Fossette plications are shallow and
primarily restricted to the posterior half of the prefossette (one to
three) and the anterior half of the postfossette (one or two). Older
individuals tend to lack all plications. Unworn MSCH is about 33 mm
for P2s, 47 mm for P34s and 51 mm for M12s. Deciduous premolars have
elongate, obliquely oriented protocones broadly connected to
protoselene; open hypoconal grooves until late wear; simple
fossettes; and small or absent pli caballins. The anterostyle of the
DP2 is not large and is broadly connected to the rest of the tooth.

301

&U

2cm

Figure 48. Occlusal views of upper cheekteeth of Ca1 . (Calippus)
placidus from the Lapara Creek Fauna, Bee County, Texas (early
Clarendonian). A. TMM 31081-75, R P2, Farish Ranch Site. B. TMM
31132-617, R M12, Bridge Estate Site.

302

Lower cheekteeth of Cal . placidus (Table 30) show notable
advancement from the primitive Calippus-grade, with relatively
elongated metaconids and metastylids, increased depth and persistence
of the lingual flexids, some flattening of the labial borders, and a
minor reduction in depth of the ectoflexid in slightly worn molars.
No enamel plications except the protostylid are present in moderately
worn teeth (pli entoflexid having disappeared). Lower deciduous
premolars (e.g. TMM 30896-479; Quinn, 1955, Plate 6.3) also have
moderately elongated, well separated metaconids and metastylids, and
lack ectostylids.

Discussion. Calippus placidus has had a very tortuous taxonomic
history, due in part to an inadequate lectotype and no knowledge as
to the stratigraphic horizon of the type series. Moderate to
heavily-worn teeth of Cal . placidus are not easily differentiated
from equally worn specimens of Pseud, gratum (Cope, 1892; Quinn,
1955; Webb, 1969a; Webb and Hulbert, 1986), a similar sized equid
with which Cal. placidus coexisted in the Clarendonian of Nebraska
and South Dakota. Leidy's (1869) type series of ten isolated teeth
includes specimens referable to both taxa (e.g. Leidy, 1869, Plate
18, Figs. 40, 43, and 44 are Cal_. placidus; Figs. 39, 41, 47 and 48
are Pseud, gratum), and others which are indeterminant. Leidy (1869,
p. 279) himself recognized that some of the specimens listed above
could represent Pseud, gratum. Gidley (1906a; 1907) attempted to
better characterize Cal. placidus by referring specimens to it froi
Big Springs Canyon, South Dakota as "neotypes." Unfortunately, as
noted by Webb (1969a), all of Gidley's material is referable to

)m

303
Pseudhipparion, not Calippus. When Matthew and Stirton (1930) named
Calippus, with Pro to. placidus as the subgenotypic species, they
referred to it as a Valentinian species. Quinn (1955), while
correctly recognizing its presence in the Clarendon and Lapara Creek
Faunas, also stated that Cal. placidus was from the Valentinian of
Nebraska. Webb (1969a), however, concluded that the type series was
not Valentinian, but Clarendonian (from his Minnechaduza Fauna), and
referred five specimens from the Ash Hollow Formation to Cal .
placidus. The evidence for this derives from the type series
including Pseud, gratum, an Ash Hollow Formation taxon, rather than
Pseud, retrusum, the corresponding Valentine Formation species (Webb,
1969a; Webb and Hulbert, 1986). I agree with Webb (1969a) that Cal.
placidus occurs in the Cap Rock and the lower part of the Merritt Dam
Members of the Ash Hollow Formation of Nebraska. There it is found
with Pseud, gratum. Cor. occidentale, Neo. affine, Hipparion
tehonense. Nan. fricki, Cal. martini. Pro, supremus and Plio. pernix;
a typical, diverse middle Clarendonian equid assemblage. Webb
(1969a, Fig. 20b) also referred specimens from the upper Merritt Dam
Member (Xmas-Kat Quarry Zone) to Cal. placidus. These specimens are
referable to Pseud, skinneri (Webb and Hulbert, 1986). The subgenus
Cal. (Calippus) is apparently absent from the Xmas-Kat Fauna, and all
younger faunas of the Great Plains.

Quinn (1955) recognized four small protohippine species in the
Lapara Creek Fauna: Cal. anatinus; Cal . optimus; Cal. cf. placidus;
and Astro hi ppus curtivallis. Webb (1969a) later referred all four to
a single taxon (Cal. anatinus). Following Forsten (1975), Cal.

304
anatinus is here recognized as a junior synonym of Cal_. regulus (see
below). She noted that the remaining three taxa are distinctly
larger than Cal. regulus, and suggested that they were referable to
Pseudhipparion. Webb and Hulbert (1986) concluded that the holotype
of A. curtivallis (TMM 30896-196) is indeed referable to
Pseudhipparion. and it thus became the type of the Lapara Creek
sample of Pseudhipparion (i.e. Pseud, curti vallum) . However,
specimens recognized by Quinn (1955) as Cal . optimus, Cal . cf.
placidus and the figured upper premolars of A. curtivallis are not
referable to Pseudhipparion, but to Cal. placidus (Fig. 48). The
numerous referred specimens now known from Nebraska indicate that the
cheekteeth of Cal. placidus do resemble those of hipparionines in
some features (e.g. its expanded metaconid-metastylid complex), thus
perpetuating the confusion between it and Pseudhipparion. The two
can be distinguished by the more rapidly connected protocone, the
greater tendency in worn teeth for lost pli cabal 1 ins and hypoconal
grooves, and simpler fossettes in Cal. placidus. Cranial ly, the two
are quite distinct, with Calippus having a much better developed
DPOF, shorter diastema, and widened, squared-off muzzle.

Cal. (Calippus) regulus Johnston, 1937

Protohippus proplacidus OSBORN, 1918, pp. 139-141 (in part).
Calippus sp., HESSE, 1936, p. 65.

305
Calippus regulus JOHNSTON, 1937, pp. 905-907; STIRTON, 1940, p.
188; QUINN, 1955, p. 27; WEBB, 1969a, p. 81; FORSTEN, 1975, pp.
44-48.
Calippus anatinus QUINN. 1955, pp. 30-35; WEBB, 1969a, p. 82 (in

part).

Type specimen. WT 878, R maxilla with P2-M3.

Type locality. Clarendon Fauna, Grant Lease Site, Donley Co.,
Texas (see Schultz, 1977, Fig. 6).

Strati graphic occurrence and age of type locality. Ogallala
Formation or Group; middle Clarendonian, about 10.5 ma.

Distribution. Late Barstovian of northern Great Plains; early and
middle Clarendonian of southern Great Plains; early Clarendonian of
Texas Gulf Coastal Plain.

Referred specimens. Pawnee Creek Formation, Logan Co., Colorado:
AMNH 9037 assoc. R p2,p34,ml-m3 & L ml-m2, and 5 incisors.

Burge Fauna, Brown Co., NB. June Quarry: F:AM 60441 palate with
L P2-M3 & R P3-M3; Quinn Mastodon Quarry: F:AM 60486 L M12. Lucht
Quarry: F:AM 60458A L P2; 60458B L M12; 60466 R M12; 60494 R
mandible with p3-m3; 60495, 60496 2 mandibles with dp2-dp4.

Clarendon Fauna, Donley Co., TX. MacAdams Quarry: F:AM 60414,
60416, 60430, 60467 skulls with adult dentitions; 60415 skull with R
& L DP2-M2; 60419, 60422, 60434, 60490, 4 R maxillae with P2-M3;
60423 R maxilla with P2-M2; 60417, 60418, 60469, 114174 4 L maxillae
with P2-M3; 114175 L maxilla with P2-M2; 60412 L maxilla with P3-M1;
60427 L maxilla with P3-M2; 60429 assoc. R maxilla with P2-M3, R
mandible with p3-m2, and L mandible with il,p2-m3; 114177 R mandible

306
with p3-m2; 114178 R mandible with dp2-dp4; 60433 L mandible with p2-
m3; 60432 L mandible with dp2-ml. The F:AM, PPM, UCMP, TMM and other
institutions have additional samples of Cal. regulus from the
Clarendon Fauna.

Lapara Creek Fauna. See Forsten (1975, pp. 44, 46).

Revised Diagnosis. Very small, hypsodont equid with toothrow
lengths generally between 75 and 85 mm; unworn M12 MSCH about 46 mm;
very short, broad rostrum; DPOF long, shallow, unrimmed and runs
anteriorly to connect with buccinator fossa. Cheektooth enamel
morphology more simple than Cal. placidus or Cal . proplacidus.
Metaconid of p2 very reduced or absent. Linguaflexid very shallow,
metaconid and metastylid broadly confluent on molars after slight
wear.

Description. The facial region of Cal. regulus is well preserved
on a few specimens from the type region (e.g. F:AM 60430, F:AM
60417). The DPOF is a long, narrow, shallow depression (Fig. 49); it
is shallower and less distinctly rimmed than in Cal. placidus. The
DPOF runs anterodor sally to the lOF to become confluent with the
buccinator fossa (Fig. 49). The two are separated only by a low
ridge dorsal and just anterior to the P2. The nasal notch is not
retracted further than the anterior portion of the P2. The post-
canine diastema is very short (about 27 mm. Fig. 49). The muzzle
(measured across the I3s) is relatively broader than in any other
known species of the subgenus, about 60% of the UTRL. In the
topotypic sample, the DPI is vestigial or absent in adults.

307
The cheekteeth of Cal. regulus are easily distinguished from Cal .
proplacidus and Cal. placidus both on the basis of smaller size
(Tables 32, 33) and morphology. Dental differences with Cal.
elachistus n. sp. are outlined below. As noted by Johnston (1937),
the upper cheekteeth have extremely simple fossettes, generally
lacking all plications, except in early wear-stages, when several
very shallow folds may be present. The pli caballin is usually
absent on molars, small or absent on premolars. The elongated
protocone becomes broadly connected with the protoselene after
relatively little wear; as noted by Forsten (1975) it is oriented
anterolabial-posterolingually on both molars and premolars, and does
not connect with the hypocone. The hypoconal groove closes to form a
lake and subsequently disappears with wear more rapidly than in Cal.
placidus. The styles are relatively very delicate, especially on
molars, and the metastyle is usually absent. Unworn or slightly worn
MSCHs are slightly less than in Cal. placidus, about 31 mm for P2s,
42 mm for P34s, and 46 mm for M12s. Upper deciduous premolars as
described by Quinn (1955, p. 31).

Lower cheekteeth of Cal. regulus (Table 33, Fig. 49D), as is
typical in Calippus, undergo drastic enamel morphology changes
through ontogeny. In early wear-stages, the metastylids are
relatively large and elongated, the linguaflexids moderately well
developed, the ectoflexids shallow, and one or two pli entoflexids
are generally present (these are better developed and more persistent
in premolars). The protostylid is small but distictive. With wear,
the metastylid shortens, the linguaflexid becomes very shallow

Figure 49. Cal . (Calippus) regulus from MacAdams Quarry, Donley
County, Texas (Clarendon Fauna). I. F:AM 60430, left lateral view of
skull. B. F:AM 114176, lateral view of left mandible and symphysis.
C. F:AM 60430, occlusal view of left P2-M3. D. F:AM 114176, occlusal
view of right and left il-13, c and left p2-m3.

309

0 2cm

310

Table 32. Standard univariate statistics for upper cheekteeth of
Calippus regulus from the Clarendon Fauna, Donley County Texas
(middle Clarendonian) and from the Lapara Creek Fauna, Bee and Live
Oak Counties, Texas (early Clarendonian), and of Calippus elachistus
n. sp. from the Archer Fauna, Alachua County, Florida (latest
Clarendonian - early Hemphillian). Format as in Table 2.

SPECIES

C. regulus

C. regulus

C. elachistus

FAUNA

CLARENDON

LAPARA CREEK
P2

ARCHER

APL

17.1,0.75,25
15.8-18.7,4.38

16.1,1.08,5
14.5-17.4,6.67

14.5,1.12,4
13.1-15.8,7.70

BAPL

14.6,0.83,9
12.9-15.7,5.72

14.1,0.85,5
12.8-14.8,6.00

10.9,0.36,4
10.1-11.5,6.73

TRW

13.1,0.52,25
12.2-14.3,4.00

12.6,0.59,5
11.9-13.5,4.70

13.1,0.36,4
12.7-13.7,2.77

PRL

3.9,0.44,25
3.3-4.8,11.19

3.8,0.37,5
3.2-4.1,9.70

3.9,0.47,4
3.4-4.5,11.88

PRW

3.2,0.33,25
2.6-3.9,10.37

3.1,0.30,5
2.9-3.6,9.45

P34

2.9,0.29,4
2.5-3.3,9.80

APL

14.7,0.99,44
12.6-16.7,6.58

13.3,0.39,6
12.8-13.8,2.91

13.4,0.31,6
13.0-13.8,2.28

BAPL

12.3,0.48,7
11.6-12.8,3.85

11.8,0.92,6
10.7-13.1,7.80

9.9,0.43,5
9.3-10.5,4.38

TRW

14.7,0.84,43
12.0-16.1,5.72

14.4,0.55,7
13.8-15.4,3.83

14.3,0.48,6
13.7-14.9,3.32

PRL

5.3,0.42,45
4.1-6.5,7.94

5.0,0.29,7
4.5-5.4,5.89

4.9,0.60,6
4.1-5.7,12.24

PRW

3.3,0.26,44
2.6-3.7,7.99

3.2,0.13,7
3.0-3.4,4.03

3.2,0.27.6
2.8-3.5,8.63

311

Table 32~continued

M12

APL

13.9,1.21,64
11.1-16.3,8.69

14.2,1.46,21
11.7-16.9,10.28

12.9,0.89,7
11.8-14.0,6.91

BAPL

10.9,0.48,26
9.9-11.8,4.40

10.9,0.42,21
9.8-11.8,3.88

9.1,0.30,7
8.7-9.5.3.33

TRW

13.6,0.88,64
10.6-15.5,6.44

12.8,0.65,22
11.3-14.1,5.06

12.2,0.89,8
11.1-13.9,7.28

PRL

5.5,0.42,64
4.6-6.3,7.61

5.2,0.40,22
4.2-5.8,7.62

4.9,0.61,6
3.9-5.6,12.58

PRW

3.1,0.28,64
2.4-3.7,9.18

2.9,0.29,22
2.5-3.4,10.28

2.7.0.21.6
2.4-2.9.7.83

312

Table 33. Standard univariate statistics for lower cheekteeth of
Calippus regulus from the Clarendon Fauna, Donley County, Texas
(middle Clarendonian) and from the Lapara Creek Fauna, Bee and Live
Oak Counties, Texas (early Clarendonian), and of Calippus elachistus
n. sp. from the Archer Fauna, Alachua and Polk Counties, Florida
(latest Clarendonian - early Hemphillian) . Format as in Table 2.

SPECIES

C. regulus

C. regulus

C. elachistus

FAUNA

CLARENDON

LAPARA CREEK
P2

ARCHER

apl

14.1,0.61,10
13.2-14.8,4.35

13.8,0.47,10
12.8-14.2,3.39

13.5,0.83,4
12.6-14.5,6.14

bapl

11.9,0.21,3
11.7-12.1,1.75

11.7,0.66,6
10.7-12.4,5.66

9.7,0.81,4
9.2-10.9,8.29

atw

6.3,0.45,10
5.6-6.9,7.19

6.0,0.14,10
5.8-6.3,2.28

6.2,0.54,4
5.8-7.0,8.74

ptw

8.1.0.51,10
7.5-9.2,6.27

7.6.0.34.10
7.2-8.1.4.44

7.7,0.21,4
7.5-8.0,2.67

mm!

4.5,0.53,10
3.3-5.1,11.71

4.2,0.71,10
3.4-5.6,16.89

5.8,0.08,4
5.7-5.9,1.41

entl

6.4,0.56,10
5.1-7.3,8.89

6.0,0.49,10
5.0-6.7,8.13

p34

6.3,0.36,4
6.0-6.8,5.73

apl

14.9,0.86,25
12.9-16.7,5.89

14.3,0.74,16
12.9-15.4,5.18

13.9,1.08,16
11.7-15.6,7.81

bapl

12.0,0.55,10
11.0-12.7,4.56

11.6,0.62,10
10.5-12.4,5.30

9.9,0.43,13
8.9-10.5,4.33

atw

8.5,0.62,25
7.2-10.2,7.31

8.2,0.70.17
7.0-9.3,8.57

8.3,0.47,16
7.4-9.2,5.70

ptw

8.6,0.70.25
7.2-9.5,8.20

8.4,0.68,17
7.0-9.5.8.09

8.4,0.36,16
7.5-8.9,4.26

mml

6.8.0.42.25
5.8-7.6,6.09

6.6.0.48.17
5.7-7.4,7.23

7.4.0.45.16
6. 5-8. '0,6. 15

entl

6.6,0.57,25
5.1-7.8,8.61

6.4,0.81,17
4.9-7.6,12.58

7.1,0.65,16
5.8-8.3,9.15

313

Table 33 — continued

ml2

apl

14.5,1.30,21
12.0-17.2,8.97

14.1,1.41,20
11.1-16.1,9.97

13.5,1.26,13
11.5-15.0,9.37

bapl

11.4,0.67,5
10.7-12.4,5.85

11.2,0.58,14
10.1-12.5,5.15

9.2,0.50,10
8.4-10.3,5.45

atw

6.9,0.48,21
5.9-7.8,6.91

6.9,0.73,20
6.0-9.5,10.47

7.1,0.45,13
6.5-7.7,6.27

ptw

5.9,0.43,21
5.1-6.7,7.19

6.1,0.75,20
5.1-8.6,12.25

6.7,0.46,13
6.2-7.6,6.88

mml

5.8,0.53,21
5.2-7.3,9.11

5.7,0.52,20
4.9-6.6,9.12

6.1,0.51,14
5.2-7.1,8.33

entl

4.9,0.81,21
4.0-6.5,16.45

4.9,1.05,20
2.5-7.1,21.38

6.0.0.96,13
3.9-7.1,15.82

314

allowing the metaconid and metastylid to become broadly confluent,
and the metaflexid quickly retreats. These changes occur very
rapidly, so that a tooth takes on the appearance of what in other
protohippines is present in late wear-stages, but after only a third
of the original crown is worn off. The metaconid of the p2 is very
reduced or absent (Fig. 49D). Lower deciduous premolars have larger
protostylids, and persistently larger metastylids that are about
equal in size to the metaconids on the dp34. The dp2, unlike the p2,
has a well developed metaconid that is only slightly smaller than the
metastylid. The ectoflexid is shallow on the dp2, not penetrating
the isthmus; but is deeper on the dp34. This, coupled with a deep
linguaflexid, keep the metaconid and metastylid well separated (e.g.
F:AM 60432).

Discussion. Ever since Johnston's (1937) description, Cal.
regulus has generally been used as the model when comparing other
genera with Calippus (e.g. Webb, 1969a, p. 134). This naturally
resulted from it being well represented in many museum collections,
and the continuing confusion surrounding the genotypic species Cal.
placidus. Calippus regulus, however, displays a combination of
primitive and derived features that are not representiti ve of the
genus or subgenus as a whole. These include its ultrasimple enamel
morphology, reduced styles, poorly developed lingual flexids and
extremely small size.

The earliest records of Cal. regulus are from the late Barstovian
of Colorado and Nebraska. A similar, but notably even smaller
population is recognized from the late Barstovian and early

315
Clarendonian of Florida, and is described below as Calippus sp. The
early, northern Great Plains populations are slightly larger than the
topotypic sample, and retain some more primitive features (e.g. a
larger DPI). Calippus regulus was evidently very rare in the
northern Great Plains during the late Barstovian. Of the nineteen
quarries listed by Skinner and Johnson (1984) from the Burge Member,
specimens referable to Cal . regulus were found in only three, and in
relatively few nunters. During the early half of the Clarendonian,
Cal. regulus is common in the southern Great Plains (Beaver and
Clarendon Faunas), and the Texas Gulf Coastal Plain, but is no longer
present in more northern faunas. Previous biogeographic
interpretations considered Cal placidus and Cal. regulus as northern
and southern counterparts, and for them to have been allopatric.
Webb (1969a) even discussed the possibility that they were clinal
variants of a single species. However, the recognition of Cal .
placidus in the Clarendon and Lapara Creek Faunas disproves this
hypothesis. The interval during which Cal. regulus is recognized
(about 13 to 10 ma) was for most equid genera a period of speciation
and relatively rapid morphological evolution. Calippus regulus
instead generally displays morphologic stasis through this period.
In part, this can be attributed to its already having attained a
relatively high degree of hypsodonty (HI=4.2) in the early
Clarendonian, well in advance of its larger contemporaries (Table
26).

Calippus regulus from the Texas Gulf Coastal Plain was described
by Quinn (1955) as a new species, Cal . anatinus. I follow Forsten

Figure 50. Histograms of basal crown lengths (BAPL) of combined
samples of P3s and P4s (A-D), and of Mis and M2s (E-H) for four
populations of Cal . (Calippus). A, E. Cal. regulus. Lapara Creek
Fauna, Texas Gulf Coastal Plain. B, F. Cal ."regulus. Clarendon
Fauna, Texas Panhandle. C, G. Calippus sp., lower Bone Valley
Formation, Central Florida. D, H. CaTT elachistus n. sp.. Love Site,
Central Florida. The two Texas populations of CaT. regulus are of
approximately the same size, but are much larger than the samples
from Florida. Each square represents one individual.

H R HFhn

xE

317

n.mrFffft

T~n n

r. ^ .n.rfftnnn

rfi

i;Q__n r-

XL

B

n n n

H^

_[Xn a □ □ p-

9.0 10.0 11.0 12.0 13.0

BASAL CROWN LENGTH (mm)

318

Table 34. Measurements of upper and lower cheekteeth of Calippus sp,
from lower horizons of the Bone Valley Formation, Polk and
Hillsborough Counties, Florida. Specimens from three superposed
faunas: A, Bradley Fauna, late Barstovian; B, lower Agricola Fauna,
latest Barstovian; and C, upper Agricola Fauna, early Clarendonian.
Format as in Table 31.

UF 23979
UF 61324
UF 23983
UF 50756
UF 61323
UF 28421
UF 28549
UF 93201
UF 28542
UF 28680
UF 93202
UF 68993

TOOTH SIDE FAUNA APL TRW PRL PRW BAPL MSCH

P34
M12
M12
M12
M3
P2
P2
P34
M12
M12
M3
M12

12.8
9.8
13.0
11.9
11.2
14.3
16.0
14.0
10.1
12.4
12.1

13.4

11.9
9.2
11.1
13.6
13.9
11.0
11.7
10.3
10.5

4.3
4.3
5.0
4.9
4.3
3.7
4.1
5.4
4.2
5.5
5.0
4.5

3.0
2.5
2.5
2.7
2.2
2.7
3.4
3.0
2.8
2.5
2.0
2.2

9.6 20.3

8.6
10.8
12.9
13.4
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UF 93210
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9.8 17.2

9.9 26.2

319

(1975) in considering Cal. anatinus a junior synonym of CaT_. regulus.
The differences in size (Fig. 50; Tables 32, 33) and morphology of
the Lapara Creek and Clarendon samples of this tiny horse are
inconsequential. No available specimens from Florida appear to be
referable to this species. Instead, there are at least two different
varieties of very small Calippus from Florida, as described below.

Cal. (Calippus) sp.

Referred specimens. Bradley Fauna, Bone Valley Region. Kingsford
Mine: UF 61323 R M3; 61324 L M12; 61325, 61343 2 L p34. Nichols
Mine: UF 23960, 23983, 50756 3 M12; 23979 R P34.

Lower Bone Valley Formation (? Bradley Fauna), Four Corners Mine:
UF 93210 R p2.

Agrico Fauna, Bone Valley Region. Red Zone, Phosphoria Mine: UF
28421 R P2; 28419, 28420 2 L M12; 28422 R M3; 28477 L p34. Gray
Zone, Phosphoria Mine: UF 28549 L P2; 28542, 28680 2 L M12; 28540 R
M3; 28541 L M3; 28543, 28544 2 L ml2. Hookers Prairie Mine, Polk
Co., FL: UF 93201 R P34; 93202 R M3.

Ashville Site: UF/FGS V-60086 R M12; -6087 R M3; -6110 L M12;

-6111 L M3.

Description and discussion. A limited sample of isolated teeth
from the Bradley and Agricola Faunas (Waldrop and Webb, in prep; Webb
and Hulbert, 1986) of the lower Bone Valley Formation are clearly
referable to Cal. (Calippus). In enamel morphology they are
extremely similar to Cal. regulus, in particular the very simple

320
fossettes, reduced styles, and persistently isolated hypoconal lake
in upper cheekteeth (Figs. 45D-45F), and well developed protostylids,
large pli entoflexids in early wear-stages, relatively deep
ectoflexids and shallow linguaflexids in lower cheekteeth (Fig. 450 .
They differ from Cal. regulus in their smaller size (Table 34; Fig.
50), relatively well developed p2 metaconid (UF 93210), and probably
shorter unworn crown heights. Maximum unworn M12 MSCH for these
specimens is estimated to have been no more than 40 mm, although the
limited number of unworn or slightly worn teeth does not allow this
parameter to be accurately predicted. Cal. (Calippus) sp. is of
similar size as younger samples from Florida (Cal . elachistus. Table
34 and Fig. 50), but differs considerably from them in enamel
morphology.

Cal. (Calippus) elachistus new species

Calippus cf. regulus. WEBB et al., 1981, p. 527.

Type specimens. Holotype, UF 32139, R mandibular fragment with
m2-m3. Paratypes, UF 53431 R P2; 53448 L M2; 53585 R p34. All
collected by FSM personnel between 1974 and 1981.

Type locality. Love Site, 1.5 km N of Archer, Alachua Co.,
Florida.

Stratigraphic occurrence and age of type locality. Fluvial
sediments of the Alachua Formation; very late Clarendonian, about 9.0
ma.

321

Topotypic sample. UF 53618-53620 3 R DP2; 68839 R DP34; 96323 L
DP34; 53430 R P2; 53432-53434 3 L P2; 53435-53436, 53578. 53580 4 R
P34; 53437-53441, 53598 6 L P34; 53576-53577, 53579 3 R M12;
53442-53445, 53447, 53599 6 L M12; 53450, 53616-53617, 53575 4 L M3;
53601 assoc. L ml-m2; 59161, 92951-92952 3 R dp34; 92953 L dp34;
53581-53584, 96979 5 R p2; 64527, 96565 2 L p2; 53586-53591,
68951-68952 8 R p34; 53593-53597, 59163-59164, 68954-68955 9 L p34;
53603-53610. 59166. 68953. 68956 12 R ml2; 59172, 68958 2 L ml2;
53611-53614 4 R m3.

Etymology, elachistos. Greek for smallest or least.

Distribution. Very late Clarendonian through early Hemphillian
(about 6.2 to 9.0 ma) of central Florida.

Referred specimens. Haile 19A: UF 47320 R M12; 47325 L m3.

McGehee Farm: UF 45640 R M12; 45641 L M3; 18471 R p34; 17313 R
ml2; 7238 R m3.

Nichols Mine: UF 92999 L M3; 23957 L ml2.

Manatee Dam Site: UF 11932 L M3; 95366 L ml2.

Diagnosis. Occlusal dimensions of cheekteeth much smaller than
all other species of Calippus. but Cal. regulus; slightly smaller in
early to middle wear-stages and significantly smaller basal crown
lengths than Cal. regulus. Protostylid reduced on p3-m3. Metaflexid
and linguaflexid better developed and more persistent with wear than
in Cal. regulus. Metastylid and hypoconulid not extremely elongated
in early wear-stages on ml-m3. Ectoflexid reduced in depth on
permanent and deciduous cheekteeth, generally not penetrating
isthmus, except in heavily worn molars. Pli entoflexid absent on

322

molars. Fossettes simple, without plications except in earliest
wear-stages. Styles weak, but slightly stronger than those of Cal .
regulus. Pli caballin absent or vestigial. Hypoconal groove closed
with onset of wear, persists as a lake until middle wear-stages on
premolars; disappears in very early wear-stages of molars.

Description. The known sample of Cal. elachistus is almost
exclusively isolated cheekteeth, and its facial and incisor
morphology are therefore unknown. The holotype, UF 32139, consists
of a mandibular fragment with a moderately worn m2 and slightly worn
m3 (Figs. 51K, 52; Table 35). No distinctive portion of the ramus,
e.g. its ventral border, remains with the specimen. As lower dental
morphology changes so drastically with wear in Calippus, the holotype
is best compared with similarly worn specimens of other species (e.g.
F:AM 114176, Cal. regulus). In UF 32139, the ectoflexid does not
penetrate the isthmus on either the m2 or m3 (as it does in F:AM
114176). The rounded metastylids are well separated from the
metaconids, however, by relatively deep, V-shaped linguaflexids and
anterolingual projections of the entoflexid (Fig. 51K). The labial
borders of the metaflexid and entoflexid are relatively flat, with
little or no tendency to be curved. The protostylids are small, and
do not extend labial ly beyond the protoconid.

Based on the topotypic sample, the upper cheekteeth of Cal .
elachistus resemble those of Cal. regulus in their small size (Figs.
46, 47, 50; Table 32) and simple fossettes. Upper premolars have
moderately well developed parastyles and mesostyles, and some have

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326

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328

very slight metastyles. In this, they more closely resemble Cal.
placidus than Cal. regulus. A weak pli cabal 1 in may be present, but
only in early wear-stages. The protocone varies in shape from oval
to very elongated (Figs. 51A-51D, 53A), and is broadly connected to
the protoselene. The preprotoconal groove is shallow or absent. The
hypoconal groove is open in earliest wear-stages, usually becomes an
isolated lake rather quickly, and disappears during late wear-stages.
For example, UF 53441 retains an open hypoconal groove with a MSCH of
about 29 mm, the heavily worn UF 53435 (MSCH=17.9 mm) still retains
its hypoconal lake, although UF 53439 (MSCH=19.0 mm) does not.
Neither a pli protoloph nor pli hypostyle are observed in even the
least worn P34. In early wear-stages, the posterior half of the
prefossette may have one to three shallow plications, and a
moderately developed prefossette loop can be present. The anterior
half of the postfossette bears at most a single, shallow plication.
With moderate wear (i.e. MSCH of 25 mm or less), all plications are
obliterated. In the P2, the anterostyle is generally not well
separated from the ectoloph, and is not well developed. Three DP2s
from the Love Site are referred to Cal. elachistus rather than the
similarly sized Pseud, skinneri (Webb and Hulbert, 1986). These DP2s
have poorly developed anterostyles (Fig. 51E), while a DP2 referred
to Pseud, skinneri (UF 90263) has a well developed anterostyle. The
DP2 fossette borders are more complexly plicated than their permanent
counterparts (Fig. 51E), and the hypoconal groove persists as a lake
until late wear. All three DP2s have appresion facets for a DPI, as
does UF 53433, a P2.

329

Upper molars are slightly smaller than the premolars (Tables 32,
35), with more delicate styles, pli caballin absent, simpler
fossettes, and more elongate protocone. The hypoconal groove is
generally very shallow and disappears with relatively little wear
(Fig. 510. Occasionally, as in UF 53443, the hypoconal groove is as
deep as in premolars. In very early wear (e.g. UF 53576 or UF
53577), the internal fossette margins may bear several very shallow
plications; they are shallower than those on comparably worn
premolars and are lost with wear more rapidly. Unworn or slightly
worn MSCH for the M12 is about 40 mm.

The p2 is represented by nine specimens from the Love Site. Their
metaconids are stronger than in Cal. regulus (contrast Fig. 51F with
49D), although they vary from a small angular structure projecting
anteriorly from the metastylid, to rounded and almost equal to that
of the metastylid. The ectoflexid is very shallow and does not
penetrate the isthmus (Fig. 51F). The hypoconulid is well separated
from the entoconid by a deep, U-shaped flexid until middle wear. The
other lingual flexids are deep and well developed. In early wear a
small pli entoflexid and pli caballinid may be present. The p34 are
well represented in the topotypic sample. The metastylid is rounded
to slightly elongate-oval, subequal in size to the rounded metaconid
(Figs. 51G, 51H). The two are well separated throughout most of the
crown by the deep lingual flexids. The linguaflexid is broadly
U-shaped, and much better developed than in Cal. regulus. The
ectoflexid is shallow and never penetrates the isthmus. The
protostylid is small, much less prominent than in other members of

330
the subgenus. Pli entoflexids are not observed, but the sample does
not include any very slightly worn p34s. Several dp34s are referred
to Cal. elachistus. Compared to those of Cal . regulus. they have
shallower ectoflexids that just barely penetrate the isthmus, and
shallower, broader V-shaped linguaflexids. The entoflexid is
especially elongated, but unplicated (Fig. 511). The protostylids
are reduced, but stronger than in the p34. Lower molars are
especially notable for their reduced ectoflexids, which only
occasionally penetrate the isthmus, and persistent lingual flexids
(Figs. 51J, 51K, 53B). The metaflexid, which is rapidly reduced with
wear in Cal. regulus (e.g. the ml in Fig. 49D, note that F:AM 114176
is a relatively young adult), is retained in Cal . elachistus and not
markedly retracted in depth until crown height is less than 15 mm.
The linguaflexid is also much better developed than in the molars of
Cal. regulus, and persists throughout the entire crown. The
metaconid and metastylid are of approximately the same size, and are
oval. The metastylid and hypoconulid are not extremely elongated in
very early wear, as is characteristic of Cal. regulus and Cal .
placidus. This is reflected in the maximum apl observed in slightly
worn molars; for Cal. elachistus this is about 16.5 mm, for Cal .
regulus it exceeds 17.0 mm. The protostylid is present, but reduced
or vestigial. Unworn or slightly worn mcchs are about 30 mm for the
p2 (UF 96979), 35 mm for the p34, and 40 mm for the ml2 (UF 59166).

Discussion. Calippus elachistus is known from five localities in
central Florida. The majority of known specimens are from the Love
Site, the type locality, and are latest Clarendonian (Webb et al..

331
1981). Two nearby and slightly younger (early Hemphillian)
localities also contain specimens referable to Cal . elachistus,
McGehee Farm and Haile 19A. Similar-aged taxa are rarely recovered
from the Bone Valley Formation, most terrestrial specimens are either
older or younger. However, a well worn lower molar from the Bone
Valley, UF 23957, is definitely referable to Cal. elachistus rather
than the older sample described above as Cal . (Calippus) sp.
Especially notable in this specimen are its persistent entoflexid and
linguaflexid, and the relatively shallow ectoflexid; all derived
character states found in Cal . elachistus.

