Nanodelphys, an Oligocene didelphine

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GEOLOGICAL SERIES

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FIELD MUSEUM OF NATURAL HISTORY

Volume VI Chicago, October 31, 1939 No. 26

NANODELPHYS, AN OLIGOCENE DIDELPHINE

By Paul 0. McGrew

Assistant, Paleontology

In a former paper (McGrew, 1937) the genus Nanodelphys was
described and tentatively referred to the subfamily Thlaeodontinae.
The reference was based on its agreement in molar structure with
the subfamily diagnosis given by Simpson (1929). However, small
size, Oligocene occurrence, and lack of knowledge of premolar struc-
ture tended to make this assignment somewhat dubious.

In the course of sorting and cataloguing a collection of micro-
mammals from the Brule* of northwestern Nebraska, three additional
specimens were encountered which are unquestionably referable
to Nanodelphys minutus. Teeth previously unknown in this genus,
M1 and MA, are preserved on the new specimens and offer further
material for comparison.

A review of the existing Didelphidae has shown that the dentition
of Nanodelphys is similar in many respects to that of certain living
forms, especially Marmosa and Dromiciops. The only constant
difference between Nanodelphys and all species of Marmosa is the
subequal para- and metacones in the former genus. Although fairly
constant within any given species of Marmosa, the stylar cusps
vary greatly between different species. In some (especially M.
beatrix) the stylar cusps are almost exactly like those of Nanodelphys
and the Thlaeodontinae.

Except for their reduced stylar cusps, the molars of Dromiciops are
almost identical with those of Nanodelphys in size and shape, and in
having subequal para- and metacones. The metastylar spur is variable
among the Didelphinae, being slight in some and prominent in
others. Thus each character which was thought to be diagnostic
of the molars of the thlaeodontines (see Simpson, 1935) may be
matched in one or another living didelphine. The only character
remaining which is truly diagnostic for the Thlaeodontinae seems
to be the bulbous premolars. Although these teeth are unknown

No. 455 393

1, ■■■■

394 Field Museum of Natural History — Geology, Vol. VI

in Nanodelphys, the agreement of this form with certain members
of the Didelphinae, coupled with its Oligocene age, makes its reference
to that subfamily almost certain.

Nanodelphys mi nut us McGrew.

Holotype.—FM. No. 25708,1 portion of left maxillary with M*"*,

Referred specimens. — F.M. No. P25709, portion of right maxil-
lary with M^. F.M. No. P25719, portion of left maxillary with
M*~±. F.M. No. P25720, portion of left" maxillary with M^.

Description. — With the exception of its greater antero-posterior
length in relation to transverse diameter, M1 agrees exactly with M^
and M-. In relation to their antero-posterior diameters, M- and M^
are wide transversely, with large external shelves. From the antero-
external corner of each, projects a spur, the outer border of which
is confluent with the outer border of the tooth. This spur bears
the relatively low stylar cusp A.2 Immediately posterior to A and
external to the paracone is the very prominent stylar cusp B. Be-
hind B is a rather deep U-shaped valley (deeper on M^) in which
stylar cusp C may be greatly reduced or absent. Stylar cusp D
is rather low and unites posteriorly with cusp E to form an antero-
posterior crest external to the metacone. The paracone and meta-
cone are nearly or quite equal in size and height and the V between
them is shallow. The antero-external crest of the paracone unites
with the anterior slope of stylar cusp B, and the postero-external
crest of the metacone unites with stylar cusp E. The paraconule
and metaconule are absent. The protocone is very high and is
situated antero-internally, lying immediately mesial to the para-
cone. The protocone, paracone and stylar cusp B lie in an almost
straight transverse line. The antero-external crest of the protocone
extends in front of the paracone to meet the inner base of stylar
cusp A; its postero-external crest terminates at the base of the meta-
cone. MA is very narrow antero-posteriorly and has stylar cusps
A and B as well as the paracone and protocone well developed, but the
posterior stylar cusps are lost, and the metacone is greatly reduced.

