Auditory Region in North 

American Fossil Felidae: 

Its Significance in 

Phylogeny

GEOLOGICAL SURVEY PROFESSIONAL PAPER 243-G
Auditory Region in North 

American Fossil Felidae: 

Its Significance in 

Phylogeny

By JEAN HOUGH

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952, PAGES 95-115

GEOLOGICAL SURVEY PROFESSIONAL PAPER 243-G

Detailed descriptions and illustrations of the 

ear region in some fossil and recent genera, 

and a proposed revision of super family 

classification of the Carnivora

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1953
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price 20 cents (paper cover)
CONTENTS

Abstract ___________________________________________

Introduction. ______________________________________

Acknowledgments_____ _ _____________________________

General characters of the auditory region in Oligocene 

Felidae. _________________________________________

Auditory bulla_ ________________________________

Basicranial foramina, ___________________________

Generic descriptions _ _ _____________________________

Subfamily Machaerodontinae _ __________________

Hoplophoneus- _____________________________

General characters- _______---__---__-___

Auditory bulla_ ________________________

Basicranial foramina ____________________

General characters. _____________________

Middle and inner ear structure- __________

Basicranial foramina. __________^____.___

Pliocene machaerodonts, ____________________

Smilodon __________________________________

General characters. _____________________

Internal structure of the auditory bulla____

Structure of the middle and inner ear_ 

Basicranial foramina. _-___-_-__________-

Page 

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102

	Page 

Generic descriptions—Continued

Subfamily Nimravinae________---___-_-___-_--__ 103

Dinictis (Oligocene species)__________________ 103

External characters _____________________ 103

Internal structure of the bulla and middle ear. 103

Basicranial foramina. ___________________ 103

Dinictis cyclops Cope (John Day species) ______ 105

Nimravus- _________________________________ 106

Subfamily Pseudaelurinae______________________ 106

American genera.__________________________ 106

Asiatic and European genera.________________ 106

Summary and conclusions______________________ 106

Homology of basicranial features of the Feloidea______ 107

Septum bullae_-_______-_--------__------------- 107

Form and position of the septum _____________ 1C7

Mode of development of the bulla____________ 1C9

Basicranial foramina._____-____-_______--:____-_ 110

Summary and conclusions________-____-_-___-__ 112

Evolution of the intracranial circulation _______ 112

Evolution of the auditory bulla_______________ 112

Proposed taxonomic changes_____-___-_--___- 113

Summary of superf amilies and families ________________ 113

Selected references-_________________________________ 115

ILLUSTRATIONS

Page 

FIGURE 5. Hoplophoneus primaevus oreodontis---------- 98

6. Smilodon californicus--.------------------- 100

7. Smilodon californicus.-- _________________ . 100

8. Diniclis felina---------------------------- 104

9. Dinictis cyclops___________________________ 105

12.

13.

Pag«

___ 10° 

________________ 10°

Cam's dingo. __________-_-_____-___-_-_-_ 110

Vulpes velox---------------------------- 111

FIGURE 10. Viverricula ind. rasse. 

11. Felis catus- ________--

AUDITORY REGION IN NORTH AMERICAN FOSSIL FELIDAE: 

ITS SIGNIFICANCE IN PHYLOGENY

By JEAN HOUGH

ABSTRACT

The auditory region of the North American fossil Felidae is 

described in detail. In the Oligocene Felidae the characters of 

this region, especially the foramina associated with the veins 

and arteries of the head, are like those of the modern Canidae 

rather than the Felidae. On the contrary, all of the middle 

Miocene (post-John Day) and later genera have typical felid 

characters in this part of the skull. This has profound significance for the phylogeny and major taxonomy of the family. 

If any of the species of Oligocene felids are ancestral to the 

modern forms, an evolution of both the venous and arterial 

system of the head as well as the auditory bulla must have taken 

place. This is quite possible, for not only is there theoretical support for it in the ontogeny of modern genera, but there are species 

that have characters linking the Paleofelides to the Neofelides. 

Nevertheless, postulating such an evolution is a radical step as 

it throws doubt upon the validity of the current superfamial 

classification of the Carnivora. This arrangement is based primarily on the homology of the two-chambered bulla, and the 

presence or absence of the postglenoid foramen. If, as this 

paper attempts to show, these structures are not homologous, 

but have evolved independently in the Viverridae and Felidae 

(and in other families), the categories Aeluroidea and Arctoidea 

of Flower (Feloidea and Canoidea of Simpson) have no phylogenetic significance, but are at best convenient divisions applicable to modern genera only.

INTRODUCTION

The threefold division of the Carnivora into Aeluroidea, Cynoidea and Arctoidea was based by Flower 

(1869) primarily on the characters of the auditory region, especially the presence or absence of a septum dividing the bulla into two chambers, and the arrangement of the basicranial foramina. In these features, 

the Aeluroidea (Viverridae, Felidae, Hyaenidae) represent one extreme, the typical arctoid Carnivora (Mustelidae, Procyonidae, Ursidae) another. The Cynoidea 

(Canidae) Flower thought intermediate between the 

two. In the Aeluroidea the interior of the bulla is divided into two chambers by a septum which completely 

closes off the chambers except for a small opening just 

below the fenestra cochleae; the postglenoid foramen is 

reduced or absent, the condyloid foramen concealed by 

the foramen lacerum posterius, the carotid canal reduced to a vestige and the posterior carotid foramen 

(where present at all) very inconspicuously placed in a

common fossa with the posterior lacerate foramen. Tv 3 

Arctoidea, on the other hand, have a simple, one-chambered bulla, a large postglenoid foramen, a large condyloid foramen quite distinct from the foramen lacerum 

posterius, a well-developed bony canal for the carotid 

artery and a large posterior carotid foramen also distinct from the posterior lacerate foramen. The Cynoidea have some features of each group. There is a partial septum, the postglenoid foramen is moderately 

large, the condyloid foramen is smaller than in the 

Arctoidea and the carotid canal less conspicuously developed. The posterior carotid foramen is a narrow 

slit opening into the common fossa with the foramen 

lacerum posterius.

These characters were probably considered by 

Flower, and certainly by Turner (1848) who originated 

the idea, as no more than morphological correspondences the use of which gave a more natural classification 

(sensu Dobzansky, 1941, p. 363) than the use of adaptive characters of the limbs and teeth. Mivart, ho^- 

ever, in a series of papers (1882,1885,1890) elaborated 

on the idea extensively, giving it an archetypal significance by compiling long lists of features in the soft 

parts and skeleton linked, as he thought, with the key 

characters of the basicranium. With the rise of the 

evolutionary theory, this archetypal concept of homology gave way in turn to a phylogenetic one. Homology indicated common ancestry, proof of which was to 

be sought first in ontogeny, and later, as the fossil 

record became better known, in paleontological history.

The first result of this shift in zoological theory was 

the reduction of Flower's threefold classification to a 

twofold one. Flower had considered the partial senturn found in many canids, and especially well developed in Oanis yubatus homologous with the septum 

bullae of Felis, at least in the morphological sense. (It 

has the same position and where the bullae is well inflated appears to be an intermediate stage in the evolution of the typical felid septum.) Winge's studies 

(1895) seem to show that the septum of Oanis was, in 

fact, homologous in mode of origin (not position) whh 

the septae and rafters that radiate from the cris^a

95
96 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

tympani across the walls of the bulla in some mustelids. 

These are ossified from folds of the mucuous lining. 

In spite of the fact that this homology was disputed'by 

Van Kampen (1905) who denied that the septum in 

Canis originated from mucous folds and considered it 

rather a part of the original wall become concave by 

bone apposition on the outer side and simultaneous resorption on the inner side, Winge's classification continued to be universally accepted for over half a century. This was in part due, however, to support 

given to the idea of the homology of the basicranial 

characters of the Cynoidea and Arctoidea by certain 

phylogenetic theories of Matthew (Wortman and 

Matthew, 1899). These theories, which derived the 

Procyonidae and Ursidae from Miocene canids, were 

based almost wholly on dentition and tended to 

make the Canidae the central stock of the arctoid Garni vora. Their influence was so great that except for 

a few minor shifts of certain problematical families 

and the substitution of the names Canoidea and 

Feloidea by Simpson, (1945), for the Arctoidea and 

Aeluroidea of Flower the resulting division of the Garni vora into two superfamilies (and the phylogeny derived from this) has, to the writer's knowledge, not 

been challenged until recently.

The increase in knowledge of the fossil Carnivora, 

however, has brought many new facts of morphology 

and phylogeny to light. Some of these were presented 

by the writer in an earlier paper (Hough, 1948), in 

which it was shown that the derivation of the Procyonidae and Ursidae from Miocene canids is untenable 

when characters other than those of the dentition are 

taken into consideration. The work of Scott and Jepsen (1937), Jepsen (1933, 1941) on the fossil Felidae 

has emphasized the antiquity of this family, and its 

separation from the Viverridae. These facts, together 

with much unpublished data known to specialists in the 

field, tend to cast doubt on the validity of the superfamily arrangement of the Carnivora and to pose many 

taxonomic problems for which to date no consistent solution has been offered. In fact, the general taxonomy 

of the order has blundered along in a curious kind of 

compromise by which one set of criteria are used for determining the systematic position of recent forms and 

quite another that of the fossil genera. The recent 

Camdae, for example, are included in the Canoidea 

because of the supposed homology of the septum present in some canids with that of such of the arctoid Cariiivora as have septae, and because of a hypothetical 

relationship of fossil forms based on dentition. 