Cal. elachistus is the youngest known member of the subgenus Cal .
(Calippus). Although based on only a few specimens, Cal. elachistus
apparently persisted into the late early Hemphillian of Florida (Fig.
53) without significant morphological change. This is evidenced by
its presence at the Manatee County Dam Site.

Subgenus Grammohippus new subgenus

Type species. Calippus (Grammohippus) martini Hesse, 1936.

Included species. ?Cal. (?G. ) circulus (Quinn), 1955, n. comb.;
Cal. (G.) cerasinus n. sp., Cal. ( G^. ) hondurensis (Olson and McGrew),
1941, n. comb.; Cal. (£. ) maccartyi n. sp.

Etymology, grammodes. Greek for linear and hippos, Greek for
horse. In reference to the linearly arranged incisors of the genus.

Diagnosis. Small to medium-sized equids with toothrow lengths
between 100 and 135 mm. Protocone oval or elongate-oval, connected

332

to protoselene (only rarely isolated in very early wear-stages). Pli
caballin single, large in premolars, variable in niolars. Relatively
simple fossettes, with moderately developed plications limited to the
upper half of the crown. Hypoconal groove generally remains open
longer than in Cal . (Calippus); variably persistent and occasionally
forms a lake; usually completely lost in latter wear-stages; lost
earlier with wear in premolars than molars. Large para styles and
mesostyles; moderately well developed metastyles often present.
Upper cheekteeth moderately curved, more so than in Cal . (Calippus),
although less than in Pliohippus. Protostylids relatively poorly
developed or absent on permanent lower cheekteeth; if present moder-
ately developed only on the lower third (or less) of the crown. DPOF
long, narrow, shallow, unpocketed, poorly rimmed posteriorly;
probably absent in some younger species. Rostrum short, relatively
broad; muzzle width varies from 452 to greater than 60% of the UTRL.

Discussion. Members of the subgenus Grammohippus are easily
distinguished from those of Cal. (Calippus) by their greater size,
stronger styles, more curved upper cheekteeth, and rudimentary or
absent protostylids. Specimens here assigned to Grammohippus have
been variously placed in Pliohippus, Astro hi ppus or Protohippus.
While these four taxa can be easily differentiated by their facial
fossae morphology, and Grammohippus has the unique Calippus incisor
arrangement, isolated cheekteeth and some toothrow series cannot
always be unequivocally assigned to a genus. In general, Pliohippus
upper cheekteeth differ from those of Grammohippus by being larger,
more curved, having more rapid closure and loss of the hypoconal

333
groove, simpler fossettes, and much more frequent connection between
the protocone and hypocone. Protohippus upper cheekteeth tend to be
larger, have better developed pli caballins and prefossette loops,
and often have isolated protocones in early wear-stages. Astro hi ppus
upper cheekteeth are less curved, have simpler fossettes, more
rudimentary pli caballins, and more rapid loss of the hypoconal
groove. The lower cheekteeth of all four share many plesiomorphous
characters. Discrimination among genera is further complicated by
frequent parallel evolution of certain characters, especially those
related to the elongation of the metaconid-metastylid complex and
greater development of the lingual flexids.

Five species are referred to Grammohippus, ranging in age from
late Barstovian to early Hemphillian. While this subgenus evidently
diverged from Cal . (Calippus) sometime in the early Barstovian, no
records exist prior to the late Barstovian (Cold Spring Fauna).
However, it is unlikely that early specimens of Grammohippus would be
readily distinguished from Protohippus or Pliohippus, unless very
complete cranial material was available. "Pro." castilli was
described by Cope (1885) from the Tehu.ichila Fauna, Hildalgo, Mexico,
possibly of late Hemphillian age (based on supposed co-occurence with
Agriotherium; Miller and Carranza-Casteneda, 1984). The occlusal
dimensions of the holotype (AMNH 8344) fall well outside the observed
range of Cal . (G.) hondurensis, but it otherwise resembles that
species in its enamel morphology, especially the relatively small
protocone. "Pro." castilli thus may represent a late surviving
member of Cal. (Grammohippus). However, a sample of five upper and

334
three lower cheekteeth from the Corinto Fauna, El Salvador (Webb and
Pern'go, 1984, Fig. 12B) compare favorably with the type of "Pro."
cast! Ill in size as well as morphology. Their large size and deep
ectoflexids suggest referral instead to a equine genus (larger
samples are needed for a more precise identification). That the
morphology of AMNH 8344 compares so very favorably with both proto-
hippines and equines emphasizes that isolated cheekteeth are
unreliable indicators of phylogenetic relationships among these
equids. Additionally, there are several late early Hemphillian
records of Calippus from the Great Plains mentioned by Tedford et al.
(in press). These are currently under study by M. R. Voorhies and M.
F. Skinner, and probably are also referable to Cal. (Grammohippus) .

?Cal. (?Grammohippus) circulus (Quinn), 1955 new combination

Merychippus perditus (Leidy), HESSE, 1943, p. 171 (in part).
Pliohippus circulus QUINN, 1955, pp. 22-24 (in part).
Merychippus circulus (Quinn), FORSTEN, 1975, pp. 32-35 (in
part).

Type specimen. TMM 31191-10, assoc. R p4-m3.

Type locality. Sam Houston Local Fauna (Hesse, 1943, p. 171), San
Jacinto County, Texas.

Stratigraphic occurrence and age of type localtiy. Fleming
Formation, Cold Spring Fauna; late Barstovian, about 13.0 ma.

Distribution. Known only from the middle late Barstovian (about
13.5 to 12.5 ma) of the eastern Texas Gulf Coastal Plain.

335

Referred specimens. Cold Spring Fauna. Cold Spring l.f., San
Jacinto Co.. TX: TMM 31219-327 R P2; -160 R P34; TAMU 3027 R M12;
TMM 31219-326 L m3. Noble Farm l.f., TAMU locality No. 19, Grimes
Co., TX: TAMU 3019, 3020 2 L M12; 3021 R M3; 3022 R ml2; 3023-3024 2
L ml2; 3025 R m3; 3026 L m3.

Revised diagnosis. Cheekteeth with least unworn crown height of
known species of the subgenus; unworn molar MSCH about 40 mm.
Smaller than Cal. martini , with less complex fossettes, poorly
developed pli caballins on premolars, and variable, often strong
protostylids.

Description. ?Calippus circulus is at present known only from a
few isolated teeth; its generic referral is thus somewhat problematic
until more complete material is discovered. The P2, TMM 31219-327,
is moderately worn (Fig. 54A; Table 36) and the anterior third is
broken off. The well connected protocone is round to slightly oval
with a small preprotoconal groove (Fig. 54A) . The fossettes are very
simple with only a trace of a pli prefossette, and there is neither a
pli caballin nor hypoconal groove remaining at this wear-stage. The
moderately worn P34, TMM 31219-160, is very typically calippine, with
a connected, elongate-oval protocone, small pli caballin, simple
fossettes, well developed parastyle, and a slight metastyle (Fig.
54B, Table 36). The tooth is moderately curved (ROC = 40 mm). Upper
molars are represented by three specimens. The barely worn TAMU 3027
has a MSCH of only 38 mm. The other two specimens are heavily worn.
The protocone is elongate-oval, broadly connected to the protoselene,
and with a shallow but persistent preprotoconal groove. Fossettes

336
are simple; the pli caballin is vestigial, and the hypoconal grooves
close without forming a lake.

The associated lower series that constitutes the hoi o type was
illustrated and exhaustively described by Quinn (1955, pp. 23-24).
The referred lowers match the type in size and general enamel
morphology, although many of the molars have stronger protostylids.
They can be well developed on the lower third of the crown and
present to near the top of the unworn crown. On others, including
the type series and most of the referred m3s, the protostylid is much
weaker, and is at best moderately developed only near the base of the
crown. Smaller and less high crowned than CaJ^. martini, the lowers
otherwise resemble that better known taxon. The metaconid-metastylid
complex is relatively unexpanded, and the lingual flexids shallow,
short and nonper si stent.

Discussion. Quinn (1955) described ?Cal. circulus as a primitive
member of Pliohippus based on two specimens, the type lower series
and a juvenile upper dentition (TMM 31219-165). The latter includes
the right and left DP2-DP4, the right M1-M2 (Quinn, 1955, Plate 3,
Figs. 5-7), and the left M2-M3. The upper molars of TMM 31219-165
have strong pli caballins, moderately complex fossettes, and isolated
protocones in early wear-stages, all of which suggest a referral to
Protohippus rather than Pliohippus or Calippus. They are also larger
than other upper cheekteeth from the Cold Spring Fauna which appear
to be those of a primitive, moderate-sized member of Cal.
(Grammohippus). The latter are judged to better correspond with the

337

B

2cm

Figure 54. Occlusal views of upper cheekteeth of ?Ca1ippus
(?Grainmohippus) circulus from the Cold Spring local fauna, San
Jacinto County, Texas (late Barstovian). A. TMM 31219-327, R P2,
B. TMM 31219-160, R P34.

338

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341

type lowers of ?Cal . circulus. The total sample is quite limited,
and more complete specimens are needed to confirm the association of
upper and lower teeth proposed here. In the absence of cranial
material, the provisional referral to Calippus rather than Pliohippus
is based on the moderate size (contemporary populations of Plio.
mirabilis in Nebraska are much larger), the strong styles, and the
moderately developed protostylids of the Cold Spring sample. Forsten
(1975) grouped Quinn's (1955) Plio. circulus and Eoequus wilsoni into
a single taxon (Merychippus circulus). Most of the larger specimens
from the Cold Spring Fauna do pertain to a single species, although I
follow Hesse (1943) in referring them to Protohippus perditus (see
below). The few specimens here referred to ?Cal . circulus differ
from those of Pro, perditus by being smaller, much shorter crowned,
having simpler fossettes, rapidly connected protocones, less elongate
lingual flexids and weaker protostylids. ?Calippus circulus is at
present recognized only from the Texas Gulf Coastal Plain.

Cal. (Grammohippus) martini Hesse, 1936

Protohippus perditus Leidy, GIDLEY, 1906a, pp. 136-139 (in

part); GIDLEY, 1907, pp. 882-883 (in part); QUINN, 1955, pp.

19-20 (in part).

Callippus martini HESSE, 1936, pp. 52-54.

Pliohippus (Astro hi ppus) martini (Hesse), STIRTON, 1940, pp.

190. 192; FORSTEN, 1975, pp. 48-53 (in part).

Pliohippus sp., GREGORY, 1942, pp. 412-413.

342

Protohippus martini (Hesse), QUINN, 1955. pp. 21-22.

Equus laparensis QUINN, 1955, pp. 58-61 (in part).

Equus sp., QUINN, 1955, pp. 61-62.

Astro hi ppus martini (Hesse), WEBB, 1969a, pp. 95-96; SCHULTZ,

1977, p. 48.

Astrohippus sellardsi (Quinn), WEBB, 1969a, p. 96 (in part).

Type specimen. UCMP 32814, associated L P2-M3.

Type locality. Cragin Quarry (UCMP V-3516), Beaver County,

Oklahoma.

Strati graphic occurrence and age of type locality. Ogallala
Group; middle Clarendonian, about 10.0 to 11.5 ma.

Distribution. -Early to middle Clarendonian of the northern and
southern Great Plains; early Clarendonian of the Gulf Coastal Plain
of Texas and Florida.

Referred specimens. Clarendon Fauna, Donley Co., TX.
Chamberlain's Quarry No., 7: F:AM 114163 assoc. R & L mandibles.
MacAdams Quarry: F:AM 114165-114168, 114173 5 skulls; 114169-114172,
117036 5 maxillae; 117038-117040 3 mandibles. C. Risley Ranch Site:
TWM 255-34 L mandible with p2-m3; -35 L mandible with p2-p4; -31 L
M12. Noble Ranch Site: JWT 1498A R maxilla with P2-M3; JWT 1498B L
maxilla with P4-M3. Grant Lease Site: JWT 880A R mandible with p2-
m2; WT 941 R maxillae with P4-M2. Many additional specimens,
including isolated teeth measured in this study are known from this
fauna, and are housed in the F:AM, PPM, UCMP and TMM collections.

Minnechaduza Fauna. Gallup Gulch Quarry, Cherry Co., NB: F:AM
114156 R maxillae with P4-M1; 114157 R P2; 117018 L P2; 117023,

343
117024. 117029 3 R P34; 117019, 117021, 117022 3 L P34; 117020,
117028 2 L M12; 117026 R Ml; 117027 R M2; 114159 assoc. R & L
mandibles with p2-m3; 114160 assoc. R & L mandibles with c,p2,dp3-
dp4,ml-m2; 114161 L mandible with dp2-m2; 117034, 117035 2 ml2.
Mensinger Quarry, Cherry Co., NB: F:AM 117031 L P34; 117032 assoc. R
& L mandibles with dp2-ml. Big Spring Canyon, Bennett Co., South
Dakota: AMNH 10838 juvenile skull (Gidley, 1906a, Figs. 3-5).
Hollow Horn Bear Quarry, Todd Co., South Dakota: F:AM 117008
premaxillae with R & L 11-13; 117009 L maxilla with M1-M2; 117010 R
P34; 114148, 114149, 117011, 117012 4 R M12; 114135-114147, 117013-
117017 18 mandibles. Dawson Locality No. 3 (SDSM locality V-553),
Todd Co., South Dakota: SDSM 55154 assoc. skull, mandibles and post-
cranial elements of immature male individual. Additional specimens
from this fauna in the UCMP collection are listed in Webb (1969a).

Lapara Creek Fauna. Buckner Ranch Site, Bee Co., TX: TMM
30896-127 assoc. R P2-M3; -195 assoc. L P2-P4; -188 palate with R
DP2-DP4 and L DP2-M1; -569 crushed skull with R P4-M3; -418 assoc. R
P4-M1; -533 L p2; -545 assoc. R p2-p4 and L p2-m3; -207 R mandible
with dp2-ml; -501 L mandible with dp2-dp4; -535 L dp2; -420E R p34.
Farish Ranch Site, Bee Co., TX: TMM 31081-169 R M12; -1244 L M12;
-1253B L p34. Bridge Estate Site, Bee Co., TX: TMM 31132-190C,
-366B 2 R P34; -190B L P34; -169, -334B, -366A 3 R M12; -430 assoc. R
p3-p4; -343 assoc. L p4-m3; -357 L dp34; -445 L dp2; -445B R dp34;
-498 R p34; -13A, -285A, -400, -569 4 L ml2. Medio Creek, Site No.
19, Bee Co., TX: TMM 31170-73 R P34; -74B R dp34; -74A R ml2; -13A L
ml2.

344
Agricola Fauna, Bone Valley Region. Gray Zone, Phosphoria Mine:
UF 28552. 93326 2 L P34; 28551 R M12; 28579 L m3; 55886 assoc. L
p2-nil. Brewster Haynsworth Mine: UF 24375 R M3 (Berta and Galiano,
1984, Fig. 2). Fort Green Mine: UF 57358 R p34; 55888 L p34; 52409
R ml2.

Revised diagnosis. Largest described species of Calippus, with
toothrow lengths of 125 to 140 mm and unworn molar crown height of
about 57 mm. Metastylid poorly separated from metaconid by
relatively shallow and rapidly retracting linguaflexid and
entoflexid. Muzzle width about 452 of toothrow length.
Description. Subsequent to its original description,
relationships between Cal. martini and other taxa have been based
almost exclusively on characters of the upper cheekteeth (e.g.
Stirton, 1940). This is the first documentation of the facial and
incisor morphology of the species, although Gidley (1906a) figured
and described as the "hypotype" of Pro, perditus a skull here
referred to Cal. martini . The topotypic sample and that from the
nearby Beaver Quarry are limited to cheekteeth and mandibular
fragments. Crania from various quarries of the Clarendon Fauna
reveal the facial characters of Cal_. martini. Upper cheekteeth of
Cal. martini are abundant in collections of the Clarendon Fauna, and
they do not differ in size or morphology from the holotype (Tables
36, 37). The medium-sized protohippine from the Clarendon Fauna has
long been recognized as being conspecific with Hesse's (1936)
species. The following cranial features are based on skulls whose
dentitions also match those of the type. Although all are crushed or

345
distorted to varying degrees, their facial nrorphology is consistent.
The malar region lacks any fossa of the Pliohippus-type. There
occasionally is a small, shallow depression, which is often
accentuated by crushing. Similar shallow depressions are variably
observed in "Merychippus," Pseudhipparion. Neohipparion, and other
species of Calippus (Skinner and Taylor, 1967; MacFadden, 1984a; Webb
and Hulbert, 1986). The DPOF (best preserved on F:AM 114173 and
117036; see also Gidley, 1906a, Fig. 3) is located high on the face,
dorsal to the M3 to P3, about 60 mm above the alveolar tooth margin.
It is long (about 75 to 85 mm), relatively narrow when compared to
that of Protohippus, and with a less distinct posterior margin. The
ventral, anterior, and dorsal margins all blend into the surrounding
facial region without rims. The preorbital bar is moderately narrow,
like that of Protohippus, with a length of about 17 mm. The lacrimal
bone is included in the posterior region of the DPOF. The nasal
notch does not extend over the P2. The rostrum is relatively short
compared to Protohippus, and especially to Pliohippus. The
premaxillae and mandibular symphyses are expanded as in Cal.
(Calippus), with the enlarged first and second incisors arranged
linearly or nearly linearly to form a broad, straight biting surface.
The muzzle width is about 45% of the UTRL. This is somewhat less
than in more advanced species of Calippus (Fig. 43), but relatively
wider than similarly sized equids.

Upper cheekteeth of Cal_. martini (Tables 36, 37; Fig. 558) have
large parastyles and mesostyles. Protocones are oval (elongate-oval
in early wear), have rounded or pointed posterior ends, and are of

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348

Table 37. Standard univariate statistics for upper cheekteeth of
Calippus martini from the Clarendon Fauna, Donley County, Texas
(middle Clarendonian), from the Minnechaduza Fauna, Brown and Cherry
Counties, Nebraska and Todd County, South Dakota (middle
Clarendonian), and from the Lapara Creek Fauna, Bee and Live Oak
Counties, Texas (early Clarendonian). Format as in Table 2.

FAUNA

CLARENDON

MINNECHADUZA
P2

LAPARA CREEK

APL

25.4,1.17,19
23.6-27.6,4.60

24.5,1.10,3
23.4-25.6,3.66

24.7,0.62,3
24.2-25.4,2.53

BAPL

21.3,1.57,12
17.5-22.8,7.41

21.3,0.78,2
20.7-21.8,3.66

20.2, ~ ,1

TRW

19.9,1.07,18
17.7-22.1,5.40

19.3,1.40,3
18.3-20.9,7.25

18.8,0.35.3
18.5-19.2.1.87

PRL

5.9,0.41,19
5.3-6.9,7.03

5.6,0.40,3
5.2-6.0,7.14

5.7.0.28.2
5.5-5.9.4.96

PRW

4.5,0.48,19
3.1-5.2,10.68

4.3,0.10,3
4.2-4.4,2.33

P34

3.8,0.12,3
3.7-3.9,3.04

APL

21.9,1.47,37
18.6-24.6,6.71

21.5,0.65,11
20.4-22.5,3.01

20.9,0.66,5
20.2-22.0.3.17

BAPL

16.4,0.87,21
15.2-18.9,5.34

16.2,0.58,7
15.2-16.9,3.60

16.1.0.52.3
15.5-16.4.3.23

TRW

22.1,1.22,37
20.1-24.5,5.51

21.7,1.15,10
20.0-23.8,5.29

21.1.1.19.6
19.0-22.4.5.66

PRL

7.5,0.91,37
6.1-9.4,12.10

6.9,0.51,10
6.1-7.5,7.35

7.2.0.59.7
6.1-7.8,7.75

PRW

4.4,0.38,37
3.7-5.4,8.57

4.4,0.38,10
3.9-5.0.8.66

4.0.0.20.7
3.7-4.3.5.11

349

Table 37 — continued

APL 21.2,1.58,42

17.5-23.6,7.42

BAPL 16.2,0.91.23

15.0-18.0,5.62

TRW 20.5,1.82,44

15.8-24.1,8.89

PRL 8.0,0.80,44

5.6-10.0,10.01

PRW 4.0,0.41,44

3.3-5.0,10.15

M12

20.6,1.28.13
18.9-23.0,6.22

15.3,0.50,8
14.7-15.9,3.28

20.7,1.45.13
17.4-22.8,7.01

7.6,0.82,13
5.7-8.5,10.74

4.1,0.33,13
3.5-4.5,8.05

20.1.0.64.5
19.4-21.0.3.17

15.7,1.67.4
13.5-17.3.10.64

19.5.1.79.5
16.6-21.2.9.17

7.1.0.49.5
6.3-7.6.6.86

3.7,0.31,5
3.2-4.0,8.46

350

Table 38. Standard univariate statistics for lower cheekteeth of
Calippus martini from the Clarendon Fauna, Donley County, Texas
(middle Clarendonian), from the Minnechaduza Fauna, Brown and Cherry
Counties, Nebraska and Todd County, South Dakota (middle
Clarendonian), and from the Lapara Creek Fauna, Bee and Live Oak
Counties, Texas (early Clarendonian). Format as in Table 2.

FAUNA

CLARENDON

MINNECHADUZA
P2

LAPARA CREEK

apl

21.0,0.71,10
19.8-21.8,3.36

19.7,1.01,7
18.4-21.3,5.10

20.3,1.30,5
18.8-21.9,6.41

bapl

17.4,0.73,10
16.7-19.1,4.18

18.2,0.36.3
17.9-18.6,1.98

atw

8.6,0.85,10
7.5-10.1,9.89

8.4,0.45,7
7.8-9.1,5.33

8.3,3.94,5
7.7-8.8,4.74

ptw

11.2,0.65,10
10.1-12.1,5.82

10.8,0.28,7
10.3-11.1,2.61

10.3,0.51,5
9.7-10.8,4.98

mm1

7.2,0.87,10
5.7-8.7,12.14

7.3,0.72,7
6.2-8.1,9.83

6.9,1.34,5
4.6-8.0,19.37

entl

8.5,0.54,10
7.5-9.2,6.40

5.7,1.78,7
3.3-8.1,31.50

p34

8.4,2.32,5
4.8-10.7,27.63

apl

21.8,0.90,17
20.2-23.7,4.12

19.1,1.55,9
16.9-21.0,8.08

19.2,0.32,3
19.0-19.6,1.67

bapl

16.6,0.58,15
15.7-18.0,3.49

16.4,0.99,2
15.7-17.1,6.04

atw

11.4,0.80,17
10.2-13.0,7.05

11.6,0.92,9
10.1-12.5,7.93

11.3,1.32,3
9.9-12.5,11.66

ptw

12.1,1.00,16
10.4-13.9,8.23

11.5,0.59,9
10.8-12.4,5.09

11.9,0.38,3
11.5-12.2,3.18

mml

9.7,0.63,17
8.6-11.2,6.48

8.4,0.58,9
7.3-9.0,6.86

9.4,1.65,3 ■
8.3-11.3,17.58

entl

8.8,0.85,17
7.2-10.2,9.69

6.2,2.62,9
3.2-9.6,42.21

7.3,1.32,3
6.1-8.7,18.09

351

Table 38 — continued

ml2

ap1

22.3,1.95,29
18.4-27.3,8.73

18.0,2.39,11
15.5-21.6,13.27

21.4,1.80.5
18.9-23.7,8.39

bapl

16.3,0.79,29
15.2-17.9,4.85

16.6,1.38,5
15.6-18.9,8.29

atw

9.4,0.78,28
8.1-11.5,8.29

9.3,0.99,11
7.8-11.3,10.56

9.1,0.77,5
8.4-10.0.8.50

ptw

8.9,1.00,29
7.3-12.6,11.25

7.7,0.51,11
6.8-8.4,6.57

8.6,0.65,5
7.8-9.6,7.58

mcnl

8.5,0.70,29
7.3-10.0,8.25

6.7,1.08,11
4.3-8.2,15.95

8.9,1.28,5
7.8-11.1,14.37

entl

5.9,0.95,29
4.3-8.1,15.95

4.1,1.72,11
1.2-6.2,42.20

6.2,2.02,5
4.2-9.6,32.52

352

E
E

I
I-
O

z

UJ
LU

z
o
o
o

o

GC
0.

8-

7-

6-

5-

C. martini
Minnechaduza Fauna

C. maccartyl
Moss Acres

C. martini

Clarendon Fauna

C. martini
Lapara Creek Fauna

C. ceraslnus
Love Site

C. ceraslnus

Xmas-Kat Fauna

C. hondurensis
Gracias Fauna

1

— r—
12

— r-
13

14 15 16 17 18

BASAL CROWN LENGTH (mm)

Figure 56. Bivan'ate plot of basal crown length (BAPL) versus
protocone length (PRL) of combined samples of Mis and M2s for four
species of Calippus (Grammohippus) . One standard deviation is
plotted on both sides of the mean value for the following
populations: Cal . martini , Minnechaduza, Lapara Creek and Clarendon
Faunas; Cal » cerasinus. Love Site and Xmas-Kat Faunas; Cal .
hondurensis, Gracias Fauna. Also plotted are the values for UF
90299, a molar of Cal . maccartyi from the Moss Acres Racetrack Site.

353

moderate length relative to tooth size. The protoconal connection is
narrow and constricted by a deep preprotoconal groove in early
wear-stages; it is more open in later wear-stages. The protocone is
oriented in an oblique, anterolabial-posterol ingual direction, more
so in premolars than molars. A long, single pli cabal 1 in is evident
in moderate to slightly worn premolars; smaller or absent with
greater wear. Pli caballins are typically small or absent on molars,
and infrequently well developed. Fossette plications are usually
simple and shallow, but better developed than those of Cal.
(Calippus). Premolars in early wear-stages usually have two to four
plications on each of the internal fossette borders, sometimes
bifurcated, and with moderate development of a prefossette loop. Pli
protoloph and pli hypostyle are either single and shallow, or, more
frequently, absent. A P34 with a MSCH of 18 mm or less typically has
lost all plications. The fossette s of the molars are even simpler,
and most plications are lost very early in ontogeny. The hypoconal
groove closes to form a lake about in middle wear-stages, but the
crown height at which this occurs varies. Well worn molars (i.e.
those with less than half of their original crown height) generally
lack all fossette plications, pli caballins and a hypoconal groove.
The protocone rarely connects to the hypocone, and then only in very
heavily worn molars. Deciduous premolars are similar in fossette
complexity and pli cabal 1 in development as the permanent premolars.
The hypoconal groove, however, remains open longer, until late
wear-stages. A moderate -si zed DPI (about 10 mm long) is present and

354
remains with the permanent dentition. Unworn or slightly worn MSCHs
are about 45 mm for the P2, 52 mm for the P34 and 57 mm for the M12.

The lower cheekteeth of Cal . martini display the primitive
protohippine pattern (Fig. 55A) . The premolars have smaller, more
lingually situated metastylids than metaconids. Therefore, posterior
width is typically greater than atw (Table 38), although the
difference is much less in older individuals. In early wear-stages,
the linguaflexid and a well developed anterolingual extension of the
entoflexid "pinch off" the metastylid from the metaconid (Fig. 55A) .
With wear, both contract, thus broadening the connection between
them. The metaflexid rapidly retreats with wear, creating a broad
confluence between the protoconid, metaconid and protolophid (Fig.
55A). The ectoflexid is relatively shallow on the p2, not
penetrating the isthmus. In the p34, its depth is variable; in early
wear-stages it generally slightly penetrates the isthmus, to a point
deeper than the level of the base of the entoflexid. In later
wear-stages, it may retreat. Molars are much narrower than
premolars, with relatively short metaconid-metastylid complexes
(Table 38), and with the isthmus completely divided by the deep
ectoflexid. The lingual flexids are shallow and rapidly contract
with wear. Plications are uncommon; a small pli cabal linid is rarely
observed in slightly worn premolars, and a pli entoflexid is somewhat
more common in both slightly worn molars and premolars. Usually a
weakly developed protostylid is present only on the lower 15 to 25 mm
of the crown of the p3-m3, thus reaching the occlusal surface only in
older individuals. Lower deciduous premolars in early wear resemble

355
the permanent premolars with shallow ectoflexids and lingually placed
metastylids. The dp2 has a well developed paraconid and an angular
metacom'd that is relatively large for a protohippine. With wear,
the ectoflexids deepen and the dp2-dp4 take on a more molariform
appearance, although with more expanded metaconids and metastylids.
Protostylids are moderately developed on the lower two-thirds of the
crown (e.g. TMM 30896-207; see also Hesse, 1936, Fig. 2).
Ectostylids are absent. A small, vestigial dpi may be present with
the juvenile dentition, but it is lost with the eruption of the p2,
and its alveolus is reabsorbed.

Discussion. As can be judged from the synopsis of usage, the
nomenclatural history of Cal . martini is complex. Some of the
confusion originated with Hesse's (1936) description. He failed to
list any measurements taken on the holotype, and the type figure
(Hesse, 1936, Fig. 1) is not natural size as stated in the caption,
but reduced by about 20%. This created a misconception in some that
the species is considerably smaller than it really is. Measurements
of the type are listed in Table 36. The Lapara Creek sample of Cal.
martini closely agrees with other referred populations in size (Fig.
56, Tables 37, 38) and morphology. The remainder of the confusion
can be traced to Stirton's (1940) transfer of CaJ_. martini to Plio.
(Astro hi ppus).

Stirton (1940) described Astro hi ppus as a new subgenus of
Pliohippus, with "Pro." ansae as the subgenotype. Stirton (1940)
hypothesized that A. ansae was ancestral to Equus. and that "A."
martini was ancestral to A. ansae. "A." martini was in turn thought

356
to be descended from "Merychi ppus" perditus. While subsequent work
has documented that Dinohippus, and not Astro hi ppus. is the sister-
group of Equus (Lance, 1950; Bennett, 1980; MacFadden, 1984b; also
see Chapter 6), most authors have followed Stirton (1940) in consid-
ering martini as a member of Astro hi ppus. Quinn (1955) is a notable
exception, as his systematic approach was vertical rather than the
horizontal definitions of Stirton (1940). Almost all the characters
of the cheekteeth that Stirton (1940) used to unite Ca]_. martini and
A. ansae are either primitive for the Equini, or are judged to have
evolved in parallel (see Chapter 6). He needed a late Miocene link
between Merychi ppus s.l. and A. ansae, so that there would be a
complete North American phylogenetic sequence of species from
Hyracotherium to Equus. Calippus martini was inserted into this
sequence based on its moderate size, appropriate age, and suitable
upper cheektooth morphology. However, the derived Calippus muzzle
morphology prevents Cal . martini from being ancestral to A. ansae or
Equus. Furthermore, the well -developed MF of Astro hi ppus (lacking in
Cal. martini) is a shared derived character of equines.

Gidley (1906a) described and figured a skull (AMNH 10838) from the
Little White River Region of South Dakota as Protohippus perditus.
Osborn (1918) and Tabrum (1981) have both suggested that AMNH 10838
does not represent that same taxon as Pro, perditus. Examination of
the specimen reveals some descrepancies with Gidley's (1906a)
description, confirms that it is not referable to Pro_. perditus
(especially as redefined below), and demonstrates instead a referral
to Cal. martini. Dental characters that suggest this are its very

357

high crowned Ml (Gidley, 1906a, Fig. 4), lack of a pli caballin,
simpler enamel pattern, smaller DPI, and slightly smaller size than
Pro. perditus. Its facial morphology also resembles those described
above from the Clarendon Fauna (rather than skulls referred to Pro.
perditus below). In particular are the absence of a MF, narrow
preorbital bar, and narrow DPOF with poorly defined margins and no
posterior pocket. AMNH 10838 is slightly dorsoventrally crushed,
especially along the naso-maxillary suture, deforming and to some
extent deepening the DPOF. The impressions on the dorsal roof of the
skull discussed by Gidley (1906a) also resulted from postmortem
distortion. Unfortunately, the anterior portion of the skull has
been broken off, and is no longer associated with the specimen.
Judging by Gidley's (1906a) illustrations and descriptions, however,
AMNH 10838 had an expanded, Calippus-type muzzle. The postcanine
diastema was short. The width across the incisive border was listed
by Gidley as 48 mm. As the specimen was a young juvenile, that still
retained the DI2 and DI3, the muzzle width would no doubt have grown
to match those of adult individuals of Cal . martini (to about 55 to
60 mm).

Additional specimens referable to Cal. martini have subsequently
been recovered from a number of Clarendonian localities in South
Dakota (Gregory, 1942; Tabrum, 1981; see also referred specimens
listing), including an additional immature skull, SDSM 55154. The
latter is associated with a mandible, the only known definitely
associated upper and lower dentitions for the species. It resembles
AMNH 10838 in all its facial characters, has a short, broad muzzle.

358
and its dp4 lacks an ectostylid. This absence is a derived character
state of Calippus, and not characteristic of Protohippus. Stirton
(1940, p. 190) questioned whether the juvenile mandible Hesse (1936,
Fig. 2) illustrated belonged to the same taxon as the type upper
dentition. The referred juvenile rami, including that of SDSM 55154,
indicate that Hesse's referral was correct.

About 45 km to the south, in north-central Nebraska, and in
stratigraphically equivalent horizons (Skinner and Johnson, 1984),
Cal. martini is an uncommon member of the Minnechaduza Fauna. Quinn
(1955, p. 21) referred to this population in a general way, and a
small sample was listed by Webb (1969a). The combined Nebraska and
South Dakota sample is slightly smaller than the Clarendon population
(Tables 37, 38), but the two are indistinguishable in dental and
facial morphology. For example, the length of the protocone relative
to the APL averages 34% and 38% in Clarendon premolars (P34s) and
molars (M12s), respectively. In the northern plains samples, the
values are 32% and 37%.