Comparisons. — Nanodelphys is closer in molar structure to
Marmosa beatrix than to any other known didelphid, living or fossil.
It differs, however, in certain significant characters which appear

1 This specimen previously bore the number Walker Museum No. 1545. In
the interest of keeping the collection as a unit, however, the specimen was trans-
ferred, together with certain others which I had collected, to Field Museum.

2 Simpson's (1929) designations of the stylar cusps are followed.

M..P* ■

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££

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An Oligocene Didelphine

395

to be primitive. The molars of the Oligocene form are smaller and
more compressed antero-posteriorly; the external shelf is broader
and more deeply cleft; the stylar cusps are similarly arranged, but
the second (B) is larger and higher. The paracone is reduced in
M. beatrix and not in Nanodelphys. The V-shaped notch between
the paracone and metacone is shallow in Nanodelphys and deep
in the living species. The protocone shelf of Nanodelphys is more
compressed antero-posteriorly.

Nanodelphys differs greatly from the contemporary Peratherium.
It is much smaller and the molars are more compressed antero-
posteriorly. Stylar cusp B is much more strongly developed, and

Fig. 114. Nanodelphys minutus McGrew. Crown view of molar dentition,
M1"4. X 20. Composite, drawn from P25719 and P25720. Drawing by Mr
Frank Gulizia.

cusp C, which is rather strong in Peratherium, is either greatly re-
duced or absent. The paracone of Peratherium is reduced and the V
between the paracone and metacone is much deeper. The proto-
cone of Nanodelphys is much higher than that of Peratherium. In
the latter the protocone shelf isV-shaped, whereas it is U-shaped in
Nanodelphys. The external shelf is more deeply cleft in Nanodelphys
and the metacone of M> is more reduced.

Nanodelphys differs from Peradectes as it does from Peratherium
and Marmosa. Thylacodon, being known only from a lower jaw, can
not be directly compared, but it is much larger than Nanodelphys.

Relationships. — Without more complete material it would be
premature to speculate about the exact position of Nanodelphys
within the Didelphinae. The molar teeth are sufficiently primitive
for the genus to be regarded as structurally ancestral to any or all

396 Field Museum of Natural History — Geology, Vol. VI

of the living forms. The fact that Peratherium is closer in tooth
structure to most living murine opossums and to Didelphis suggests
that Nanodelphys did not hold so central a position. By reduction
of the stylar cusps Nanodelphys might have given rise to Dromiciops,
but it seems improbable.

TERTIARY DIDELPHIDS AND PHYLOGENY

The consensus among most writers on didelphid phylogeny has
been that Marmosa represents the most primitive, structurally
ancestral form. Dollo (1899), Bensley (1903), and Gregory (1910)
have expressed the belief that all living genera of Didelphidae are
structural descendants of that genus. Tate (1933) suggested two
principal lines of descent, one giving rise to Didelphis, Chironectes,
Lutreolina and Metachirus, and the other to Monodelphys, Philander,
Marmosa, Glironia, and Dromiciops, the latter two branching from
a marmosoid ancestor. The evidence for regarding Marmosa as
prototypal is found in its unmodified prehensile hands and feet,
accompanied by generally arboreal habits — conditions which are
presumably primitive.

Several writers — Bensley (1906), Gregory (1910), and Simpson
(1928) — have implied that the separation into the several existing
genera occurred relatively recently (i.e. post-Oligocene), from Pera-
therium. As there is little or no structural change observable from
Peratherium to Marmosa this view is supported by the paleontologic
evidence.

Only one limited group of opossums in North America appears
to have escaped extinction at the end of the Cretaceous (Simpson,
1928). This apparently direct, conservative line has been known
from two Tertiary genera,1 Peradectes of the Paleocene, and Pera-
therium of the Eocene, Oligocene, and Miocene (McGrew, 1937).
The dental structure of these forms is very close to certain species
of Marmosa; so close, in fact, that satisfactory characters with which
to separate them from the recent genus are hard to find. Peradectes
is slightly more primitive in that it retains the para- and metaconules
and the somewhat less reduced paracone. The stylar cusps of any
of the Tertiary species may practically be duplicated in living forms.

The almost complete absence of aberrant species or genera
among the fossils seems to have led to the assumption that there

1 Thylacodon pusillus Matthew and Granger has been described from the
Puerco. On the basis of the holotype of this species it is not possible to be certain
of its relationships.