Daphoenus, which has a demi-bulla virtually identical 

with that of both the modern Nandiniu and the fossil 

Paleoprionodon contemporary with Dapkoenus, is also

included in the Canoidea but on the basis, presumably, 

of the dentition, or of an alleged canid ancestry.

Paleoprionodon and Paradaphoenus, wture basicranial characters are almost exactly alike, ar?, placed 

in different superfamilies, one in the Feloidea and the 

other in the Canoidea presumably on the basis of dentition although the dental characters of Paleoprionodon differ from those of Paradaphoenus in the same 

way that those of Poiana differ from Civetwtis—modern viverrines included by Gregory (1939) in the same 

subfamily. The basicranial foramina of the fossil 

Felidae have long been known to be eanoid (Scott and 

Jepsen, 1937; Jepsen, 1933) but, although these features 

are considered of paramount importance in th?- classification of Modern carnivores, they have been entirely 

ignored in the superfamily allocation of the fossil 

Felidae. The writer feels that the inconsistencies are, 

in fact, so great that a paleontologist from M^.rs, with 

no inherited prejudices based on the magic of names 

would be hard put to understand our classification at 

all.

This confusion in taxonomy has arisen, of course, 

from a confusion as to the definition and significance 

of homology. As applied to modern carnivores, the 

concept, in practical usage at any rate, has largely an 

archetypal significance. Applied to fossil forms, 

homologies are used as a means of tracing phylogenies. 

The result, naturally, is extremely illogical. Zangerl 

(1949), impressed by some of these inconsistencies and 

the circular reasoning which is both a cause and a 

result, has argued recently for a return to a purely 

archetypal definition of homology. This, however, is 

clearly impossible under current evolutionary theory, 

the soundness of which seems, at least in the present 

state of knowledge, firmly established. Attempting to 

turn back the clock, zoologically speaking, wo^ld lead 

only to further confusion. A phylogenetic definition 

of homology is the only theoretically sound one. In 

any case, the dilemma is more apparent than rerl. The 

two concepts of homology, properly interpreted, support one another. True correspondence in structure 

can only be the result of similar ontogenetic development and this in turn depends ultimately on a common 

phylogenetic origin. General correspondence of structure, and even in some instances detailed similarities 

can, of course, be the result of parallelism and convergence. (For a full discussion of this see Haas and 

Simpson, 1946.) However, the writer believes that 

in mammals, at least, these processes can be distinguished if all lines of evidence are properly evaluated. 

It is the duty of a good phylogenicist to do this, however 

difficult the task may be.
AUDITORY REGION IN FOSSIL FELIDAE 97

In fossil Felidae the difficulty is particularly great 

because of the large amount of parallelism and convergence, not only in the dentition, as is generally recognized but, as will be shown in this paper, in the 

basicranial structure as well. The studies here presented are an attempt to examine as thoroughly as 

possible the facts of the supposed homologies on which 

the major taxonomy of the Feloidea is based and to 

propose a theory of phylogeny supported by, or at least 

not inconsistent with, these facts.

ACKNOWLEDGMENTS

Some of the data on which the study is based were 

gathered from museums other than the U. S. National 

Museum under a grant from the Geological Society of 

America prior to the writer's employment with the 

U. S. Geological Survey. The writer wishes to thank 

the council of the Geological Society of America and 

the staffs of the various museums in which this 

preliminary work was done, for their valuable 

cooperation.

GENERAL CHARACTERS OF THE AUDITORY REGION IN 

FOSSIL FELIDS

AUDITORY BULLA

The structure of the bulla in the Oligocene Felidae 

is difficult to interpret. No known specimen has a 

complete bulla, and many have no remnants of it preserved. Some skulls, especially those more recently 

collected and carefully prepared, have a considerable 

portion remaining—in most specimens the anterolateral wall, including the auditory meatus and the 

crista tympani. A few have traces of the posterior 

and medial walls. Moreover, a careful examination 

of the bones in contact with the roof of the bulla—the 

basioccipital, basisphenoid, exoccipital and petrosal— 

show unmistakable impressions of a bulla even in skulls 

where no remnant now remains in place. Piviteau 

has described this same condition in the skulls of the 

European species, EusmMis fiidentatus (Piviteau, 1931, 

p. 31, PI. VI, fig. 1).

The anterolateral portions of the bulla, which are 

present in many specimens, have been interpreted as 

an anterior (tympanic) chamber similar to that of the 

living Viverridae or Felidae—interpretations differ as 

to which. Plausible as this idea is (and consistent 

with the accepted taxonomy of the Felidae) it is almost 

certainly not correct. Aside from the impressions on 

the roofing bones, mentioned above, there is evidence 

in the remnants of the bulla itself that that structure 

was complete, fully ossified and similar in shape and 

size to that of the Canidae.

Eemnants of the bulla that remain intact in spec; - 

mens of Hoplophoneus and Dinictis from the White 

River formation are not the same in size or shape in 

any two skulls, or even on both sides of the same skull. 

The edges are irregular and jagged. They are, therefore, quite unlike the regular, smoothly margined, 

horse-shoe shaped demi-bulla of such fossil forms as 

Paleoprionodon and Daphoenus, or the modern viverr' d 

Nandinia. Moreover, a demi-bulla, in those forms in 

which it occurs, lies at a very low angle and covers only 

the antero-lateral portion of the auditory region. It 

does not touch the basisphenoid. The margins, which 

are incurved, are in contact with the promontorium 

except directly ventral to the fenestra cochleae. In 

Hoplophoneus and Dinictis, on the other hand, tl *, 

circle of bone around the auditory meatus arches 

around the middle ear structures. It may be in contact 

with the basisphenoid by a broad strip of bone, if that 

much of the bulla is present, but it is never in contact at 

any point with the promontorium. It seems to correspond very closely to a portion of the antero-lateral 

wall of the normal one-chambered bulla of the Canida0-.

Examination of a number of miscellaneous dog ar d 

wolf skulls that were collected after being exposed to 

weathering shows that the bulla is broken in nearly 

all such specimens. The portions remaining are exactly those found in the saber tooth carnivores—tl °> 

anterior wall where it is re-enforced by its juncture 

with the postglenoid process, the basispenoid, tH 

crista tympani and in some cases the medial and po^1 - 

terior walls. The incomplete state of the bullae, therefore, in the fossil specimens in question, can be almost 

certainly attributed to the conditions of fossilization, 

that is, to exposure to weathering for a considerable 

length of time before burial, followed by rapid entombment under a heavy load of sediment. These are 

exactly the conditions known to exist in a flood-plain 

type of deposition, such as that of the White River 

formation.

The portions of the bulla could, of course, represent a 

part of the lateral wall of a two chambered bulla tl Qanterior chamber of which was globular, as in tl 3 

domestic cat. Opposed to this is the contact with tl ? 

basisphenoid (which never occurs in the Felidae), and 

the absence of any trace of a septum bullae. This 

septum is an extremely strong structure. Attempts to 

break the bulla of a cat or viverrine will easily prove 

that this is so. Moreover, a complete septum like thnt 

of the Felidae leaves a strong impression on the periotic, 

as can be ascertained by examination of modern specimens, and no such imprint is present even in skul> 

whose preservation is almost perfect. It seems virtually impossible therefore, that a septum bullr Q,
98 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

&•>**?3!Pia; •• C^jv'Y '!'* ••*•£*••

pp

FIGURE 5.—Hoplophoneus primaevus oreodontis Cope, Princeton Museum. 10515, Xl%-
AUDITORY REGION IN FOSSIL FELIDAE 99

corresponding to that of the modern Felidae in form 

and position was present in the Oligocene genera.

BASICRANIAL FORAMINA

The basicranial foramina of the Oligocene Felidae 

are as anomalous as the structure of the auditory region. 

They are distinctly not feloid—(Scott and Jepsen, 1937, 

Piviteau, 1931, and others) in number or position. 

There is an alisphenoid canal, and a large postglenoid 

foramen.. The condyloid foramen is large and well 

separated from the foramen lacerum posterius. The 

carotid canal is well defined and terminates either in a 

space between the alisphenoid and promontorium or a 

large foramen lacerum medium. The posterior carotid 

foramen is behind the foramen lacerum posterius and 

well separated from it. These characters are all canoid 

and point to a venous and arterial system of the head 

almost at the opposite extreme from that of the modern 

Felidae.

These characters as well as those of the bulla will be 

considered in more detail in the following descriptions.

GENERIC DESCRIPTIONS

SUBFAMILY MACHAERODONTINAE 

HOPLOPHONEUS

GENERAL CHARACTERS

The space occupied by the auditory cavity is narrow. 

(See fig. 5.) This is due, in part, to the narrowness of 

the basicranium itself, and in part to the enormous development of the mastoid processes. These form short 

broad columns extending forward and downward well 

below the plane of the basicranium. The width is so 

great that the medial margin is on a line with the inner 

margin of the glenoid fossa. Comparison with Cams 

and Felis (where the mastoid hardly appears on the 

under surface of the skull) reveals that the space for 

the promontorium and structures of the middle ear is 

very restricted. The promontorium is large and 

rounded, but the depth of the cavity makes it appear 

buried in the basicranium. It is in fact, somewhat 

deeper below the level of the basioccipital than in modern carnivores, or in the contemporary Dinictis,

"fhe paroccipital process projects backward from the 

base of the mastoid and forms a distinct leaflike 

process. The size of the process, and its distinction 

from the mastoid, vary from individual to individual 

in the species from the Brule formation. In all known 

specimens from the Chadron formation it is well developed and similar in shape and size to that of the 

contemporary daphoenids.