Quinn (1955) recognized a total of eight medium to large-sized
protohippines and equines in the Lapara Creek Fauna (Pro, perditus,
Equus sp . , E. laparensis, Hippotigris sellardsi, H^. parastylus, Plio.
supremus, Dinohippus subvenus, and Asinus sp.). Webb (1969a)
recognized the first four as a single taxon, which he referred to as
Astro hi ppus sellardsi, and the other four as Pliohippus supremus.
Forsten (1975) also recognized just two taxa, but in a different
combination. She referred to Pliohippus (Astro hi ppus) martini the
first six listed taxa, and only the latter two to Plio. (Pliohippus)

359

cf. Plio. supremus. Based on relatively complete skulls and
mandibles, contemporary faunas from the Great Plains (e.g. Clarendon
and Minnechaduza) contain at least three medium to large-sized
equines and protohippines: Cal. martini. Pro, supremus and Plio.
pernix. Dinohippus may also be present, as Tedford (pers. comm.)
recognizes it as early as the late Barstovian, but it is not yet
clearly documented in Clarendonian faunas. As previously indicated,
Calippus, Protohippus and Pliohippus are often difficult, or even
impossible, to distinguish on the basis of isolated cheekteeth, which
make up the bulk of the Lapara Creek sample. However, some of the
more complete specimens from this fauna can be relatively confidently
referred to each of the three taxa found in the more northern faunas.

Forsten (1975, p. 52) noted that her sample of "Plio." martini
varied considerably in morphology, and that two morphs could be
distinguished: a smaller population with hypoconal lakes, weaker
(often absent) pli cabal 1 ins, poorer styles, and weak or absent
protostylids; and a larger population with stronger styles, pli
caballin persistent and large in premolars and present in molars, and
large, well developed protostylids. She also noted that some of the
deciduous lower premolars lacked ectostylids (protostylids of her
terminology) and others had them (Forsten, 1975, p. 51). She
included these two populations in a single species because their
range in size greatly overlapped and they had other characters in
common. Samples from the Clarendon and Minnechaduza Faunas indicate
that these are among the consistent dental differences that
distinguish Cal. martini and Pro, supremus, respectively. While the

360
two are clearly distinct based on muzzle and facial characters, they
are of about the same size, and overall their cheekteeth greatly
resemble one another.

A limited sample from a lower horizon in the Bone Valley Formation
of south-central Florida is referable to Cal . martini . Its
morphology and size (Table 36; Figs. 55A, 55B) agree with the other
referred samples. They are larger than younger populations of Cal .
(Grammohippus) from the same region. Calippus martini is an
important biochronologic indicator in the Bone Valley. Its presence
in the Gray Zone (late Agricola Fauna) of Phosphoria Mine indicates a
Clarendonian age for this fauna. An M3 of Cal . martini (UF 24375)
suggests that the type of Pliocyon robustus Berta and Galiano (1984)
is Clarendonian, as the two specimens were found in close proximity
in undisturbed sediments.

Cal. (Grammohippus) cerasinus new species

Astrohippus martini (Hesse), WEBB et al., 1981, p. 527.

Type specimen. F:AM 114100, partial adult skull containing left
maxilla with P2-M3, and portions of the left facial region, orbit and
bra incase.

Type locality. Leptarctus Quarry (NE 1/4, NE 1/4 sec. 28, T34N,
R25W, Sparks Quad.), Cherry Co., Nebraska

Stratigraphic occurrence and age of type locality. Upper Merritt
Dam Member, Ash Hollow Formation, Ogallala Group. From channel
deposits incised into the Cap Rock Member (Skinner and Johnson,

361

1984). Xmas-Kat Fauna! Zone, very late Clarendonian, about 9.5 to

10.0 ma.

Topotypic sample. F:AM 114124 L P2; 114125-114126 2 R P34; 114127
L P34; 114128 R M12; 114129-114132, 114241 5 L M12; 114133 L M3;
114134 R p34.

Etymology, cerasinus, Greek meaning of or related to cherries.
In reference to the county which produced the holotype and thousands
of other vertebrate fossils.

Distribution. Very late Clarendonian (about 9.0 to 10.0 ma) of
Nebraska and Florida.

Referred specimens. Xmas-Kat Quarries Fauna, Cherry Co., NB.
Xmas Quarry: F:AM 114096 R mandible with i2,c,p2-m2; 114097 L male
mandible and symphysis with L i3,c,p2-m3 and R i2-i3,c; 114099 assoc.
R mandible with p2-m2 and L mandible with p2-ml; West Line Kat
Quarry: F:AM 114117 L P2; 114242 R P34; 114102 114118 2 R M12;
114103-114104 2 L M12; 114101 L mandible with p2-m3; 114119 R p34;
114120 R ml2; Quarter Kat Quarry: F:AM 114122 R M12; 114240 L M12;
114238 R ml2; Kat Quarry: F:AM 114115 L mandible with p2-ml;
Connection Kat Quarry: F:AM 114123 L ml2; East Kat Quarry: F:AM
114105 L P34; 114121 L p34; Wade Quarry: F:AM 114160 R mandible with
ml-m3. Precise locality and stratigraphic data for these sites are
in Skinner and Johnson (1984).

Love Site: UF 32268 assoc. R P4-M3 and L M1-M3; 32281 assoc. R
M1-M2; 32286 assoc. R DP2-DP4; 60315 assoc. R and L Ml; 65238-65239,
90266 3 R DP2; 65240-65241 2 L DP2; 65242, 92993 2 L DP34; 35974,
60251-60267 18 R P2; 36144. 60234-60246, 60248-60250 16 L P2;

362
60268-60275, 60277-60287, 60314, 60328, 60351-60352 23 R P34;
60288-60291, 60293-60294, 60297-60300, 60302-60306, 60308-60313,
60359 22 L P34; 60276, 60316-60327, 60329-60350, 92957 36 R M12;
60292, 60296, 60301, 60307, 60353-60358, 60360-60368 20 L M12; 60380-
60394 15 R M3; 60369-60379 11 L M3; 32143 R mandibular fragment with
p3; 32141 R mandible with dp2-dp3; 32194 R mandible with p3-m2; 32201
R mandible with p3-m3; 32206 L mandible with p3-m3; 32215 L mandible
with p2-p3; 96548 R dp2; 96549-96454 6 L dp2; 65246-65247, 92956,
96547 4 R dp34; 65243-65245, 92954-92955, 96545-96546, 96977-96978 9
L dp34; 59178-59184, 64528, 65248, 69804, 96557-96559 13 R p2; 59176-
59177, 64508, 96555-96556, 96976 6 L p2; 59185-59200, 68786 17 R p34;
59951-59956, 59958-59969 18 L p34; 59990-59999, 60207-60218 22 R ml2;
59970-59989 20 L ml2; 60219-60225, 68784-68785 9 R m3; 60226-60233 8
L m3.

Archer Fauna, Bone Valley Region. Nichols Mine: UF 24648 R ml2;
24634 R m3. Swift Mine: UF 18922 L Ml.

Diagnosis. Smaller than Cal. martini and with less high-crowned
cheekteeth. Unworn M12 MSCH about 50 mm; toothrow lengths of 105 to
110 mm in moderate wear. Moderately curved upper cheekteeth with
strong styles; anterolabial-posterol ingually oriented, elongate-oval
protocones with rounded lingual borders and shallow preprotoconal
grooves; hypoconal groove variable in depth, persistently open in
molars, closed to form lake and then lost with wear in premolars; pli
caballin vestigial in premolars, absent in molars. Protocone
relatively and absolutely longer than that of Cal . hondurensis.
Lower cheekteeth with small metastyles relative to metaconids.

363
generally with deeper ectoflexids than Cal . hon dure n sis, and with
more poorly developed protostylids.

Description. The holotype, F:AM 114100 (Figs. 57A, 58A; Table
36), is a partial skull of a young adult. The M3 is in the process
of erupting and its posterior half is as yet unworn. The ventral
half of the facial region is slightly crushed, but nearly complete.
The malar region lacks a distinct fossa, but contains a slight oval
depression equidistant between the anterior margin of the orbit and
the lOF. This depression resembles those sometimes found in crania
of Cal. martini, and may have been caused or accentuated by the
crushing. The malar crest is not expanded (as it is in
Pseudhipparion), and extends anteriorly just dorsal to the Ml
mesostyle. The lOF is located about 43 mm anterior from the orbit,
and 38 mm dorsal to the alveolar border above the Ml parastyle. F:AM
114100 is broken dorsal ly 5 mm above the lOF, so the condition of the
DPOF is unknown. The anterior-most point of the lacrimal is present
(about 32.5 mm in front of the orbit), and does not form part of the
DPOF (Fig. 57A).

The upper cheekteeth are moderately curved, with ROC of P34s
between 45 and 50 mm, and for M12s, between 38 and 45 mm. The styles
are moderately strong, and the P3 through M2 generally have a
moderate metastyle (Figs. 58A-58E). The protocone is elongate-oval
with a pointed posterior end. The protocone connects to the
protoselene at the onset of wear, and, in early wear-stages, the
connection is constricted by a moderate preprotoconal groove and the
postprotoconal valley. By mid-wear (e.g. the Ml of the holotype).

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> «00 Z3

C >>

I— (O +-> <U •
ro •!- C > U-
W» C 3 O
3 O O _I

I— T3 O
O C 'CM

O <U >»CJ ■-•

o s- s- I s:

in a>

ro CM

+J

«^ CT>

<D (0

>, to CM

I- 1—

1- <a o

3

s_ s- le

CJ5 <U

(O ^

•r- J=

3 OJ Lu

U. ■•->

cirz =)

367

o =>

. CVJ +J
(8 CM T- ■
■O CO 5

IJ. • >i >»

UJ ^ r—

. Q-'l-

, E >

' • >» <0

: ^ </) a>
1 CO -c

I CLXJ

i -o c >.

(O >—

I -J <u

I (U +J

• I— (O

I CO J2 s_

I ^ •!- oi

• CsJ -o -o

: ir> c o

^o m E

Q E «

o

LjJ • >,

1 _i r>. ••->

14- < <n c

0 »o 3

CO t3- 0

^ . r-~ .-• 0

+J <0 CT^ >-<

<u -o o^ >,

<u •■- wn s 5-

+J s- <t s-

^ 0 iJ^ •• <u

<u .— :d Li- ^

<u u. 0

j= •

0 T3 0 • •>

C U. >,

J- <o s-

<U • I-

2 (TJ CM • (0

0 -i<: ■-• '— 3

r- w E S- Cr

(0 <o

<4- 1. _J <U W

0 ja 3 <o

0) • E

(O ^ >-l +J X

S r~ ■=

OJ '4- CJ^ CT) ••

•1- 0 CJ^ •!- 0

> LO 1—

c to •>

I— <0 Li_ ^CO

(0 ..- => •.-

W> C ^1

3 0 • Q-CM

1— "O CQ 1 •!-

0 C CM

U <U O.QC

0 S_ •

« ^ _J T3

^ CO C

• 0 0.-0 10

cn q;

ir> <u _J ■»-> CO

+J <T3 E

0) nJ ••■-1

1. 1— 10 0 CM

3 LO 0 Q.

Dl 0) CJI W

•1- ^ cri to «

Li.

■t-i LO ro 0

CQ

369

370

Table 39. Standard univariate statistics for upper cheekteeth of
Calippus cerasinus n. sp. from the Xmas-Kat Fauna, upper Merritt Dam
Member, Ash Hollow Formation, Cherry County, Nebraska (latest
Clarendonian) and from the Love Site, Alachua Formation, Alachua
County, Florida (latest Clarendonian), and of Calippus hondurensis
from the Gracias Fauna, Department of Lempira, Honduras" Format as
in Table 2.

SPECIES

C. cerasinus

C. cerasinus

C. hondurensis

FAUNA

XMAS-KAT

LOVE
P2

GRACIAS

APL

23.1,1.78,2
21.8-24.3,7.65

20.0,1.52,26
17.8-22.9,7.60

22.2,0.75,3
21.5-23.0,3.38

BAPL

18.3,0.35,2
18.0-18.5,1.94

16.3,0.80,25
14.5-18.1,4.91

18.8, — ,1

TRW

16.7,0.76,3
16.2-17.6,4.53

16.4,0.78,28
14.7-17.9,4.79

16.0,0.42,3
15.7-16.5,2.60

PRL

4.4,0.15,3
4.2-4.5,3.50

4.5,0.39,26
3.9-5.8,8.62

4.3,0.12,3
4.2-4.4,2.71

PRW

3.6,0.35,3
3.3-4.0,9.76

3.6,0.27,25
3.1-4.1,7.32

P34

3.7,0.10,3
3.6-3.8,2.70

APL

18.8,0.64,6
17.8-19.6,3.41

17.1,1.07,35
14.7-19.1,6.27

17.9,0.75,10
16.6-19.2,4.18

BAPL

13.8,0.80,3
13.0-14.6,5.81

12.7,0.56,29
11.7-14.4,4.37

14.9,0.40,6
14.2-15.3,2.69

TRW

18.8,0.52,6
18.0-19.5,2.77

18.2,0.89,34
16.6-19.8,4.90

18.5,0.89,12
16.1-19.3,4.81

PRL

6.5,0.86,6
5.7-7.6.13.40

5.7,0.68,33
4.4-7.3,11.84

4.7,0.34.12
4.2-5.5,7.20

PRW

3.9,0.18,6
3.7-4.2,4.53

3.6,0.27,32
3.0-4.2,7.53

3.7,0.38,12
2.9-4.4,10.18

371

Table 39 — continued

M12

APL

19.0,0.94,13
17.2-20.8,4.96

16.4,1.23,46
13.8-19.4,7.50

16.9,0.73,7
15,9-17.9,4.32

BAPL

13.5,0.63,10
12.5-14.0,4.70

12.6,0.60,45
11.6-14.1,4.77

14.1,0.40,3
13.7-14.5,2.84

TRW

17.4,1.41,13
14.0-19.1,8.11

17.2,1.05,48
13.3-19.3,6.07

17.5,1.02,7
16.0-18.5,5.84

PRL

6.1,0.44,12
5.5-6.8,7.18

5.6,0.67,47
4.3-7.7,11.80

5.2,0.69,7
4.2-6.0,13.17

PRW

3.6,0.27,12
3.1-4.1.7.63

3.5,0.34,47
3.0-4.7,9.89

3.5,0.41,7
3.2-4.3,11.51

372

Table 40. Standard univariate statistics for lower cheekteeth of
Calippus cerasinus n. sp. from the Xmas-Kat Fauna, upper Merritt Dam
Member, Ash Hollow Formation, Cherry County, Nebraska (latest Claren-
donian) and from the Love Site, Alachua Formation, Alachua County,
Florida (latest Clarendonian), and of Calippus hondurensis from the
Graclas Fauna, Department of Lempira, Honduras. Format as in Table
2.

SPECIES C. cerasinus
FAUNA XMAS-KAT

ap1

bapl

atw

ptw

imnl

entl

apl

bapl

atw

ptw

mml

entl

18.3,0.60,5
17.5-18.9,3.28

7.5,0.85,5
6.2-8.4,11.40

10.0,1.08,5
8.5-11.2,10.73

6.6,0.71,5
5.4-7.3,10.81

6.1,1.80,5
3.5-7.8,29.55

18.7,1.25,9
16.6-19.9,6.69

10.2,0.97,9
8.9-11.4,9.44

10.9,0.80,9
9.8-11.7,7.36

8.5,0.71,9
7.5-9.4,8.31

7.3,1.61,9
4.3-9.3,21.89

£. cerasinus
LOVE
p2

16.8,0.92,8
15.8-18.7,5.45

13.2,0.17,4
13.0-13.3,1.32

7.8,0.35,8
7.2-8.3,4.47

10.2,0.46,7
9.5-10.7,4.48

6.8,0.59,8
5.8-7.8,8.72

5.7,1.06,8
3.9-7.3,18.55

p34

17.3.1.35,35
15.0-19.8,7.80

13.4,0.35,22
12.7-14.2,2.63

10.5,0.72,36
8.7-11.6,6.82

10.6,0.84,37
7.8-11.8,7.91

7.8,0.68,36
6.6-9.2,8.66

6.4,1.39,36
3.9-8.9,21.62

C. hondurensis

GRACIAS

20.5,0.85,3
19.6-21.3,4.17

15.5,0.07,2
15.4-15.5,0.46

7.6,0.25,3
7.3-7.8,3.33

10.5,0.12,3
10.4-10.6,1.10

7.8,0.36,3
7.4-8.1,4.62

7.7,0.32,3
7.3-7.9,4.19

17.8,0.82,11
16.6-19.1,4.60

14.5,0.94,5
13.6-16.0,6.52

10.4,0.89,11
8.1-11.1,8.53

10.8,1.00.11
8.3-11.8,9.32

8.9,0.43,11
8.0-9.6,4.80

6.3,1.29.10
3.9-8.0,20.45

373

Table 40~continued

ml2

ap1

17.3,2.01,10
13.7-20.5,11.61

17.2,2.24,35
14.2-22.4,12.97

15.7,1.40,12
14.3-19.3,8.92

bapl

13.4,0.35,2
13.1-13.6,2.65

12.6,0.59,27
11.5-13.8,4.69

13.0,0.21,5
12.8-13.3,1.59

atw

8.5,0.99,11
7.1-10.5,11.60

8.3,0.66,38
7.0-9.9,7.89

8.5,0.32,12
8.0-9.1.3.82

ptw

7.5,0.51,11
6.6-8.1,6.75

7.8,0.60,38
6.7-9.0,7.65

7.3,0.51,12
6.6-8.2,7.04

nvnl

6.9,0.58,11
5.6-7.5,8.31

6.7,0.86,36
4.9-8.5,12.72

6.6,0.73,12
5.8-8.3.11.12

enti

4.1,0.72,11
2.7-5.0,17.66

4.5,0.94,38
2.8-6.7,20.92

3.3,0.47,11
2.6-4.3,14.23

374

the preprotoconal groove becomes shallow and the protoconal
connection widens; further wear accentuates this. The PRL is
relatively similar to that of Cal. martini, averaging about 33 to 35%
of APL in P3-M2, and the protocone is similarly oriented in an
oblique, anterolabial-posterolingual direction (Fig. 58B). The pli
caballin is small and nonpersistent in the premolars, and absent in
molars. Fossette plications are also similar in number as those of
Cal. martini, but are slightly less persistent with wear, as in Cal.
hondurensis. Single, shallow pli protolophs and pli hypostyles are
variable in early wear-stages, only rarely observed in older
individuals. In premolars, the posterior half of the prefossette is
the most complex, with from one to four shallow plications in early
wear-stages (Fig. 58A); generally zero or one by mid-wear; and
unplicated in later wear-stages (Fig. 58D). The anterior half of the
postfossette bears at most two shallow plications in early wear (more
comnonly one or none), these are lost by middle wear-stages. In
molars, the pli protoloph and pli hypostyle are rarer, and, if
present, less persistent. The inner borders of the fossettes
generally have one plication each in early wear-stages; these are
shallow and nonpersistent. The hypoconal groove closes almost at the
onset of wear on the P2-P4, forming a lake that persists for about
the upper third of the crown, and is then lost at MSCHs of about 30
mm. The M12 of the Xmas-Kat Fauna sample generally retain open
hypoconal grooves until late wear-stages. Two individuals (F:AM
114102 and 114130), however, have lost the hypoconal groove at crown
heights of 40.0 and 31.0 mm, respectively. The M12s of the Love Site

375
sample tend to lose the hypoconal groove much earlier on average,
generally at MSCHs of 32 to 35 mm, although in some it may persist to
a MSCH of 26 mm or less (e.g. UF 60344). In both faunas, the groove
of the M12 rarely forms an isolated hypoconal lake (only one example
from the Love Site sample of about 50 molars); the structure just
becomes increasingly shallow until it disappears. Unworn or slightly
worn MSCHs are about 36 mm for the P2, 47 mm for the P34 and 50 mm
for the M12.

Deciduous upper premolars (Figs. 58F, 58G) have rudimentary pli
caballins in early wear, that are soon lost. Protocone shape and
orientation, styles, and fossette complexity resembles that of
permanent premolars. The hypoconal groove is open in very early
wear-stages, closes to form a lake, and is lost in late wear-stages.

Lower cheekteeth (Table 40; Fig. 59) are smaller than those of
Cal. martini, but similar in morphology. The premolars in early wear
have the metastylid well separated from the metaconid by the
linguaflexid and an anterol ingual projection of the entoflexid (Fig.
59E). The metastylid is notably smaller than the metaconid, and it
is generally positioned more 1 ingual ly. The ectoflexid on the p2 is
shallow and does not penetrate the isthmus; on the p34, it generally
partially penetrates the isthmus, deeper than the labial borders of
the metaflexid and entoflexid. With wear, the flexids retract,
broadening the dentine confluence of the conids. By latest
wear-stages (Fig. 59F, p3), the metaflexid and linguaflexid are
particularly shallow. The molars in earliest wear-stages have
relatively more expanded metaconids and metastylids than in Cal .

376

martini. The lingual flexids are shallower and less well developed
than those of the premolars, particularly the entoflexid. The
isthmus is completely divided by a deep ectoflexid, that, until it
begins to retract in late wear, separates the metaconid and
metastylid. Typical of Calippus, the lingual flexids retreat with
wear (contrast Figs. 59B, 59C, and ml of 59F). Protostylids, if
present, are restricted to the lower part of the crown and are weak.
In the Love Site sample, more than 90% of the p3-m3 bear not even the
slightest trace of a protostylid. Plications are rare, and generally
limited to minor pli entoflexids in early wear-stages. The dp2 has a
persistently shallow ectoflexid, lacks a pli caballinid or isthmus
plications, and has a well developed metaconid. The dp34 differ from
those of Cal_. martini by having deep ectoflexids and linguaflexids in
early wear-stages. Protostylids are more vestigial than in Cal.
martini, and ectostylids are absent. Unworn or slightly worn mcch
are about 30 mm for p2s, 45 mm for p34, and 48 mm for ml2.

The incisors and muzzle region of Cal. cerasinus are at present
best known from mandibular symphyses (e.g. F:AM 114097, Figs. 57B,
59F). They are very similar to those of Cal. martini and Cal.
hondurensis. The occlusal surface of the R and L il2 form a straight
line, the il2 are large relative to other equids, and the male lower
canines are especially massive and conical. The muzzle width appears
to be at least 50% of the UTRL.

Discussion. Calippus cerasinus is closely related to Cal .
hondurensis. The two are inseparable on the basis of size (Fig. 56;
Tables 39, 40), and differ only in details of cheektooth morphology

377
and crown height. The most important of these are length, morphology
and orientation of the protocone, the formation of a hypoconal lake
on the P34, the strength of the pli cabal! in, the depth of the
ectoflexid on p3-m3, and the relative size and separation of the
metaconid and metastylid on p34. The unworn crown height of Cal.
hon dure n sis cheekteeth are about 10? greater than those of Cal.
cerasinus.

Calippus cerasinus is at present recognized from two faunas that
are quite separated from one another geographically, but that seem
very close biochronologically (see also Webb et al., 1981; Webb and
Hulbert, 1986; Tedford et al., in press). Much of the apparent size
differences between the two populations (Fig. 56; Tables 39, 40) are
related to differences in age distributions. The Xmas-Kat sample
(especially the uppers) includes a greater proportion of younger
individuals, which accounts for its greater means for many of the
characters. The basal lengths of molars and premolars indicate that
individuals from the Xmas-Kat population averaged only about 5 to 8%
larger than those from the Love Site. This minor size difference is
not considered sufficient to separate the two as distinct species.

Cal. (Grammohippus) hondurensis (Olson and McGrew), 1941
new combination

Pliohippus sp., FRICK, 1933, p. 528.

Pliohippus hondurensis OLSON and MCGREW, 1941, pp. 1232-1235;

WEBB and PERRIGO, 1984, pp. 245, 247-249 (in part).

378

Type specimen. WM 1769, palate with R P2-M3 and L P2-P4.
Type locality. Rancho Lobo, 6 km NW of Gracias, Department of
Lempira, Honduras.

Stratigraphic occurrence and age of type locality. Gracias
Formation; early Hemphillian, about 7 to 9 ma.

Topotypic sample. In addition to those listed by Olson and McGrew
(1941): F:AM 27029 L maxilla with P2-M3; 27028 L maxilla with P2-M2;
27021 assoc. R and L DP2-DP4; 27030-27032, 27040 4 mandibular
fragments with teeth; UP 17754 assoc. R P3-M1; UP 17755 assoc. L Ml-
M3; UP 92339 L P2; 92340, 92344 2 R P34; 92341 R M3; 92342-92343 2 L
M3; 92326 assoc. R p2-m3; 17758 R p2; 92327-92333 7 R p34; 92347-
92348 2 L p34; 92334, 92345-92346 3 R ml2; 17782, 92338 2 L ml2;
92335-92337 3 L m3; 92349 L mandibular fragment with m3. The P:AM
sample also includes a number of isolated teeth and post-cranial
elements.

Distribution. Early Hemphillian (about 7.0 to 9.0 ma) of Honduras
and Plorida. Late (?) Hemphillian of Mexico.
Referred specimens. -Gracias Pauna, Saddle Locality, Honduras (see
Webb and Perrigo, 1984, Fig. 3 for location of UP sites in the
Gracias Formation of Honduras): UP 92351 L M12; 92350 R p34; 17745 L
ml2; New Year Locality, Honduras: UP 17774, 92358-92360 4 R P34;
92355-92357 3 L P34; 92361-92364 4 R M12; 92365-92366 2 R M3; 92352-
92354, 92367 4 L M3; 92370 R p2; 92372 L p2; 92368-92369 2 R p34;
92373-92374 2 L p34; 92371 R ml2; 92375 L ml2; El Carrizal Locality,
Honduras: UP 92376-92377 2 L P34; 92378-92379 2 R P34; 18017 L ml2.
Tehuichila Fauna, Hildalgo, Mexico: AMNH 8343 L P34.

379

Mixson's Bone Bed. Levy Co.. FL; F:AM 113641 L P2; 113642-443643,
113645 3 L M12; 113646 R P4; 113648 R M3.

Revised diagnosis. Smaller than Cal. martini or "Pro." castilli,
with moderately worn toothrow lengths of about 101 to 112 mm. Unworn
M12 MSCH about 55 mm. Protocone small, oval, with persistent
preprotoconal groove and flattened lingual border. Hypoconal groove
shallow; persistently open until late wear-stages in molars; closed
earlier in premolars, without hypoconal lakes on P34. Molars with
pli caballins in early wear. Ectoflexid generally shallower than in
Cal. cerasinus, rarely penetrating isthmus in p2-p4. Large
metastylid on p34. Protostylids variably developed.

Description. The facial region of Cal. hondurensis is unknown.
The most complete cranial material includes the holotype and F:AM
27029, both of which preserve only the ventral-most portion of the
face. The anterior portion of the malar crest is well preserved on
F:AM 27029. As in Cal. cerasinus, it is uninflated. Its
anterior-most part is directly dorsal to the Ml parastyle.

The cheekteeth of Cal. hondurensis were admirably described by
Olson and McGrew (1941). Of particular note was their attention to
ontogenetic variation in enamel morphology. A slight drawback was
their failure to distinguish between molars and premolars in their
discussion of upper cheekteeth, as they did with the lowers. The
following discussion will highlight those features of Cal.
hondurensis that differ from those of other members of Cal.
(Grammohippus), that allow Florida specimens to be referred to this

380
Central American taxon, and that allow it to be placed in Calippus
rather than Pliohippus.

As noted by Olson and McGrew (1941) in their diagnosis, a
characteristic feature of Cal. hondurensis is its relatively short
protocones (Table 39; Fig. 55C). For the Honduras sample, the P34
protocone length averages 26% of the APL; the Ml protocone, 3U.
Those of the premolars in particular are much smaller than those of
Cal. martini or Cal. cerasinus, that average between 32 to 36% of the
APL. Other important features are the persistently deep
preprotoconal groove and the flattened lingual border of the
protocone (Fig. 55C). The difference in the preprotoconal groove
between Cal. hondurensis and Cal. cerasinus is best judged comparing
similarly worn teeth, e.g. Figs. 55C and 58D. In Cal. hondurensis.
the premolars in early wear-stages have moderately well developed pli
caballins, and the molars have small ones; these along with the
fossette plications are lost by middle wear-stages. A hypoconal lake
is formed only on the P2 in the available F:AM and UF samples. In
the P34, the well developed hypoconal groove in early wear becomes
progressively shallower with wear, and is generally lost at MSCHs of
about 28 mm. The hypoconal groove generally persists in the molars
until late wear-stages, although it can be lost in teeth with MSCHs
as great as 30 mm. Unworn or slightly worn MSCHs for P34 are about
51 mm and about 55 mm for the M12.

Lower cheekteeth (Table 40) differ notably from those of Cal.
cerasinus in the greater relative size of the metastylid (especially
on slightly worn premolars), in the shallower ectoflexids, and in the

381

deeper and more expanded linguaflexids at similar wear-stages.
Protostylids are variably developed, but are generally present on the
p3-m3. They usually begin to be expressed on the occlusal surface
when crown heights reach from 20 to 30 mm, and can be moderately well
developed (e.g. F:AM 27031), although not to the degree of
Protohippus or Cal. (Calippus) .

The incisor region is best preserved on WM 1771 (Olson and McGrew,
1941, Plate 2B). The symphysial region is similar to, but relatively
even more massive than, that of Cal. cerasinus (e.g. F:AM 114097),
and the male canines are equally massive and conical. The enlarged
symphysis and short diastema are characteristic of Calippus.

Discussion. Olson and McGrew (1941) assigned their new species to
the genus Pliohippus, but failed to note any distinctive (i.e.
derived) characters that it shared with that taxon. In a brief
section discussing relationships, they exclude Nannippus because of
its isolated protocones, and "Pro." placidus because of its
straighter upper cheekteeth and (supposed) less complex fossettes.
Pliohippus upper cheekteeth differ from those of "Plio." hondurensis
in having rapidly closed hypoconal grooves, very frequent connection
of the protocones and hypocones (Skinner et al., 1977), and are more
curved. Connected protocones and hypocones are very rarely observed
in Cal. (Grammohippus) populations (1 to 2% of observed molars).
Pliohippus lower cheekteeth lost the protostylid in the late
Barstovian. "Plio." hondurensis dentally is very similar to Cal .
martini and Cal. cerasinus. The few known incisor arcades associated
with cheekteeth of "Plio." hondurensis. especially WM 1771, appear to

382
show Calippus-like features. "Plio." hondurensis is therefore
transferred to Cal. (Grammohippus).

The topotypic sample of Cal. hondurensis was derived from fluvial
sediments in Honduras. The first major collection was made by Blick
in 1929, and later briefly mentioned by Frick (1933) in his
description of the proboscideans. Olson and McGrew (1941) and Webb
and Perrigo (1984) reported the presence of Cal. hondurensis not only
at Rancho Lobo, but at a number of other localities within the
Gracias Formation. As noted above, specimens from El Salvador
referred to Cal. hondurensis by Webb and Perrigo (1984) are much
larger than that species, and have much deeper ectoflexids. They do
not represent Cal. hondurensis, but rather some member of the equine
clade. Generic identification of the sample will require more
complete specimens. A premolar from the Tehuichila Fauna, AMNH 8344,
is indistinguishable from topotypes of Cal. hondurensis.

Olson and McGrew (1941) concluded that the age of the Gracias
Fauna was Clarendonian, primarily based on the stage of evolution of
the equids. McGrew (1944a) later adjusted the age upwards into the
Hemphillian based on the presence of Osteoborus cynoides. Webb and
Perrigo (1984) reviewed the Gracias Fauna, and confirmed its age as
early Hemphillian. The other common equid in the Gracias Fauna is
Cormohipparion ingenuum, that was originally described from Mixson's
Bone Bed in Florida (see above).

A limited sample of six upper and two lower cheekteeth from
Mixson's Bone Bed apparently represent a population of Cal .
(Grammohippus) referable to Cal. hondurensis rather than Cal .

383
cerasinus. Important features observed in the sample (Fig. 55C;
Table 36) are short protocones with flattened labial borders; deep,
persistent preprotoconal grooves; and strong pli caballins on
premolars. The presence of Cal. hondurensis at Mixson's would seem
to confirm a Hemphillian age for the Gracias Fauna.

Cal. (Grammohippus) sp.. cf. Cal. hondurensis

Referred specimens. McGehee Farm: UF 17259 L DP34; 9506, 17236A
2 R P34; 17236B L P34; 18323, 16624 2 L M12; 17237 L M3; 18940 R p34;
17242 R ml2.

Haile 19A: UF 45948/47489 assoc. R P2-P4 and L P2-M3; 47322,
65733 2 partial upper cheekteeth

Discussion. This limited sample of cheekteeth is definitely
referable to Cal. (Grammohippus), but is morphologically intermediate
between Cal. cerasinus and Cal. hondurensis. Most of the specimens
are either heavily worn or broken, thus hindering specific
identification. UF 18323 (Fig. 55D) is one of the best preserved
specimens, and of the sample it most resentiles Cal. cerasinus in its
protocone morphology. Others do have better developed and more
persistent preprotoconal grooves, as is characteristic of Cal .
hondurensis. The lingual border of the protocone varies from rounded
as in UF 18323 to slightly flattened as in UF 17236 and UF 17259.
The protocone orientation is less oblique than in Cal . cerasinus. but
more than in Cal. hondurensis. On UF 52963, the metastylid is
relatively large, as in Cal. hondurensis. This sample was referred

384
to "Pliohippus" hondurensis by Waldrop (1971), who was the first to
recognize the close relationship between the Central American and
Florida samples. The McGehee and Haile 19A populations probably
represent a slightly older sample within an evolving chronospecies
than that of Mixson's, but larger, more complete samples are needed
before they can be referred to a species with a high degree of
confidence.

The three principal north-central Florida localities of the Archer
Fauna (the Love Site, McGehee Farm and Mixson's Bone Bed) otherwise
share a common equid fauna at the species level, except for some
absences at Mixson's. While other mammalian taxa are similarly
shared (e.g. camelids, dromomerycids), others differ (see Chapter 4).
The degree of evolution of Cal. (Grammohippus) suggests the relative
ages for the three sites are, from oldest to youngest. Love, McGehee
and Mixson 's.

Cal. (Grammohippus) maccartyi new species

Pliohippus cf. hondurensis Olson and McGrew, BECKER, 1985a, p.
29.

Type specimen. UF 69951, badly crushed anterior half of skull of
adult male with R and L 11-13, C, P2 and L P3-M3; assoc. mandibular
symphysis and lower cheekteeth, R and L il-i3, c, p2 and L p4-m2.
Skull and mandible were found in near occlusion and certainly
represent a single individual. Collected by R. McCarty on 5 March
1985.