An Oligocene Didelphine 397

was little or no diversification among Tertiary didelphids. The
conclusion reached from this reasoning has been that the relatively
diverse living didelphids represent incipient branches of a new ex-
pansion. Bensley (1906) stated this view as follows: "The existing
Didelphyidae of South America, which might at first sight be re-
garded as surviving remnants of the original didelphyid radiation,
may be shown to represent a third radiation which is at the present
time in its very incipient stages. Of these three radiations the
Australian, and the existing South American ones are directly trace-
able to minute primitive didelphyid forms like the existing genera
Marmosa and Peramys, or Peratherium." I am of the opinion,
however, that such conclusions may well prove erroneous when
additional specimens are known.

The living opossums show rather wide diversity of habit with
corresponding foot adaptations. Thus, Marmosa is typically ar-
boreal with complete opposable hallux and well-developed plantar
pads; Monodelphys is terrestrial with reduction of the fifth digit
and planter pads; Chironectes is aquatic and has highly modified
webbed feet. The dentitions of these genera are very similar, how-
ever, and no differences in tooth structure may be correlated with
the widely different habits. Foot structure, then, is a most important
factor in the determination of exact relationships and phylogeny
within the Didelphidae — apparently more important than dental
structure in such a conservative group. The fact that we do not
know the feet of the Tertiary didelphids is, therefore, a serious handi-
cap in the attempt to fit the fossil forms into a phylogenetic picture.

Although the dentition of Peratherium is usually regarded as
primitive and prototypal (Winge, 1893; Bensley, 1903; Gregory,
1910; Tate, 1933) there is some indirect evidence which indicates
that this genus was actually so specialized in foot structure that it
could not have been ancestral to most living didelphids. This
possibility is suggested by two rather striking facts: (1) Peratherium
is abundant1 and is found commonly in the clays of the White River
Oligocene. (2) It is nearly always found in direct association with
such mammals as rabbits (Paleolagus) , terrestrial rodents (Ischy-
romys, Eumys, Heliscomys, etc.), small artiodactyls (Leptomeryx,
Hypertragulus, Hypisodus), horses (Mesohippus), and camels
(Poebrotherium) .

1 In a few Sunday collecting trips I have found more than seventy-five jaws
and maxillaries of Peratherium. When its small size is considered, with the con-
sequent probability that many specimens were overlooked, such abundance is
striking.

398 Field Museum of Natural History — Geology, Vol. VI

Study of the mammals contained in the clays of the White River
series led Matthew (1901) to regard them as "strictly terrestrial."
He stated: "The analogy of the clay fauna is with that of the modern
plains, of the sandstone fauna with that of the modern forests (with
some aquatic forms)." The abundance of specimens of Peratherium
in the White River clays indicates that it formed an important com-
ponent of the life of the time. The number of specimens of the
genus is greater than that of all insectivore genera combined.1

It is highly unlikely that an arboreal creature would occur in
such abundance with terrestrial forms. The obvious conclusion,
therefore, is that Peratherium was terrestrial. Further, to maintain
existence so successfully2 among the numerous placentals it must
have been considerably modified in foot structure. This would
suggest that Peratherium, although having the generalized didel-
phine dentition, could hardly have been ancestral to all of the recent
Didelphidae, unless arboreal modifications were secondary, which,
according to Dollo (1899), does not seem to be the case. It is pos-
sible, of course, that a terrestrial form such as Monodelphys could be
a direct descendant of Peratherium.

The presence of Nanodelphys in the Oligocene proves that there
was at least some diversity of marsupials in the middle Tertiary of
North America. It is very probable that many and diversified
arboreal opossums lived throughout the Tertiary, but their habitus
so rarely occasioned their presence in areas of deposition that we
do not know them as fossils. It may be that the Tertiary didelphids
would not be regarded as "stereotyped" or "monotonously un-
varied" (Simpson, 1928) if they were adequately known.

It seems likely that many of the recent genera of didelphines
originated in the early Tertiary. This view is supported by the
occurrence of Lutreolina and Didelphis in the lower Pliocene of
South America (Patterson, 1937). These early Pliocene forms are
almost identical with living species of the same genera and do not
appear to be more primitive.