AUDITORY BULLA

Because the auditory cavity is so narrow, the bulla 

is almost triangular. This was determined by care229829—53———2

ful preparation by G. L. Jepsen of the type specimen 

of H.oreodontis, PrincetonMuseum 10515 (fig.5) wlich 

disclosed a considerable portion of the bulla including 

the rim around the external auditory meatus, and the 

anterior and medial wall broken off level with the basioccipital. This wall tapers almost to a point anteromedially and broadens posteriorly. The medial v^all 

is curved and moderately inflated but the floor is flattened giving a pill box shape.

The lateral wall is in reality lateromedial so that the 

meatus faces obliquely forward, directly into the Hse 

of the postglenoid process. The mastoid and postglenoid processes together form a long passageway, 

open ventrally, through which a cartilaginous tuba 

auditiva undoubtedly passed. The connection between 

the exterior of the skull and the sound producing apparatus thus follows a very roundabout route. The 

resonating chamber also is extremely small and vdth 

no extension into the mastoid or paroccipital as in recent 

carnivores such as Ta&idea or Ursus which have a sir all, 

flattened bulla.

THE BASICRANIAL FORAMINA

There is a long alisphenoid canal terminating in a 

foramen rotundum situated at one end of a common 

fossa with the foramen ovale. This relationship is 

precisely that of Canis except that, due to the relative 

shortness of the cranial portion of the skull in Hoplophoneus the fossa extends mediolaterally parallel to 

the base of the postglenoid fossa rather than anteroposteriorly as in Canis.

The postglenoid foramen is large. The posterior 

carotid foramen and the foramen lacerum posterius are 

separate but they are in the same relative position a-* in 

the Canidae and may have been enclosed in a common 

fossa. The condyloid foramen is in the same position 

as in Canis, but is larger.

EUSMILIS 

GENERAL CHARACTERS

The U. S. National Museum specimens of this genus 

have no trace of an auditory bulla. The general aspect 

of the auditory region is like that of Hoplophonwts, 

differing only in the enormous size of the mastoid 

process. In older individuals this process reaches the 

proportions of that of Smilodon, but the difference from 

HoplopJwneus is more than a difference in size. The 

mastoid is falciform with a flattened posterior surface 

inclined obliquely forward. The exoccipital is flattened against the dorsal half of this surface and mr.kes 

a sutural contact with it. There is no distinct paroccipital process. The appearance of the hinder par* of 

the basicranial region resembles that of the bears, 

Hetmcyon, the walrus, and the South American saber-
100 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

tooth marsupial TTiylacosrmlis, and strongly suggests 

that this exaggerated development of the mastoid auditory bulla is determined both by the size of the head and 

the canine teeth.

In a specimen at the South Dakota School of Mines 

(2815), are remnants of a bulla, including the anterolateral wall, the crista tympani and the external auditory meatus. The last is a short tube whose sides are 

made up of the base of the postglenoid process anteriorly, and of the mastoid posteriorly. A flattened projection of the tympanic bridges the space between these 

two processes and forms the floor. The very large 

crista tympani is projected far into the auditory cavity. 

A very peculiar sort of septum is formed by what appears to be an extension of the base of the postglenoid 

process continuous with the roof of the meatus. The 

structures of the middle ear lie above this septum. The 

condition is somewhat similar to that found in Ampkicyon, and also resembles SmUodon, where the bulla is 

divided into upper and lower chambers.

MIDDLE AND INNER EAR STRUCTURE

The promontorium is large and round, and situated 

almost in the center of the auditory cavity. The lateral 

and posterior surfaces are almost vertical. The fenestra 

cochleae lies about midway along the external face. The 

f enestra vestibuli is in the usual position just opposite 

the meatus, slightly anterior of the anterior margin of 

the mastoid process. Just above this opening is the 

minute aperture of the facial canal. The length and 

position of the external part of this canal is determined by the peculiar conformation of the mastoid. A 

deep groove extends from the base of this process to its 

tip. It is parallel to the anterior margin of the process 

and separated from it by only a thin ridge of bone. 

Apparently, the facial nerve and accompanying blood 

vessels leaving the apertura canalis facialis passed 

under the spur of bone from the base of the mastoid 

and from there followed along the groove to the tip of 

the process. This course does not differ in its position 

in relation to the mastoid from that of other carnivores 

but appears to do so because of the size and forward 

inclination of the mastoid process.

The carotid canal is clearly marked by a groove in 

the basioccipital extending anteriorly about to the 

midpoint of the medial margin of the promontorium. 

Apparently the internal carotid artery entered the cranium at that point.

BASICRANIAL FORAMINA

The basicranial foramina are essentially the same in 

number and size as those of Hoplophoneus. There is 

an alisphenoid canal. The foramen ovale and foramen 

rotundmn occupy a large fossa lying obliquely along

the ridge leading to the base of the postglenoid 

peduncle. There is a large postglenoid foramen. The 

posterior carotid foramen is large and lies v?.ry far 

back. It is separate from the foramen lacerum posterius. The condyloid foramen is also separate and 

very large.

PLIOCENE MACHAERODONTS

Two specimens from the Ash Hollow formation of 

Nebraska (one of which is in the Nebraska Str.te Museum and will be described in detail shortly by C. B. 

Schultz, the other in the Frick collection and also to 

be the subject of a detailed paper some time in the 

future), illustrate in an interesting way the further 

evolution of the auditory region in the Eu^miloid 

group.

The specimens consist of two very complete ard wellpreserved skulls and lower jaws with some associated 

skeletal material. They are clearly machairodcnts but 

of a line divergent from the typical Smilodon of the 

Kancho la Brea tar pits. The dentition is of the hoplophonoid type with most of the characteristic features 

developed to a much greater degree than in SirModon. 

As the writer pointed out in an earlier paper (Hough, 

1950), weakness of the lower jaw in the latter seems 

to be a degenerate feature. These specimens not only 

have proportionally more alongate and recurved sabers 

but also strongly developed flanges to the lower jaw 

with flaring lobate margins which closely resemble 

those of the marsupial Thylacosmilis. The reduction 

of the premolars and the enlargement of the carnassial 

has proceeded to such an extent that P4 and Mj are 

the only functional cheek teeth. They extend along 

the entire margin of both jaws and have th°* backward inclination characteristic of the hoplophoneid 

and eusmiloid group. In youth the high croons are 

trilobate and trenchant. Even in old age they remain 

efficient shearing instruments because the occlusal relations are such that the wear is oblique (almost a 

45 degree angle, in fact), and the crowns may 1 3 worn 

to the gums on one margin while retaining a shr.rp cutting edge on the other.

As would be expected, the mastoid processes are 

strongly developed, almost covering the entire auditory 

region. The tympanic bulla is represented by only a 

small swelling on the extreme medial portion of the 

auditory cavity. This cavity is therefore largely excavated in the mastoid, the hypotympanic sinus expending 

far into the mastoid process as in many modern mustelines. The condition parallels that of Smttodon, 

to be described in detail later, but differs enough to 

emphasize the divergence of the lines of descent. (In 

the writer's opinion there were many lines of descent
AUDITORY REGION IN FOSSIL FELIDAE 101

from the widespread hoplophoneid population of the 

early Oligocene.)

The smaller skull, which is also younger geologically 

as it comes from the middle level of the Ash Hollow 

formation, has a shorter upper canine with less curvature and a moderately developed flange to the lower 

jaw. Morris Skinner, who collected the specimen, rec9fearn

SMILODON

GENERAL CHARACTERS

The auditory region of the well-known Pleistocene 

saber tooth from the Eancho la Brea Tar pits has been 

fully described by Merriam and Stock. The b?sic 

structure is the same as in Hoplophoneus, but this similarity is masked by the enormous development of the

FIGURE 6.—Smilodun californicus Merriam, Chicago Natural History 

Museum 12409 ; ventral view of auditory bulla, X 1. Anterior at top, 

median side at right.

FIGURE 7.—Smilodon californicus Merriam, Chicago Natural History 

Museum 12563; section through auditory region to show horizontal 

septum, X 1. Anterior at top, median side at right.

ao auditory ossicle fenr

b bulla, remnant flm

ce cartilaginous entotympanic fl.p

earn external auditory meatus fr

eb entotympanic part of bulla fs

eo exoccipital gcc

fc condyloid foramen gf

fenc fenestra cochlaeae mp

Symbols used on figures

fenestra rotundum pp

foramen lacerum medius p

foramen lacerum posterius rs

foramen rotundum s

stylomastoid foramen tb

groove for carotid canal tm 

glenoid fossa

mastoid process tr

paroccipital process

promontorium

radiating septae

major septum

tympanic bulla

remnant of inbent margin of

tympanic 

tympanic ring

ogiiized its transitional nature. This is confirmed by 

the auditory region. The mastoid is less markedly developed along the posterior margin of the basicranial 

region and much less extended over the auditory cavity. 