385

Type locality. Moss Acres Racetrack Site, 5.8 km E of Morriston,
Marion Co., Florida.

Stratigraphic occurrence and age of type locality. From a massive
clay deposit, Alachua Formation; late{?) early Hemphillian, about 7
ma.

Topotypic sample. UF 65249 L DP34; 95407 R P2; 90299 L M12; 95397
R p34; 90287 R ml2; 90298 3 lower cheektooth fragments.

Etymology. Named for Russell McCarty of the Florida State Museum,
who collected and prepared the holotype and several of the topotypes.
Formation of the species name follows Recommendation 21a of the
International Code of Zoological Nomenclature (1964, p. 109).

Distribution. Known only from the early, probably late early
Hemphillian (about 6.0 to 7.5 ma) of north-central Florida.

Referred specimens. With 4A: UF 45537 L P2; 17240 R P34; 45540 L
P34; 45535-45536 2 R M12; 45538 L M3; 53460, 53487 2 R p34; 53463 R
ml2; 61348 R m3.

Diagnosis. Small species of Cal . (Grammohippus) with toothrow
lengths of about 100 mm. Preprotoconal groove deep, persistent.
Protocones elongated, not short as in Cal. hondurensis; lingual
borders rounded to slightly flattened; oriented slightly obliquely.
Hypoconal groove open until mid-wear; forms lakes on P2-P4. Pli
cabal! in small, single; fades with wear; vestigial or absent in
molars. Plications simple but persistent, not lost until heavy wear.
Upper cheekteeth not as curved as other species of Grammohippus.
Lower cheekteeth with widely expanded metaconids and metastylids;
lingual flexids more persistent than other species; variable

386

protostylids; enamel plications in early wear-stages. Ectoflexid
shallow on p2-p4, only moderately deep on ml-m3. Muzzle width about
602 of UTRL.

Description. Calippus maccartyi is as yet known only from a small
number of specimens, but its dental morphology (especially the
lowers) indicates the presence of a distinct species of Grammohippus.
The holotype (UF 69951) is one of the five known Tertiary equid
specimens from Florida with associated upper and lower dentitions.
The other four (two individuals of Nannippus and two of Cormohip-
parion) are also from the newly discovered Moss Acres Racetrack Site.
UF 69951 consists of the anterior (pre-orbital ) half of a skull, but
it has been crushed laterally such that no facial characters can be
recognized. The specimen does suggest that any fossa was shallow at
best. The premaxillary region is the least damaged part of the
cranium, but it is still cracked and distorted. The teeth that are
present, however, are very well preserved, except for the left 13,
which has the top 10 mm of its crown broken off. Much of the
mandibular symphysis is preserved intact and undistorted. The
incisors display the characteristic Calippus morphology (Fig. 61):
il2 are aligned in a straight row; the i3 was originally positioned
at a sharp angle to them, but with wear its occlusal surface has
become aligned with that of the il2. The width across the i3s of UF
69951 is 58.4 mm. Due to the post-mortem crushing, this value is
probably within 2 mm of the true width, and is probably too small (as
the teeth are compressed laterally). The diastema between the i3 and
c is short (4.6 mm). The left c is 7.5 mm long and 6.1 mm wide.

387

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388

Figure 61. Occlusal view of mandibular symphysis of Calippus
(Grammohippus) maccartyi n. sp.; UF 69951, holotype; from Moss Acres
Racetrack Site, Marion County, Florida. Teeth present: R il-i3; L
il-iS, c; R side of symphysis is broken and the iS has been restored
to near its original position.

389

Upper cheekteeth of Cal. maccartyi (Table 36; Figs. 60A-60C) are
smaller than average-sized individuals of Cal. cerasinus or Cal .
hondurensis, but fall within their observed ranges. UF 69951 is an
adult, with the occlusal surface of the M3 fully worn, and a Ml MSCH
of about 27 mm. The P2 of UF 69951 seems relatively more heavily
worn, perhaps pathologically, when compared to the other teeth. The
P2 protocone is short and rounded, with a broad connection to the
protoselene. It has no pli cabal lin, and the hypoconal groove is a
small lake on the left side, while the right side has lost all trace
of it. Fossette plications are limited to a vestigial pli
prefossette and a single, modest pli postfossette. The metastyle is
still relatively prominent. On the less worn UF 95407, there is a
small pli cabal lin, a deep hypoconal groove that is in the process of
being closed off by a labial projection from the hypocone, and an
oval, very obliquely oriented protocone. The fossettes are also
simple, although the single pli prefossette and pli postfossette are
deeper than in UF 69951. On the P3 and P4, the protocone is large,
more elongate-oval in shape, oriented anterolabial-posterolingually,
and with a slightly flattened lingual border (Fig. 60A) . The
preprotoconal groove is moderately deep, so that the protoconal
connection is notably constricted. A single, small pli caballin is
present on both the P3 and P4 of the type. The more heavily worn
premolars from the referred With 4A sample lack pli caballins, but
still have moderate preprotoconal grooves. The P4 of UF 69951
retains an open hypoconal groove, while the P3 has an isolated lake.
The preprotoconal grooves of the Ml and M2 are shallower than those

390
of the premolars, thus broadening the protoconal connection, and the
protocone is less obliquely oriented (Fig. 60A) . The type Ml and M2
both lack a pli cabal lin, but the less worn UF 90299 has a very small
one. The hypoconal groove closes on molars variably during ontogeny;
it would close on UF 90299 at a MSCH of about 20 mm, but would be
present until late wear on UF 45535. On both M3s the hypoconal
groove opens directly into the postfossette, a not uncommon condition
in Calippus M3s. The M3 of UF 69951 also has an isolated protocone,
a feature not observed in a sample of 25 specimens of Cal . cera sinus
from the Love Site. An isolated protocone is rarely observed in M3s
of Cal. martini. Molars in early wear-stages (as exemplified by UF
90299) have very deep preprotoconal grooves.

The fossettes of the P3-M3 are similar. A pli hypostyle or pli
protoloph are not observed, except during earliest wear-stages. The
opposing inner fossette margins are closely appressed (Figs. 60A,
60B), more so than in other species of Grammohippus. Fossette
plications are shallow, unbranching and not numerous, but are
retained until the MSCH reaches about 20 mm or less. With the
limited sample, unworn crown heights are not directly observable.
The specimen with the greatest MSCH (UF 45535, 40.2 mm) has formed
roots and has a completely worn occlusal surface. Therefore, its
unworn crown height would have been at least 5 to 10 mm greater. ROC
of available specimens of Cal. maccartyi varies from 55 to 85 mm,
much greater than that of Cal. cerasinus or Cal. hondurensis (their
OR is 38-50 mm). The crowns are not as straight as those of Cal.
(Calippus), however.

391
The lower cheekteeth of Cal . maccartyi (Table 36; Figs. 60D, 60E)
are considerably advanced over other species of Grammohippus. with
large, widely flairing metaconids and metastylids. They greatly
resemble the basic enamel pattern observed in Astrohippus, as the
metaconid, metastylid and unpenetrated isthmus form a "Y" (Fig. 60D).
In premolars (Figs. 60D, 60E), the ectoflexid is shallow, the labial
borders are rounded or only slightly flattened, and the lingual
flexids are deep and persistent through much of the crown. The
metaconid of the p2 is large and well developed. In earliest
wear-stages, there may be plications extending posteriorly from the
isthmus and/or protolophid on both premolars and molars. Molars
resemble the premolars more than in any other species of Calippus,
but do differ in their deeper ectoflexids and narrower occlusal
surfaces. On p3 to m3, the protostylid is a variably developed ridge
that extends to near the top of the unworn crown, and that often
becomes more prominent with wear (Fig. 60D). Even extremely worn
molars (e.g. UF 53463) retain well developed lingual flexids.

Discussion. Calippus maccartyi is recognized from only two early
Hemphillian localities in north-central Florida. The combined
presence of Indarctos and Machairodus at With 4A indicate a late
early Hemphillian age (Becker, 1985a; Tedford et al., in press).
Neither is present at Moss Acres, but its fauna (Table 1) indicates a
similar but younger age than either the Mixson's or McGehee local
faunas. Cal. maccartyi represents one of the youngest known species
of Cal. (Grammohippus), and is the most dervived in terms of dental
evolution. The lower cheekteeth of Cal. maccartyi greatly resemble

392

those of Astro hi ppus, however this is interpreted to represent
parallelism and not an especially close phylogenetic relationship
(see below). Pseud, simps on i is a third equid lineage that evolved a
similar morphology (Webb and Hulbert, 1986).

Genus Protohippus Leidy, 1858

Protohippus LEIDY, 1858, p. 26.

Type species. Pro, perditus (Leidy), 1858.

Included species. Pro, supremus Leidy, 1869; Pro, gidleyi n. sp.

Chronologic and geographic distribution. Late Barstovian through
early Hemphillian of Great Plains and Florida; late Barstovian and
early Clarendonian of Texas Gulf Coastal Plain; possibly Clarendonian
of California.

Revised diagnosis. Medium to large-sized, hypsodont, tridactyl
equids with toothrow lengths generally between 125 and 145 mm in
mature individuals. MF absent; DPOF large, teardrop-shaped,
relatively shallow; distinctly rimmed dorsally and posteriorly in
earlier populations, often with a small posterior pocket; less
distinct in later populations, without a pocket. Lacrimal bone
large, included in posterior region of DPOF. Diastema short; rostrum
broad, but not to the degree of advanced species of Calippus;
incisors form typical rounded equine arcade. Upper cheekteeth with
large, elongate-oval protocones that are isolated from the proto-
selene to varying degrees during early wear-stages (most prevalent on
P34 and MS); moderately large, single pli caballins on P34 (smaller

393
and less persistent with wear on molars); simple but relatively
persistent fossette plications; hypoconal groove generally remains
open until at least middle wear; prominent parastyles on P34. Large
protostylids on permanent and deciduous lower cheekteeth. Variably
developed ectostylids on dp2-dp4.

Discussion. Leidy (1858) first named Protohippus as a subgenus of
Equus. but later (e.g. Leidy, 1869) raised it to generic rank. Its
wide-spread use in the latter half of the 19th Century is evidenced
by Leidy, Marsh and Cope having described 11 species of Protohippus
before 1900 (Gidley, 1907). However, many of these were subsequently
regarded as synonymous and/or belonging to other genera (Stirton,
1940; Webb, 1969a), and only three species of Protohippus are here
recognized as valid. In a series of papers based on an increasing
number of relatively complete specimens with more accurate locality
data, Gidley (1904; 1906a; 1907) was able to redefine Protohippus and
clearly distinguish it from Pliohippus and Merychippus. Gidley's
(1907) concepts of Pliohippus and Protohippus were essentially fol-
lowed by Osborn (1918) and Matthew (1926). McGrew and Stirton (e.g.
McGrew, 1938; McGrew and Meade, 1938; Stirton, 1940) proposed a hori-
zontal reorganization of equid genera, in which a number of "primi-
tive" species thought ancestral to a number of advanced genera were
all transferred to a single genus, Merychippus. Pro, perditus (the
genotype) was one of these, and Protohippus was subsumed within
Merychippus as a subgenus. The chronologic distribution of species
played a major role in determining generic assignments in their
scheme. They considered the boundary between the Miocene and

394

Pliocene to fall between the Devil's Gulch and Burge Faunas, and all
late Miocene non-anchitheriine equids were considered to belong in
Merychippus. The characters they used to define Merychippus are all
primitive, and can no longer be considered valid reasons for taxo-
nomic grouping. MacFadden and Skinner (e.g. MacFadden and Skinner,
1981; MacFadden, 1984a) have recognized pre-Burge equid populations
with Merychippus -grade dentitions as members of advanced genera
(Hipparion and Cormohipparion). A similar, vertical repartitioning
of the taxa Stirton (1940) assigned to Merychippus (Protohippus) is
therefore appropriate, and can be based on the strati graphically-
controlled Frick collection of crania and associated dentitions.

Protohippus perditus (Leidy), 1858

Equus (Protohippus) perditus LEIDY, 1858, pp. 26-27.

Protohippus perditus (Leidy), LEIDY, 1869, pp. 275-277, GIDLEY,

1906a, pp. 136-139 (in part); GIDLEY, 1907, pp. 882-883 (in

part); OSBORN, 1918, pp. 129-130; QUINN, 1955, pp. 19-21 (in

part); EVANDER, 1978, p. 41.

Protohippus or Hippotherium profectus COPE, 1889, p. 447.

Merychippus perditus (Leidy), COPE, 1892, p. 943; MCGREW and

MEADE, 1938, pp. 200-202; STIRTON, 1940, p. 182; HESSE, 1943,

pp. 168-169; FORSTEN, 1975, p. 31.

Eoequus wilsoni QUINN, 1955, pp. 54-58.

Merychippus circulus (Quinn), FORSTEN, 1975, pp. 32-35 (in

part).

395

Type specimen. USNM 619, a R maxniary fragment with P4-M3.

Type locality. Exact locality unknown; from "the valley of the
Niobrara River" (Leidy, 1858, p. 20), in Nebraska.

Strati graphic occurrence and age of type locality. Unknown, but
probably from the Valentine Formation (Devil's Gulch or Crookston
Bridge Member?) or stratigraphic equivalent; late Barstovian, about
13 ma.

Distribution. Late, but not latest, Barstovian (about 12 to 14
ma) of the northern Great Plains and the Gulf Coastal Plain of
Florida and Texas.

Referred specimens. Devil's Gulch Fauna, Devil's Gulch Horse
Quarry, Brown Co., NB: F:AM 60350-60352, 60358, and 114067 5 skulls;
F:AM 114091 mandible with dp2-m2. There are many additional, mostly
uncatalogued, crania, mandibles and teeth in the F:AM collection from
this fauna. Additional material from the slightly older Crookston
Bridge (Evander, 1978) and Norden (Skinner and Johnson, 1984) Faunas
is also referable to Pro, perditus, and is principally housed in the
UNSM and F:AM collections.

Cold Spring Fauna. Cold Spring l.f., San Jacinto Co., TX: TMM
31219-165 assoc. R DP2-DP4,M1-M2 and L DP2-DP4,M2-M3; -230 partial
skull with R DP3-DP4,M1-M2 and L DP1-DP4,M1-M2; -61, -328 2 L P2;
-253 R P34; -329, -330 2 L P34; -331, TAMU 3030 2 R M12; TMM
31219-332 L M12; -333 R M3; -5 L M3; -203 assoc. R and L mandibles
with dp2-dp4 (probably same individual as 31219-165); -43 R mandible
with dp2-ml (probably same individual as 31219-230); -204 R mandible
with p4-m3; -337 L mandible with p2-ml; -138 L assoc. p4-m3; -168

396
assoc. (?) L p3-p4; TAMU 3027 R dp4; TMM 31219-334 R p2; -336 R p34;
-335, TAMU 3028, 3029 3 L p34; TMM 31219-338-340 3 L ml2. Noble Farm
l.f.. Grimes Co., TX: TAMU 3031-3033 3 R P34; 3034 L M12; 3035 L
mandible with dp2-m2; 3036 R p34. Chapel Hill, Washington Co., TX:
TMM 31272-8 L M3; Goodrich l.f., Polk Co., TX: TMM 31183-30, -37 and
-66 assoc. skull with R and L P2-M3 and R and L mandibles with p2-m3
(holotype, Eoequus wilsoni ; Quinn, 1955, Plates 10-13).

Bradley Fauna, Bone Valley Region. Kingsford Mine (Paige No. 1
Dragline): UF 61344 L P4; 95902 R M3.

Revised diagnosis. Slightly smaller and less hypsodont than Pro.
supremus, with toothrow lengths of about 120 to 135 mm and unworn M12
MSCH of about 47 mm. Relatively short postcanine diastema and large
DPI. Shorter, more oval protocones than other species of Pro to hi p-
pus; also shorter metaconid-metastylid complexes and entoflexid
lengths.

Description. The holotype of Pro. perditus (Osborn, 1918, Fig.
102) lacks precise locality data, and was recovered from a region
where vertebrate fossils have been found ranging from the early Mio-
cene to the Pleistocene. A large sample of upper dentitions from the
Devil's Gulch Horse Quarry (DGHQ) closely match USNM 619 in size and
morphology, and are here referred to Pro, perditus following unpub-
lished work by Morris Skinner. This sample also includes associated
mandibles and crania, thus permitting a more complete description of
one of the earliest named North American equid species.

The cranial morphology of Pro, perditus is well preserved on sev-
eral skulls from the DGHQ, especially F:AM 60350 and 60351. No MF or

397
depression is evident on these specimens, as well as USNM 619 or TMM
31183-30 (Quinn, 1955, Plate 12). The DPOF is large, oval or
teardrop-shaped, running from above the anterior half of the M3 to
the posterior half of the P3. Its greatest length is about 80 mm;
its maximum height measured perpendicular to the latter and just
posterior to the lOF is about 45 mm. The posterior and dorsal mar-
gins of the DPOF on the lacrimal and nasal bones are well rimmed, and
there is a slight posterior pocket. The preorbital bar is narrow
(about 13.5 to 15.5 mm). The postcanine diastema is shorter than
that of Pro. supremus, and the incisor region is only slightly
expanded (Fig. 43; the muzzle width is about 38% of the UTRL). A
relatively large DPI (12 to 13 mm long) is retained with the adult
dentition, functionally occludes with the p2, contains several
distinct cones and lophs, and resembles those of Pliohippus.

The upper cheekteeth of Pro, perditus (Table 41; Fig. 62A) are
characterized by oval (elongate-oval in early wear) protocones that
are isolated from the protoselene in very early wear-stages (Quinn,
1955, Plate 10.1), but which then rapidly connect. When isolated,
the protocones have large anterolabial spurs. Protocones of the
premolars are notably shorter than those of the molars. In heavily
worn molars, the protocone not uncommonly connects with the hypocone.
Fossette plications are relatively simple, and not as numerous as in
Pro. supremus or Pro, gidleyi, nor is the prefossette loop so well
formed. By moderate wear-stages, only a single pli prefossette and
pli postfossette remain (Fig. 62A). The hypoconal groove remains
open until moderate wear; it may simply fade with wear, or persist as

398
an isolated lake. The pli cabal! in is generally less prominent than
in Pro. supremus or Pro, gidleyi, and is frequently absent in
moderately worn teeth. The upper cheekteeth are moderately curved,
with ROC usually about 45 to 55 mm. Examples of measurable slightly
worn or unworn teeth are rare. MSCHs for the slightly worn P2 and P3
of TMM 31183-30 are about 36 and 42 mm, respectively. The slightly
worn Ml of TMM 31219-230 has a MSCH of 43.3 mm. Two very slightly
worn molars from the DGHQ have MSCHs of 42 and 45 mm. Thus unworn
MSCH of the M12 probably lies between 45 and 50 mm. The DP2-DP4
resemble the permanent cheekteeth, but the protocone is relatively
much shorter, and the fossette plications are more numerous and
persistent in early wear-stages (e.g. TMM 31219-165). Small pli
caballins are present and the hypoconal groove remains open even in
heavily worn DPs.

Lower cheekteeth (Table 42) are typically protohippine, with large
protostylids on p3-m3 and dp34. The metastylid is equal or subequal
to the metaconid in size. Permanent premolars in early wear most
often have a long isthmus that connects to the metaconid, and the
metastylid buds off the metaconid posteriorly and lingual ly. In
some, the ectoflexid can be deep, and penetrate the isthmus to
varying depths (this morph is very common in the Cold Spring sample).
In the majority of observed premolars from the DGHQ, the ectoflexid
is shallow and does not, or only shallowly, penetrate the isthmus,
however. The metaflexid contracts rapidly with wear (the primitive
protohippine condition), as do the linguaflexid and entoflexid to a
lesser degree. The p2 and dp2 have flattened anterior margins.

399

Table 41. Standard univariate statistics for upper cheekteeth of
three species of Protohippus: Pro, perditus from the Devil's Gulch
Member, Valentine Formation, Brown County, Nebraska (late Barstovian);
Pro. supremus, combined sample from the Burge Fauna, Valentine Forma-
tToh and the Minnechaduza Fauna, Ash Hollow Formation, Brown and
Cherry Counties, Nebraska (latest Barstovian - middle Clarendonian) ;
Pro. gidley n. sp. from the Archer Fauna, Alachua Formation, Alachua
r^unty, Florida (latest Clarendonian - early Hemphill ian) ; and Pro.
gidleyi n. sp. from the Cambridge Fauna (UNSM loc. Ft-40), FronTTer
County, Nebraska (late early Hemphillian) . Format as in Table 2.

TAXON _P. perditus _P. supremus _P. gidleyi _P. gidleyi

FAUNA DEVIL'S GULCH BURGE/MINN. ARCHER CAMBRIDGE

P2

APL 25.9,1.25,5 27.5,1.02,13 25.1,1.02,13 27.3,0.64,2

23.9-27.2,4.82 25.1-28.6,3.72 23.5-27.0,4.05 26.8-27.7,2.34

BAPL 19.2. - .1 22.4,0.83,4 20.3,1.07,13

21.6-23.5,3.68 18.7-22.0,5.26

TRW 19.3,1.21,5 21.7,1.06,13 19.7,0.81,11 22.2,1.41,2

17.9-20.8,6.27 19.7-22.8,4.86 18.2-20.7,4.10 21.2-23.2,6.37

PRL 5.5,0.53,5 6.0,0.44,13 5.6,0.27,13 6.3,0.42,2

4.9-6.3,9.71 5.2-6.8,7.33 5.1-6.0,4.73 6.0-6.6.6.73

PRW 4.7,0.53,5 5.0,0.44,13 4.1,0.23,11 5.3,0.85,2

4.0-5.3.11.36 4.3-6.1.8.88 3.7-4.5,5.56 4.7-5.9.16.01

P34

APL 21.3,1.90.9 23.7,1.32,33 22.4,1.50,37 22.2,2.24,5

18.6-24.9,8.93 20.9-26.0,5.56 19.0-25.2,6.67 18.9-24.9,10.1

BAPL 19.2,1.02.12 16.3,0.70,36 17.7, — ,1

17.0-20.6,5.33 15.1-18.0,4.31

TRW 22.6,0.44,9 24.3,1.12,33 22.3,0.98,37 23.3,1.07,5

22.1-23.2,1.95 20.8-25.9.4.60 20.3-24.1.4.42 22.6-25.2,4.50

PRL 7.3,0.73,9 7.8,0.89,33 8.1.0.97.38 8.8,1.45,5

6.0-8.5,10.04 6.3-10.7,11.42 6.4-9.9,12.02 7.0-10.2,16.5

PRW 4.6,0.55.9 4.8.0.24.32 4.5.0.29,38 5.1.0.54,5

3.6-5.5,11.99 4.5-5.4,5.03 3.9-5.4,6.40 4.5-6.0,10.53

400

Table 41— continued

M12

APL 20.1,1.77.11 23.0,1.87,42 21.0,1.35,32 22.4,2.72,11

16.9-23.1,8.83 20.0-27.3,8.14 17.4-23.2.6.43 18.1-26.8,12.1

BAPL 15.0, — ,1
TRW

18.5,0.70,16 15.5,0.88,30 18.4,0.74,6

17.3-19.9,3.79 13.9-17.8,5.70 17.8-19.7,4.02

PRL
PRW

21.5,0.80,11 22.5,1.46,44 20.5,1.06,32 22.3,1.00,11

19.9-22.8,3.72 18.0-24.7,6.50 18.5-22.5,5.18 20.3-23.5,4.47

8.0,0.84,11 8.7.0.99,43 8.0,0.81,33 8.2,1.31,11

6.7-9.2,10.56 7.1-10.5,11.31 6.5-10.0,10.08 6.6-10.6,13.8

4.5,0.49,11
3.6-5.2,10.84

4.5,0.49,43
3.2-5.5,10.80

4.2,0.32,32
3.7-4.8,7.44

4.9,0.36,11
4.4-5.3,7.29

401

Table 42. Standard univariate statistics for lower cheekteeth of
three species of Protohippus. Same populations as in Table 41.
Format as in Table 2.

TAXON

P. perditus

P. supremus

P. gidleyi

P. gidleyi

FAUNA

DEVIL'S GULCH

BURGE/MINN.

P2

ARCHER

CAMBRIDGE

apl

21.5,0.84,19
19.9-22.9,3.92

23.2,1.14,8
21.8-24.7,4.93

22.0,1.05,12
20.7-24,4,4.79

23.4,1.61,6
20.7-25.5,6.87

bapl

18.1,0.87,9
16.5-19.4,4.79

19.5,0.72,5
18.7-20.6,3.68

atw

8.8,0.87,19
6.9-10.4,9.94

9.0 0.79,8
8.1-10.4,8.78

9.2,0.46,11
8.4-9.7.5.01

9.8,0.19,6
9.5-10.0,1.92

ptw

11.3,0.91,19
9.0-12.8,8.01

11.8,0.49,8
11.1-12.4,4.12

11.8,0.77,12
10.3-12.7,6.56

12.5,0.60,6
12.0-13.5,4.79

mm!

6.1,0.90,19
4.3-7.7,14.76

6.9,0.91,8
5.5-8.2,13.18

8.4,0.62.12
6.8-9.3,7.41

9.6.1.18,6
8.2-11.4,12.3

entl

6.9,1.45,19
4.1-8.9,21.22

8.2,1.56,8
5.8-10.0,19.04

p34

9.2.1.26.12
6.5-11.7.13.65

10.2,1.86,6
6.6-11.5,18.2

apl

22.1,1.06,31
20.2-24.9,4.81

23.6,1.41,25
20.8-25.7,5.98

21.5,1.19,47
19.1-24.7,5.54

23.3,0.77,9
21.8-24.5,3.29

bapl

19.5,0.52.9
18.8-20.3,2.67

16.7,0.70,30
15.4-18.2,4.18

19.2.1.13.7
17.7-21.1,5.90

atw

12.0,1.12,31
9.5-14.7,9.36

12.5,0.92,25
10.8-14.4,7.38

12.6.0.63.47
11.1-14.0.5.01

13.2.0.61,9
12.3-14.0,4.60

ptw

12.6,1.02,31
10.2-14.4,8.10

13.3,0.71,25
12.2-14.9,5.38

12.1,0.64,46
10.8-13.8,5.28

13.2,0.67,9
12.0-13.9,5.12

mml

10.1,0.47,31
9.0-11.2,4.61

10.7,0.55,25
9.7-12.0,5.07

11.1,0.55,47
10.0-12.4,4.91

12.5.0.65.9
11.7-13.4.5.15

entl

7.7,1.68,31
4.3-10.5,21.89

9.4,1.78,25
5.4-12.6,18.87

• 8.5,1.17,47
3.7-10.0,13.79

10.6.0.28,9
8.2-12.3,12.0

Table 42 — continued

ml2

40 2

apl 20.8,1.90.38

17.1-25.8,9.11

bapl

atw 10.0,1.00,38

7.9-12.4,9.96

ptw 8.5,0.70,38
6.9-9.9,8.23

mm! 8.6,0.54,37

7.7-10.5,6.26

entl 4.4,1.27,38

1.0-7.0,29.18

23.0,2.23,23
19.0-26.4,9.71

19.1,0.25,5
18.7-19.3,1.30

10.2,0.82,23
8.2-11.3,8.04

8.6,0.47,23
7.8-9.5,5.41

9.4,0.63,23
8.2-10.6,6.65

5.5,1.22,23
3.5-8.3,22.18

21.0.2.03,64
17.4-27.2,9.69

15.9,0.52,44
15.0-16.9.3.30

10.6.0.58.64
8.6-11.6.5.45

8.7,0.54,65
6.9-9.8,6.22

9.3,0.79.66
7.8-11.7.8.50

6.4,1.25,65
2.2-9.7,19.47

23.1,1.99,11
19.0-25.9.8.60

18.6,0.79,6
17.2-19.5.4.25

10.8,1.01.10
9.1-12.6,9.39

9.0,0.59,10
8.0-9.9.6.54

10.5.0.84.11
9.0-11.7.8.01

7.8,1.31.11
5.2-9.4.16.77

Figure 62. Occlusal views of upper cheekteeth of Protohippus from
Florida. A. UF 61344, Pro. perditus, L P4, Kingsford Mine, Bradley
Fauna (late Barstovian)7~Pblk County. 8. UF 28553, Pro, supremus, L
P4, Grey Zone, Phosphoria Mine, Agricola Fauna (early Clarendonian),
Polk County. C-F. Pro, gidleyi n. sp.. Love Site, latest
Clarendonian, Alachua County. C. UF 62482, L P2. D. UF 62497, R
P34. E. UF 62500, R P34. F. UF 62540, R M12.

404

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407
Table 44, Comparison of cranial character states of Protohippus and

Pliohippus.

CHARACTER

Pro. perditus

Pro. supremus

Malar fossa

absent

absent

DPOF

large, shallow

large, v. shallow

Muzzle width

slightly enlarged

enlarged

Protocone con-
nection

occassional ly isolated
in early wear

often isolated
with spur

Protocone shape

oval

oval to elongate-
oval

Fossette complexity

simple to moderate

moderate,
persistent

Pli cabal 1 in

moderate

strong

Radius of curvature

45-50 mm

50-55 mm

Hypoconal groove

closed with moderate wear

closed after
heavy wear

M12 MSCH

45 mm

55 mm

protostylid (p3-m3)

well developed

well developed

protostylid (dp34)

well developed

well developed

ectostlid (dp2-dp4)

present

present

metastylid size

slightly smaller

equal

relative to
me ta con id

Referred samples Devil's Gulch, Crookston

Bridge, Nor den. Cold Spring
and Bradley Faunas

Burge, Minnecha
duza. Clarendon,
Lapara Creek and
Agricola Faunas

408

Plio. mira ball's

present, often pocketed

large, deep, well pocketed

normal

rarely isolated and only
1n earliest wear-stages

rounded to oval

very simple

small, not persistent

35-40 mm

closed with slight wear

53 mm

rudimentary or absent

rudimentary

absent

smaller

Plio. pernix

well developed

large, deep, pocketed

normal

very rapidly connected;
very rarely isolated

oval or elongate-oval

very simple

small, not persistent

35-40 mm

closed with slight wear

58 mm

generally absent

generally absent

absent

smaller

Devil 's Gulch and
Crookston Bridge
Faunas

Burge, Minnechaduza, Big
Spring Canyon, Snake
Creek, Clarendon and
Lapara Creek Faunas

409

Molars greatly resemble those of Cal . martini, except for the strong
protostylids, slightly larger metastylids, and lesser mcch. The
moderately well-cemented deciduous lower premolars are characterized
by deep linguaflexids and ectoflexids that nearly divide the tooth.
With wear, the linguaflexid retreats, along with the metaflexid
leaving a broad area of confluence between the metastylid, metaconid
and protoconid. Moderate wear exposes large ectostylids on the
dp2-dp4, that rise about 5 to 6 mm above the base of the crown.
Heavier wear reveals hypostylids that are especially well developed
on the dp3.

Discussion. Protohippus perditus has long been recognized as a
characteristic member of the fauna from lower units of the Valentine
Formation (McGrew and Meade, 1938). As noted above, Gidley's (1907)
"neotype" of Pro. perditus (AMNH 10838) is instead referable to Cal.
martini. The relatively complete referred material from the
Valentine Formation allows a better understanding of Pro, perditus,
and aids the generic diagnosis. The referred specimens from the Gulf
Coastal Plain, including the type of "Eoequus" wilsoni and UF 61344,
resemble those from the DGHQ and USNM 619 in size, hypsodonty, and
general dental morphology (Table 43; Fig. 62A), and indicate that the
species was wide-spread during the late Barstovian.

Protohippus profectus was recovered along with the type of Pseud.
retrusum (Cope, 1889), which suggests a late Barstovian age. It is
synonymized with Pro, perditus rather than Pro, supremus because of
its smaller size, weak fossette plications, and less well developed
pli caballins. In the lower units of the Valentine Formation, Pro.

410
perditus is found with the slightly larger Plio. mirabilis (Leidy,
1858). Pliohippus mirabilis differs from Pro, perditus in its very
deep DPOF, its well developed MF, and a number of dental characters
outlined in Table 44. The two cannot be synonymous, as was proposed
by Stirton (1940, p. 182).

Protohippus supremus Leidy, 1869

Protohippus supremus LEIDY, 1869, p. 328 (in part).

Protohippus simus GIDLEY, 1906a. pp. 139-140; GIDLEY, 1907, pp.

925-926; OSBORN, 1918, pp. 136-138.

Pliohippus supremus (Leidy), GIDLEY, 1907, pp. 889-890 (in

part); OSBORN, 1918, pp. 150-151; STIRTON, 1940, p. 192; QUINN,

1955, pp. 24-26 (in part); WEBB, 1969a, pp. 83-95 (in part);

FORSTEN, 1975, p. 53.

Pliohippus simus (Gidley), MCGREW and MEADE, 1938, p. 201;

STIRTON, 1940, p. 192.

Hippotigris sellardsi QUINN, 1955, pp. 46-48.

Hippotigris clarendonensis QUINN, 1955, 49-50.

Hippotigris parastylus QUINN, 1955, pp. 50-51.

Pliohippus martini (Hesse), FORSTEN, 1975, pp. 48-53 (in part).

Pliohippus (Pliohippus) cf. Plio. supremus (Leidy), FORSTEN,

1975, pp. 53-61 (in part).

Lectotype specimen. ANSP 11280.1, a slightly worn L P34.
Selected by Gidley (1907) from the syntypic series, he referred to it
as a Ml, but his measurements clearly indicate which specimen he

411
chose as the lectotype, as later figured by Osborn (1918, Fig.
118.2).

Type locality. Exact locality unknown. Little White River region.
South Dakota.

Stratigraphic occurrence and age of type localtiy. Probably
Clarendonian deposits of the Ogallala Group; about 10 to 11 ma.

Distribution. Latest Barstovian and Clarendonian of northern
Great Plains (about 10.0 to 12.0 ma); Clarendonian of southern Great
Plains, Gulf Coastal Plain of Florida and Texas.

Referred specimens. Little White River region, SD: AMNH 980
partial skull with R 13, R and L DP1-M3 (type, fro. si mus ) ; AMNH
10871 L maxilla with P2-P4, M2-M3.