1 This statement is based upon more than three thousand specimens of small
mammals which I personally have collected in the Brule of northwestern Nebraska.

2 This fact may help to account for the complete absence of indigenous pla-
cental mammals in Australia. If marsupials did originally migrate to Australia
over a land bridge, instead of being "waif" immigrants, they were probably ac-
companied by insectivores. The ability of Peratherium to thrive in competition
with the White River insectivores suggests the possibility that the original Aus-
tralian marsupials may have been victorious over the placentals in the struggle
for existence.

An Oligocene Didelphine 399

Dromiciops has usually been regarded as a descendant of a mar-
mosine. The paracone of this genus, however, is not reduced — a
very primitive character — suggesting an early pre-Peratherium
separation of this genus. It seems improbable that the paracone
was secondarily enlarged, since it is known to have been equal in
size to the metacone in primitive genera such as Pediomys and
Nanodelphys.

It seems probable that the modifications seen in living didel-
phines may have had their origin at the time of the original early
Tertiary mammalian expansion. After that time the limits of
expansion in North America would have been determined by the
few ecologic niches left open by placentals. In Australia and, to a
lesser degree, South America similar obstacles to expansion were
not encountered.

MEASUREMENTS
(In millimeters)

P25708 P25709 P26719 P25720
MU-p ... ... 1.5

MATr ... ... 1.3

M2A-p 1.5 1.5 1.6 1.6

M2Tr 1.6 2.0 1.7 1.6

MaA-p 1.3 ... 1.6

MaTr 1.7 ... 1.8

M*A-p ... 1.0

M*Tr ... 1.9

LITERATURE CITED
Bensley, B. A.

1903. On the Evolution of the Australian Marsupialia; with Remarks on the

Relationships of the Marsupials in General. Trans. Linn. Soc. Lond., (2), 9,

pp. 83-217, 3 figs., pis. 5-7.

1906. The Homologies of the Stylar Cusps of the Upper Molars of the Didel-

phyidae. Univ. Toronto Studies, Biol. Ser. No. 5, pp. 149-159, figs. 1-6.

Dollo, L.

1899. Les ancetres des Marsupiaux, etaient-ils arboricoles? Miscellanees
Biologiques, pp. 188-203.

Gregory, W. K.

1910. The Orders of Mammals. Bull. Amer. Mus. Nat. Hist., 27, pp. 1-524,
figs. 1-30.

Matthew, W. D.

1901. Fossil Mammals of the Tertiary of Northeastern Colorado. Mem. Amer.
Mus. Nat. Hist., 1, Part 7, pp. 355-447, figs. 1-34, pis. 37-39.

McGrew, P. O.

1937. New Marsupials from the Tertiary of Nebraska. Jour. Geol., 45, pp.
448-455, figs. 1-4.

Patterson, B.

1937. Didelphines from the Pliocene of Argentina. Proc. Geol. Soc. Amer.,
1936, p. 379.

400 Field Museum of Natural History — Geology, Vol. VI

Simpson, G. G.

1928. American Eocene Didelphids. Amer. Mus. Nov., No. 307, pp. 1-7,
figs. 1-5.

1929. American Mesozoic Mammalia. Mem. Peabody Mus., 3, pp. I-XV>
1-171, figs. 1-62, pis. 1-32.

1935. Note on the Classification of Recent and Fossil Opossums. Jour. Mamm.,
16, pp. 134-137.

Tate, G. H. H.

1933. A Systematic Revision of the Marsupial Genus Marmosa, with a Discus-
sion of the Adaptive Radiation of the Murine Opossums. Bull. Amer. Mus.
Nat. Hist., 66, pp. 1-250, figs. 1-29, pis. 1-26.

WlNGE, H.

1893. Jordfundne og nulevende Pungdyr (Marsupialia) fra Lagoa Santa,
Minas Geraes, Brasiliens. E. Museo Lundii, 2, pp. 1-132.