The tympanic bulla is large for a machairodont and 

highly inflated, especially dorsoventrally. There is 

apparently little extension of the hypotympanic sinus 

into the mastoid process, although this point requires 

further investigation.

mastoid processes, which are the most conspicuous external features of the basicranium (figs. 6, 7). In 

some specimens this overgrowth of the mastoid process 

is so great that it completely bridges the external auditory meatus and is in contact with the base of the postglenoid process. In almost all specimens the breadth 

aiiteromedially equals that of 'the auditory bulla. In 

fact, as Merriam and Stock point out (Merriam z.nd 

Stock, 1932), in many skulls the bullae appear as slight
102 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

swellings on the inner side of the heavy mastoid. In 

only one specimen described by them (University of 

California, no. 11256) and a few immature skulls examined by the writer is the bulla larger than the 

mastoid.

The paroccipital forms a distinct leaflike process that 

projects backward much as in Hoplophoneus and not 

like that of EusmUis.

INTERNAL STRUCTURE OF THE AUDITORY BULLA

The tympanic itself is flask shaped, with a long tubular meatus similar to that of Hyaena. In the majority 

of skulls it is highly inflated and has a steep medial 

wall. The auditory meatus is roofed by the squamosal, 

which also forms the anterior wall. The posterior wall 

is formed of the mastoid. In specimens in which the 

mastoid does not come in contact with the postglenoid 

process the floor is formed of a narrow wedge of the 

tympanic. This wedge becomes narrower but persists 

even if completely covered over by the mastoid.

The cavity of the bulla is divided by a septum which 

is not, however, in the same position as that of Felis, and 

in the writer's opinion is not a septum bullae. The 

septum in Snulodon is a horizontal sheet of bone dividing the bulla into dorsal and ventral parts. The 

dorsal or upper chamber is the smaller. The hypotympanic sinus is almost entirely dorsal of the cavum tympani and continues into the paroccipital. The much 

more extensive ventral chamber containing the acous-. 

tic portion of the ear extends from the foramen lacerum 

medium to the base of the paroccipital process and 

extends laterally into the mastoid process, which is 

hollowed out and lined with the tympanic. Merriam 

and Stock describe essentially the same condition. 

They term the two divisions the outer and inner chamber. The ventral chamber, however, is "outer" only 

anteriorly, where of course it communicates with the 

external auditory meatus. On the other hand, the 

"inner" chamber of Merriam and Stock extends forward, beyond the ectotympanic chamber not only medial to, but actually above that chamber. It is topographically more accurate, therefore, to term the two 

divisions upper and lower.

The lower or tympanic chamber extends medially to 

cover all of the petrosal except a small portion of the 

promontorium just around the fenestra cochleae. Just 

below the promontorium at this point a narrow slitlike aperture provides communication with the upper 

chamber. From the inner roof of the latter several 

ridges radiate to the lateral margins. In many specimens one of these is strongly enough developed virtually to divide the chamber into an outer and inner 

portion.

THE STRUCTURE OF THE MIDDLE AND INNER TAR

The external auditory meatus extends very far into 

the tympanic cavity. It is a narrow tube with a very 

thick floor formed, as stated before, of a thin TFedge of 

the tympanic underlain by the mastoid. The external 

opening is very far forward. From this the meatus 

slants posteriorly and dorsally. The crista tympani is 

thus obliquely placed, the lowest part being ju^t opposite the internal opening of the Eustachian tube. Thereis no extension of the hypotympanic sinus along the 

sides of the meatus. The dorsal chamber, however, 

extends above the meatus for almost its entire, length.

The promontorium is large and broadly oval. It 

slopes gradually and equally in all directions. The 

fenestra cochleae is also large and round, and faces 

posterolaterally. Because the septum lies just above 

and anterior to the fenestra, it opens into the ventral 

chamber.

The fenestra vestibula faces anterolaterally. Lateral and anterior of it is the very large fossa for the 

tensor tympani. The epitympanic recess is deep, extending well under the roof of the meatus. A short 

sulcus facialis extends from- the fenestra vesfibuli to 

the base of the ridge leading downward and somewhat 

laterally to the stylomastoid foramen. This foramen 

lies far forward because of the extreme anterior extension of the mastoid process. A ridge along the anterior 

margin of the mastoid process is pierced by a cr.nal that 

evidently formed the bony third part of the facial 

canal, which is thus almost vertical.

BASICRANIAL FORMINA

There is no alisphenoid canal. The poefcglenoid 

foramen, which varies in size but is minute in some 

specimens, is entirely hidden by the coalescence of the 

mastoid and postglenoid processes. The condyloid 

foramen and the foramen lacerum posterius are somewhat separate, but connected by a common groove. 

The degree of separation is varied. In some skulls 

the two foramina are about as close together as those of 

the lion and tiger and may be said to have a common 

opening. In others they are as far apart as ir the dog 

and the groove connecting them is shallow. It is interesting that in the true felid, Panthera atrox contemporary with Smilodon, the two are well separated. 

Merriam and Stock report that only 4 or 5 of a total of 

20 specimens have a condition resembling that of Felis.

The carotid canal was not conspicuous in any of the 

skulls examined by the writer and Merriam and Stock 

do not describe it although the position is indicated in 

one of their illustrations (1934, pi. 15, fig. 1). The 

carotid artery was evidently minute in relation to the 

size of the size of the head in fact, possibly degenerated
AUDITORY REGION IN FOSSIL FELIDAE 103

beyond that of Felis. The posterior carotid foramen 

opens into a common fossa with the foramen lacerum 

posterius and is also inconspicuous.

SUBFAMILY NIMRAVINAE 

DINICTIS (OLIGOCENE SPECIES)

EXTERNAL CHARACTERS

Many specimens of Dinictis, like those of Hoplophoneus, have no bulla. There are more, however, in 

which parts of the bulla are preserved, and in all cases 

these specimens are also more complete otherwise. In 

the skull of a young individual of Dinictis, U.S.N.M. 

15889, collected from Niobrara County, Wyo., almost 

the entire anterior part of the bulla is intact (fig. 8), 

An American Museum specimen, figured by Matthew 

(1910) as Dinictis squ-alidens Cope also has a wellpreserved auditory region with enough of the bulla to 

show clearly its shape and size.

The parts of the bulla that remain do not in any way 

correspond to the anterior chamber of the bulla of the 

recent Felidae. In the National Museum specimen, for 

example, the anterior portion of the bulla on the left 

side extends in contact with the basisphenoid about 

halfway along the medial margin of that bone. No 

flattening or differentiation distinguishes this medial 

portion of the bulla from that immediately surrounding the auditory meatus. On the right side only a circular rim of bone around the auditory meatus remains. 

The broken edge is irregular and there is no trace of a 

septum.

Impressions on the overlying bones, and also the portions which remain, show that the bulla in Dimctis 

must have been very large and well inflated. It extended from a point well beyond the base of the postglenoid process anteriorly, almost to the edge of the 

skull laterally and posteriorly to the base of the paroccipital process. The inflation was even, giving the 

bulla a globular shape similar to that of the modern 

Canidae.

The external auditory meatus faces laterally and only 

slightly forward differing markedly from Eoplophoneus in this respect. It is oval in outline and 

formed almost entirely of the tympanic. The two legs 

are almost in contact across the roof excluding the 

squamosal. The mastoid process, although more prominent than in the living Canidae and Felidae, is small 

compared to that HoplopJioneus- It consists of a 

rugose knob of a size usual for Procyon.

The paroccipital process projects backward as a flattened, triangular lobe very like that of Daphoneus.

INTERNAL STRUCTURE OF THE BTTLLA AND MIDDLE EAR

The auditory cavity proper is shallow, as is usual in 

dinictids, and in contrast to HoplopJioneus. The an229929—53———3

terior part is roofed by an extension of the alisphen oid 

that meets the basisphenoid laterally and is in contact 

with the promontorium by a narrow process. From 

the aiiteromedian corner a ridge runs parallel to the 

raised rim of the basisphenoid. Lateral to this, a 

groove marks the position of the Eustachian tube, and 

medially a similar groove leads into a large open space 

between the posterior margin of the alisphenoid and 

promontorium. This condition is unlike that of either 

the Canidae or Felidae where the alisphenoid meets 

the base of the promontorium and completely roofs 

the cavity, somewhat as in the Ursidae.

The epitympanic recess is relatively shallow and does 

not extend far under the meatus. There is a conspicuous fossa in the squamosal just anterior of the base 

of the mastoid process. This is somewhat similar to 

the suprameatal fossa of the Procynidae but it is deeper, 

and more medial and posterior in position.

The promontorium is pear-shaped, much as in 

Daphoemis. The fenestra vestibuli is small and faces 

laterally. A narrow spur bridges the space between 

this and the mastoid. Along this a groove passes f:~om 

the fenestra vestibuli to the large round foramen stylomastoideum primitivum. From this a wider groove 

deeply excavated in the knob like mastoid continues 

obliquely downward and slightly forward along the 

peduncle to its tip. This groove undoubtedly is the 

external part of the facial canal and marks the exit 

of the facial nerve from the skull.

The fenestra cochlaeae faces postero-laterally and is 

located very far back—again a similarity to Daph-oenus.

BASICRANIAL FORAMINA

An alisphenoid canal, whose posterior opening is in 

a common fossa with the foramen ovale, is present. 