Burge Fauna, Cherry Co., NB. Burge Quarry: F:AM 60356 skull with
R and L DP1-M3; 108187, 114058-114063 7 maxillae or palates; 60353,
60357 2 assoc skulls, R and L rami. Midway Quarry: F:AM 60354
assoc. skull, R and L rami.

Clarendon Fauna, Donley Co., TX. MacAdams Quarry: F:AM 111728
assoc. skull and rami. C. Risley Ranch Site: TMM 255-29 R mandible
with p3-m3 (type, H^. clarendonensis) ; 255-17 L ml2.

Lapara Creek Fauna. Bridge Estate Site, Bee Co., TX: TMM
31132-284D R P34; -541, -542 2 R M12; -459 L mandible with p2-m3
(type, H. parastylus); -335 assoc. p4,m2-m3; -237 L ml2. Buckner
Ranch Site, Bee Co., TX: TMM 30896-503 assoc. R and L P2-M3 (type,
H. sellardsi ); -206 and -541 assoc. mandibles with R p3-m3 and L
p2-m3; -240, -476 2 R mandibles with dp2-ml; -420C, F assoc. L m2-m3;
-447 R p34; -420G L p34. Farish Ranch Site, Bee Co., TX: TMM

412
31081-1183 L p34; -664 R mandible with p2-m3; -168E, F assoc. p4-ml;

-1210 L p2.

Agricola Fauna, Bone Valley Region. Gray Zone, Phosphor i a Mine:
UF 28553 L P34. Nichols Mine: UF 25125 R P4.

Revised diagnosis. Large Pro to hip pus with toothrow lengths of
about 130 to 145 mm, and unworn molar crown heights of about 54 mm.
Larger and more hypsodont than Pro, perditus, with a broader muzzle,
smaller (on average) DPI, more elongate protocone, and more complex
fossette plications. Hypoconal groove present until late wear-
stages; forms lake on premolars. Protocones isolated from protose-
lene in early wear-stages of P3-M2, until moderate wear on M3; not as
isolated as those of Pro, gidleyi. Metastylid large, well separated
from metaconid by well developed, persistent lingual flexids.

Description. Based on AMNH 9820 (holotype. Pro, si mus ) and a
number of crania from the Burge Member of the Valentine Formation,
the facial region of Pro, supremus greatly resembles that of the
genotypic species. Pro. perditus. No MF is present. The DPOF is
approximately the same size and in the same position as in Pro_.
perditus, but it is notably shallower and less well-rimmed (Osborn,
1918, Plate 21.1). The Burge specimens retain a well defined
posterior rim and a very slight pocket. Clarendonian specimens (e.g.
AMNH 9820 and F:AM 111728) have an even shallower and less well
defined DPOF without a posterior pocket, but are otherwise identical
to the latest Barstovian population. As noted by Gidley (1906a) in
his description of Pro, si mus, the muzzle is very broad (about 45? of
the UTRL), much greater than that of a similarly-sized, typical equid

413
(Fig. 43). The first two incisors are not linearly arranged, as in
Calippus, but are slightly arcuate.

The upper cheekteeth of Pro, supremus (Tables 41, 43; Figs. 62B,
63) have very strong styles, including a well developed metastyle.
The P2 has a shorter, rounder protocone than the other teeth; it is
connected to the protoselene in all known specimens. The fossettes
of the P2 tend to be simpler, and the hypoconal grooves close earlier
than in the P34. The P34 have large, widely-open parastyles and
mesostyles, and small metastyles that are retained until late wear-
stages. The protocone of the P34 is elongate, with wear it becomes
shorter and wider. In early wear-stages, the protocone is isolated
from the protoselene, but has a large labial ly-directed spur. With
wear, the spur connects with the protoselene (Fig. 63); this
connection is at first greatly constricted by a deep preprotoconal
groove, this condition persists until until at least moderate
wear-stages. The P34 protocone orientation is markedly oblique (Fig.
62B), and in late wear-stages, the protocone does not connect with
the hypocone. The P34 have a large, usually single, but occasionally
branched, pli caballin that is reduced and lost at MSCHs of about 25
to 30 mm. The hypoconal groove remains open at least until moderate
wear-stages; it closes to form a lake and disappears at a greater
crown height than in the molars. Fossette plications are relatively
complex and persistent for a member of the Equini, as only very
greatly worn P34 totally lack plications (Fig. 63). A pli protoloph
and pli hypostyle are uncommon, but occasionally found on slightly
worn teeth. The posterior half of the prefossette almost always has

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two deep plications surrounding a large prefossette loop in moderate
to slightly worn teeth, with a third accessory plication possible.
The opposing side of the postfossette has a deep pli postfossette and
an accessory plication. At moderate wear-stages, the accessory
plications are lost, and only the deep folds remain. These are
gradually lost only in very heavily worn P34s.

The molars exhibit basically the same pattern as the P34 (Fig.
63), although the pli caballin is smaller and lost earlier in wear,
the hypoconal groove remains open until late wear-stages (and does
not form a lake), and the protocone orientation is not as oblique.
In late wear-stages, the protocone of the M12 may unite with the
hypocone (Fig. 63 and F:AM 111728), isolating the postprotoconal
valley as a fossette. This occurs less frequently and typically only
in much more deeply worn teeth than in Pliohippus. In terms of
degree of isolation of the protocone, the M3 ranks highest, followed
by the P34, then the M12, and finally the P2. Even moderately to
heavily worn M3s can retain isolated protocones, for example the left
M3 of AMNH 9820. This same pattern is observed, to an overall
greater degree of isolation, in the younger species Pro. gidleyi.
The deciduous premolars are similar to those of Pro, perditus, having
more complex internal fossette borders than permanent teeth,
persistent plications, and rounded protocones. The DPI is retained
with the adult dentition, but is relatively (and usually absolutely)
smaller than that of Pro, perditus (^=10. 3 mm; 0R=9. 2-11.1 mm; n=5).
P3-M2 are moderately curved, with ROC generally between 45 and 50 mm.
Unworn upper cheekteeth that can unambiguously be assigned to Pro_.

417
supremus are rare, thus unworn MSCHs are estimated from slightly worn
teeth, and should be considered minimum values. These estimates are
about 38 mm for the P2 and about 55 mm for the P3-M2.

Lower cheekteeth of Pro, supremus (Table 42) are especially char-
acterized by large protostylids that appear on the occlusal surface
shortly after the onset of wear, and relatively large metastylids.
In premolars, the metastylid is expanded equally with the metaconid.
This, in conjunction with large, deep lingual flexids in early and
moderate wear-stages gives the premolars a hipparionine-like appear-
ance. The contraction of the lingual flexids is delayed relative to
that observed in Pro, perditus and most species of Calippus. The
ectoflexid of the premolars is quite variable in its depth of
penetration of the isthmus, but is most often shallow. In general,
the isthmus connects to the metaconid, or between the metaconid and
metastylid, but occasionally to the metastylid as observed by Quinn
(1955, Plate 9.5). The molars also have enlarged and expanded meta-
conids and metastylids, but are otherwise of typical protohippine
morphology. Lower deciduous premolars are slightly larger, but
similar to those of Pro, perditus, with low ectostylids and large
protostylids on dp34. The dp2 has a flattened anterior border, and
frequently a small protostylid. The anterior margin of the p2 is
often similarly truncated in later wear-stages.

Discussion. Leidy (1869) based Pro, supremus on three isolated
upper cheekteeth from different individuals. He figured two of the
specimens (Leidy, 1869, Plate 27.3 and 27.4), and described the third
as unworn. Gidley (1907, p. 889), acting as first revisor, selected

418
one of the figured specimens (ANSP 11280.1) as the lectotype, the
tooth Leidy (1869) described in most detail and figured in Plate 27.4
(re-illustrated by Osborn, 1918, Fig. 118.2). Gidley's (1907) choice
of a lectotype is critical, as the two principal syntypes apparently
represent distinct species of different genera. The lectotype, here
interpreted to represent Protohippus, is a premolar, and not a Ml as
was stated by Gidley (1907) and repeated by Osborn (1918). Quinn
(1955, p. 24) also recognized that it is a P34, but failed to grasp
its phylogentic significance. The specimen has the following
characters that indicate that it is a premolar and not a molar: 1)
parastyle open and very large (it is somewhat larger than indicated
in the illustrations); 2) mesostyle widely open, not constricted; and

3) its angle of attrition is anterior (the method of Bode, 1931).
This determination is important, as the dimensions of ANSP 11280.1
(Table 43), while matching those of referred P34s, are much larger
than average for molars of Protohippus. The paratype (ANSP 11280.2)
is a true molar (probably a M2), despite its much greater APL than
the lectotype. Besides size, the lectotype has six characters that
indicate its referral to Protohippus rather than Pliohippus:

1) protocone isolated from protoselene; 2) very strong pli cabal! in
that nearly touches the protocone; 3) very long prefossette loop that
extends lingual ly further than the main body of the prefossette;

4) deep hypoconal groove that would have remained open until late
wear-stages; 5) large parastyle; and 6) radius of curvature of about
50 mm. All of these are characteristic of premolars from the
referred sample of Protohippus supremus, and differ considerably from

419
the conditions found in contemporary Clarendonian Pliohippus popu-
lations (Table 44; pers. obs. and Skinner et al., 1977), The para-
type is referable to Pliohippus based on its greater size, lower
radius of curvature (40 mm), smaller prefossette loop, and the
absence of a pli cabal 1 in. While Gidley (1907) did not clearly state
which of the two he considered the type, the measurements he gives
are those of the specimen that Osborn (1918) later stated was the
lectotype. As his purpose was to place Leidy's species in
Pliohippus, Gidley's (1907) choice of a lectotype was ironically
incorrect, as his study was otherwise the first to clearly enumerate
the differences between Protohippus and Pliohippus, and used
characters that were ignored by later workers (e.g. Stirton, 1940).

The lectotype of Pro, supremus matches in size, curvature, and
morphology a well represented sample from the very late Barstovian
and Clarendonian of Nebraska and South Dakota. Although similar in
many features, it is more advanced than, and clearly distinct from.
Pro. perditus (as was first recognized in his description of Pro,
simus by Gidley, 1906a). The important generic characters this
referred sample shows are: lack of a MF; large, shallow DPOF;
broadened muzzle; isolated protocones in early wear-stages; and well
developed protostylids. The large series of associated dentitions in
various wear-stages from the Burge Fauna indicate that the differ-
ences between the types of Pro, supremus and Pro, si mus (both were
collected from the Little White River region of South Dakota) result
from differing degrees of wear, and that the two are not specifically
distinct. Based on priority, the proper name is Pro, supremus.

420
Protohippus and Pliohippus lived contemporaneously, and apparently
sympatrically, in Texas and the Great Plains from the late Barstovian
to the early Hemphillian. Gidley (1907), primarily using cranial
characters, distinguished the two into basically the arrangement used
here, and allied Calippus (his Protohippus placidus) with Proto-
hippus. Later studies (e.g. McGrew and Meade, 1938; Stirton, 1940)
emphasized the use of upper cheekteeth to determine relationships (at
the expense of cranial and lower cheektooth features), and contem-
porary populations of the two genera were frequently lumped into one
species. For example, Stirton (1940) proposed that Pro, perditus and
Pliohippus mirabilis were synonyms, and Webb's (1969a) referred
sample of "Pliohippus" supremus includes specimens of both
Protohippus and Pliohippus. Table 44 contrasts the features of
Protohippus and Pliohippus, and is based on the large series of
associated skulls and mandibles in the Frick collection.

Webb (1969a) provided the most complete discussion of the rela-
tionships of Pliohippus s.l. (including Protohippus as recognized
here) in what might be termed the post-Stirton (1940) period. Webb
correctly concluded (in my opinion) that many of the previously
named, large, Clarendonian species of Pliohippus were synonymous.
Webb (1969a, p. 95) hypothesized that species of Pliohippus could be
divided into two groups, one with a shallow "lacrimal" fossa and no
MF, the other with deep malar and lacrimal fossae. He bemoaned the
lack of an adequate sample of skulls with which to test this hypoth-
esis. The Frick collection, then unavailable to Webb for study,
contains such a sample. Another factor then creating confusion was

421
the common conception that Pliohippus pachyops from the Clarendon
Fauna displayed a "Protohippus"-type face and a "Pliohippus"-type
dentition, suggesting that the two could not be separated. The plio-
hippine dental features of the type of Plio. pachyops include dp3 and
dp4 with very reduced protostylids and no ectostylids, and the con-
nected protocone on the slightly worn Ml. Recently, the holotype of
Plio. pachyops has been further prepared, and removal of matrix in
the ventral preorbital region revealed the presence of a small MF
similar to the one found on the type of Pliohippus fossulatus. also
from the Clarendon Fauna (D. Winkler, pers. comm.). Pro, si mus thus
cannot be synonymized with Plio. pachyops, as Webb (1969a) suggested.

The results of this study indicate that Webb's (1969a) preferred
hypothesis about Clarendonian Pliohippus s.l. was correct in its
essential point (i.e., there are two taxa clearly differentiated on
the basis of facial fossae and other characters), but that the names
he chose for the two (Pliohippus supremus and Pliohippus pachyops)
were incorrect. Instead, the presence of two genera are indicated,
Pliohippus s.s. and Protohippus. With the referral of Pro, supremus
to Protohippus, the next available name for the large Clarendonian
Pliohippus is Pliohippus pernix Marsh (1874), the genotypic species.

A number of species and specimens from beyond the type region are
referable to Pro. supremus. "Hippotigris" clarendonensis Quinn from
the Clarendon Fauna resembles Pro, supremus rather than Cal. martini
or Pro, pernix with its large metastylids, well developed lingual
flexids and protostylids, and reduced ectoflexid depth on ml-m3.
F:AM 111728, which was illustrated by MacFadden (1984a, Figs. 66 and

422
69) as Neohipparion affine, is another Clarendon specimen of Pro.
supremus. Based on examination of the F:AM, TMM and PPM collections.
Pro. supremus is rare in the Clarendon Fauna, while Cal ♦ mar ti n i and
PI 10. pernix are common. Similarly, it is rare in the Minnechaduza
Fauna, although common in the Burge. As the decline coincided with
the appearance of Cal. martini, competition with that species may
have played a role in its drastic reduction in abundance. Pro.
supremus is also present, but again rare relative to Cal . martini and
Plio. pernix, in the Lapara Creek Fauna. Quinn (1955) named two
species of "Hippotigris" from the Lapara Creek Fauna, H^. sellardsi
and H. para stylus, that are synonymized with Pro, supremus. The
three figured upper teeth (Quinn, 1955, Plate 4.1-4.3) are also
referable to Pro. supremus, although the lowers called "Pliohippus"
supremus (Plate 4.4) are instead referable to Plio. pernix. Two
specimens from Florida, UF 28553 (Fig. 22B; Table 16) and UF 24125
also represent Pro, supremus. Although moderately worn, UF 28553
still retains a well developed prefossette loop and a pli caballin,
the hypoconal groove is open, and the protoconal connection is
tightly constricted. The slightly worn UF 24125 (MSCH = 48.5 mm) has
an isolated protocone with a large spur, and a large prefossette
loop. It has a ROC of 65 mm.

423
Protohippus gidleyi new species

Dinohippus or Pliohippus sp., HIRSCHFELD and WEBB, 1968,

pp. 247, 249.

cf. Pliohippus sp., WEBB et al., 1981, p. 527.

Type specimens. Holotype, UF 62473, associated R P2-M3 and L
P2-M1. Paratype, UF 32173, R mandible with p2-m3, missing symphysis
and most of ascending ramus.

Type locality. Love Site, 1.5 km N of Archer, Alachua Co.,
Florida.

Stratigraphic occurrence and age of type locality. Fluvial sedi-
ments of the Alachua Formation; very late Clarendonian, about 9.0 ma.

Topotypic sample. UF 32261 R maxilla with P2,P3-M3; 32298/32299
assoc. R P3-M3 and L P2-M3; 32269 assoc. R P2-P3,M1,M3 and L P4-M3;
67703 assoc. R M1-M3; 60875 assoc. R M1-M2; 32279 assoc. L P4-M3;
65237, 69821 2 R DP2; 36044, 36095, 36101, 36123, 96882 5 L DP2;
65231-65232, 68849-68850, 92958-92959, 96893-96900 14 R DP34; 65233-
65236, 92960, 96883-96892 15 L DP34; 36031, 36057, 60245, 62471-
62472, 62474-62475 7 R P2; 36146, 36225, 36236, 62476-62477, 62479-
62482, 92992 10 L P2; 61350, 62493-62502, 62504-62510, 62537 19 R
P34; 61349, 62483-62491, 62513-62521 19 L P34; 62536, 62539-62540,
62542-62550 12 R M12; 62522-62532, 62534-62535 13 L M12; 68822-68824.
68826-68831 9 R M3; 68832-68838 7 L M3; 32207 R mandible with p3-m3;
32167, 32209 2 L mandibles with p3-m3; 32242 L mandible with p4-m2;
32205 assoc. R dp2-dp3; 64402 assoc. L dp2-dp4; 67704 assoc. R p3-m3;
67747 assoc. R p4-m3; 32129, 32135, 32140, 32220, 32243, 32288.

424
36279, 67729, 67746, 68776, 68782, 68787 12 partial mandibles or
assoc. lower dentitions; 69802, 90267, 96538 3 R dp2; 90187, 90268,
90269, 96537, 96917 5 L dp2; 90278-90279, 96539 3 R dp34; 90270-
90277, 96540-96544 13 L dp34; 36290-36296. 96955-96957 9 R p2; 36297-
36300, 67701-67702, 92961. 96331, 96950-96951 10 L p2; 67705-67723 19
R p34; 67724-67728, 67730-67745, 67748 22 L p34; 67779-67800, 68781
23 R ml2; 67749-67778. 92962 31 L ml2; 68770-68779, 92991, 96533 12 R
m3; 68758-68769, 96523, 96534 14 L m3.

Etymology. Named in honor of James W. Gidley, an outstanding
scholar of mammalian systematics and evolution; especially for his
contributions to the study of Protohippus.

Distribution. Very late Clarendonian to early Hemphillian of
Florida (about 6.5 to 9.0 ma); early Hemphillian of Nebraska.

Referred specimens. McGehee Farm: UF 45634 R M12; 17138 R p2;
19238 R p34; 16633, 45622 2 R ml2; 7239 L ml2; 45630 R m3.
Haile 19A: UF 52963 L p34.

Mixson's Bone Bed: F:AM 113639 assoc. R P4 and L P2-M3.
With 4A: UF 45521 assoc. R and L DP2-DP4,M1.
Cambridge Fauna, UNSM loc. Ft-40. Frontier Co., NB: UNSM 90641
skull; 2634 R maxilla with P2-M3; 4024, 4072-4075, 4078-4079, 4082,
4251 9 isolated upper cheekteeth; 2635 assoc. R mandible with p2-m2
and L mandible with p2-m3; 2951, 4046-4047, 4049-4050, 4052, 4054.
4056-4058, 4062-4065, 4067, 4237 16 isolated lower cheekteeth.

Diagnosis. Protohippus intermediate in size between Pro. perditus
and Pro. supremus, with toothrow lengths of 125 to 135 mm. Unworn
M12 MSCH about 58 mm. Protocones of P3 and P4 generally isolated for

425
uppermost 20% of crown, then connected to protoselene at MSCHs of 30
to 40 mm. M3 protocone also often isolated until moderate wear-
stages, but may connect earlier; protocones of P2, Ml and M2 gener-
ally isolated only in very early wear-stages; protocone of P3-M2
large, elongated. Anterostyle of P2 reduced. Lower cheekteeth
similar to those of Pro, supremus but with more expanded metaconid-
metastylid complexes, more persistent lingual flexids, and less
prominent protostylids. Paraconid of p2 and dp2 less flattened
anteriorly than in Pro, supremus. Ectostylid of dp2-dp4 rudimentary.

Description. The holotype, UF 62473 (Fig. 64A; Table 43), con-
sists of an associated assemblage of upper cheekteeth of a young
adult. The M3 had only partially erupted, as its posterior half is
not yet fully worn. The specimen evidently represents an individual
whose remains were scattered by currents, as the teeth were recovered
from several contiguous quadrants, and were not recognized as being
associated in the field. That they represent a single individual is
evidenced by similarity of preservation, their identical wear-stage,
and the goodness of fit between them. The P2 (Fig. 64A) resembles
other moderately worn individuals in the referred sample with its
rounded protocone, well developed preprotoconal groove, lack of a pli
caballin, deep hypoconal groove, simple fossettes, and relatively
short anterostyle. The P34 have larger styles, moderate pli cabal-
lins, deep hypoconal grooves, and oval -elongate protocones with
constricted protoconal connections and pointed posterior ends. The
protocone of the right P4 is still isolated (Fig. 64A), but its spur
is within 1 mm of the protoselene, and it would no doubt have con-

426
nected after slightly more wear. The Ml and M2 of UF 62473 differ
from the P34 only slightly in size (Table 43), but do not have pli
cabal! ins, their protocones are more broadly connected and less
obliquely orientated, have weaker styles, and smaller prefossette
loops. The protocone of the M3 is connected to the protoselene by a
very narrow isthmus; most M3s of similar MSCH in the topotypic sample
have isolated protocones.

Upper cheekteeth of _Pro. gidleyi (Figs. 62C-62E, 64A, 64B; Tables
41, 43) resemble those of Pro, supremus in most regards. They are
only moderately curved, with ROC of molars usually between 50 and 60
mm. The P2 in early wear (Fig. 62C) has a rounded, isolated proto-
cone with a spur, and the postprotoconal valley is often confluent
with the prefossette (e.g. UF 62481, 62482). A strong metastyle is
usually present, but it tends to fade with wear, as does the pseudo-
parastyle. The anterostyle is often weak, giving the P2 a more blunt
appearance, rather than its its usual triangular form. The prefos-
sette and postfossette are confluent in over half the sample of P2s
from the Love Site, although they are separate in almost all of the
heavily worn specimens (Fig. 64B). In early wear, the P2 can have
well plicated fossettes (e.g. UF 62476), but these soon fade with
wear, leaving at most a single pli prefossette and pli postfossette.
Pli caballins are rarely present, and almost always weaker than those
of the P34. With wear, the protoconal connection widens, the fos-
settes loose all plications and become more narrow, and with heavy
wear, the hypoconal groove is lost. The P34 (Figs. 62D, 62E) have
strong styles, including metastyles, deep hypoconal grooves that

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423

429

2cm

Figure 65. Occlusal views of upper and lower cheekteeth of
Protohippus gidleyi n. sp. from the Love Site, latest Clarendonian,
Alachua County, Florida. A. UF 67704, associated R p3-p4, early
wear-stage. B. UF 67769, L ml2, early wear-stage. C. UF 45622, R
ml2, early moderate wear-stage. D. UF 90274, L dp34. E. UF 65232,
R DP34.

Figure 66. Histograms indicating at what wear-stage the protocone
connects to the protoselene, and the hypoconal groove becomes closed
in upper third and fourth premolars of the Love Site population of
Protohippus gidleyi n. sp. A. Percentage of specimens in each 5 mm
wear-class with (shaded) and without (unshaded) connected protocones.
All specimens with less than 502 of original crownheight have
connected protocones. B. Percentage of specimens with open hypoconal
grooves (unshaded) and those that have lost the hypoconal groove
(shaded). Numbers above each wear-class indicate the sample size for
each group.

431

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432

persist until about 45% of the crown is worn (Fig. 66), and moder-
ately complex fossettes. The hypoconal grooves are almost always
lost without forming a lake. A single, generally small pli protoloph
or pli hypostyle is occasionally present in the upper quarter of the
crown. In early wear-stages, the posterior half of the prefossette
may have up to four (two or three are more common) plications, and
the anterior half of the postfossette usually bears one or two. The
prefossette loop is well developed, but is usually not as long as in
Pro. supremus. Moderate to heavily worn P34s generally retain one or
two plis prefossette and a single, deep pli postfossette. These too
tend to be lost as MSCHs reach 21 mm and less. This is also the
period when the pli cabal lin is usually lost. The protocones tend to
be long, often with flattened to slightly concave lingual borders.
The MSCH at which the protocone attaches to the protoselene is vari-
able (Fig. 66), but usually between 30 and 40 mm. Prior to con-
necting, the protocone bears a large, anterolabial spur (Fig. 62E).
After the connection, the preprotoconal groove remains deep until
latest wear-stages (Fig. 64B).

The M12 tend to be of about the same APL as the P34, but somewhat
narrower (Table 41). As is typical for protohippines, the fossette
plications are less numerous and are lost at earlier wear-stages than
in the P34, and pli caballins are prominent only in earlier wear-
stages (Figs. 62F, 64A) . The protocone is rapidly connected with
wear, is oriented much less obliquely than in the P34, and becomes
connected to the hypocone with heavy wear. The protoconal connection
remains constricted throughout much of the crown, with a deep prepro-

433
toconal groove. Metastyles are much less prominent than on the P34.
The hypoconal groove remains open until the MSCH reaches 20 mm or
less. Unworn or slightly worn MSCHs are about 39 mm for P2, 50 mm
for P34, and 58 mm for the M12.

Deciduous upper premolars are narrower counterparts to their per-
manent successors (Fig. 65E). The DP2 has a short protocone and a
poor pli caballin. The DP34 have elongate protocones, generally
strong pli caballins, well developed styles, and moderately simple
fossettes. The hypoconal groove is deep and a pli dihypostyle is
usually present.

Lower cheekteeth of Pro_. gidleyi (Tables 42, 43; Figs. 64C,
65A-65D) especially resemble those of Pro_. supremus, the principal
difference being that the younger species tends to exhibit advanced
features, such as more elongated metaconids and metastylids, through
a greater percentage of the crown. The paratype, UF 32173, is a
typical example of a moderately worn individual (Fig. 64C). Deep
lingual flexids are retained on all but the ml, which is starting to
lose the metaflexid, and shorten the metastylid. The lower premolars
retain expanded metaconids and metastylids, and relatively deep
lingual flexids even at crown heights of less than 20 mm. In very
early wear-stages, the bases of the metaflexid and entoflexid may
bear several plications (Fig. 65B), but these are soon lost with
wear. The p34 ectoflexid is a broad "V", generally penetrating into
the isthmus to a depth about that of the base of the entoflexid (Fig.
65A). The ectoflexid of the p2 is shallower, not penetrating the
isthmus, and its paraconid is usually angular in moderate to early

434
wear-stages, becoming more blunt with heavy wear as in Pro, supremus.
In the molars, the ectoflexid almost always separates the isthmus.
In early wear-stages, the deep, "V"-shaped linguaflexid and the
ectoflexid nearly completely separate the metaconid and metastylid,
except for a narrow commissure (Fig. 65C). With wear, both retreat,
so that there is greater dentine confluence between the metaconid and
metastylid (Fig. 64C). In early to moderate wear-stages the meta-
stylid is nearly as large as the metaconid, but tends to be angular
while the latter is more rounded. Only in later wear-stages is the
metastylid noticeably smaller and less lingual ly placed than the
metaconid. Moderate protostylids appear on the occlusal surface
shortly after the onset of wear on the p3-m3, and may at first be
isolated from the protoconid (e.g. the m2 of UF 67704); they are
stronger in p34 than ml-m3, but vary with age. The labial borders of
the protoconid and hypoconid are rounded. Lower deciduous premolars
are like those of Pro, supremus (Fig. 65D), but have more rudimentary
ectostylids. The strong protostylids, however, serve to distinguish
them from the dp2-dp4 of Pliohippus. As in the permanent teeth, the
protostylid is often isolated from the protoconid in early wear-
stages (e.g. UF 64402).

Cranial features of Pro, gidleyi are known only from UNSM 9064, a
nearly complete skull from the referred Ft-40 population from
Nebraska. The dentition of UNSM 9064 is extremely worn and nondi-
agnostic (except to indicate that it is a protohippine). The
broadened muzzle and short diastema distinguish it from Dinohippus,
the only large equine in the fauna. It is larger, and with a less

435
broadened and robust muzzle than in advanced species of Cal .
(Grammohippus). The facial region of UNSM 9064 has been distorted by
crushing, and the depressions in the malar region are of post-dep-
ositional origin. The dorsal facial region of the somewhat better
preserved right side indicates the presence of a faint DPOF located
very anterior to the orbit, dorsal to the M2 to P3, and about 50 mm
long. It is not distinctly rimmed or pocketed. Small alveoli
indicate that a DPI was retained with the permanent dentition.

Discussion. Protohippus gidleyi is the youngest and most derived
species of Protohippus. Unworn crown heights of its cheekteeth are
about 5% greater than those of Pro, supremus. Its lower cheekteeth
have the most expanded metaconids and metastylids of any protohip-
pine, and elongated metaflexids and entoflexids remain deep until
very late wear-stages. The most interesting trend evident in Pro.
gidleyi is the tendency for increased isolation of the protocone from
the protoselene. Possession of isolated protocones beyond early
wear-stages is apparently a derived condition in advanced equids
(Webb and Hulbert, 1986), but is generally considered structurally
inferior to the connected condition (Stirton, 1941). The trend in
Protohippus for increased protocone isolation, along with the
successful radiation of the hipparionines, suggests that this
hypothesis is incorrect.

The topotypic sample of Pro, gidleyi contains a number of upper and
lower dentitions, along with many isolated cheekteeth, thus allowing
a good estimate of individual and ontogenetic dental variation. Sev-
eral early Hemphillian sites from Florida contain a few teeth that

436
cannot be distinguished from the Love Site sample of Pro, gidleyi.
UF 45521, a juvenile individual from the late early Hemphillian, is
only provisionally referred to Pro, gidleyi. The protocone of the Ml
is relatively small and the fossettes are somewhat more plicated than
in the topotypic population. The sample from the late early Hemp-
hillian of Nebraska suggests that the latter feature nfiay be a chrono-
clinal trend within Pro, gidleyi. This sample is important, as it
includes the only known skull of Pro, gidleyi. It demonstrates not-
able differences in muzzle and fossae morphology from Dinohippus,
Pliohippus and Calippus, and corroborates the dental evidence that
the species belongs in Pro to hip pus. The minor differences between
the Love Site and Ft-40 populations are best explained by geographic
variation and chronoclinal evolution. For example, the protocone of
the M12 tends to be more isolated in the younger sample, surely a
continuation of the trend observed throughout the entire genus.

Subtribe Equina new subtribe

Type genus. Equus Linnaeus, 1758.

Included taxa. "Merychippus" stylodontus Merriam, 1919; "M . "
carrizoensis Dougherty, 1940; Pliohippus Marsh, 1874; Astro hi ppus
Stirton, 1940; Dinohippus Quinn, 1955; Hippidion Owen, 1869;
Onohippidium Moreno, 1891.

Diagnosis. Medium to large-sized equids with relatively elongated
muzzle regions. Protocones connected to protoselene during earliest
wear-stages; protostylids absent or very reduced on permanent

437
cheekteeth; ectostylids absent on deciduous premolars. Well
developed fossa in malar region; it and DPOF lost in some taxa.
Lateral phalanges reduced in size or absent altogether.

Discussion. The Equina form the sister-taxon to the Protohippina.
Early species are characterized by nfierychippine-grade dentitions and
a variably developed MF. This structure is best developed in the
well known Miocene genus Pliohippus. Excluding Pliohippus. equines
have a poorly represented pre-Hemphillian fossil record. A possible
explanation for this my lie in a predominantly West Coast distri-
bution. There are many species names for Clarendonian West Coast
"Pliohippus," but these records are based on small samples of iso-
lated teeth. The teeth referred to "Protohippus" or "Pliohippus"
tehonensis by Merriam (1915b), Stock (1935), and Drescher (1941) from
the early Clarendonian of California, and the specimen referred to
Dinohippus sp. by Nelson et al . (1984) from Utah both contain the
proper mixture of primitive and derived character states to allow
them to be the sister-taxa of some segment of the Astro hi ppus-
Dinohippus-Hippidion clade. However, cranial material is essential
for generic identification of equines, and is lacking in these cases.

Equines are especially poorly represented in Gulf Coastal Plain
faunas. The Cold Spring and Lapara Creek Faunas contain Pliohippus,
but it is uncommon, relative to hipparionines. In Florida, no
unquestionable specimens are known until the early Hemphillian (Moss
Acres). During the late Hemphillian, when various equines like
Dinohippus, Astro hi ppus and Onohippidium numerically dominated all
western and Great Plains equid faunas, hipparionines remained

43i
numerous and diverse in Florida. Even into the late Blancan,
Cormohipparion and Nannippus are wore numerous at some sites (e.g.
Macasphalt Shell Pit) than Equus. The reason for this difference is
interpreted to be ecological. The Clarendonian Chronofauna must have
evolved under relatively warm and mesic climatic conditions (contra
Janis, 1984; see Webb, 1977). This is based on the northernly late
Neogene distributions of Alligator and large Geochelone (Woodburne,
1959; Hibbard, 1960; Voorhies, 1971), and on the great diversity of
the large mammalian fauna. Through the Hemphillian, progressive
drying resulted in a less diverse fauna (Webb, 1977), and the
monodactyl equids "took over." In may be inferred that mesic
conditions continued to prevail in Florida, the most prominant
exception to this trend. This allowed otherwise typical Miocene taxa
like Cormohipparion, Pseudhipparion (Webb and Hulbert, 1986), and
protoceratids (Webb, 1981) to flourish into the Pliocene. The same
species of Dinohippus, Astro hi ppus, and Equus are known from the
Pliocene of Florida as are found in western faunas (Robertson, 1976;
MacFadden, 1986), but they are rare.

Genus Pliohippus Marsh, 1874

Type species. Pliohippus pernix Marsh, 1874.

Included species. Plio. mirabilis (Leidy), 1858; Plio. nobilis
Osborn, 1918.

Chronologic and geographic distribution. Late Barstovian to early
Hemphillian of the Great Plains; early Clarendonian and possibly late

439
Barstovian of Gulf Coastal Plain. Numerous records and named species
from the West Coast are at present generically indeterminant.

Diagnosis. Medium to large equine with very curved upper cheek-
teeth; shallow hypoconal groove that is lost early in wear; fossette
plications simple or absent; molar protocone frequently connected to
hypocone. Metaconid and metastylid poorly separated; relatively deep
ectoflexids; protostylids very reduced or absent on deciduous and
permanent cheekteeth; ectostylid absent on dps. Both DPOF and MF
deep, well rimmed posteriorly, often pocketed. Moderate preorbital
bar. Early populations tri dactyl, later populations monodactyl .