INDEX

VOLUME V

Ahumada meteorite, 1
Arispe meteorite, 2

Bishop Canyon meteorite, 3

Davis Mountains meteorite, 4
Davis Mountains meteorite, analysis
of, 9

Greenland, composition of sands from,
24

Labrador, composition of sands from, 22

Macquarie River meteorite, 12
Macquarie River meteorite, analysis

of, 14
Mineral composition of sands, labora-
tory procedure for determination of,
17-20

Quebec, composition of sands from, 20

Rawson-MacMillan Expedition, 17

South Bend meteorite, 14

VOLUME VI

Adinotherium, 17-21, 95, 107, 114, 210,
212, 214, 221, 222, 276, 278, 279,
286, 298

ovinum, 17, 212-214, 220-222, 282,
286-288
Adpithecus; see Notopithecus
Aelurodon, 329
Ailuropoda, 325, 333, 334, 336, 337, 338

melanoleuca, 334
Ailurus, 325, 333, 334, 336, 337

fulgens, 333
Aletocyon, 337

multicuspis, 331
Allognathosuchus, 315, 318

mooki, 318
Amblypoda, 352, 373, 381
Ameghinotherium, 132
Amherst brain cast, 279
Amphicyon americanus, 349

amnicola, 348

aurelianensis, 349

frendens, 348

idoneus, 348

ingens, 348

palaeindicus, 349

pontoni, 349

reinheimeri, 348

riggsi, 341-350

shabbazi, 349

sinapius, 348
Ancylocoelus, 166, 215

frequens, 15-17; (Colpodon[sp.), 94,
166, 215-216
Ankylodon, 267, 269, 271

annectens, 269-271
Araucanian-Entrerian series, 132
Archaeohyracidae, 131
Arctostylopidae, 108

Argyrohippus, 96, 97, 98, 161, 162, 164,
281

boulei, 161, 162

fraterculus, 96-98, 161, 162, 164, 166

praecox, 161-165

sp., 97, 109
Argyrohyrax, 21; see Plagiarthrus

proavus; see Plagiarthrus proavus
Arsinoitheria, 373
Artiodactyla, 373
Asmodeus, 100, 299

sp., 100, 107
Astrapotheria, 24, 25, 110, 176, 373
Astrapothericulus, 170
Astrapotherium, 110, 167, 173, 175-176

magnum, 167, 175

Bacteria in stony meteorites, 179
Barylambda, 229

(Titanoides), 173, 174, 229-230, 361-
364, 365, 367, 369, 370, 371, 372

faberi, 230, 365, 372

group, 370-371
Barylambdidae, 361, 371, 372
Barylambdinae, 230, 372
Bassariscus, 325, 326, 327, 331, 332,
335, 336, 338

astutus, 326
Bathmodon; see Coryphodon
Bathyopsis, 374, 376, 377, 382

fissidens, 374
Bathyopsoides, 373-374, 376, 377, 379,
380, 382

harrisorum, 373, 374-378, 379, 380,
381
Balhyurus sculpinensis, 40, 59

sp., 44, 59
Bes8oecetor, 268

401

402 Field Museum of Natural History — Geology, Vol. VI

Bison bison, 308, 310, 311
Blarina, 247, 249, 256
Blarina brevicauda, 247, 306
"Blarinae," 256
Borhyaena, 63, 64
Borhyaenidae, 65
Borhyaeninae, 65
Braincasts, method of making, 273

Canis, 329, 330, 346, 347, 348

familiaris, 307-308

latrans, 306, 311

lupus, 309, 311
Camivora, 373
Casamayor formation, 132
Castoroides ohioensis, 306
Ceratiocaris leesi, 155

markhami, 142
Ceratosuchus, 315-316

burdoshi, 316-318
Cervalces roosevelti, 310

scotti, 310
Cervus canadensis, 310
Chert, analysis of, 82
Chironectes, 396, 397
Chrysemys sp., 311
Cochilius, 21, 86, 121, 134, 135

volvens, 23, 88
Colhue-Huapi formation, 132
Collon-Cura formation, 132
Colpodon, 15, 165, 166

propinquus, 94

sp., 166; see Ancylocoelus frequens
Condylarthra, 369, 373, 382
Conularia manni, 147
Coresodon, 109, 281