The position of this fossa is much as in Hoplophoneus, 

that is, just medial to, and on a line with, the anterior 

rim of the glenoid fossa. There is a large postglenoid 

foramen. The carotid canal lies in a distinct groove 

in the basioccipital extending from the foramen lacerum medium to the posterior medial corner of the 

bulla. The medial margin of the promontorium meets 

a process from the basioccipital which forms a roof 

for this canal for a short distance. The posterior carotid foramen is at the extreme postero-medial corner 

of the bulla. Just adjacent to it but entirely separate 

is the foramen lacerum posterius. The condyloid foramen is large and situated just behind and slightly 

medial to the depression in the rim of the auditory cavity, which, when the bulla was present, marked the 

common exit of the foramen lacerum posterius and the 

posterior carotid foramen.
104 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

mp

PP

enc

•flP

FIGURE 8.—Dinlctis felina Leidy, F. S. National Museum 15889 ; a young individual,
AUDITORY REGION IN FOSSIL FELIDAE 105

FIGURE 9.—Dinictis cyclops (Cope), U. S. National Museum 16558, XL

DINICTIS CYCLOPS COPE (JOHN DAY SPECIES)

The matrix has not been removed from the remnants 

of the large completely ossified bulla which was evidently present in the type specimen, American Museum 

of National History 6930. Further preparation, which 

would remove the cast of the interior of the bulla

formed by the matrix, did not seem necessary as a skull 

in the National Museum (16558) from the same locality 

also has the floor of the bulla broken away but with no 

hard matrix, so that the overlying well-preserved 

structure is exposed (fig. 9). This is closely similar 

to that of the White Kiver dinictids, except in two
106 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

very significant respects. The roof is more completely 

ossified, with the alisphenoid meeting the base of the 

promontorium laterally and forming the anterior margin of the large foramen lacermn medium medially. 

More important still, there appears to be a trace of a 

septum bullae. This is actually represented by only a 

low broken ridge, but it is in the same position as that of 

Fells and the anteroexternal surface of the promontorium is flattened and grooved in such a way as to 

indicate strongly the presence of a well-developed 

anterior chamber. If this interpretation is correct, 

however, the chamber was relatively large and well 

inflated, similar to that of Felis rather than of PanThe basicranial foramina present no significant 

change from the condition in the Oligocene genera. 

There is an alisphenoid canal with a large foramen 

rotundum transversely placed. The postglenoid foramen is unusually large. The condyloid foramen is also 

large and well separated from the foramen lacermn 

posterius.

The posterior carotid foramen is large and, although 

posterior in position, is separate from the foramen lacermn posterius. The carotid canal is represented by a 

deep groove extending directly forward from the posterior carotid foramen, along the medial margin of the 

promontorium, to the foramen lacerum medium.

NIMRAVVS

The auditory region of the White River species, 

Nimravus bumpensis does not differ in any important 

respect from that of Dinictis except that the bulla, 

judging from the portion which remains in the type 

specimen and the cast of the interior of the bulla present 

on one side, was smaller and less inflated. The basicranial foramina are the same in size, number and arrangement.

The John Day species Nimravus gomphodus and 

Nimramis (Archaehims) debilis have remnants of a 

highly inflated, well rounded bulla. These remnants in 

Nimravus debilis consist of a broad circle of bone 

around each auditory meatus. In shape and symmetry 

they strongly suggest an anterior chamber. There is no 

trace of a septum so that if a division of the bulla existed in these early forms the septum must have been one 

that did not reach the roof of the auditory chamber. 

Moreover, if an anteroexternal chamber existed, it was 

relatively large and highly inflated as in most species 

of Felis. This is in contrast to the Pseudaelurinae.

SUBFAMILY PSEUDAELURINAE 

AMERICAN GENERA

The auditory region of Pseudaelui^us intrepid us has 

been admirably described by Stock (1934, pp. 1052-

1053). This description is summarized here, with a 

few notes for the sake of comparison.

The bulla, which although completely ossified is small, 

is divided into two externally visible chambers. The 

anterior chamber is much the smaller and very much 

flattened, as in Panthera and certain tropical species of 

Felis. The posterior portion is globular, very much 

higher than the anterior, and has a steeply sloping medial wall. The auditory meatus is triangular, with no 

lip or tubular prolongation. The anterior wall is in 

contact with the base of the postglenoid process. The 

posterior wall meets the mastoid process. The floor of 

the meatus appears to be composed only of the squamosal.

The mastoid process is but little developed and entirely separate from the paroccipital process. The 

latter is a triangular flattened lobe that is directed 

backward much as in Daplwenus.

Compared with the small size of the bullae, the basioccipital region between them appears very broad.

The cranial foramina are transitional. There is an 

alisphenoid canal. The postglenoid foramen seems to 

have been very minute. (This part of the skull is 

crushed so that the size and position could not be exactly ascertained.) The posterior lacerate foramen is 

large and well removed from the condyloid foramen. 

The carotid canal could not be traced but the posterior 

carotid foramen apparently opened into the foramen 

lacerum posterius.

ASIATIC AND EUROPEAN GENERA

M'etailw^us of the upper Miocene of China, as described by Teilhard de Chardin (1945) has an auditory 

region closely similar to that of Pseudaelwms. The 

bulla is two chambered, with the anterior external 

chamber much the smaller and flattened, and the posterior chamber globular much like that of Felis.

Therailurus from the Pliocene of France (Eiviteau, 

1931) also has a flattened anterior chamber to the bulla, 

but this is much smaller in relation to the highly inflated 

posterior chamber than in Metallurus.

In both Metdihirus and Therailurus^ however, the 

basicranial foramina show a notable advance in a feloid 

direction. There is no postglenoid foramen, no alisphenoid canal and the carotid and condylar foramina 

are closely connected with the foramen lacerum posterius.

SUMMARY AND CONCLUSIONS

Two facts stand out clearly from the foregoing descriptions :

1. The auditory region in the Oligocene Felidae is 

distinctly canoid both in the absence of a septum bullae
AUDITORY REGION IN FOSSIL FEUDAE 107

and in the form, number, and position of the basicranial 

foramina.

2. The auditory region in the post-Oligocene Felidae 

(Machaerodonts as well as true felines) has the diagnostic characters of the Feloidea.

So impressed was Teilhard de Chardin with this distinction that he based his classification upon it, but 

without any phylogenetic implications, as he expressly 

states. The Oligocene Felidae, the Paleofelides of his 

classification, are sharply separated from the postOligocene Neofelides. These two major categories are 

subdivided into normal and saber-tooth types. This 

arrangement, especially when presented in diagrammatic form, brings out forcibly the parallelism which is 

such an essential feature of the family, but leaves the 

phylogenetic relationships very much in doubt. (It 

also does not express the parallelism with entire correctness, since there are both saber-tooth and normal type 

canines in the Nimravinae and Pseudaelurinae.)

The Asiatic record, with which Teilhard's classification is primarily concerned, commences with the Miocene. As he points out no "primitive" Oligocene cats 

are found in China, even in otherwise richly fossiliferous beds of that age. The situation in North America 

is quite different. The Oligocene record of the family 

is well documented and, although few Miocene and Pliocene specimens are known at the present time, they provide a series of transitional forms linking the early 

Machaerodonts with the Pleistocene /Smilodon, and the 

Nimravinae with the Felinae. It seems reasonable tc 

suppose, therefore, if the currently accepted phylogeny 

of the Felidae first proposed by Matthew (1910) is correct, that an evolution of the auditory bulla toward increasing complexity took place in both subfamilies. In 

the Machaerodonts, a horizontal septum was formed, 

something like that of the Hyaenidae, dividing the cavity of the bulla into a lower, anterior chamber and an 

upper, posterior chamber. In addition, radiating rafters and septae complicate the walls of the posterior 

chamber, much as in certain modern mustelines such as 

the wolverine.

In the Felinae, the septum was formed in the posir 

tion of that of Fells but was at first an incomplete septum similar to that found in certain of the Canidae. 

Increasing ossification in this region produced a complete septum that divided the bulla into the typical 

anterolateral and posteromedial chambers.

The basicranial foramina underwent a transformation as the venous and arterial system of the head 

changed from a canoid to a feloid type. This evolution, like that of the septum bullae, was a gradual thing 

that first developed to different degrees in individuals 

and was only slowly fixed in the entire population.

It is possible, of course, to insist on the rigid homology of the two-chambered bulla and on this basis to 

exclude all of the Oligocene genera, Nimrti'vus and 

Dinictis as well as Hoplophoneus and Eusmttis, from 

the ancestry of the Felinae. Under this hypotl Asis 

such ancestry must be sought in a series entirely independent of the North American fossil forms as we 

know them.

This view has not been without its defenders. Cope 

originally separated all of the fossil Felidae, including 

Pseudaelurus (which, of course, he did not know from 

complete North American specimens) from the modern 

family. The basis for his Nimravidae, as a later discussion made clear, was the nature of the basicranial 

foramina;

Gregory's classification (1939) follows a similar pattern. His section Machaerida apparently includes 

both the Machaerodontinae and the Nimravinae, and 

the evolutionary series he erects, 011 the basis of the 

auditory bulla, consists of Paleoprionodon —>Cryptoprocta -*Felis. Of course, he considered this sequence 

only a morphological series illustrating the postulated 

evolution of the auditory bulla. Nevertheless, if the 

auditory bullae did evolve in this way, the fossil Felidae are automatically excluded from the ancestry of 

FeMs. No known fosil felid has an auditory bulla 

at all resembling that of Cryptoprocta.

Aside from the fact that phylogenies such as these 

do not correspond to the fossil record as we know it 

and ignore the transitional stages between the Fimravinae and Felinae, in the writer's opinion there is 

little in the morphology and embryology of recent 

forms to warrant such a rigid application of the principle of homology. Since, in any case, a transformation of the venous and arterial system of the head must 

have taken place (Paleoprionodon, like all Oligo?ene 

carnivores, has a canoid type of basicranial foramina) 

a review of the whole question seems in order.