Discussion. Pliohippus is primarily known from the Great Plains
where it is continuously represented from the middle Barstovian
through the early Hemphillian (ca. 14.5 to 6.0 ma). Only scattered
records are known from the Gulf Coastal Plain, and named West Coast
taxa commonly referred to Pliohippus are either known only by denti-
tions and will require intensive study to determine their generic
affinities (e.g. "?_." fair bank si, "P^. " tantalus), or seem to be more
closely related to the Dinohippus-Hippidion clade (e.g. "P^. " spec-
tans, "P." edensis). Barstovian species of Pliohippus are moderate-
sized (toothrow lengths of 130 to 140 mm) and each lateral toe has
three well formed but notably small phalanges. Clarendonian indi-
viduals (here included in a single species, the genotype P_. pernix)
are about 10% larger, while Hemphillian specimens (_P. nobilis) are
extremely large (toothrow lengths of up to 180 mm) and monodactyl
(based on the F:AM collection). Thus, in this genus, monodactyly
evolved during the Clarendonian (Hussain, 1975). The DPOF is

440
elongate-oval, deep, usually well pocketed and located about 15 to 20
mm in front of the orbit. Its ventral border is well rimmed and
clearly separates the DPOF from the MF (Stirton and Chamberlain,
1939; MacFadden, 1984b). The variability of the MF is well docu-
mented in the F:AM samples from the Devil's Horse Gulch, Burge and
MacAdams Quarries. It is invariably present, but can be almost as
shallow as that of "Merychippus" sejunctus with only well defined
posterior and ventral margins. The other extreme, represented by
UCMP 33481 (Stirton and Chamberlain, 1939), is for a very deep,
pocketed, multi -chambered MF with all of its margins well defined.
Dentally, Pliohippus is characterized by very strongly curved upper
cheekteeth, simple enamel patterns, shallow hypoconal grooves that
are lost fairly early in ontogeny, and frequent connection between
the protocone and hypocone in the molars. Pliohippus was classically
thought to be ancestral to the other monodactyl equids, Equus and/or
the South American Hippidion-group. However, it is now clear
"...that a chronocline of Pliohippus species with dual facial fossae
and simple, highly curved teeth became a dead-end phylum during Early
Hemphillian time..." (Skinner et al., 1977, p. 359) and that mono-
dactyly evolved at least twice within the Equidae.

cf. Pliohippus sp.

Referred specimens. Bradley Fauna, Bone Valley Region. Nichols
Mine: UF 23977 R p34. Kingsford Mine: UF 61345 assoc. R p3-m2.

441
Description and discussion. The two specimens listed above are
nearly identical in morphology and very probably represent the same
taxon. The following characters suggest referral to a Barstovian
Pliohippus (e.g. Plio. mirabilis): protostylid very reduced to a
thickened ridge of enamel on lower third of the crown; metastylid
notably smaller than metaconid, while the two are unexpanded and
poorly separated by shallow, nonpersistent lingual flexids; entoconid
and hypoconulid poorly separated; and rounded labial borders. The
size (Table 45) and overall morphology suggests a moderate-sized
equine or protohippine. Protohippus is eliminated by the weak
protostylid and the nonpersistent lingual flexids. The two specimens
most likely represent either Pliohippus near Plio. mirabilis, or a
primitive species of Calippus (Grammohippus). such as Cal. circulus.
There are some similarities with the holotype of the latter species
(TMM 31191-10), but these are mostly plesiomorphous for the Equini,
except for the reduced protostylids in both. The molars of UF 61345
are much broader than those of TMM 31191-10, have shallower lingua-
flexids resulting in more confluence of the metaconid and metastylid,
and lack any trace of a pli entoflexid. These characters suggest
that the Florida specimens do not represent Cal. circulus, although
the samples are so limited that this cannot be excluded. Pliohippus
seems the more likely choice; if so these two specimens represent the
sole sample of the genus known from Florida. Recovery of even a
single upper cheektooth could confirm this assignment, as their
morphology is often distinctive. UF 61345 is the specimen Webb and

442

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Fauna.

Genus Astro hi ppus Stirton. 1940

Type species. Astro hi ppus ansae (Matthew and Stirton), 1930.

Included species. A^. stockii (Lance), 1950.

Chronologic and geographic distribution. Late Hemphillian of the
Great Plains, Mexico, and Florida.

Diagnosis. Relatively small equine with very high crowned cheek-
teeth, very simple enamel patterns, and relatively straight upper
cheekteeth. Moderately developed DPOF and MF, not distinctly
separated. Preorbital bar length narrow. Probably monodactyl.

Discussion. MacFadden (1984b) described the facial morpholgy (as
known) of this genus. Other characterics of Astro hi ppus are its
moderate size (toothrow lengths of 115-135 mm), very hypsodont
dentitions, simple fossettes, elongated protocones that do not
connect with the hypocones, nonper si stent hypoconal grooves, widely
expanded metaconids and metastylids, and shallow ectoflexids. The
deciduous premolars retain relatively well developed protostylids.
As Pliohippus has greatly reduced protostylids (or they are absent),
a species of Pliohippus s.s. is unlikely to be ancestral to either
Pino hi ppus or Astro hi ppus, which retain them.

444
Astrohippus stockii (Lance). 1950

MacFadden (1986) described the very limited (n=3) sample of _A.
stockii from the Palmetto Fauna of the Bone Valley Region of Florida.
No additional specimens have been recovered subsequent to the com-
pletion of his study. A single specimen is also known from the
Lockwood Meadows l.f. (MacFadden, 1986).

Genus Dinohippus Quinn, 1955

Type species. Dinohippus leidyanus (Osborn). 1918.

Included species. £. mexicanus (Lance), 1950. Possibly also
"Plio." interpolatus (Cope), 1893 and "Plio." spectans (Cope), 1880.

Chronologic and geographic distribution. Hemphillian; widely
distributed across North America.

Diagnosis. Large, monodactyl equines with moderately developed
facial fossae; DPOF lies on maxillary and nasal bones with little or
no contribution by the lacrimal; malar fossa very shallow or absent.
Nasal notch deep, lies dorsal to the P2 or P3. Upper cheekteeth less
curved than in Pliohippus, more so than in Equus. Hypoconal groove
open to near base of crown; protocone does not unite with hypocone as
in Pliohippus. Metapodials elongate, not shortened as in Hippidion-

group.

Discussion. Quinn (1955) erected Dinohippus for what he thought
was a dead-end phylum related, but not ancestral, to Equus. His
ancestor-descendant lineage leading to Equus at first glance seems

445
entirely different than Stirton's (1940), but much of the difference
is merely a matter of nomenclature. Quinn's (1955) Eoequus wilsoni
is a junior synonym of Pro, perditus (see above), and his Equus
laparensis is a junior synonym of Cal . martini. Protohippus perditus
and Calippus martini were also main line segments in Stirton's phy-
logeny of Equus. The facial, dental and post-cranial features of
Dinohippus have been described by Lance (1950), Sondaar (1968),
Skinner et al . (1977), Bennett (1980) and MacFadden (1984b; 1986).
These studies all suggested that Dinohippus was either "ancestral"
to, or has a sister-group relationship with, Equus. Dinohippus first
definitely appeared in the early Hemphillian, with records from
Florida (see below) to California and Oregon. Complete cranial ma-
terial and large sample sizes are unknown until the late Hemphillian,
by which time it was perhaps the most common equid in North America
(MacFadden, 1984b). Relative to Equus, Dinohippus appears to be a
paraphyletic assemblage of populations, as it has no uniquely apomor-
phous characters. Through the Hemphillian, populations of Dinohippus
show progressive shallowing of the facial fossae, increased persis-
tence of the hypoconal groove, increased enamel complexity, retention
of plications through a greater percentage of the crown, elongation
of the protocone, increased crown height, and straighter upper cheek-
teeth. The final product of this morphocline was Equus. A strictly
cladistic nomenclature would include "Dinohippus" within Equus.

446
Dinohippus sp.

Referred specimens. Moss Acres Racetrack Site: UF 95399 crushed
partial skull with R DP2-DP4,M1 & L DP1-DP4,M1; 92995 assoc. R & L
DI1-DI3, unerpted lis. & L DP1-DP2; 69952 R M12; 69953 partial
mandibular symphysis with L Il-C.

Description. The juvenile cranium is dorsoventrally crushed but
retains many important features. It is the oldest known skull
definitely referable to the genus. A large, elongate-oval DPOF is
located high on the face. The posterior margin is well defined but
not pocketed. It is located 27 mm from the orbit on the better
preserved right side. The dorsal margin is also well defined, but
not strongly rimmed. The ventral margin is poorly defined, as is the
anterior portion of the fossa. The anteriormost point of the fossa
is located about 13 mm anterior to the lOF. The ventral border of
the fossa is about 3 or 4 mm dorsal to the lOF. With the crushing,
the greatest depth of the fossa cannot be determined, but it was
probably not very deep. The total length of the fossa in this
juvenile specimen is about 65 mm (+/- 5 mm due to the distortion).
The malar region is crushed on both sides of UF 95399, but there is
no trace of a fossa in these regions. The specimen could not have
had a deep, "PI iohippus "-style MF, although a shallow depression is
possible (but not observed).

The dentition of UF 95399 is in the same wear-stage as UCMP 30202
(Matthew and Stirton, 1930, Plate 49.2), a maxilla of "Plio." inter-
polatus from the Coffee Ranch l.f. In both the postfossette of the

447
0P4 had not yet fully formed. The Ml of UF 95399 had erupted through
the maxilla, but had not yet begun to wear. The DP2-DP4 length of UF
95399 is 89 mm, about 10% less than UCMP 30202. Three slightly worn
juveniles of D^. mexicanus measure 94-95 mm (Lance, 1950, p. 43). The
prefossette of the DP2 is confluent with the postprotoconal valley in
both, although it is fully formed in the more heavily worn UF 92995.
The fossettes are simple with very shallow, small plications. In
both UF 95399 and UCMP 30202 the protocone of the DP2 and DP3 are
rounded, while that of the DP4 is oval with a pointed posterior end.
In UF 95399, the DP3 and DP4 both bear a moderate pli cabal 1 in, a
structure not present on the Texas specimen. The DPI is blade-like,
with maximum basal dimensions of 18.4 x 7.1 mm (UF 92995); that of UF
95399 is 15.5 mm long.

UF 69952 is a moderately worn (MSCH = 54.5 mm) upper molar, prob-
ably a M2. It has a low ROC of 45 mm. The fossettes are simple,
with a total of only two plications, both on the posterior half of
the prefossette. The protocone is relatively short (Table 45), oval,
with a pointed posterior end. The lingual protoconal border is
convex. The parastyle is strong but ungrooved. The hypoconal groove
is shallow and widely open. There is a very small pli caballin.

Discussion. The morphology of this sample of Dinohippus appears
to be relatively primitive. Thus, this population may be of impor-
tance in elucidating the origin of the genus. The preorbital bar
length (27 mm) is not great, and intermediate between that observed
in Pliohippus and younger Dinohippus (although the low value may in
part be due to the specimen's juvenile age). Other, relatively

448

primitive, character states observed in this sample are the short,
rounded protocone, the convex lingual border of the protocone, the
very simple fossettes, and the moderate curvature of the M12.
Discovery of more specimens, especially lower cheekteeth, would
greatly aid the phylogenetic interpretation of this population of
Dinohippus sp.

Dinohippus mexicanus (Lance), 1950

A small number of isolated cheekteeth of this progressive species
were recently described from the Upper Bone Valley Fauna by MacFadden
(1986). Until further, more complete specimens are found in this
region, little can be added to his descriptions. As he noted, the
presence of D. mexicanus provides additional evidence that the fauna
is of latest Hemphillian age. Its rarity in the fauna (along with
Astro hi ppus) is notable, and must reflect considerable ecological
disparity with contemporary western faunas that are dominated by
these two monodactyl equids (see above).

CHAPTER 6
PHYLOGENETIC ANALYSIS AND CLASSIFICATION

Introduction and Historical Perspective

Many problems of relationships and evolutionary
patterns within the perissodactyls still exist and
will continue to do so. Even for the very-well-
known horses there are problems at every level.
[E. C. Olson, 1971, p. 412]

It is no secret that the fossil record of perissodactyls, and
especially horses, is relatively complete and abundant. This has
resulted in a vast literature devoted to the study of fossil equids
since they were first discovered in Europe in the 1820s and North
America in the 1850s. However, this has also led to the general
conclusion that the phylogeny of the Equidae is especially well
understood in contrast to that of other mammals. Most previous
phylogenies of the family (especially those of Stirton and Simpson)
were constructed within a theoretical framework currently termed
"evolutionary taxonomy" (Mayr, 1969; Wiley, 1981), as opposed to
those based on cladistics (phylogenetics) or phenetics. A basic
difference between strict cladistic and evolutionary taxonomy is the
acceptance of paraphyletic groups in the latter system. Tradi-
tionally, equid classification has employed a number of paraphyletic
groups, e.g. the genera Merychippus, Parahippus and Pliohippus (Figs.
67A, 67B). Simpson's (1945) subfamilial divisions Hyracotheriinae
and Anchitheriinae are also obviously paraphyletic assemblages. To

449

450

some extent, the arbitrary nature of this arrangement of genera and
subfamilies was realized; e.g. Simpson (1953, p. 260) noted that
"...some of the groups named as genera represent structural stages
rather than genera by a truly phylogenetic definition." It is now
widely realized that phylogenetic analysis produces a more natural
arrangement of taxa, one that reflects the true evolutionary history
of a group (Wiley, 1981, and references therein).

The early phylogenies of the Equidae, as proposed by Huxley,
Kovalevsky and Marsh in the late 1800s, were merely series of struc-
tural grades placed in stratigraphic succession (e.g. Marsh, 1879).
Gidley (1907) was probably the first person to address the problem of
equid phylogeny in a modern sense. He divided the family into four
subfamilies (Hyracotheriinae, Anchitheriinae, Protohippinae and
Equinae), but noted (Gidley, 1907, p. 869) "...while phylogeny has by
no means been ignored, . ..[these]. ..subdivisions of the Equidae are
founded on a basis of structural affinities rather than on phylo-
genetic relations." Presumably the reason for doing this was his
belief that material available to him was inadequate to place the
known genera in a truly phylogenetic arrangement (Gidley, 1907, p.
870). Two decades later, W. D. Matthew (1926) was able to propose a
phylogenetic arrangement of equid genera. For Matthew, equid genera
were still regarded as evolutionary stages, each of which could give
rise to one or more successive genera. Matthew's (1926) arrangement
made some important contributions to our understanding of equid
phylogeny. Most important was the refutation of the concept that
equids were a direct orthogenetic sequence of genera proceeding from

451
Hyracotherium to Equus. He also recognized that advanced, hypsodont
horses formed two distinct clades (Hipparionini and Equini as used
here), and that North American hipparionines represented at least
three distinct lineages. This last point was further elaborated by
Matthew and Stirton (1930), although it was Stirton (e.g. 1940) who
formally recognized them as distinct genera. Stirton 's (1940) well
known phylogeny of the Equidae is in large measure a derivation of
Matthew's. Conceptually, the two are very similar, although Stirton
formally recognized some later Tertiary groups (Calippus and Astro-
hippus) as distinct, explicitly noted the relative positions of some
species in the phylogeny, and benefited from a better understanding
of the Cenozoic timescale. The resemblances between the two are
apparent in Figure 67, in which they have been converted into cla-
distic form. In doing so, species regarded as "ancestral" to certain
groups (e.g. "Merychippus" isonesus in Fig. 67B) by Stirton are given
sister-group status. Stirton 's phylogeny was an eclectic combination
of horizontal and vertical classification. With respect to the
Equinae, many of the "primitive" species were placed in a horizontal
grade (Merychippus s.l.), from which descended five vertical clades.
In this sense, Merychippus is an example of the familar "waste-
basket" taxon widely employed by evolutionary taxonomists. Stirton 's
(1940) phylogeny was popularized by Simpson (1944; 1951; 1953), who
used it to examine various evolutionary mechanisms, and it has
endured at the generic level to this day with little modification
(e.g. MacFadden, 1985). The only substantive changes (other than
those at the species level, e.g. by MacFadden 1984a; Webb and

452

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Figure 67. Previous phylogenetic hypotheses of advanced equids
expressed in cladistic form. A. Matthew (1926). B. Stirton
(1940). C. Quinn (1955). Matthew and Stirton expressly used
paraphyletic taxa in their classifications, e.g. the genera
Merychippus and Pliohippus. Quinn did not use paraphyletic taxa,
but his arrangement of equid genera differs considerably with both
the traditional phylogenies of Matthew and Stirton, and the results
of this study's cladistic analysis.

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454

Figure 68. Forsten's (1984) cladogram expressing the interrela-
tionships among the hipparionines. This arrangement is not
supported by the results of this study (see Figures 73 and 74).

455

Hulbert, 1986) have been the recognition of three more "advanced"
genera (Dinohippus, Cormohipparion and Pseudhipparion), making a
total of eight lineages independently rising out of Merychippus s.l.

Only one serious alternative to the phylogeny of Matthew and
Stirton has been proposed, that of Quinn (1955). Quinn's arrangement
(expressed cladistically in Fig. 670. while strictly a vertical phy-
logeny, did not distinguish between primitive and derived characters,
did not take into proper account ontogenetic and individual variation
(thus badly oversplitting some taxa; Webb, 1969a; Forsten, 1975), and
was based almost entirely on relatively incomplete Texas Gulf Coastal
Plain specimens. The major difference between the phylogenies of
Quinn and Stirton (Fig. 67) was that Quinn considered part of the
equine clade (that containing Equus and closely related forms) as the
sister-group of the hipparionines. Other, more minor differences,
were 1) that Neohipparion was considered closer to Hipparion than was
Nannippus, 2) Pseudhipparion was excluded from the hipparionines and
considered related to Calippus and Astrohippus (Stirton, 1940; 1947,
considered Pseudhipparion to be a side branch within Nannippus). and
3) Protohippus and Calippus were not considered to be closely
related. As noted previously (p. 445), a major difficulty in inter-
pretting Quinn's phylogeny and comparing it to those of others, is
understanding his specific and generic level taxonomy.

Forsten (1984) has recently proposed a cladistic phylogeny of the
hipparionines, reproduced here as Figure 68. As noted on p. 159, she
improperly "redefined" Cormohipparion by excluding its hipparionine-
grade species, although she did not specifically state which ones

456
these are. Presumably this would have to exclude Cor, occidentale.
the genotype species, as it undoubtedly has hipparionid lower cheek-
teeth. Forsten (1984) also included Nannippus in Hipparion. failed
to state what characters unite Hipparion and Neo hipparion, and united
Old and New World taxa in Neohipparion based on the presence of
grooved incisors. Incisors associated with cheekteeth of Neo.
leptode and Neo. eury style are not grooved, and the validity of this
character is doubtful.

Cladistic analysis produces phylogenies in the form of testable
hypotheses. Previous phylogenies of the Equidae were based on a
limited number of characters. Some, especially that of Stirton
(1940), almost exclusively used upper cheekteeth. With the current
improved knowledge of cranial characters for many taxa (due in large
measure to the Frick collection), a cladistic analysis of advanced
equids is detailed below. The results are compared with previous
phylogenies, and a new classification of these horses is proposed.

Methods

States for 60 characters and 57 taxa of advanced equids were
compiled from Chapter 5 and from the literature (Table 46). These
included all of the species described in Chapter 5, except for ?Cal.
circulus which is currently too inadequately known. Only North
American taxa were considered, as Old World horses were beyond the
scope of this study (since they were ultimately derived from North
American species, a phylogenetic analysis of the latter is essential
for interpreting their relationships, but not the converse). Also

457
included were species not known from the Gulf Coastal Plain (e.g.
Nan. lenticular is and Neo. leptode), and twelve late Hetningfordian to
Barstovian species of "merychippine" grade. These were "Merychi ppus"
gunteri . "M. " primus. "M . " isonesus. "M . " sejunctus, "M . "
carrizoensis, "M . " stylodontus, "Neo. " coloradense, "Cor. " goorisi.
Hipparion shirleyi. Pro, vetus, Plio. mirabilis. and M. insignis.
Character states for the latter taxon were based on the Echo Quarry
sample described by Skinner and Taylor (1967). Evander (1986) has
questioned their referral of this material to that genus and species.
Regardless of nomenclature, it is an important, well represented
sample. Parahippus leonensis was used as the out-group in all
analyses, based on the well represented middle Hemingfordian Thomas
Farm sample (Forsten, 1975; Hulbert, 1985). Para, leonensis (or its
junior synonym Para, vellicans; synonymy follows Downs, 1956 and
Forsten, 1975) has long been regarded as "ancestral" to Merychi ppus
s.l. (Schlaikjer, 1937; Stirton, 1940; Downs, 1956), making it the
best candidate for an out-group.

Cladograms were constructed both "by hand" and by use of the
computer program PAUP. PAUP computes most parsimonious tree(s) for
taxa using a number of different methods and options (Swofford,
1985). Options used here were: rooting using the out-group method;
weighing all characters equally regardless of the number of character
states they contain (WEIGHTS SCALE option); optimizing the character
states of hypothetical taxonomic intermediaries with the FARRIS
option; and obtaining all equally most parsimonious trees with the
SWAP=ALTERNATE method of branch-swapping in conjunction with the

458

MULPARS option. The number of taxa and characters being studied
prevents the exact determination of the truly most parsimonious tree
(i.e. through the use of PAUP's ALLTREES or BANDB options). The
computer time required to calculate truly most parsimonious trees
with PAUP becomes prohibitive (i.e. >24 hours on an IBM PC) when more
than 12 to 16 taxa are analyzed together. Instead, the program must
use a complex algorithm to obtain the heuristically best solution to
the problem (Swofford, 1985). As a matter of convenience, trees
obtained with this algorithm will be termed "most parsimonious" for
the remainder of this study. Using the TOPOLOGY command, cladograms
constructed "by hand" were analyzed by PAUP for comparison with the
trees derived using the parsimony criterion.

Of the 60 characters (Table 47), 13 are cranial features (of which
six relate to the morphology and position of the facial fossae);
three are characters taken from the incisors; 42 from the cheekteeth
(22 uppers, 17 lowers, 3 general); one postcranial character; and
general size. Lack of associated post-cranial and cranial material
for many species prevents a greater use of post-cranial characters in
the study. However, the overall basic morpholgy of equid post-
cranial elements is relatively conservative among the advanced equids
(Schlaijker, 1937) compared to other mammalian families. In species
that demonstrate multiple character states for a particular feature,
the one most commonly observed was assigned in Table 46. This did
not happen very often, as the character states were selected and
divided so as to avoid this. However, given the great intraspecific
variation observed in equid cheektooth enamel patterns, some

459

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Table 47. Description of characters and character states used in the
phylogenetic analyses. Characters with three or more states were
considered to be transformational sequences (morphoclines).

CHARACTER

1. Depth of nasal notch

2. depth of DPOF

3. DPOF posterior pocket

4. DPOF anterior margin

5. preorbital bar length

6. DPOF shape

7. size of lacrimal bone

8. frontal bones

9. zygomatic arch buckle

10. long process of premaxilla
extends past nasal notch

11. malar region

CHARACTER STATES

0 very shallow

1 deep, over anterior half of P2

2 deep, over posterior half of P2

3 very deep, passed the P2

0 absent or rudimentary

1 shallow

2 moderate

3 deep

0 not present

1 slight pocketing

2 deeply pocketed

0 confluent with face

1 well defined or rimmed

0 narrow (<5 mm)

1 moderate (5-15 mm)

2 long (>15 mm)

0 elongate-oval

1 oval

0 relatively large

1 relatively small

0 not notably domed

1 notably domed

0

1

present
absent

0

1

yes
no

0

1

2

3

inflated, no fossa
variably shallow depression
moderate fossa
deep fossa

464

Table 47 — continued

12. relative muzzle length

13. relative muzzle width

14. incisor arcade

15. incisors

16. lower incisors

17. relative size of DPI

18. deciduous premolars

19. P2/DP2 anterostyle

20. protocone shape

21. relative protocone size

22. protocone lingual border

0 very short

1 short

2 moderate

3 elongated

4 very elongated

0 normal

1 broadened

2 very broad

0 arcuate

1 straight

0 normal, rooted

1 very hypsodont

2 ever-growing, rootless

0 normal

1 very procumbent

0 1 ar ge

1 small

2 very reduced or absent

0 mesodont, little or no cement

1 weakly cemented

2 subhypsodont, well cemented

0 well developed

1 reduced

2 very reduced

0 round

1 oval

2 elongate-oval

3 elongated

4 very elongated

0 small

1 moderate

2 large

0 round or convex

1 straight

2 straight or concave

3 concave

Table 47--continued

465

23. protocone spur

0 large, persistent

1 large, only in early wear-stage

2 reduced, only in early wear

3 absent or very rare

24. protocone spur connects
to protoselene

25. timing of protocone
connection to protoselene
on P34

26. timing of protocone

connection to protoselene
on M12

0 yes

1 no

mmediately after onset of wear

n very early wear-stage

n early wear-stage

n early moderate wear-stage

n late moderate wear-stage

n late wear -stage

solated to base of crown

mmediately after onset of wear

n very early wear-stage

n early wear-stage

n early moderate wear-stage

n late moderate wear-stage

n late wear-stage

solated to base of crown

27. protocone connection to
hypocone

28. pli cabal 1 in on premolars

0 never

1 rarely, always in late wear

2 commonly

0 absent or very rare

1 weak or nonpersi stent

2 strong, single

3 strong, often multiple

29. pli caballin on molars

0 absent or very rare

1 weak or nonpersi stent

2 strong, single

3 strong, often multiple

30. external fossette plications

0 not plicated or very simple

1 persistently plicated

2 multiple pli protoloph common

31. internal fossette plications

0 absent or very rare

1 very simple

2 simple, nonpersi stent

3 simple, persistent

4 moderate

5 complex to moderate

6 persistently very complex

Table 47 — continued

466

32. protocone orientation
on P34

33. metastyle

34. mesostyle

35. hypoconal groove closure

36. hypoconal groove

0 anteroposterior

1 markedly oblique

0 generally absent

1 often present, not strong

2 very well developed

0 relatively weak

1 moderate

2 strong

3 strong, notably constricted

0 open to base of crown

1 closed in moderate wear-stage

2 closed in early wear-stage

3 closed in very early wear-stage

0 does not form lake when closed

1 forms isolated lake

37. depth of hypoconal groove

0 deep

1 shallow

38. orientation of hypocone

39. ROC of upper cheekteeth

40. ectostylids on dp2-dp4

41. protostylids on dp34

42. strength of dp34 protostylids

0 anteroposterior

1 oblique

0 low (strongly curved)

1 moderate

2 high, teeth not curved

0 absent or rudimentary

1 moderate

2 very strong

0 present

1 absent

0 "Hippodon" grade

1 moderate

2 strong

43. protostylids on p3-m3

0 present

1 absent

Table 47--continued

467

44. strength of protostylids
on p3-in3

45. protostylid attachment

46. metaconid-metastylid complex

47. metaconid-metastylid

48. p2/dp2 metaflexid

0 "Hippodon" grade

1 moderate

2 strong

3 strong, recurved posteriorly

0 attached to protoconid

1 isolated when it first appears

2 persistently isolated

0 small, unexpanded

1 expanded

2 elongated

3 very elongated

4 extremely elongated

0 poorly separated

1 well separated in early wear-
stage only

2 persistently well separated

0 rarely closed

1 frequently closed by
metaconid plication

49. isthmus plications

50. para lo phi d plication

51. pli cabal linid on premolars

0 absent or very rare

1 pli entoflexid only

2 frequent, but nonper si stent

3 frequent, persistent

0 absent or rare

1 frequent

0 absent

1 small, only in early wear

2 well developed, persistent

3 as in 2, but often multiple

52. pli cabal linid on molars

0 absent

1 small, only in early wear

2 moderate, lasts until mid-wear

3 persistent, strong

53. ectoflexid depth on premolars

0 deeply penetrates isthmus

1 slightly penetrates isthmus

2 shallow, no penetration

3 very shallow

468

Table 47 — continued

54. ectoflexid depth on molars

0 completely penetrates isthmus

1 depth reduced in early wear-
stages, then as in 0

2 depth reduced until moderate
wear-stages, then very deep

3 shallow, no penetration

55. labial borders of proto-
conid and hypoconid

56. position of metaconid rela-
tive to metastylid on molars

57. general size (mean
UTRL +/- 5 mm)

58. unworn Ml MSCH or
ml mcch, +/- 2.5 mm

59. same as 58

0

rounded

1

flattened

0

the same

1

notably more linguad

0

very small , 80 mm

1

small, 90 mm

2

100 mm

3

110 mm

4

120 mm

5

130 mm

6

140 mm

7

150 mm

8

>155 mm

0

20 mm

1

25 mm

2

30 mm

3

35 mm

4

40 mm

5

45 mm

6

50 mm

7

55 mm

8

>58 mm

0

<58 mm

1

60 mm

2

65 mm

3

70 mm

4

75 mm

5

80 mm

6

>83 mm

60. lateral digits

0 present, relatively large

1 notably reduced

2 absent

469

individuals will not match all the character states listed in Table
46 for any given taxon.

Results and Classification
Preliminary Analyses

There were three primary goals of this phylogenetic analysis. The
first was to determine the cladistic interrelationships of the
species. The second was to use that information to delineate generic
and other monophyletic supraspecific groups within the Equinae. The
third was to examine the true phylogenetic relationships of
merychippine-grade taxa with others traditionally assigned to more
"advanced" genera. The results of the analyses are not completely
conclusive, and further analysis with more characters should clarify
some relationships. One potential source for additional characters
is the basicranium. Webb {1969a) gave a detailed description of a
skull of Pseud, retrusum. and noted several differences between its
basicranium and those of Pliohippus and Equus. The large F:AM sample
of skulls of Pseudhipparion, Cormohipparion. Calippus, Protohippus,
Pliohippus and various merychippines should demonstrate the range of
intraspecific variation of these characters, and determine this
region's potential value for equid systematics. Another potential
source of additional characters is the post-cranial skeleton,
especially the distal limb elements. Recent discoveries of
associated individuals at Moss Acres and the Poison Ivy Quarry make
this more feasible than before.

47 0
In the first preliminary analysis, as many taxa as possible were
examined simultaneously. The maximum number of taxa PAUP (Version
2.4) can analyze at once is 45. Thus 12 taxa from the original data
set had to be excluded. Those deleted had incomplete data, or were
so similar to others that they added little information to the over-
all tree (e.g. Nan, bee ken sis, as it was obviously closely related to
Nan. peninsulatus). Using all 60 characters, three equally parsimon-
ious trees were produced, of which one is shown in Figure 69. These
differed only in the relative positions of Pseud, gratum. Pseud,
hessei and Pseud, skinneri. so there is essentially but one most
parsimonious arrangement of the 45 taxa. The tree shown in Figure 69
indicates that advanced equids consist of two major clades. If
merychippine-grade species are not considered, four monophyletic
hipparionine clades are recognized, Hipparion, Cormohipparion (plus
Nan, fricki), Neo hipparion and Nannippus. The other major clade
contains the following monophyletic groups: Pseudhipparion,
Protohippus, Calippus (excluding Grammohippus), Astrohippus and
Pliohippus. Dinohippus and Cal. (Grammohippus) are paraphyletic.
Many of the features (and problems) of this tree (and others produced
with slightly different combinations of characters and taxa) are
similar to those observed by Kirsch and Archer (1982) in a study of
computer-generated cladograms of carnivorous marsupials. Comparisons
between the two studies are appropriate because both have species as
their terminal taxa (instead of, e.g. Novacek's [1986] analysis of
mammals at the ordinal level), both use similar tree-generating
programs with parsimony criteria, and in both, dental traits far

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473

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479

Table 48. Consistency indices (CIs) for individual characters in the
cladogram depicted in Figure 69. The CI for a single character is
the minimum possible number of changes over the entire tree divided
by the actual number of changes for the character. A character that
evolved only once over a given tree, and has no reversals, has the
maximum possible CI, 1.00. Numbers for characters refer to those in
Table 47.

CHARACTER

CI

CHARACTER

CI

CHARACTER

CI

1

0.25

21

0.40

41

1.00

2

0.20

22

0.25

42

0.40

3

0.20

23

0.33

43

0.50

4

0.33

24

0.50

44

0.27

5

0.22

25

0.43

45

0.67

6

1.00

26

0.38

46

0.33

7

0.33

27

0.22

47

0.22

8

1.00

28

0.22

48

1.00

9

1.00

29

0.29

49

0.33

10

0.50

30

0.29

50

0.25

11

0.25

31

0.26

51

0.43

12

0.25

32

0.33

52

0.50

13

0.67

33

0.18

53

0.50

14

0.50

34

0.75

54

0.33

15

1.00

35

0.25

55

0.25

16

1.00

36

0.25

56

0.33

17

0.25

37

0.50

57

0.22

18

0.40

38

0.50

58

0.24

19

0.40

39

0.29

59

0.31

20

0.44

40

0.40

60

0.50

48 0

outnumber other types of characters. The amount of homoplasy is
great. The overall consistency index (CI) is only 0.34, while 83% of
the characters had individual CIs equal to or less than 0.50 (Table
48). Groups were thus not delineated by sets of uniquely derived
character states, but by different contiinations of character sets
(polythetic sensu Kirsch and Archer, 1982). To achieve maximum
parsimony, in this and in many other trials, the algorithm often
proceeds in directions that are very unlikely in an evolutionary
sense. For example, there are many instances of decreasing crown
height, deepening ectoflexids, and shortening protocones and
metaconid-metastylid complexes. All of these, while not impossible,
are extremely unlikely in equid evolution. Thus, the tree in Figure
69 would appear not to accurately reflect the true evolutionary
history of the Equinae.