Coryphodon, 172, 173, 174, 352, 353,
354, 356, 357, 358, 359, 360, 361,
362, 364, 365, 369, 370, 371, 372

group, 370-371

wortmani, 357
Coryphodontidae, 370, 371-372, 381
Creodonta, 382

Crinoidal stems, Labrador, 36
Crista meati, 85
Crocidura russula russula, 254

group, 254
Cynarctinae, 337
Cynarctoides, 324, 325, 327, 328, 330,

331, 336, 337, 338
Cynarctus, 323, 324, 325, 327, 329, 331,
335, 336, 337

acridens, 323, 324, 328, 336

crucidens, 323, 324, 329

saxatilus, 323, 324

Dalmanites pratteni, 67
Daphaenodon, 346, 347, 348, 350
Daphaenus, 346, 347
Deep River beds, 341
Deseado formation, 132, 299
Didelphidae, 393, 398

Didelphys, 396, 398

Dinoceras, 377

Domnina, 246-248, 250, 255-256

gradata, 246, 247, 248-255
Dromiciops, 393, 396, 399

Echinosoricinae, 268
Elachoceras, 382
Elasmosaurus platyurus, 385

serpentinus, 385-390
Embassis, 246

Entelonychia, 6, 23, 24, 297, 298
Entomolestes, 268
Eobasileus, 382
Epitypotherium, 132, 135
Erinaceidae, 245, 267, 268
Erinaceinae, 268
Eumys, 397
Eurygeniops, 108
Eurygenium, 108
Eurygenius, 108
Eutrachytherus, 119, 130

modestus, 133
Eutypotherium, 130, 131, 293

Ferrissia fusca, 304
Fossaria obrussa, 304
Fossils of Northeast Labrador, sources
of, 49

Gastroliths of Elasmosaurus serpenti-
nus, 390

Glironia, 396

Goldman, E. A., on Post-Glacial Indian
Dog, 307

Goniobasis livescens, 304

Gravel pits in Coles County, Illinois,
geology of, 303-304

Gypsonictops, 267

Gyraulus altissimus, 304

Haplolambda, 365, 367, 370

quinni, 365-367
Hegetotheriidae, 108, 131, 134-135, 136,

222, 224, 297, 299-300
Hegetotherium, 128, 129, 200, 204, 205,

212, 222, 223, 274, 276, 277, 293,

294, 295, 296, 297
mirabile, 200-203
Helicotoma rawsoni, 39, 59
Heliscomys, 397
Helisoma anceps, 304
Hemiechinus, 268
Heterosorex, 255, 256
Hicoria sp., 304, 312
Homalodotheriidae, 108, 225, 298-299
Homalodontotherium; see Homalodo-

therium
Homalodotherium, 100, 106, 207, 215,

216, 224, 225, 242-243, 288, 291,

292, 293, 297, 298, 299

Index

403

cunninghami (segoviae), 6-9, 99, 113-
117, 216-220, 222, 223, 225, 233-
242, 288-293

segoviae; see H. cunninghami
Homo sapiens, 308, 309
Hormotoma labradorensis, 37, 59
Hormotoma minuta, 38, 59
Hylomys, 268
Hypertragulus, 397
Hypisodus, 397
Hyracoidea, 222, 373

Ictops, 264

Illinois, fossil vertebrates from, 303

Interatheriidae, 108, 131, 134, 136, 222,

224, 297, 299
Interatherium, 134, 136, 204, 206, 207,

209
robustum, 204-206, 224
Interhippus, 109
Ischyromys, 397
Isoproedrium, 132
Isotemnidae, 108, 299
Isotypotherium, 132, 135

Labrador fossils, 33
La Flecha deposit, 165, 166
Larix sp., 304
Leidyosuchus, 318, 319, 320

acutidentatus, 320

multidentatus, 320

riggsi, 318-320

sternbergii, 320
Leontinia, 92, 99, 105, 108, 126, 216

gaudryi, 92-94, 105, 107

sp., 93
Leontiniidae, 108, 225, 297
Leptacodon, 266, 267

tener, 267
Leptictidae, 266, 267
Leptomeryx, 397
Limestones, Sculpin Island, 62

Silliman's Fossil Mount, 52
Limnoecus, 254
Loxolophodon, 352
Lutreolina, 398
Lynx sp., 311