HOMOLOGY OF BASICRANIAL FEATURES OF THE 

FELOIDEA

SEPTUM BULLAE

FORM AND POSITION OF THE SEPTUM IN THF 

FELOIDEA

It is well known that the form and position of the 

septum, and. consequently of the two chambers into 

which it divides the bulla, differ very much in the 

Viverridae and Felidae, and even more widely in the 

other families usually included in the Feloidea. In 

the Viverridae the septum, which is really the posterior 

wall of the anterior chamber, is in contact with the 

basisphenoid medially for some distance so that the 

tympanic chamber is entirely anterior in position and
108 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

the eiitotympanic posterior. In the typical Viverridae 

the anterior chamber is always the smaller, and somewhat flattened. The size of the posterior chamber may 

vary, but these relationships remain the same. In the 

Felidae the septum, also the posterior wall of the anterior chamber, has no contact with the basisphenoid, 

but curves posteriorly and laterally from the anteromedial corner of the bulla and meets the crista tympani 

at a point just opposite the stylomastoid foramen. The 

tympanic takes no part, therefore, in the medial wall 

of the bulla which is formed throughout by the entotympanic in contact with the bones of the midline of 

the skull. The chambers formed are anterolateral and 

posteromedial. In the Felinae, as in the Viverridae, 

there is considerable variation in the proportions of the 

two chambers, but the anterior chamber (even if highly 

inflated, as in Felis catus) is always the smaller. In 

Panthera and some of the tropical species of Felis the 

anterior chamber is much flatter and very narrow 

antero-posteriorly.

In Hyaena the principal septum extends lateromedially from a point just opposite the stylomastoid 

foramen across the fenestra cochleae to the medial 

coner of the bulla as in Felis but, since it is a horizontal sheet of bone extending posteriorly almost the 

whole length of the auditory cavity, it divides the bulla 

into a very large anterior ventral chamber, and a much 

smaller posterior upper one. The former is the real 

bulla. The latter is not a separate chamber formed by 

an eiitotympanic, but a cavity in the base of the paroccipital process. Projecting from the horizontal septum there is a ridge somewhat in the position of the 

septum of Canis, but very much shorter in most specimens. It is the greater or lesser development of this 

ridge that gave rise to the various early statements, 

seemingly contradictory, as to the presence or absence 

of septae.

Pocock (1916) sought to homologize the septum in 

Hyaena with that of the Viverridae. No doubt it does 

represent the posterior wall of the tympanic chamber, 

but in this sense it is equally homologous with the posterior wall of the bulla in the Canidae. It is certainly 

not, so far as form and position are concerned, homologous with the septum in either Felis or Viverra.

The structure of the bulla in Proteles is unique, and 

unlike that of either Hyaena or the Felidae, but with 

some points of resemblance to that of the Viverridae. 

The anterior chamber of the bulla is flask-shaped and 

has a long tubular meatus resembling that of many of 

the Mustelidae. It appears complete in itself with a 

well-rounded convex posterior wall. This wall is 

paper-thin and composed entirely of the tympanic. 

The promontorium lies far forward and is completely

fenc

FIGURE 10—Viverrteula indica rasse (Horsfield), U. S. Fational Museum 154917; young individual, X2.

FIGURE 11.—Felis catus Linnaeus, U. S. National Museum 188652, young 

individual, X2.
AUDITORY REGION IN FOSSIL FEIIDAE 109

enclosed by the anterior chamber, the posterior wall 

of the chamber lying posterior of the f enestra cochleae. 

A well-marked sulcus in the periotic, with a raised 

bony rim, extends past the fenestra cochleae and into 

a bony canal between the mastoid process and the posterior chamber. This chamber is an entotympanic ossification, but is not closely homologous with that of 

the Felidae and Viverridae. The anterior wall is applied to the under surface of the anterior chamber and 

united to it by suture. Laterally, there is a suture between the entotympanic and the mastoid which can be 

traced from the posterolateral corner of the auditory 

meatus downward and backward to the posterolateral 

corner of the posterior chamber. At this point it joins 

the paroccipital process—which is very large and leaflike, and forms a deep cup which embraces the posterior 

wall of the bulla. A large part of the lateral wall of 

the bulla is thus formed by the mastoid rather than by 

the entotympanic. Dorsally, the mastoid process is 

hollowed out into a deep rounded cavity. At the antero-medial corner of the posterior chamber a shelf 

is pressed against the posteromedial wall of the anterior chamber. It extends about halfway across the 

cavity of the bulla, swinging around posteriorly to 

merge with the posterior wall. A narrow strip of entotympanic forms the lateral rim of the cavity in the 

mastoid process, but does not floor the cavity. In the 

ventral lateral wall of the posterior chamber a few 

septae radiate from the floor perpendicularly to the 

anterior wall.

MODE OF DEVELOPMENT OF THE BULLA

As would be expected, the differences in the form and 

position of the two chambers of the bulla in the adult 

"aeluroicl" Carnivora are foreshadowed by the differences in the mode of development.

In the Viverridae the anterior (tympanic) chamber 

develops very early and is completely ossified in adult 

form before there is much ossification of the posterior 

(entotympanic) chamber. In a very young individual 

Viv&ricula indica raase (U.S.N.M. 154917, fig. 10), 

whose milk teeth were not erupted, the anterior chamber is completely ossified. It is a horseshoe-shaped 

demi-bulla precisely like that of the fossil forms 

Daphoenus vetus and Paleoprionodon, and of the adult 

Nandinm (a recent South American viverrid in which 

the entotympanic remains cartilaginous throughout 

life). Ossification of the entotympanic takes place 

first along the medial and posterior margins of the 

cartilaginous entotympanic, a strip between these ossifications and the anterior chamber remaining cartilaginous until very late in development. The form of 

the tympanic changes very little. In the earliest stages,

the margins of this chamber are curved upward in such 

a way as to be almost in contact with the promontoriura. 

This incurved margin forms the septum bullae of the 

adult. As the strip dividing the tympanic and entotympanic ossifies, the latter coalesces at the point of 

contact with the septum. A real interior wall to the 

posterior chamber is thus not formed, and the septum 

bullae is not composed strictly (as is sometimes stated) 

by the fusion of two sheets of bone, but of one—the 

tympanic—with only a slight participation of the entotympanic at the extreme ventral border.

In a felid corresponding in age to the specimen of 

Viverricula mentioned above the only ossification of 

the bulla is the tympanic ring, a narrow rim of bone 

encircling the auditory region and lying parallel to 

and slighly above the promontorium. The space enclosed by this ring is very much greater than that enclosed by the anterior chamber in Viverricula. In a 

specimen of Felis catus that died at birth (fig. 11) only 

a very small part of the posteromedial border of the 

promontorium lies outside the tympanic ring. The 

upper margin of the ring is slightly incurved, but is 

not in contact with the basisphenoid or the petrospl. 

As ossification proceeds, the ring becomes filled in ventrally, leaving open the large oval external auditory 

meatus. Simultaneously with this ossification of the 

anterior chamber, ossification also commences from a 

tympanic center. This is at first entirely posterior, bnt 

the growing entotympanic appears to force the original 

tympanic ring downward and forward to an oblique 

position, leaving a wide space filled with cartilage between the medial margin of the tympanic chamber and 

the basisphenoid. This is gradually filled in by bone 

developed, possibly, from both centers to form the 

medial border of the posteromedial chamber. There 

is no stage in Felis where the tympanic forms a complete chamber as in Vivemcula, with the entotympanic 

cartilaginous.

At birth the auditory region of Ccmis is strikingly 

similar to that of Felis—much more than the auditory 

region of Felis resembles that of any viverroid studied. 

There is an ossified ring present in Ccmis in essentially 

the same position as that of Felis, but it is flatter and 

crosses the promontorium dorsal and posterior to the 

ventral rim of the fenestra cochleae. In a specimen of 

Canis dingo which died at birth only the faintest rim 

of the posterior part of the auditory region is not encircled by the tympanic ring (fig. 12). In Canis as in 

Felix this ring shifts forward and downward as further 

ossification takes place. This shift is very much less 

in all cases than in Felis, but varies according to the 

size and degree of the inflation of the fully developed 

bulla. The part anterior and ventral to the tympanic
110 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

ring is formed by an outgrowth of ossification filling 

in the space enclosed by the ring—except the auditory 

meatus. Posteriorly, ossification takes place from cartilage as in the formation of the entotympanic in FeUs 

(fig. 11). However, this proceeds simultaneously with 

the growth of the tympanic anteriorly and the two 

fuse indistinguishably without forming a complete septum or separate chambers.

Van der Klaauw (1931, p. 277) states that an entotympanic is developed in cartilage in Canis, but seems 

to ossify out of the tympanic ring making the bulla 

simple and seemingly formed by the tympanic alone.

fenc

FIGURE 12.—Canis dingo Meyer, U. S. National Museum 8742, at 

birth, X5.