To further investigate the interrelationships of these taxa, three
additional trees were computed. In one (Fig. 70), the same 45 taxa
were used, but only those characters with CIs of 0.50 or greater in
Table 48. The result is a highly consistent, but much less fully
resolved tree, with numerous multichotomies. In the second (Fig.
71), all 60 characters were used, but only with genotypic species.
The third tree (Fig. 72) also included all 60 characters, but only
Barstovian or older taxa were analyzed. Comparisons of these trees,
and with the one in Figure 69, reveal both differences and similar-
ities. The presence of "M^. " carrizoensis unduly affects character
polarities, as PAUP invariably made it the sister-taxon to all more
"advanced" equids (Figs. 69, 72), rather than just the sister-taxon

481
to the Equini. This species has a combination of very primitive
(e.g. low crown height, deep premolar ectoflexids) and very advanced
(e.g. rapidly connected protocones, simple fossettes, malar fossa)
characters (Munthe, 1979; Quinn, 1984). Other taxa, e.g. Calippus
cerasinus, also appear to have certain combinations of advanced and
primitive characters that force them into "unexpected" positions in
the computer-generated tress. The problem is not so much where the
computer places these taxa in the tree, but how that position affects
judgements of character polarity in other OTUs.

The three trees (Figs. 70-72) all share with the one in Figure 69
a monophyletic hipparionine clade, although of differing composition.
Pseudhipparion is included in this clade, rather than with the
equines and protohippines. Calippus is the sister-taxon to other
equines in Figures 69 and 71, while in the other analyses it and
Protohippus are sister-groups. Contrasts between the trees in
Figures 69 and 70 are especially instructive. One is based on only a
few, but highly consistent characters (overall CI=0.79), the other on
many characters, most of which are homoplasous (Table 48). Both
reveal different aspects of equid evolution. The tree in Figure 70
probably represents the true major dichotomies within the advanced
Equinae (i.e. the Equina, Protohippina and Hipparionini as defined in
Chapter 5). The tree in Figure 69 emphasizes that parallelism and
character reversal were extremely commonplace in equid evolution (as
has long been noted), and that a strictly parsimonious approach is
unlikely to correctly classify the group (cf. Felsenstein, 1978;
Kirsch and Archer, 1982; Gosliner and Ghiselin, 1984).

48 2

As justified by these preliminary results, the next two sections
will discuss the results of analyses run separately for hipparionines
and nonhipparionines (protohippines plus equines). To some extent,
this limited the amount of observed parallelism, and allowed for more
judicial generic assignments. In each case, the most parsimonious
cladogram will be contrasted with a "hand-drawn" tree. The latter
are only slightly less parsimonious, do not contain unlikely
evolutionary events (e.g. decreasing crown height), and are more
compatable with the fossil record.

Phylogenetic Analysis of Hipparionine Taxa

Figures 73 and 74 present two alternative phylogenetic hypotheses
concerning 28 species of hipparionines. Figure 73 was generated by
PAUP based on all sixty equally weighted characters discussed above
(Table 46). It has a length of 116.8 steps, which converts to a CI
of 0.45. The cladogram in Figure 74 was generated "by hand" using
the same set of characters. While parsimony was one criterion used
in its construction, subjective judgements were also made as to which
characters were more important (weighting), and which were thought to
be more likely to have evolved in parallel in various genera
(Gosliner and Ghiselin, 1984). It has a length of 119.5 steps (2.3%
longer than the other tree), and a CI of 0.44. As opposed to the
situation described below for the Equini, there is actually very
little difference between the two trees, only the relative positions
of two taxa are different. In the most parsimonious tree (Fig. 73),
Merychippus insignis (Echo Quarry population) and "H." coloradense

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48 7

form successive sister-taxa to the remainder of the hipparionines.
In the other tree (Fig. 74), M^. in sign is is considered to be the
sister-taxon of only Hipparion, Cormohipparion and Nannippus. and
"M." colora dense the sister-taxon of only Pseudhipparion and
Neo hipparion. In all other respects the two trees are identical.
Based on Figure 74, the cladistic relationships among hippari-
onines are determined by the following groups of derived characters:
Node 1. The Hipparioni are united by:

a. moderately deep DPOF (secondarily shallow in several groups);

b. DPOF with slight posterior pocket (secondarily lost in
several groups);

c. oval protocones;

d. nonpersistent protoconal spur;

e. protocone not connected to protoselene until moderate wear-
stage;

f. molars with pli caballin;

g. moderately developed, persistent internal fossette
plications;

h. strong protostylid on dp34;
i. moderately well developed protostylid on p3-m3;
j. expanded metaconid-metastylid complex;

k. metaconid and metastylid well separated in early wear-stage;
1. unworn molar crown height 30 mm or more.
Node 2. "M. " coloradense, Pseudhipparion and Neohipparion share:

a. elongate-oval protocone;

b. protoconal spur not very persistent, reduced;

488

c. shallow prenxDlar ectoflexid;

d. well cemented, subhypsodont deciduous premolars;

f. increased unworn molar crown height, 40 mm or more.
Node 3. "M." colora dense is primitive for all known characters

relative to Pseudhipparion and Neohipparion.
Node 4. Pseudhipparion and Neohipparion share:

a. shallow DPOF, not well rimmed;

b. DPOF lacks posterior pocket;

c. moderate preorbital bar length;

d. markedly oblique premolar protocone orientation;

e. metaconid and metastylid persistently well separated.
Node 5. Pseudhipparion is derived relative to Neohipparion by:

a. deeper nasal notch;

b. frontal s notably domed;

c. zygomatic arch lacks pronounced buckle (Webb, 1969a);

d. protocone connects to protoselene in early moderate wear-
stage;

e. protocone connects to hypocone in late wear-stage of molars;

f. hypoconal groove closed in early wear-stage;

g. hypoconal groove forms isolated lake after closing;
h. reduced size, UTRL about 110 mm or less.

Node 6. Pseud, retrusum is derived relative to all other species of
Pseudhipparion by:

a. rapid connection of molar protocone to hypocone;

b. increased unworn molar crown height, about 45 mm.

48 9
Node 7. Pseud, curti vallum. Pseud, gratum. Pseud, hessei. Pseud.
skinneri and Pseud, simpsoni share:

a. strong protostylid on p3-tn3 (later reduced in some species);

b. stronger, more persistently open metaflexid;

c. increased ROC;

d. reduced size, UTRL about 100 mm or less.

Node 8. Pseud, curti vail urn is derived relative to Pseud, gratum.
Pseud, hessei. Pseud, skinneri and Pseud, simpsoni by:
a. shallower molar ectoflexids in early wear-stage.

Node 9. Pseud, gratum. Pseud, hessei. Pseud, skinneri and Pseud.
simpsoni share:

a. more elongated protocone;

b. protocone size large relative to tooth length;

c. hypoconal groove closed in early wear-stage;

d. increased unworn molar crown height, about 50 mm.

Node 10. Pseud, gratum is derived relative to Pseud, hessei. Pseud.
skinneri and Pseud, simpsoni by:

a. protocone isolated until late moderate wear-stage in P3-M2;

b. increased unworn molar crown height, about 54 mm.

Node 11. Pseud, hessei , Pseud, skinneri and Pseud, simpsoni share:

a. molar protocone connected to protoselene in early wear-stage.
Node 12. Pseud, hessei is derived relative to Pseud, skinneri and

Pseud, simpsoni by:

a. premolar protocone often connected to protoselene in early or

very early wear-stage.

490
Node 13. Pseud, skinneri and Pseud, simps on i share:

a. very hypsodont incisors;

b. reduced DPI;

c. protocone lingual border flattened;

d. molar protocone never connected to hypocone;

e. simpler, less persistent fossette plications;

f. earlier loss of hypoconal lake on P2-P4;

g. reduced protostylid on p3-m3;
h. reduced size, UTRL about 90 mm.

Node 14. Pseud, skinneri is derived relative to Pseud, simps on i by:

a. very early loss of hypoconal lake on P2-M3.
Node 15. Pseud, simps on i is derived relative to Pseud, skinneri by:

a. rootless, ever-growing incisors;

b. incipiently hypselodont cheekteeth;

c. lack of pli calallin;

d. simpler fossettes, fossettes absent in late wear-stage;

e. very strong mesostyle;

f. ectostylids absent on dp2-dp4;

g. protostylids reduced on dp34 and p3-m3, or absent;
h. widely expanded metaconid and metastylid;

i. very shallow ectoflexid on molars.
Node 16. Neo hip par ion is derived relative to Pseudhipparion by:

a. DPI reduced in relative size;

b. more elongated protocone, without spur;

c. protocone lingual border straight or concave;

d. protocone isolated from protoselene to base of crown;

491

e. ectostylid absent on dp2-dp4;

f. metaconid-metastylid complex elongated;

g. isthmus plications common;

h. pli caballinids developed on premolars and molars, at least
in early wear-stages;

i. molar ectoflexid shallower in early wear-stage;
j. labial borders of protoconid and hypoconid flattened;
k. increased unworn molar crown height, at least 55 mm.
Node 17. Neo. affine is derived relative to other species of
Neohipparion by:

a. persistently simple fossette placations;

b. large size, UTRL about 140 mm.

Node 18. Neo. trampasense. Neo. leptode, Neo. eurystyle and Neo.
gidleyi share:

a. DPOF absent or vestigial;

b. very long preorbital bar;

c. lacrimal bone reduced in size;

d. moderately elongated muzzle;

e. DPI absent in adult and some juvenile dentitions;

f. premolar pli caballin often branched or multiple;

g. very strong protostylids on p3-m3 and dp34;
h. metaconid-metastylid complex very elongated;

i. isthmus plications present on most teeth, usually persistent;

j. paralophid plicated;

k. premolar pli caballinid well developed and persistent;

1. molar pli caballinid at least moderately developed;

492
m. premolar ectoflexid very shallow, never penetrates isthmus;
n. molar ectoflexid shallow in early and early moderate wear-
stages;
0. increased unworn molar crown height, about 60 mm.

Node 19. Neo. trampa sense is primitive for all known characters
relative to Neo. leptode, Neo. eurystyle and Neo. gidleyi.

Node 20. Neo. leptode, Neo. eurystyle and Neo. gidleyi share:

a. very elongated protocone;

b. extremely elongated metaconid-metastylid complex,
linguaflexid U-shaped persistently;

c. molar pli cabal linid strong, persistent;

d. increased unworn molar crown height, about 65 mm;

e. increased size, UTRL usually greater than 130 mm.

Node 21. Neo. leptode is primitive for all known characters relative

to Neo. eurystyle and Neo. gidleyi except for:

a. increased size, UTRL about 140 mm.
Node 22. Neo. eurystyle and Neo. gidleyi share:

a. protocone lingual border usually concave;

b. very strong, anteriorly curved metastyle;

c. strong, constricted mesostyle;

d. posteriorly curved, deeply grooved or bifurcated parastyle;

e. protostylid curved posteriorly;

f. molar ectoflexid persistently shallow;

g. increased unworn molar crown height, about 70 mm or greater.

493
Node 23. Neo. eury style is derived relative to Neo. gidleyi by:

a. larger protocone relative to tooth length;

b. premolar pli caballinid often branched or multiple.

Node 24. Neo. gidleyi is primitive for all known characters relative

to Neo. eurystyle except:

a. increased size, UTRL about 150 mm.
Node 25. M. insignis, Hipparion, "M . " goorisi. Cormohipparion and

Nannippus share:

a. persistently strong, often multiple pli caballin on
premolars;

b. persistently strong, usually single pli caballin on molars;

c. pli protoloph and pli hypostyle relatively persistent;

d. moderate to complex internal fossette plications.

Node 26. M. insignis is primitive for all known characters relative

to Hipparion, Cormohipparion and Nannippus.
Node 27. Hipparion, "M . " goorisi, Cormohipparion and Nannippus

share :

a. increased preorbital bar length;

b. inflated malar region, lacks depression or fossa;

c. moderately elongated muzzle;

d. large protoconal spur present only in early wear-stage.

e. increased ROC;

f. deciduous premolars weakly cemented.

Node 28. Hipparion is derived relative to "M^. " goorisi ,
Cormohipparion and Nannippus by:
a. deep nasal notch;

494

b. less complex fossette plications;

c. metastyle absent or very reduced.

Node 29. H. shirleyi is primitive for all known characters relative

to H. tehonense and H^. forcei except:

a. small size, UTRL about 100 mm.
Node 30. H^. tehonense and H^. forcei share:

a. well cemented deciduous premolars;

b. DPOF not pocketed;

c. reduced lacrimal bone;

d. oval protocone;

e. reduced protoconal spur;

f. protocone isolated from protoselene until late wear-stage on
P3-M3;

g. reduced fossette complexity, especially pli protoloph and pli
hypostyle less persistent;

h. metaconid and metastylid persistently well separated;

i. increased unworn molar crown height, about 45 mm.
Node 31. H. tehonense is derived relative to H. forcei by:

a. reduced P2 anterostyle.
Node 32. H_. forcei is derived relative to H^. tehonense by:

a. shallower p2 ectoflexid;

b. increased size, UTRL about 130 mm;

c. increased unworn molar crown height, about 50 mm.
Node 33. "M . " goorisi, Cormohipparion and Nannippus share:

a. deep DPOF (secondarily shallow in some species);

b. anterior margin of DPOF well defined, often rimmed;

495
c. shallower premolar ectoflexids that only partially penetrate
the isthmus.
Node 34. "M." go or i si is derived relative to Cormohipparion and
Nannippus by:

a. very deep posterior pocket on DPOF;

b. reduced lacrimal bone, does not touch DPOF;

c. because of b, malar bone forms part of DPOF;

d. relatively short muzzle;

e. very reduced protostylids;

Node 35. Cormohipparion and Nannippus share:

a. elongate-oval protocones;

b. protocone isolated from protoselene until late wear-stage on
P3-M3;

c. prominent protostylid on p3-m3;

d. protostylid isolated from protoconid when it first appears on
the occlusal surface;

e. metaconid-metastylid persistently well separated by deep
lingual flexids;

f. frequent isthmus plications in early wear-stage;

g. weak pli caballinid on premolars in early wear-stage;
h. premolar ectoflexids shallow, usually do not penetrate
isthmus;

i. well cemented, subhypsodont deciduous premolars;
j. increased unworn molar crown height, about 45 mm or more.
Node 36. Cormohipparion is derived relative to Nannippus by:
a. protocone spur rudimentary or absent;

496

b. very strong ectostylid on dp2-dp4;

c. persistent isthmus plications;

d. plicated paralophid

e. increased size, UTRL about 130 mm or more.

Node 37. Cor, sphenodus is primitive for all known characters

relative to other species of Cormohipparion.
Node 38. Cor, occidentale. Cor, plicatile. Cor. in genu urn and Cor.

emsliei share :

a. protocone spur absent;

b. pli cabal linid on ml-m3 in early wear-stage;

c. ectoflexid depth of ml-m3 reduced in early wear-stage;

d. elongated diastema;

e. increased unworn molar crown height, about 50 mm or more.
Node 39. Cor. occidentale and Cor. plicatile are derived relative to

Cor, ingenuum and Cor, emsliei by:
a. increased unworn molar crown height, about 60 mm.
Node 40. Cor. occidentale is derived relative to Cor, plicatile by:

a. more elongated protocone;

b. multiple pli protoloph common;

c. increased average internal fossette complexity;

d. increased size, UTRL about 140 mm.

Node 41. Cor, plicatile is derived relative to Cor, occidentale by:

a. very elongated muzzle.
Node 42. Cor, ingenuum and Cor. emsliei are derived relative to Cor.

occidentale and Cor. plicatile by:

a. reduced depth and rimming of DPOF;

497

b. lingual border of protocone often straight or concave;

c. metaflexid of p2 and dp2 closed to a fossettid in moderate
wear-stage by plication from metaconid;

d. decreased size, UTRL about 120 mm.

Node 43. Cor. ingenuum is primitive for all known characters

relative to Cor, emsliei .
Node 44. Cor. emsliei is derived relative to Cor, ingenuum by:

a. very shallow DPOF;

b. persistently multiple pli protoloph;

c. extremely complex fossette margins;

d. very strong styles;

e. posteriorly curved protostylid;

f. elongated, angular metaconid-metastylid complex;

g. well developed pli caballinids on p2-p4, dp2-dp4, and most
molars;

h. molar ectoflexid depth reduced until moderate wear-stage.
Node 45. Nannippus is derived relative to Cormohipparion by:

a. elongated muzzle;

b. very reduced DPI, lacks hypocone or lophs, can be absent;

c. reduced P2 and DP2 anterostyle;

d. p2 short relative to p3 apl ;

e. reduced size, UTRL about 110 mm or less.

Node 46. Nan. fricki is primitive for all known characters relative

to other species of Nannippus.
Node 47. Nan, westoni. Nan, lenticularis. Nan, minor. Nan.

peninsulatus and Nan. bee ken sis share:

498

a. P2 and DP2 anterostyle very reduced;

b. pli caballins relatively weak, rarely branched or multiple,
very weak or absent on molars;

c. relatively shallow hypoconal grooves;

d. molar ectoflexid depth reduced in early wear-stage.

Node 48. Nan, westoni is derived relative to Nan, lenticularis. Nan.
minor. Nan, peninsulatus and Nan, bee ken sis by:

a. relatively simple fossette plications;

b. metastyle absent.

Node 49. Nan. lenticularis. Nan, minor. Nan, peninsulatus and Nan.
bee ken sis share:

a. reduced DPOF depth;

b. protocone spur rare, small or absent;

c. dp2-dp4 ectostylids absent;

d. reduced protostylids on p3-m3 and dp34;

e. increased unworn molar crown height, about 50 mm, and a
proportionally greater increase in premolar crown height.

Node. 50. Nan, lenticularis is derived relative to Nan, minor, Nan_.
peninsulatus and Nan, bee ken sis by;

a. isolated protocones on P2 until moderate wear-stage;

b. pli protoloph and pli hypostyle absent or nonper si stent;
e. protostylid usually isolated from protoconid for most of
crown;

d. relatively short, broad metapodials.

499
Node 51. Nan, minor. Nan, peninsulatus and Nan, bee ken sis share:

a. hypocone relatively small, long axis orientated obliquely;

b. protostylid generally very reduced or absent on p3-m3.
Node 52. Nan, minor is derived relative to Nan, peninsulatus and

Nan, bee ken sis by:

a. protoeones often relatively small, variably rounded in
premolars;

b. isthmus with persistent plieations;
e. very small size, UTRL about 85 mm.

Node 53. Nan, peninsulatus and Nan, bee ken sis share:

a. very procumbent, spatulate lower incisors;

b. DPOF vestigial or absent;

c. lingual border of protocone flattened;

d. protocone isolated from protoselene to base of crown;

e. relatively strong metastyles;

f. isthmus plications usually absent;

g. pli cabal linids usually absent;

h. labial borders of protoconid and hypoeonid flattened;
i. elongated metaconid-metastylid complex;
j. increased unworn molar crown height, about 60 mm.
Node 54. Nan, peninsulatus is derived relative to Nan, bee ken sis by:

a. elongated protoeones;

b. protocone lingual border straight or concave;

c. strong mesostyle, constricted on molars;

d. paralophid plications absent;

e. molar ectoflexid depth decreased until moderate wear-stage;

500

f. increased unworn molar crown height, about 70 mm.

g. decreased size, UTRL about 100 mm.

Node 55. Nan, bee ken sis is derived relative to Nan_. peninsulatus by:

a. very elongated muzzle;

b. robust metapodials.

The phylogenetic arrangement of hipparionine species in Figure 74
(or Fig. 73) indicates the presence of only six monophyletic genera,
Pseudhipparion, Neohipparion, Merychippus s.s., Hipparion. Cormohip-
parion and Nannippus. Two additional genera have been named, Gri p-
hippus (Quinn, 1955; genotype Pseud, gratum) and Hesperohipparion
(Dalquest, 1981; genotype Neo. floresi, recognized here and by
MacFadden, 1984a, as a junior synonym of Neo. eury style). The
cladogram indicates that use of either would result in the recog-
nition of a paraphyletic genus, or a monotypic genus. Neither of
these alternatives are justified based on the current understanding
of hipparionine phylogeny. Merychippus s.s. should be limited to
only those species which share derived character states with the
genotype, M. insignis. These may include species such as M. brevi-
dontus, M. californicus and M^. calamarius, but these taxa will
require further study to determine their exact relationships. Two
species of hipparionines, "Neo." coloradense and "Cor." goorisi
cannot be placed in any of the six recognized genera without making
it paraphyletic. Two alternatives would be to erect monotypic genera
for them, or to consider them as plesions. Plesion is a category of
variable rank that substitutes for supraspecific categories in the
Linnaean hierarchy (Wiley, 1981). It is useful when a species or a

501
small monophyletic group of species forms the sister-group of a much
more numerous clade. By using plesions, a phylogeneticist avoids
having to erect numerous new monotypic taxa, a criticism made of
early phylogenetic classifications (e.g., that of McKenna, 1975). If
supporting evidence for the Neohipparion + Pseudhipparion versus
Hipparion + Nannippus + Cormohipparion + Merychippus s.s. dichotomy
within the Hipparionini is forthcoming, the two groups should be
given formal (subtribal) designations. As the placement of Pseudhip-
parion in the Hipparionini is questioned by the parsimony criterion
(Fig. 69), I refrain from formalizing this arrangement at this time.

Phylogenetic Analysis of Protohippine and Equine Taxa

Twenty-four protohippine and equine species were analyzed in the
same manner as the hipparionines. Figure 75 represents the output of
the PAUP analysis. In this case, there is but a single most
parsimonious tree with a length of 99.4 steps and a CI of 0.46.
Figure 76 presents the cladogram done "by hand." It has a length of
102.8 steps (3.4% longer), and a CI of 0.45. Although there are some
similarities between the two, there are more differences than was the
case with the hipparionine taxa. Some of this may be due to the
absence of information concerning cranial characters for several
species of Cal . (Grammohippus). The phylogenetic hypothesis as
presented in Figure 76 is much more strongly supported by the
chronological distributions of the taxa, and contains fewer
"unlikely" evolutionary events (e.g. decreasing crown height). The
following is a listing of the character states that support the

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506

phylogeny in Figure 76. Equine species are not discussed in detail.
They have not been extensively reviewed (as have the protohippines),
and additional study will undoubtedly discover other characters to
better judge their interrelationships. They are included here solely
to demonstrate that Protohippus is not "ancestral" to either Plio-
hippus or Dinohippus, as is commonly stated in the literature (a
concept that dates back to Marsh, 1879). Rather, with Calippus. it
forms a sister-group to the clade containing Pliohippus. Astrohippus,
Dinohippus, Equus and the Hippidion-group. To formally recognize
these two monophyletic clades, the Equini is divided into the
subtribes Protohippina and Equina.

Node 1 (Figure 76). The Equini share:

a. oval protocones;

b. protocone connected to protoselene in very early wear-stage;

c. simple internal fossette margins;

d. molar metaconid notably more linguad than the metastylid;

e. increased size, UTRL about 110 mm.

[Character states a and e probably shared with hipparionines.]
Node 2. The Protohippina are derived relative to the Equina by:

a. moderate preorbital bar;

b. relatively broad muzzle;

c. cemented deciduous premolars;

d. elongate-oval protocones;

e. markedly oblique protocone orientation in premolars;

f. strong protostylid on dp34, moderate protostylid on p3-m3;

g. metaconid and metastylid well separated in early wear-stage;

507

h. decreased depth of premolar ectoflexid;
i. increased unworn molar crown height, about 35 mm or more.
Node 3. Protohippus is derived relative to Calippus by:

a. large, very broad DPOF;

b. malar region inflated, lacks fossa or depression;

c. increased size, UTRL about 120 mm or more.

Node 4. Pro. vetus is primitive for all known characters relative to

other species of Protohippus.
Node 5. Pro, perditus. Pro, supremus and Pro, gidleyi share:

a. strong premolar pli cabal 1 in;

b. large pro to sty lids on p3-m3;

c. enlarged metastylid, subequal to metaconid;

d. increased unworn molar crown height, about 45 mm;

e. increased size, UTRL about 130 mm or more.

Node 6. Pro. perditus is primitive for all known characters relative

to Pro, supremus and Pro, gidleyi.
Node 7. Pro. supremus and Pro, gidleyi share:

a. protocone lingual border often flattened;

b. delayed connection of protocone to protoselene until early or
early moderate wear-stage;

c. moderately persistent internal fossette plications;

d. metaconid and metastylid persistently well separated;

e. premolar ectoflexid very shallow, does not penetrate isthmus;

f. increased unworn molar crown height, about 55 mm.

508

Node 8. Pro. supremus is derived relative to Pro, gidleyi by:

a. larger, better developed prefossette loop;

b. increased size, UTRL about 140 mm.

Node 9. Pro, gidleyi is derived relative to Pro. supremus by:

a. shallower DPOF, lacks posterior pocket;

b. very long preorbital bar;

c. reduced P2 anterostyle;

d. increased protocone isolation, not connected on P34 and M3
until moderate wear -stage;

e. hypoconal groove closes without forming a lake;

f. ectostylids on dp2-dp4 reduced;

g. increased unworn molar crown height, about 60 mm.
Node 10. Calippus is derived relative to Protohippus by:

a. very short, very broad muzzle;

b. flattened, nonarcuate incisor margin;

c. relatively large incisors;

d. very shallow p2 ectoflexid;

e. loss of ectostylids on dp2-dp4;

f. protocone connects to protoselene immediately after onset of
wear.

Node 11. Cal. (Grammohippus) is derived relative to Cal . (Calippus)

by:

a. generally stronger metastyle;

b. deeper, more persistent preprotoconal groove;

c. protostylid of p3-m3 usually reduced, often limited to lower

509
third of the crown or absent altogether;
d. increased unworn molar crown height, about 45 mm or more.
Node 12. Cal. martini is derived relative to Cal . cerasinus, Cal.
hondurensis and Cal. maccartyi by:

a. relatively strong pli caballins on P2-P4, weak but often
present on M1-M3;

b. more persistently complex inner fossette margins;

c. increased unworn molar crown height, about 58 mm;

d. increased size, UTRL about 135 mm.

Node 13. Cal. cerasinus, Cal. hondurensis and Cal. maccartyi share:

a. relatively broader muzzle;

b. increased relative length of metaconid-metastylid complex.
Node 14. Cal. cerasinus is derived relative to Cal. hondurensis and

Cal. maccartyi by:

a. very reduced pli cabal 1 in;

b. rapidly closed hypoconal groove on P2-P4;

c. protostylids very reduced, often absent.
Node 15. Cal. hondurensis and Cal. maccartyi share:

a. more persistent preprotoconal groove;

b. protocone lingual border flattened;

c. increased size of metastylid relative to metaconid;

d. shallower ectoflexids on premolars;

Node 16. Cal. hondurensis is derived relative to Cal. maccartyi by:

a. relatively very short protocone, especially on P2-P4;

b. premolar protocone orientation anteroposterior;

c. hypoconal groove closes on P2-P4 without forming a lake.

510

Node 17. Cal. maccartyi is derived relative to Cal. hondurensis by:

a. fossettes persistently plicated, very closely apressed;

b. increased ROC of upper cheekteeth;

c. very expanded metaconids and metastylids;

d. shallow premolar and molar ectostylids;

e. decreased size, UTRL about 100 mm.

Node 18. Cal. (Calippus) is derived relative to Cal. (Grammohippus)
by:

a. early closure of hypoconal groove;

b. increased ROC of upper cheekteeth;

c. strong protostylid on p3-m3;

d. expanded metaconid-metastylid complex;

e. decreased size, UTRL about 100 mm or less.
Node 19. Cal. proplacidus and Cal. placidus share:

a. strong premolar pli cabal 1 in;

b. relatively deeper and more persistent lingual flexids.
Node 20. Cal. proplacidus is primitive for all known characters

relative to Cal . placidus.
Node 21. Cal. placidus is derived relative to Cal_. proplacidus by:

a. metaconid and metastylid enlarged, persistently well
separated;

b. shallower ectoflexids;

c. increased unworn molar crown height, about 50 mm.
Node 22. Cal. regulus and Cal. elachistus share:

a. DPI very reduced or absent;

b. very simple fossettes;

511

c. very early closure of hypoconal groove;

d. decreased size, UTRL about 80 mm or less.

Node 23. Cal . regulus is derived relative to Cal. elachistus by:

a. poorly developed styles;

b. p2 metaconid very reduced or absent;

c. increased unworn molar crown height, about 45 mm.

Node 24. Cal. elachistus is derived relative to Cal. regulus by:

a. hypoconal groove closed in very early wear-stage;

b. pli caballin vestigial or absent;

c. loss of pli entoflexid;

d. reduced protostylid;

e. shallower ectoflexids;

f. decreased basal crown lengths.

Node 25. The Equina are derived relative to the Protohippina by:

a. moderately deep DPOF (secondarily reduced in some species);

b. well developed malar fossa (secondarily reduced in some
species);

c. elongated muzzles;

d. very simple internal fossette margins;

e. lateral phalanges reduced in size or absent.

Both Figures 75 and 76 support the monophyly of the Protohippina
and Equina, of the genera Protohippus, Pliohippus and Astro hi ppus,
and of the subgenus Cal. ( Cal i ppus). Only in Figure 76 (see also
Figs. 70, 71) is the entire genus Cal i ppus (as recognized here)
monophyletic, as are its two subgenera.

512
Phylo genetic Classification

Table 49 presents a phylogenetic classification of the Hippar-
ionini and Equini based on the cladograms depicted in Figures 74 and
76. In general, conventions 1-6 of Wiley (1981, pp. 205-213) are
followed. Also, informal taxon names (Wiley, 1981, p. 199) are used
to avoid proliferation of names, as is the plesion category. The
latter is used only for species which form sister-groups to
suprageneric groups (e.g. "M^. " coloradense ) , and not for all fossil
groups as suggested by Wiley (1981; in this case almost every taxon
would be a plesion). All merychippine-grade species not assigned to
a recognized genus are uniformly designated as "Merychippus." These
should not be confused with taxa assigned to the genus Merychippus,
for which quotation marks are not used.

Only relatively minor changes to established equid nomenclature
are suggested, despite the much greater information content of the
phylogenetic classification. "Neohipparion" coloradense and
"Cormohipparion" goorisi are removed from these genera, and placed as
plesion sister-groups to combinations of genera, as noted above.
More important is the use of Merychippus in a purely phylogenetic
sense. Other species of merychippine-grade are relegated to their
phylo genetically correct positions. "M_. " pri mus and "M . " gunteri
cannot be assigned to either the Hipparionini or Equini, and appear
to retain more primitive character states than either of the two
advanced tribes. The systematic positions of these two species are
currently under investigation (MacFadden and Hulbert, in prep.).

513

Table 49. Phylogenetic hierarchical classification of the tribes
Hipparioni and Equini based on the cladograms in Figures 74 and 76.
Note that the subfamily contains other taxa in addition to these two
tribes (see Chapter 5). Pending a species-level review by MacFadden
(in prep.), no species are listed for the genera in the Equina, and
the relative positions of its constituents are left as a multi-
chotomy. Sequencing conventions follow Wiley (1981).

Family Equidae

Subfamily Equinae
Tribe Hipparionini
Genus unnamed

"Merychippus" isonesus
"Merychippus" sejunctus
Neohippanon genus group

Plesion "Merychippus" colora dense
Genus Pseudhipparion

Pseudhipparion retrusum
Pseudhipparion curti vallum
Pseudhipparion gratum
Pseudhipparion hessei
Pseudhipparion skinneri
Pseudhipparion simpsoni
Genus Neohippanon

Neohipparion affine
Neohipparion trampasense
Neohi|3parlon leptode
Neohipparion eurystyle
Neohipparion gidleyi

Hippariori ggrmij group —

Genus Merychippus sensu stricto
Merychippus insignis
M^y'yChl ppU? eaiAmar^ius etc.
Genus Hipparion

Hipparion shirleyi
Hippal^ioiT tenonense
Hipparion" force i
Plesion "Merychippus" goorisi
Genus Cormohipparion

Cormohipparion "sphenodus
Cormohipparion occidenta'le species group
Cormohipparion occidentale
Cormohipparion plicatile
Cormohipparion I'Tigenuum species group
cormohi pparion in genu urn
Cormohipparion emsliei

514
Table 49~continued

Genus Nannippus
Nannippus fricki
Nannippus westoni
Nannippus" 1ent1cularis
Nannippus" minor
Nannippus peninsulatus
Nannippus beckensis
Tribe Equini

Equini incertae sedis: ?Ca1ippus circulus
Subtri bFTftTEoWi pp 1 na
Genus Protohippus
Protohippus vetus
Protohippus" perditus
Protohipptf? supremus
Protohippus gidleyi
Genus Calippus

Subgenus Ualippus (Calippus)

Calippus placidus species group
calippus propiacidus
Calippus placidus
Calippus regulus species group
Calippus regulus
Calijjpus elachi stus
Subgen us Calippus (Gramnriohi ppus)
Calippus martinf
Calippus cerasinus
Calippus hondurensis
Calippus maccartyi"
Subtribe Equina

Pie si on "Merychippus" carrizoensis
Plesion "Merychippus" styioaontus
Equus genus group (all genera sedis mutabilus)
Genus Pliohippus
Genus Astro hi ppFs
Genus Onohippidium
Genus Hippidion
Genus hquus nncluding "Dinohippus")

515

Comparisons with Previous Phylogenies

The hypothesized relationships of the Hipparionini (Fig. 74) and
Equini (Fig. 76) presented here can be compared with the previous
hypotheses of Matthew (1926, Fig. 67A), Stirton (1940, Fig. 67B),
Quinn (1955, Fig. 67C), and Forsten (1984, Fig. 68). The results of
the cladistic analysis are more similar to those of Matthew and
Stirton. None of the changes proposed by Quinn (1955) are supported.
The major differences between Stirton 's traditional phylogeny and the
cladistic arrangement proposed here are: 1) the sister-group
relationship between Protohippus and Calippus was not recognized by
Stirton (1940; although previous workers such as Gidley, 1907,
included them in the same genus); and 2) Stirton derived Equus from
Astro hi ppus rather than "Dinohippus." The latter point has been

repeatedly questioned in the literature, and current workers gener-
ally agree that most, if not all, of the subgenera of Equus are the
sister-taxon of "D." mexicanus (Lance, 1950; Dalquest, 1978; Bennett,
1980; MacFadden, 1984b; MacFadden and Azzaroli, 1987). All of the
cladograms produced by this study agreed with this interpretation.