Macrauchenia, 172

Mammut americanum, 308

Marmosa, 393, 394, 395, 396, 397
beatrix, 394, 395

Marsland beds, 324

Marsupial sabertooth, 61

Megalonyx jeffersonii, 306

Megalonyx? sp., 306

Meleagris gallopavo, 311

Mesohippus, 397

Metacodon, 257, 263, 266-268, 269, 270,
271
magnus, 257-258, 264
mellingeri, 258-266, 269, 270

Metamynodon, 168, 176

Miniopterus, 256, 257

Miothen crassigenis; see Domnina gra-

data
"Miothen" gracile; see Peratherium

huntii
Monodelphys, 396, 397, 398
Moropus, 243
Morphippus, 96, 108, 109, 110, 164,

165, 281
Muflizia, 136-137
Mufiiziinae, 136
Musters formation, 299
Mystipterus vespertilio, transferred from

Chiroptera to Soricidae, 256-257

Nanodelphys, 393-399

minutus, 393, 394
Nectogale, 255
Neomys, 248

Nesodon, 17-21, 95, 107, 130, 200, 209,

212, 214, 221, 222, 276, 279, 281,

282, 284, 285, 286, 287, 288, 290,

291, 292, 298

imbricatus, 19, 96, 209-212, 220, 221,

222, 281-286
Nesodontidae, 109, 286
Nesohippus, 109
Nothocyon annectens, 337
Notioprogonia, 223
Notohippidae, 108-110, 279, 281, 297,

298
gen. et sp. indet., 279-281
Notohippus, 109, 164
Nolopithecus, 91, 101, 102, 103, 132
Notostylopidae, 108
Notostylops, 129, 284, 290, 299
aspectans, 9-12
brachycephalus, 9
sp., 105
Notoungulata, 6, 23, 25, 91, 92, 107,
110, 199, 223-224, 273, 297-300,
373

Odocoileus virginianus, 308, 310, 311
Oldfieldthomasia, 203, 207, 214, 215,

223, 279
Ondatra zibethica, 309
Orohippus, 107
Ovibos, 308, 312
Ovibovinae, 308

Pachyrukhos, 203, 207, 209, 222

moyani, 203-204, 224

typicus, 19
Palaeostylops iturus, 103-105

macrodon, 104
Paleolagus, 397

Pantodonta, 352, 353, 369-373, 382
Pantolambda, 230, 352, 353, 354, 356,
357, 358, 359, 360, 361, 364, 367,
369, 370, 371

404 Field Museum of Natural History — Geology, Vol. VI

Pantolambda bathmodon, 356

cavirictus, 356, 367
Pantolambdidae, 369, 370, 371, 381
Pantolambdinae, 372
Pantolambdodontidae, 370
Parastrapotherium, 110, 167
Parictis dakotensis, 324, 338
Patagonian formation, 132
Peradectes, 395, 396

PcTCLTYlVS 39T

Perathenum, 246, 247, 395, 396, 397,
398, 399

huntii, 248

sp., 247
Periphragnis, 299
Periptychidae, 369, 373, 382
Perissodactyla, 373
Phenacodus, 284, 291
Philander, 396

Phlaocyon, 325, 327, 330, 331, 335, 336,
337, 338

leucosteus, 324, 331
Phyllopod mandible, 155
Phyllopodous crustacean, new Silurian,

141
Physa gyrina, 304

Integra, 304
Pisidium sp., 304

Plagiarthrus (Argyrohyrax), 21, 107,
121, 131, 134, 135

proavus, 21-23
Plateau Valley beds, Tiffany age of, 351

vertical distribution of fossils in, 380
Pleurostylodon, 100, 105, 293, 299

biconus? 100
Poebrotherium, 397
Post-Glacial of Coles County, Illinois,

312
Proadinotherium, 94, 98

leptognathum, 95, 97

muensteri, 94-96
Probathyopsis, 373, 374, 376, 378, 382

newbilli, 378-381

praecursor, 378, 380, 381
Procavia, 222

Procyon, 325, 330, 332, 333, 334, 335,
336, 337

lotor, 309, 332

prisons, 309
Procyonidae, 323, 324, 335, 338
Prodinoceras, 373, 374, 380
Proedrium, 132
Proedrus, 132