On a later page, however, he warns against. homologizing the faint line which crosses the bulla in Cams in 

very much the same position as a similar one in Felis 

marking the division between the tympanic and entotympanic. The former he says marks the position of 

the septum in Cams and so has nothing to do with the 

similar line in Felis because the septum of Canis is not 

homologous with the septum in Felis. This seems a 

very confusing statement. The fact is that the line on 

the bulla in Canis does mark the division between the 

tympanic and entotympanic, that is, the position of the 

original tympanic ring, just as it does in Felis. The 

margins of this ring in Canis, however, are not incurved 

even originally to the same degree as in Felis and further ossification in that direction does not take place so

no septum is formed from the tympanic. The, partial 

septum found in some Canidae is a later development 

formed entirely by the inbent .margin of tl °- entotympanic. It is not homologous in the strict ontogenetic sense with that of Felis, since the septum in Felis 

is formed from both the tympanic and entotympanic, 

but neither does it correspond to the septae and rafter 

which radiate from the crista tympani in sucl mustelids as the wolverine. All of these forms, however, 

have this in common: The septae formed are neomorphs ossifying from membrane relatively late in 

ontogeny, and probably late phylogenetically as well. 

In the Viverridae, on the other hand, the posterior wall 

of the anterior chamber ossifies very early and a complete anterior chamber is formed before any ossification 

commences in the entotympanic cartilage. Ar will be 

shown, this also agrees well with the probable phylogenetic history of the bulla in the Viverridae.

BASICBANIAL FORAMINA

In all mammalian embryos, including that of man, 

there is a large postglenoid foramen. Intracranial 

blood is carried from the skull largely by the internal 

jugular. In some orders, notably the Artiodaciyla, this 

is also true of the adult—the postglenoid foremen in 

the adult is enormous, and the external jugular the sole 

vein leading from the cranium. In man, an opposite 

development takes place; the postglenoid foramen 

closes shortly before birth, the external jugular atrophies, and the lateral cranial sinus is drained by the 

internal jugular, which leaves the skull through the 

large foramen lacerum posterius.

In all adult Carnivora there is some modification of 

the embryonic condition. This is relatively, slight in 

the Arctoidea, somewhat greater in the Canidae, and 

in the Felidae and Viverridae parallels the condition in 

man.

Similarly, there are changes in the cranial arterial 

system from the embryo to the adult. These, however, 

are not inevitably linked with the venous changes, but 

can occur independently. In man, (where tli°, venous 

system is extensively modified in the adult) the internal 

carotid, which is a large and important artery in the 

foetus, remains so throughout life. In the Arctoid 

Carnivora (Ursidae, Procyonidae, Mustelidr^) also, 

the internal carotid artery is large and conspicuous in 

the adult (half the diameter of the external carotid) 

with a strongly developed bony canal and a Is rge conspicuous posterior carotid foramen. Because the 

venous system in this group also retains much of the 

embryonic condition and the internal jugular is relatively small in size the foramen lacerum posterius is not
AUDITORY REGION IN FOSSIL FELIDAE 11

FIGURE 13.—Vulpea velox Frisch, U. S. National Museum 25425, young individual, X2.

exceptionally large and does not conceal the condyloid 

foramen.

In the Felidae, both the venous and arterial systems 

are profoundly modified in the adult. The internal 

carotid artery becomes vestigal, in the domestic cat 

imperforate throughout most of its length. The ascending pharyngeal (a branch of the external carotid) 

takes over the intracranial portion of the circulation. 

This degeneration of the internal carotid reaches its 

extreme in the domestic cat. In Panthera, however 

(Davis and Story, 1943), the internal carotid although 

minute in size, is perforate at least for some distance 

beyond its origin. It passes through the middle ear 

in the normal way, enters the foramen lacerum medium 

and anastomoses with the circle of Willis. This is in 

contrast with the condition in the domestic cat where 

the ascending pharyngeal is the dominant vessel beyond 

the foramen lacerum medium.

The Viverridae, although tending in the same direction as the Felidae (the reduction of the internal carotid) , achieves this in a different manner, and to different

degrees in the various genera. In Nandinia, according to Davis and Story (1943) the internal carotid is 

a relatively slender vessel, and it is described by Tandler 

(1906) as considerably weaker than the external carotid. In Herpestes on the other hand, the caliber is 

about the same proportionally as in the Arctoid 

Carnivora, but the canal is extremely short. In all of 

the Viverridae (except Nandvrda, where the bulla is 

incompletely ossified), there is a well-developed bony 

canal similar to that of the Mustelidae, and a conspicuous posterior carotid foramen situated very anteriorly.

The changes in the venous system in the Viverridae 

have proceeded much further. Virtually all of the 

genera usually included in this family even aberrant 

forms such as Cryptoprocta and Hyaena have a minute 

postglenoid foramen and a small concealed condyloid 

foramen.

The Canidae have some characteristics that ally them 

with the Arctoidea, some with the Feloidea. The 

venous system is entirely "arctoid," with a large postglenoid foramen and conspicuous condyloid foramen.
112 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

The internal carotid is also well developed, but the 

course of the artery and the structure of the canal resemble that of the Felidae rather than that of the 

Mustelidae, Procyonidae or Ursidae. There is no bony 

canal formed of the tympanic. Instead the artery runs 

forward to the foramen lacerum medium through a 

groove formed of the periotic and the inbent margin of 

the tympanic. The posterior carotid foramen is concealed in a common fossa with the foramen lacerum 

posterius.

SUMMARY AND CONCLUSIONS 

EVOLUTION OF THE INTRACRANIAL CIRCULATION

As is pointed out above, all Oligocene Carnivora 

have a "canoid" type of cranial circulation. Even 

such forms as Paleoprionodon, which have been considered ancestral "feloids" because of the demi-bulla 

and viverroid features of the dentition, have a postglenoid foramen and a large unconcealed condyloid 

foramen. A transformation of the cranial circulation 

from the "canoid" to the "feloid" type must therefore 

have taken place—unless one is to consider the Felidae 

to have been created at the beginning of the Miocene.

As a m'atter of fact, the stages in this transformation 

are well shown by the North American specimens of 

fossil Felidae. Pseudaelurus is a perfect intermediate 

form, in these respects, between Nimravus and the 

Felinae. When the basicranial region of various other 

American pseudaelurines becomes known, still other 

stages will probably be demonstrated. It is possible, 

for example, that AdelpJiailurus (now known only from 

an incomplete skull) had somewhat the same combination of features as Metailurus of China, or Therailunis 

of the Pliocene of France, that is, no postglenoid foramen and no alisphenoid canal, a large condyloid foramen, and well-defined carotid canal with the posterior 

carotid foramen distinct from the foramen lacerum 

posterius.

The machaerodonts show a similar evolution. As 

there is good evidence that this group was distinct from 

the Nimravinae as far back as the early Oligocene, 

these changes must have proceeded independently in 

the two lines. The degeneration of the carotid artery 

seems to have taken place at a faster rate than in the 

Felinae. The union of the posterior carotid foramen 

with the posterior lacerate foramen is more complete 

and more constant in Smilodon than in Fells atrox. 

It is important to note that in both these genera, known 

from hundreds of specimens, the extreme condition, 

either way, exists as an individual variation. It seems 

probable, therefore, that all of these changes began 

as individual differences and that evolution to the

modern type consisted in the gradual fixation of such 

random variations.

This is entirely in accord with the arrangement of 

the foramina as they actually occur in the living members of the Feloidea. There is not a feloid "type". 

The changes in the venous and arterial system occur in 

different combinations and to different degrees not only 

as between the Viverridae and Felidae, but among the 

genera that comprise the respective families The 

similarity of arrangement, therefore, is far better interpreted as progressive evolution taking place independently in various vertical lines of descent, rather 

than a phenomenon linked with phyletic branching.

EVOLUTION OF THE AUDITORY BULLA

The evolution of the auditory bullae in the Felidae 

presents a more difficult problem than that of the basicranial foramina, partly because of the imperfect 

preservation of the bulla in all Oligocene felids and 

partly because of the universal belief, amounting almost to dogma, in the strict homology of tH twochambered bulla.

However, it is seen from the foregoing dircussion 

that there is no close correspondence in detail in the 

form and position of the septum which divides the 

bulla into two chambers in the Viverridae and Felidae— 

to say nothing of the Hyaenidae and Proteles. Furthermore, the mode of formation of the two chambers 

in the Felidae differs as much from that of the Viverridae as from that of the Canidae. The similarly which 

exists (the formation in the adult of two complete 

chambers) is an end result rather than a step-by-step 

correspondence in detail. In fact, the early stages in 

the formation of the bulla in the Felidae resemble 

those of the Canidae more closely than those of the 

Canidae do these of the Viverride. The Canidae, in 

turn, differ from other "canoid" carnivores in having 

an entotympanic center of ossification.

A demi-bulla of the type found in the recert Nandinia was undoubtedly "primitive" for all of the Viverridae. Gregory's assumption that Viverravus mirwtus 

has such a bulla is based on an erroneous interpretation 

of a figure of Teilhard de Chardin (1914-1915, pi. 9, fig. 

10). This figure and the description, and slso an 

examination of the specimen of Viverravus iri the 

American Museum collection show that the structure 

in question is the promontorium. The bulla in Viverrawus, as in all miacids, was unossified. Nevertheless, 

the general idea is apparently correct. The Viverridae did originate from various miacid populations 

(probably in different places and at slightly different 

times) and, the writer believes, had a demi-bnlla of
AUDITORY REGION IN FOSSIL FEUEDAE 113

this type from the beginning. Possibly there never 

was a central type at any time, and such universally 

recognized genera as Prionodon, Herpestes, Viverra. 

Arctictis etc. are each the result of the separate developof a vertical cline.

There is absolutely no paleontological evidence that 

this kind of demi-bulla was primitive for the Felidae. 