The cladogram of Forsten (1984; see Fig. 68) is difficult to
interpret because she did not state into what genus she was assigning
certain North American taxa. The following comparison is based on
the assumption that she regarded Cor, occidentale as a Hipparion, and
not as a Neohipparion (as she has done previously, see e.g. Forsten,
1975). I assume this because she used the character states weak DPOF
and cabal loid lowers to diagnose Neohipparion (and Probosidipparion ),

516

neither of which are characteristic of Cor, occidentale. Forsten
(1984) placed Corniohipparion as the primitive sister-group of all
"true" hipparionines, which to her included only Pseudhipparion,
Hipparion (with Nannippus), Neohipparion (with Stylo hi ppar ion) and
Proboscidipparion. She listed five characters at the base of her
cladogram to support this grouping (Forsten, 1984, Fig. 3), connected
protocone, developed stylids, single preorbital fossa, "normal"
nasals, and "normal" nasal openings. It is not clear whether she
interpreted these as derived and uniting the five genera, or if she
was only listing characteristic, but plesiomorphous, features of the
group, as she did not give a specific out-group. Of these five, only
developed stylids (i.e. a well developed protostylid; ectostylids are
primitive) is a synapomorphy uniting these taxa. The others are
either plesiomorphous for the Equini + Hipparionini , or too ambig-
uous. The protocone eventually connects to the protoselene at some
stage of wear in virtually all equids, so its proper use as a
character is only with regards to in what wear-stage it connects.
Forsten (1984) specifically unites Pseudhipparion, Hipparion,
Neohipparion and Proboscidipparion based on their subequally large,
well separated metaconids and metastylids (the hipparionid pattern)
and a mostly disconnected protocone. The former is an important
synapomorphy for the hipparionines (Fig. 74, Node 1), but I would
argue that this pattern is observed in early wear-stages of "M . "
goorisi and M. insignis, and so unites all hipparionines and not just
those listed by Forsten (1984). There is no disagreement that
Pseudhipparion diverged early from other hipparionines, but there are

517

numerous apomorphies uniting it at this point with Neo hip par ion and
"M. " coloradense (Fig. 74, Nodes 2 and 4). Forsten (1984, Fig. 3)
expressly presented no characters to justify uniting Hipparion,
Neohipparion and Proboscidipparion, although it can be assumed that
an isolated protocone to near the base of the crown is one. The
cladistic analysis indicates that well isolated protocones evolved
independently three times in North American hipparionines, at Nodes
16, 30 and 35 in Figure 74.

Forsten (1984) grouped North American Neohipparion with the Old
World taxa Stylo hipparion, Proboscidipparion, and Eurasian species
putatively placed in Neohipparion. This was based on two characters,
a weak or absent fossa, and cabal loid lowers. There are several
reasons for doubting this arrangement. First, the lower cheekteeth
of the genotypic species of Neohipparion, Neo. affine (=Neo.
whitneyi), are of hipparionid grade, with rounded borders of the
metaconids and metastylids, and "V"-shaped linguaflexids (Osborn,
1918, Fig. 144). Thus, even if this group was monophyletic, their
relative arrangement cannot be as figured by Forsten (1984). Second,
Forsten (1984) noted that transitional, "incipiently" caballoid taxa
first appear in the Old World in the late Turolian. The transition
from hipparionid to caballoid lowers in North American Neohipparion
occurred in the late Clarendonian-early Hemphillian, with Neo.
trampasense as a morphologic intermediary between Neo. affine and the
fully caballoid Neo. eurystyle. This is approximately three million
years prior to the appearance of incipiently caballoid hipparionines
in the Old World. All North American late Hemphillian Neohipparion

518

are too derived to be ancestral to the Ruscinian radiation of
caballoid hipparionines in Eurasia. The two must be independent
lineages that evolved in parallel. Their putative synapomorphies
were in fact acquired independently by many late Miocene/early
Pliocene equid genera. For example, in North America alone, no less
than five genera had caballoid lower cheekteeth to some degree:
Neohipparion (e.g. Neo. eurystyle; Neo. gidleyi); Nannippus (e.g.
Nan. peninsulatus, especially in deciduous premolars and in early
wear-stages, see MacFadden, 1984a, Figs. 109 and 116); Cormohipparion
(e.g. Cor, emsliei); Astro hi ppus (e.g. A. stockii); and the
Dinohippus/Equus lineage. Of these five, four also have signif-
icantly reduced or lost the DPOF (all except Astrohippus), indicating
that caballoid lowers and a weak DPOF are not a systematically secure
contination of apomorphies to unite otherwise dissimilar taxa.
Rather, they are characteristic of an advanced grade of equid that
evolved many times in various lineages under similar selection
pressures with similar results (Gosliner and Ghiselin, 1984). Also
characteristic of this grade are extremely hypsodont cheekteeth, and
advanced metapodial and phalange morphology (Sondaar, 1968; Hussain,
1974; Forsten, 1984; MacFadden, 1984a; 1986).

CHAPTER 7
BIOCHRONOLOGY, BIOSTRATIGRAPHY, AND SPECIES DYNAMICS

The strati graphic utility of equids has long been recognized by
vertebrate biostratigraphers (e.g. Osborn, 1918; Stirton and McGrew,
1935; Stirton, 1952). Horses are well represented at most sites, and
have experienced continual evolution throughout the Cenozoic, two of
the criteria necessary for a strati graphically useful taxon. The
other primary criterion is ease of recognition, which has not always
been the case with equids. Thus, much of their use has been limited
to the generic level (or more often to grades like Merychippus) . The
recent species-level revisions of MacFadden (1984a), Webb and Hulbert
(1986), and this study, along with work in progress by MacFadden,
Woodburne, Hulbert, Evander, Prothero and others, should remedy this
problem. Figure 77 illustrates the chronologic ranges of 60 equid
taxa from the early Barstovian through the Blancan. These primarily
reflect my personal observations and identifications of specimens in
most of the major museum collections (as listed on pp. xv-xvi), and,
to a much lesser degree, records taken from the literature. Some
very poorly known Barstovian taxa were not included, and it must be
re-emphasized that I have not studied equine species at nearly the
detailed level as the protohippines and hipparionines. Even so,

519

Figure 77. Chronologic distribution of equid species, with
emphasis on taxa from the Great Plains and the Gulf Coastal Plain.
Key to numbers: 1, Merychippus in sign is and other members of
Merychippus s.s.; 2, "MerycliTppus" coloradense; 3, "M^."
republicaTuTs; 4, Pseudhipparion retrusum; 5. Pseudhipparion sp.
dower Bone Valley); 6, Pseu'cTT'curti vallum; 7, Pseud, hessei ; 8,
Pseud, gratum; 9, Pseud ."IHrTneri ; 10, Pseud, simpsoni; 11,
Neohipparion affine; 12, Neo. trampaisense; 13, Neo. T?ptode; 14,
Neo. eurysTyle; 15, Neo. gT?leyi; 16, HTpparion~sFirTeyi ; 17, H.
teFonense; 18, H. forcei ; 19, "M. " goorisi; 2U, Nannippus fricTTi;
21, Nan. westonT; 22, Nan. lentTcularis; 23, Nan, minor; 24, Nan.
bee ken sis; 25, Nan. penTFsulatus; Zb, c'ormohipparion sphenodus; 27,
Cor, ingenuum; W7 Cor. emslieTT 29 , Cor, plicatile; 30, Cor.
occidentale; 31, "MT^carrizoensis; 377~"M." intermontanus; 33,
ProtohippuT vetus; 34, Pro, perditus; 35, Pro, supremus; 36, Pro.
gidleyi; 37, "M." proparvalus; 38, ?Calippus circulus; 39 , CaTT"
martini ; 40, Cal . cerasinus; 41, Calippus n. sp. from Ft-40
locality; 42,~Ual ."Tondurensis; 43, Cal. maccartyi; 44, Cal.
proplacidus; 4?7"CaT71)1acidus; 46, ^aT. regulus; 47, CaT7p"pus sp.
(lower Bone ValleyTT 48, Cal. elachistus; 49, "M." sejunctus; 50,
"M." stylodontus; 51, HippT?ion sp. (MacFadden and Skinner, 1979) ;
57, "Pliohi'ppus"^ interpolatus; 53, "Dinohippus" leidyanus; 54, "D^."
mexicanus; 5b, Equus s.1.; 5b\ Pliohippus mirabilis; 57, Plio.
pernix; 58, Plio. nobilis; 59, Astro hi ppus ansae; ZO, A. stockii.

521

CHRONOLOGIC DISTRIBUTION OF EQUID TAXA

26

II

17

18

20

30

12

13
1

21

27
29

ID

15

23

22

25

28

24

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 MA

522

31
33

32

37

49-

50

34

28

44

17-

56-

35

:i9

45-

46

57

36

40 —
42

48

58

43

51

52

53-

54

55

59

60

16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 MA

Figure 77 — continued

523

Figure 77 represents the most up-to-date, detailed data base from
which to study equid biostratigraphy, diversity and extinction during
the late Neogene.

Biostratigraphy

A detailed biostratigraphic zonation of Great Plains and Gulf
Coastal Plain faunas was constructed using the species ranges in
Figure 77. The period from about 16 ma to 4.5 ma was subdivided into
9 biochrons varying in duration from 2.5 to 0.5 million years. Abso-
lute ages are based on the summary of North American Miocene-early
Pliocene biochronology of Tedford et al . (in press). Each biochron
was defined by the concurrent range zone (CRZ) of two or three equid
species. Those taxa selected were relatively common, and, if pos-
sible, had extensive geographic ranges in both the Great Plains and
the Gulf Coastal Plain. Each biochron was also characterized by the
first and last appearances of particular species. The ages of the
boundaries of each biochron are given to the nearest 0.1 ma. In
fact, these are estimates based primarily on biostratigraphic correl-
ation and interpolation, and are probably accurate to within +0.2
ma. Current mammalian biostratigraphic practice emphasizes the use
of first appearances of immigrant taxa from other continents to
define the boundaries of land mammal ages and their subdivisions
(Tedford and Hunter, 1984; Tedford et al., in press). While
theoretically sound, this sometimes becomes difficult to apply in
practice, because defining taxa can be rare or not widely distri-
buted. I do not propose that an equid biochronology replace that

524
based on immigrants, but suggest that chronologies of widely
distributed, common autochthonous groups like canids, camel ids and
horses be used to supplement it.

Biochron 1 is the "Merychippus" coloradense - "M . " sejunctus CRZ,
representing the interval between 16 and 13.5 ma. It is the longest
and most poorly represented segment, with few taxa in common between
the Great Plains and the Gulf Coastal Plain. Last appearances are by
"M." sejunctus, "M." isonensus, "M . " goorisi. Pro, vetus; while Cor.
sphenodus, Pseudhipparion sp., and Calippus sp. have their first
appearances. M. insignis and related species are also typical of
this biochron, as are derived species of Archaeohippus and "Para-
hippus." Faunas of this period include the Lower Snake Creek, Pawnee
Creek, and the lower Burkeville faunas, as well as a recently
discovered faunule in the lowermost Bone Valley Formation (MacFadden
and Hulbert, in prep.).

Biochron 2 is the Protohippus perditus - Calippus proplacidus CRZ,
representing the interval between 13.5 and 12.0 ma. Last appearances
are by Plio. mirabilis, "M . " re publican us, ?Cal . circulus; first
appearances are by Pseud, retrusum and ?Cal . circulus. Character-
istic taxa include Hipparion shirleyi. Cor. sphenodus. and "Mery-
chippus" s.l. Faunas of this interval include those of the lower
Valentine Formation (Norden Bridge, Crookston Bridge and Devil's
Gulch), the upper Burkeville Fauna, the Cold Spring Fauna, the
Bradley and lower Agricola Faunas of the Bone Valley, and the
Ashville locality.

525

Biochron 3 is the Protohippus supremus - Cormohipparion sphenodus
CRZ, representing the interval between 12.0 and 11.3 ma. It includes
the last appearance of Pseud, retrusum, and the first appearances of
Plio. pernix, Cal. regulus. Pseud, curti vallum, and probably Nannip-
pus fricki. The Burge Fauna is the most important of the period, but
it also includes the slightly younger upper Agricola Fauna of the
Bone Valley.

Biochron 4 is the Cormohipparion occidentale - Pseudhipparion
gratum - Calippus martini CRZ, representing the interval between 11.3
and 9.3 ma. Last appearances are by Merychippus s.s. and s.l. Pseud.
curti vail urn, Cal. regulus, Cal. placidus, Prot. supremus. Nan.
fricki, and Plio. pernix; first appearances are by Cor. occidentale.
Pseud, hessei, Neo. affine, and H^. tehonense. Faunas of this period
include the extremely well known Clarendon, Minnechaduza, Upper Snake
Creek, and Lapara Creek faunas.

Biochron 5 is the Neohipparion trampasense - Pseudhipparion
skinneri CRZ, representing the interval between 9.3 and 8.5 ma. Neo_.
affine makes its last appearance during this period, while first
appearances are by Cal. cerasinus, Cal. elachistus. Cor, in genu urn.
Cor. plicatile, Plio. nobilis. Pro, gidleyi, and Nan, westoni.
Cormohipparion occidentale persists in the Great Plains. Faunas of
this period include the Xmas-Kat Quarries, J. Swayze Quarry. Arens
Quarry, Love Site, and McGehee Farm.

Biochron 6 is the Calippus hondurensis - Pliohippus nobilis -
Neohipparion leptode CRZ, representing the interval between 8.5 and
7.5 ma. It includes the last appearance of Nan, westoni, and Cor.

526
occidentale. Cor, plicatile, Cor, ingenuum and Pseudhipparion
skinneri are characteristic taxa. Faunas of this period include
Mixson's Bone Bed, Arnett, and Higgins.

Biochron 7 is the "Pliohippus" interpolatus - Calippus maccartyi -
Calippus n. sp. CRZ, representing the interval between 7.5 and 6.0
ma. It includes the last appearances of Pseud, skinneri. H. forcei ,
H. tehonense. Cor, ingenuum. Cor, plicatile. Cor, occidentale. Pro.
gidleyi, and Cal. elachistus, and the first appearances of Neo.
eurystyle. Nan, lenticularis. Nan, minor, "D." leidyanus, and the
Hippidion-group. Faunas of this period include Ft-40, Box T,
Aphelops Draw, Moss Acres, Manatee Dam, and Withlacoochee River 4A.

Biochron 8 is the Neohipparion eurystyle - Astro hi ppus ansae CRZ,
representing the interval from 6.0 to 5.0 ma. It includes the last
appearances of "Plio." interpolatus, "£. " leidyanus, and Neo. lep-
tode, and the first appearances of Neo. gidleyi and Pseud simpsoni.
Nan ni ppus minor and Nan, lenticularis are characteristic taxa.
Faunas of this period include Coffee Ranch, Optima, ZX Bar, Edson,
and Uptegrove; note that the Gulf Coastal Plain is not represented at
all in this interval.

Biochron 9 is the Pino hi ppus mexicanus - Astro hi ppus stockii CRZ,
representing the interval from 5.0 to 4.5 ma. It includes the last
appearances of Nan, minor. Nan, lenticularis, Neo. eurystyle, Neo.
gidleyi, and Pseud, simpsoni, and the first appearances of Cor.
emsliei and Nan, peninsulatus. Faunas of this period include Axtell,
Christian Ranch, Yepomera, Rancho El Ocote, and the Palmetto (Upper
Bone Valley) faunas.

527
Diversity and Extinction Patterns

Using the chronologic distributions from Figure 77, the observed
number of taxa, number of originations (by cladogenesis or immigra-
tion only, not by anagenic replacement), and number of extinctions
(true extinction, not pseudoextinction or absence in the fossil
record) were tallied for million year intervals (Table 50) and
analyzed with the methods of Webb (1969c). The analysis was limited
to species from faunas of the Great Plains and Gulf Coastal Plain.
Although western and Mexican faunas share some species with them,
they have quite different patterns of abundances and extinctions,
they lack several characteristic eastern genera (Pseudhipparion,
Calippus, Protohippus), and are not as well known. The Blancan
radiation of Equus s.l. is poorly understood^ so I have conserva-
tively treated it as a single taxon. However, several Equus lineages
are present at least by the late Blancan (Tedford, 1981).

The results of the analysis (Fig. 78) indicate that there was a
period of rapid increase in diversity through the first two-thirds of
the Barstovian. To some extent this may reflect the weakness in the
data base for taxa of this age. The rate of increase leveled off at
about 12 to 13 ma, after which there followed a six million year
period of remarkable stability in both number of total taxa (Fig.
78A) and composition (Fig. 78B). This is in spite of a great deal of
turnover at the species level through this interval (Fig. 77). This
stable period from about 13 to 7 ma corresponds to the Clarendonian
Chronofauna of Webb (1969a; 1977).

528

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Figure 78. Equid species diversity pattern through the late
Neogene, using the distributions in Figure 77, but only for taxa
from the Great Plains and the Gulf Coastal Plain. See Table 50 for
calculations. A. Running mean of equid species, divided into four
taxonomic groups. B. Data of A expressed as a percentage of the
total running mean.

15-

530

, aquin**

• protohlppincs

^hipparioninss

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100 n

531

Starting at about 7 ma, the running mean for total number of taxa
began to decline continually in each subsequent interval. There were
two pulses of rapid (catastrophic?) major extinction within what was
otherwise a period of gradual decline. Reasons for this decline are
probably primarily climatic deterioration on a continental scale,
with secondary effects from increased competition by grazing rumin-
ants, such as camelids and antilocaprids (the latter experienced
their maximum generic diversity in the Hemphillian, before declining
themselves; Webb, 1984). The first episode of major extinction
occurred at about 6.2 ma. All four lineages of the Protohippina went
extinct at this point, as well as Pliohippus s.s.. North American
Hipparion, and many species of other hipparionines (Fig. 77). This
also marked the turning point in relative diversity in Great Plains
equid faunas, which from then on were numerically dominated by mono-
dactyl equines (even though hipparionines remained more diverse
taxonomically into the Blancan). The second episode of major
extinction was at about 4.5 ma, and marked the last appearance of
Neohipparion (two lineages), Pseudhipparion, Astro hi ppus, and two
species of Nannippus. Over half of the observed taxa in this
interval went extinct at this time, the greatest percentage for any
of the million year periods (Table 50). Webb (1977; 1984) has
previously noted the severity of this episode of extinction, which
affected many more genera of mammals in North America than any other
comparable period of extinction in the late Cenozoic.

CHAPTER 8
SUMMARY AND CONCLUSIONS

Horses (Mammalia, Equidae) are a typical, oftentimes numerous,
component of the Neogene large mammal community of North America.
This study focused on the advanced equids (Subfamily Equinae) of the
Gulf Coastal Plain of Florida and Texas from about 14.5 ma to about
4.5 ma (late Barstovian through Hemphillian), and their contempor-
aries from the Great Plains. The basic questions to be answered
were: 1) how many species were present at each particular locality;
2) what species names should be applied to each population; and 3)
how are these species related to one another? Cranial characters,
particularly those of the facial fossae and muzzle region, were used,
when known, in conjunction with traditional dental characters to
answer these questions and infer systematic relationships. Morphol-
ogy of post-cranial elements, particularly of the metapodials, was
also used when specimens that could be unambiguously associated with
cranial /dental material were available (see MacFadden, 1984a).
Unfortunately, this is exceedingly rare in Gulf Coastal Plain
deposits.

At least twelve genera of advanced North American equids are
probably valid (Table 49); of these six with Gulf Coastal Plain
representatives are here described in detail (Neohipparion.

532

533

Nanm'ppus, Cormohipparion. Hipparion. Cali'ppus and Protohippus). An
additional common genus, Pseudhipparion, was recently reviewed by
Webb and Hulbert (1986), so it is not treated here in detail, but is
included in the phylo genetic analysis. Members of the subtribe
Equina were much rarer in the Gulf Coastal Plain than these seven
genera, and are only briefly described here (see also MacFadden,
1986). Merychippus, here restricted to a small, monophyletic group
of species (cf. Evander, 1986), was also present in the Gulf Coastal
Plain, but only in faunas older than 14.5 ma, and was therefore not
studied in detail.

The tribe Hipparionini is found to be a monophyletic assemblage of
six named genera: Neohipparion, Pseudhipparion, Merychippus s.s.,
Hipparion, Cormohipparion and Nannippus. Additionally, "Merychippus"
col ora dense and "M . " goorisi cannot be assigned to any particular
genus, and are placed in the tribe as plesions with generic rank
(Table 49). Hipparionines ranged widely in North America from the
latest Hemingfordian (e.g. the Snake Creek Fauna, about 17 ma) to the
late Blancan (about 2 ma), and are known from the Canadian plains to
Honduras. The distribution of hipparionine taxa in Gulf Coastal and
Great Plains faunas is summarized in Table 51.

Neohipparion forms a monophyletic group of five North American
species, three of which are recognized in the Gulf Coastal Plain.
Neo. affine is reported for the first time from the early Claren-
donian Lapara Creek Fauna of southern Texas. Isolated teeth of Neo.
affine can usually be distinguished from those of Cormohipparion
occidentale by their simpler fossette patterns, longer protocones

534

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relative to tooth size, well developed pli cabalUm'ds in very early
wear-stages of lower premolars, and reduced ectostylids in deciduous
lower cheekteeth. Neo. trampa sense, the probable direct ancestor of
Neo. leptode and Neo. eurystyle, is described from late Clarendonian
and early Hemphillian skulls, jaws and teeth from Florida, Kansas,
and Nebraska. Pli cabal linids in the lower molars (in early wear-
stages) are a critical diagnostic feature of this species, as are a
very reduced DPOF, elongated protocones, and shallow ectoflexids in
the lower premolars. Neo. eurystyle, a very advanced and hypsodont
equid, continues many of the trends first observed in Neo. tramp-
asense, especially in the "premol arizing" of the lower molars. The
newly discovered Moss Acres Racetrack is the oldest and most primi-
tive population referable to this species. The population from the
very late Hemphillian (early Pliocene) Bone Valley Region of Florida,
described by Simpson (1930) as Neo. phosphorum, falls within the
observed range of variation in size, hypsodonty, and enamel
morphology of Neo. eurystyle, as exemplified by large samples from
the Coffee Ranch and Yepomera faunas, thus corroborating MacFadden's
(1984a) synonymy of the two species.

Nannippus is a monophyletic assemblage of six species, four of
which are recognized in the Gulf Coastal Plain. The oldest popula-
tions referred to Nannippus are from the Lapara Creek and upper
Agricola faunas (very early Clarendonian). They are tentatively
referred to Nan, fricki n. sp., which is typified by a slightly
younger sample from north-central Nebraska. Nan_. fricki is rela-
tively much more abundant in the southernly Florida and Texas

544

samples, a pattern that continued throughout the Neogene for the
genus. Nan, fricki possessed a deep, pocketed DPOF that had a well
defined anterior margin. This along dental synapomorphies suggests a
sister-group relationship between Nannippus and Cormohipparion.
Later species of Nannippus reduced and eventially lost the DPOF, as
did many other late Neogene equid lineages. Simpson (1930) described
Merychippus westoni on a single specimen, a heavily worn maxilla of
uncertain stratigraphic provenience. Stirton (1940) considered it a
relatively old and primitive species of Merychippus, despite the poor
quality and isolated nature of the type. When heavily worn, upper
cheekteeth of Nannippus from the late Clarendonian Love Site match
the type of "M^. " westoni in every detail of size and morphology, and
Simpson's species is transferred to that genus. Nan, westoni ranged
from the latest Clarendonian through the early Hemphillian of
Florida, and like its contemporary Neo. trampasense, provides a
morphological link between Clarendonian and late Hemphillian members
of its genus. The Moss Acres Racetrack Site has produced the oldest
(about 7.5 ma) and most complete specimens of Nan, minor known. They
resemble younger populations on Nan, minor in their relatively
hypsodont premolars, very reduced P2 anterostyle, complex fossettes,
rounded premolar protocone, and very reduced (usually absent)
protostylid. However, in size and crown height they plesiomorph-
ically resemble Nan, westoni . By about 6.5 ma, very small
individuals of Nan, minor first appear in the Florida record (at the
Withlacoochee River 4A and Manatee Dam localities), but relatively
large individuals remained common. The type late Hemphillian (about

545

5.0 to 4.5 ma) Bone Valley population is comprised primarily of only
small individuals. Nannippus persisted into the Blancan, represented
in the Gulf Coastal Plain by Nan, peninsulatus (=Nan. phlegon;
Florida record reviewed by MacFadden and Waldrop, 1980).

Five North American species of Cormohipparion are recognized, and
all are recorded in the Gulf Coastal Plain region. The ubiquitous
late Barstovian-early Clarendonian Cor, sphenodus is recognized for
the first time in eastern North America. Limited, but diagnostic
samples of isolated teeth of this species are found in the Agricola
Fauna of the Bone Valley Region. Cor, occidentale, well known from
the Clarendonian and early Hemphillian of the Great Plains, is not
recognized in Florida, but did range as far as southern Texas, where
it is a member of the Lapara Creek Fauna. In Florida, two previously
enigmatic species described a century ago by Joseph Leidy from
Mixson's Bone Bed can now both be referred to Cormohipparion. This
is based on newly recovered and more complete material from the Love
Site and the Moss Acres Racetrack Site. The referred material ranges
in age from very late Clarendonian to late early Hemphillian, and
demonstrates moderate amounts of chronoclinal microevol ution,
especially in increasing enamel complexity. Cor, plicatile is not
recognized as yet from localities outside of peninsular Florida.
Cor, ingenuum is judged to not be the senior synonym of Nannippus
lenticular is (Cope), as was proposed by MacFadden (1984a). The
population referred to Cor, plicatile by Webb and Perrigo (1984) from
Honduras is placed in Cor, ingenuum instead. This is based on the
smaller size of the population, the principal difference between the

546
two species. Cormohippan'on has been thought to have become extinct
at the end of the early HemphiHian (Webb, 1984), and is absent from
all known late Hemphillian western faunas. However, the genus
survived in Florida until near the end of the Blancan, based on the
range of Cor, emsliei n. sp. Cor, emsliei, on average the most
complexly plicated North American equid, apparently is descended from
the similarly sized Cor, ingenuum.

Only three North American species of Hipparion are recognized, of
which two are found in the Gulf Coastal Plain. H. shirleyi is a
common member of the late Barstovian Cold Spring Fauna in Texas. H.
tehonense ranged from the early Clarendonian to the early Hemphillian
in the Gulf Coastal Plain, and is recognized in the Lapara Creek,
Agricola, Love Site, Moss Acres, and Withlacoochee 4A localities, the
latter four records being provisional.

The Equini form the sister-group to the Hipparionini . At least
seven genera comprise the Equini, of which two, Calippus and Proto-
hippus, are common constituents of Gulf Coastal Plain faunas. They
form a monophyletic clade (the subtribe Protohippina) characterized
by a short diastema, broadened muzzle, shallow DPOF, and lack of a
malar fossa. Protohippus is ancestral to neither Pliohippus nor
Equus, as is commonly purported (e.g. Stirton, 1940; Simpson, 1951;
Shotwell, 1961), nor is it synonymous with Merychippus (contra McGrew
and Meade, 1938). Quinn (1955, p. 22) reached a similar conclusion,
but his positive contributions have been generally overlooked because
of his oversplitting of clades and other incorrect phylogenetic
interpretations. The common ancestor of Calippus, Protohippus and

547

equines was a small, low crowned, primitive species, probably similar
to "Merychippus" carrizoensis or "M^. " primus.

All four recognized species of Protohippus are known from the Gulf
Coastal Plain. Pro, vetus is an early Barstovian species from the
older units of the Burkeville Fauna. Pro. perditus, the genotypic
species, is well represented in the Devil's Gulch Fauna of Nebraska
by numerous crania. These demonstrate that Quinn's (1955) Eoequus
wilsoni is a junior synonym of Pro, perditus. Leidy's Pro, supremus
has been placed in Pliohippus by most subsequent workers (e.g.
Stirton, 1940; Webb, 1969a), but examination of the lectotype tooth
reveals that it is referable to Protohippus and not Pliohippus.
Protohippus is unique among protohippine and equine genera for
increasing the duration of isolated protocones in its upper cheek-
teeth. In this respect, Protohippus gidleyi n. sp. from the very
late Clarendonian to early Hemphillian of Florida and Nebraska is the
most derived species of Protohippus.

Two subgenera of Calippus are recognized, Calippus and Gra mmo hi p-
pus n. subg. They share an uniquely modified muzzle region in which
the premaxillae and mandibular symphysis are broadly expanded and
massive, and the enlarged first and second incisors are arranged in a
straight line rather than the normal equid arcade. The nominate
subgenus includes four named small species, all found in the Gulf
Coastal Plain. Calippus, unlike most other equid genera, appears to
have had distinct lineages in Texas and Florida in the Clarendonian.
In Texas, the Barstovian Cal . proplacidus is replaced in the Claren-
donian by Cal. regulus and Cal. placidus (Table 51). In Florida, in

548

addition to Cal. proplacidus, there is a very small taxon from the
late Barstovian and early Clarendonian Bradley and Agricola Faunas
that cannot be referred to any of the four named species, but that is
too inadequately known to be described as new. It apparently gave
rise to the late Clarendonian-early Hemphillian Cal. elachistus n.
sp., one of the smallest known hypsodont equids. Species of Cal .
(Grammohippus) have previously been assigned to Pliohippus or
Astrohippus, but differ from those genera in the absence of a malar
fossa, short diastema, and broadened muzzle. Cal. martini and Cal.
hondurensis are referred to this new subgenus, as are the new
species, Cal. cerasinus from the late Clarendonian-early Hemphillian
of Nebraska and Florida, and Cal. maccartyi from the late early
Hemphillian of Florida. Species referred to Grammohippus are of
moderate size (toothrow lengths of 100 to 130 mm).

Members of the Equina are uncommon in the Gulf Coastal Plain until
the Blancan (Table 51). Pliohippus is recognized in Texas, but its
presence in Florida is questionable. Astrohippus stockii and "Dino-
hippus" mexicanus are very rare elements of the Palmetto Fauna of
central Florida (MacFadden, 1986). A more primitive population of
"Dinohippus" is found at the Moss Acres Ractrack Site, including a
juvenile cranium with a moderately well developed DPOF.

Results of a phylogenetic analysis of 57 equid species primarily
using dental and cranial characters were compared to the traditional
phylogeny of the Equinae of Matthew (1926) and Stirton (1940), and
the alternate phylogeny of Quinn (1955). Computer-generated clado-
grams indicated that equid evolution was characterized by a high

549

degree of homoplasy; parallel evolution of dental characters and
parallel reduction of facial fossae are particularly common. As
such, phylogenetic reconstruction using maximum parsimony as a goal
is unlikely to arrive at the correct branching sequence, as the
evolution of the animals was itself not parsimonious (cf. Kirsch and
Archer, 1982). A more probable outline of the major branching
sequences was determined using only highly consistent characters
(Figure 70). The advanced equids comprise two major clades, here
regarded as the tribes Hipparionini and Equini. The relationships of
genera within these tribes much more closely resembles the phylo-
genies of Matthew and Stirton than that of Quinn. In particular,
Pseudhipparion is a hipparionine, not an equine (although this is not
always its most parsimonious allocation), Calippus and Protohippus
are sister-taxa, and "Dinohippus" is the sister-taxon of Equus. Many
of the species here recognized as relatively older and more primitive
members of advanced genera were arranged paraphyletically by Stirton
(1940) into a horizontal grade called Merychippus. For example, "M . "
sphenodus is a Cormohipparion, "M . " westoni is a Nannippus, "M . "
proplacidus i s a Calippus, "M . " perditus i s a Protohippus, an d "M^. "
mirabilis is a Pliohippus (Figs. 74, 76).

With their revised taxonomy and chronologic ranges, equids now
become more precise tools for biostratigraphic correlation. Nine
biochrons are recognized between 16 and 4.5 ma, based on concurrent
range zones of equid species. Within a given geographic provenience
(e.g. Florida or Nebraska), these could be even further subdivided.
Over the last 16 million years, three phases of equid diversity are

550
apparent. From about 16 to 12 ma, there was rapid diversification,
especially by the hipparionines and protohippines. From about 12 to
7 ma, overall equid diversity was remarkably high, yet stable.
Starting at about 7 ma, equid diversity began to decline, with two
major periods of extinction at 6.2 and 4.5 ma. This decline, which
culminated about 11,000 years ago in the extinction of all New World
equids, is a component in an overall reduction in numbers of large
North American mammals through the late Cenozoic that can be related
to climatic deterioration (Webb, 1977; 1984). As their systematics
becomes increasingly more refined, equids can be used with increasing
detail to study this important phenomenon.

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BIOGRAPHICAL SKETCH

Richard Charles Hulbert, Jr., born on May 28, 1955, in San Diego,
California, is the son of Harriett Peterson Hulbert and Richard C.
Hulbert. After graduating from Memorial High School in Houston,
Texas, in May, 1973, he entered the University of Texas at Austin. In
May, 1976, he graduated with High Honors, receiving a Bachelor of
Science degree in zoology. In the fall of 1976, he re-entered the
University of Texas at Austin in the Department of Geological
Sciences. He was awarded a Master of Arts degree upon completion of
a thesis entitled "Linear Discriminant Analysis and Variability of
Pleistocene and Holocene Leporidae of Texas" in December, 1979. In
January, 1981, he enrolled in the University of Florida in the
Department of Zoology. While at Florida, he held numerous research
and teaching assistantships in both the Department of Zoology and the
Florida State Museum. Richard is a member of the Society of
Vertebrate Paleontology, the Paleontological Society, and the Willi
Hennig Society. He is interested in many aspects of mammalian
paleontology, notably systematics, evolution, paleoecology and
morphometries.

570

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation for the degree
of Doctor of Philosophy.

I^UzTaJJei^

Associa

acFadden, Chairman
Professor of Zoology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation ^r the degree
of Doctor of Philosophy.

S. David Webb, Co-chairman
Professor of Zoology

I certify that I have read this study and that in my opinion it
conforms to acceptable standards of scholarly presentation and is
fully adequate, in scope and quality, as a dissertation for the degree
of Doctor of Philosophy.

Douglas'^S. Jones

Associate ProfessQjj/of Geology

This dissertation was submitted to the Graduate Faculty of the
Department of Zoology in the College of Liberal Arts and Sciences and
to the Graduate School and was accepted as partial fulfillment of the
requirements for the degree of Doctor of Philosophy.

May 1987

Dean, Graduate School

UNIVERSITY OF FLORIDA

3 1262 08553 3528