Prosotherium, 102, 103, 134, 136
Proterixoides, 267

davisi, 267
Proterotherium, 276
Protosorex, 246, 247

crassus, 247, 248, 255
Protypotherium, 23, 128, 129, 134, 136,
204, 205, 206, 209, 212, 293, 295,
296, 297

attenuatum, 207
australe, 206-207, 209, 224
Pseudemys sp., 311

Pseudocynodictis, 325, 326, 327, 328,
331, 335, 338
gregarius, 325
Pseudotypotherium, 83, 88, 120, 121,
122, 123, 124, 125, 126, 133, 208,
209, 224, 293
pseudopachygnathum, 83-89, 116, 208,
209
Pyrotheria, 373

Rhynchippidae, 108-110
Rhynchippus, 108, 109, 110, 214, 215,

274, 276, 278, 279, 280, 281, 282,

284, 285, 286, 287, 290, 291, 292,

298 299
equinus, 12-14, 98, 214-215, 274-279
pumilus, 98-99, 214-215, 218, 225
Rhyphodon, 274, 275, 276, 277, 278,

279, 290, 291, 292, 298, 299
Rio Frias formation, 132
Rfo Mayo formation, 132
Rubber technique for braincasts, 273-

274

Santa Cruz formation, 132

Sculpin Island, Labrador, 35

Septum in notoungulate bulla, 222-223

Sorex, 247

Soricid, 245

Soricidae, 255

Sparactolambda, 352-354, 356, 357, 358,

359, 361, 362, 367, 370, 371, 372,

373
looki, 354-361
Sphaerium sulcatum, 304
Stagnicola reflexa, 304
Shlhippus, 109

Stratigraphy of northeast Labrador, 44
Sylvilagus floridanus, 306

Tachytypotherium, 130
"Taligrada," 373
Terrapene ornata, 311
Thomashuxleya, 236, 299
Thylacodon, 396
Thylacosmilinae, 65
Thylacosmilus, 61-65, 114

atrox, 62

lentis, 62
Tinoceras, 377
Titanoideidae, 372
Titanoides; see Barylambda

faberi; see Barylambda faberi

gidleyi, 229, 230

primaevus, 229, 230
Titan oidinae; see Barylambdinae
Toxodon, 19, 20, 21, 85, 96, 275, 282,
284, 286, 287

burmeisteri, 18, 19, 285

Index

405

platensis, 18, 87
Toxodonta, 12, 23, 24, 207, 222, 223

224,225,297,298
Toxodontia, 6, 23-25, 110
Toxodontidae, 108, 109, 225, 297, 298
Trachytherium, 101, 119
Trachytherus, 130-137, 280, 293. 294
295,296,297
eonturbatus, 120
grandis, 120

spegazzinianus, 101-102, 119-129
274, 279, 293
Trachytypotherium internum, 21
Trigodon, 96

Trilobite, New Devonian, 67
Trinacromerum, 385
Tupaiodon, 260, 261, 267
Tupaiodon? minutus, 267, 268
Tupaiodon morrisi, 264
Turritoma cf. 7\ ada, 39, 59
Typotheria, 21, 23, 24, 136, 297, 299-300
Typothericulus, 133

Typotheriidae, 108, 132-133, 222. 224
297, 299 '

Typotheriopsis, 84, 88, 122, 126. 133
135, 224, 293, 294, 295, 296, 297 '

chasicoensis, 293
internum, 21, 293-297
studeri, 293
Typotherium, 19, 21, 86, 122, 129. 130
131,132,133,135,295 '

m88? 131 18' 19' 83' 84' 85, 86' 87'

Uintatheriidae, 381

Uintatherium, 352, 377, 382

Ulmus sp., 304

Ungulates, 373

Upper Canadian fossils, Labrador, 31

Upper Harrison, 323

Uqufa formation, 132

Ursus (Euarctos) americanus, 309

Ursus gyas group, 309

horribilis group, 309

procerus, 309

sp. cf. U. horribilis, 309

Vulpes, 330
Xotodon, 236
"Zotodon;" see Xotodon