Both the Machaerodontinae and the Nimravinae are as 

old, if not older, than the Viverridae. The earliest 

Oligocene representatives of both the former are highly 

specialized animals. Even supposing a common origin 

with the other Carnivora, from a miacid ancestry 

(which the writer considers doubtful, at least for the 

Machaerodontinae), a long period of progressive evolution separates Hoplophomus, Dinictis, and Nimraviis 

from Viverravu-s or PaJeoprionodon or any form conceivably included in the Viverridae.

Incomplete though the bullae are in the known specimens of Oligocene felids, to anyone who has studied 

the auditory region in these forms the evidence is indisputable that the structure was simple and without a 

septum—certainly not a demi-bulla of the Daphoenu>s 

type. Therefore, it seems probable that the bullae 

evolved in the direction of increasing complexity, 

which improved the efficiency of hearing in both lines 

of descent, in various populations at various times, in 

various places. Since there was apparently more migration and consequent interchange of genes than in 

the Viverridae, this evolution was more universal and 

produced the uniformity of type so characteristic of 

later members of the phyla. This is in accord with 

the known fossil record and with the size, structure, and 

habits of the animals.

PROPOSED TAXONOMIC CHANGES

In accordance with the views expressed in this paper, 

the following modification and redefinition of the major 

taxonomic categories of the Carnivora are proposed. 

It is not supposed by the writer that this revision represents the final word on the subject. Criticism and suggestions are invited. An attempt has been made, however, to provide a basis for division into superfamilies 

that will be consistent with the morphology of the 

forms and their geologic history, in so far as that is 

known. The superfamily divisions in current use are 

especially objectionable because they cannot be properly defined, and also because, having been based originally on modern forms, they have an archetypal significance which, when extended to extinct forms readily 

lends itself to "proof" of erroneous theories of evolution.

SUMMARY OF SUPERFAMILIES AND FAMILIES

Machairodontoidea 

Hoplophoneidae 

Eusmilidae 

Machairodontidae

Diagnosis—This superfamily would include all of the 

genera listed by Simpson for the Machairodontinae, as 

well as the new forms from the Ash Hollow formation 

which are mentioned in this paper. The evidence supporting the separation of this group from the Felidae 

seems to the writer indisputable. Numerous features 

of the skull, dentition, and skeleton reveal its unity and 

its divergence from other carnivore groups. Of these 

features the most important are:

1. The size and function of the incisors, which 

throughout the history of the group remain stout gracing teeth.

2. The tendency toward the reduction of the lowQ/r 

canine, which in its most extreme development becomes 

incisoriform and no longer shears against the upper 

canine.

3. The high degree of carnassialization. Even in the 

earliest representatives of the group this is more extreme than in any of the true Felidae, and is unique 

among the Carnivora in the part played by P3. This 

tooth never has the grasping function it has in the 

Felidae, but is a shearing tooth acting with the rnsvin 

carnassial, P4. In the Ash Hollow specimens P* is 

enormously enlarged and elongate while P3 is lost 

altogether.

4. The backward inclination and peculiar growth pattern of the carnassials, which causes the wear of these 

teeth to be oblique and maintain a cutting edge even in 

old rage.

5. The size, form, and function of the upper canine, 

which is not only always extremely long in proportion 

to the skull and has a broader basal diameter than in any 

f elid, but is also more compressed and recurved.

6. The retention of primitive features, such as the 

small brain case and pronounced postorbital constriction, even in the Pleistocene members of the group.

7. The auditory region which, even in primitive mem 

bers, differs in its narrowness, depth, and the position of 

the tympanic bulla from that of the contemporary 

Dinictis. Compare, for example, figures 5 and 6, where 

the remnants of the tympanic bulla clearly show a large 

inflated structure in Dinictis and a compressed one in 

Hoplophonem. In later forms this is fused with, and 

overgrown by the mastoid. In Dinictis and Hoplophoneus, additional resonating chambers are produced, 

not by the development of a large inflated tympanic 

bulla as in the Felidae, but by excavation of the mastcid 

process. Septae, if formed, are radiating or horizcn-
114 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1952

tal and do not truly divide the bulla into tympanic and 

entotympanic chambers.

These characters, together with features of the skeleton too numerous to mention here, but which have been 

described in an earlier paper (Hough, 1950), seem sufficient justification for separation from the Felidae. 

In addition, that there is no evidence—only purely hypothetical considerations—that the machairodonts had 

a common ancestry with the Felidae, and certainly no 

evidence that any genera of the group entered into the 

composition of the modern family. In popular terms, 

the early machairodonts were not cats, nor did their 

descendants become cats in the strict sense of the word. 

They were throughout their history pseudo-felines, a 

primitive group, evidently world-wide in distribution 

judging from the known occurrences, which paralleled 

the true Felidae—but very remotely—in some features 

and which successfully over some 22,000,000 years filled 

an ecological niche similar to that now occupied by the 

modern cat family.

It is the geological long range, and the ubiquity and 

diversity, which provide the justification for the superfamily rank. Hoplophoneus, EusmMis^ and Smilodon 

(to name only the typical North American genera), although possessing the common characters listed above, 

differ pronouncedly from each other in ways which make 

ancestral relationships difficult to trace, from the known 

forms at least. This diversity, which is a matter of 

combination of characters rather than a marked divergence of any one, points to a common ancestry either 

very remote or not very unified, that is, from different 

species or even different genera, rather than from one 

interbreeding population. It is also probably that the 

sample known is small in relation to the actual number 

of genera and species which at one time existed.

Aeluroidea (or Herpestoidea, if strict rules of nomenclature are followed)

Daphoenidae

Viverridae

? Hyaenidae

Diagnosis.—Bulla always two-chambered with the 

entotympanic cartilaginous in the early forms (Daphoenidae) . Basicranial foramina canoid in Oligocene 

genera, postglenoid and condyloid foramina reduced in 

all later forms; carotid canal well-developed in all 

genera that have a completely ossified bulla; posterior 

carotid foramen large and anteriorly placed.

Discussion.—This is the most certain and stable of 

the categories. Known as early as the earliest Oligocene, or even perhaps latest Eocene of the Phosphorite 

beds of Quercy, France, the phylum has retained the 

same type of auditory bulla and the same trends in the 

evolution of the dentition throughout its history. The

inclusion of the Hyaenidae is questioned because of the 

lack of knowledge of the auditory region in Ictithermm 

and in other early representatives that could bo transitional between Hyaena and the more typical Viverridae.

Cyno-feloidea 

Canidae 

Felidae

Nimravinae

Felinae

Diagnosis.—Canidae and Felidae representing two 

diverging branches, one retaining the primitive condition of the undivided bulla with at most a partial septum, the other early developing a rudimentary septum 

which in later forms becomes complete, dividing the cavity of the bulla into two chambers. Basicranial foramina but little modified from the embryonic condition in 

the Canidae and early Felidae (Nimravinae); in the 

later Felidae becoming highly specialized with the complete closure before birth of the postglenoid foramen 

and atrophy of the internal carotid artery.

Dismission.—This is the most radical change proposed and will seem at first thought to be without 

foundation. Modern Canidae and Felidae, however, 

have more characters in common than usually recognized. Neither have any close affinity with ary other 

family—common opinion notwithstanding. Both 

families are highly specialized for their particular 

habits of life in all features of the dentition aid skeleton. Carnassialization in both has been brought to a 

high degree of perfection, in the Canidae in conjunction with an equally effective crushing dentition, in 

the Felidae with all functions of the teeth sacrificed to 

that of shearing flesh. The Canidae are strictly cursorial; the Felidae semi-cursorial with an advanced 

type of foot mechanism adapted to their particular 

mode of attack. Traced backward, however, the characters of the two converge toward each other and also 

toward the primitive Viverridae. All writers on the 

subject have pointed out the viverrid characters of 

Pseudocynodictis and the numerous resemblances, in 

all part of the anatomy, between Daphoerius and 

Dinictis. The Oligocene canids and felids, however, 

agree with one another and differ sharply f ~om the 

Oligocene Viverridae (the Daphoenidae of this classification) in the characters of the auditory region. 

Therefore, the earliest separation from closely similar 

contemporaries can be conceived to be on this basis. 

If only the Oligocene Carnivora were known, the 

writer believes that the major taxonomic grouping, if 

any were attempted, would certainly be on this basis. 

The Canidae and Felidae, nevertheless, must have diverged before the Oligocene and pursued a separate 

evolution in dental characters. After the Oligocene
AUDITORY REGION IN FOSSIL PEMDAE 115

this divergence became also marked in the basicranial 

region because of the more rapid evolution of the 

felid branch in this respect. The result was the 

convergence in the Felidae of characters of the bulla 

and the venous and arterial system of the head toward 

the viverrid condition. 

Arctoidea

Procyonidae

Ursidae

?Mustelidae

Diagnosis—Bulla simple, without septae or rafters 

in all early forms and in most later ones. When septae 

and rafters do form, these are radiating ridges that 

do not bring about a bipartite division of the bulla. 

Increasing complexity of the bulla (which aids in resonance) takes the form of hollowing out of the mastoid, 

the formation of cancellous tissue in the mastoid and 

parocciptal, and extension of the hypotympanic sinus 

along the sides of the meatus. Basicranial foramina 

persistently primitive with little modification from the 

embryonic condition. Postglenoid foramen always 

large, the carotid canal a bony tub© in the medial wall 

of the bulla, the posterior carotid foramen large and 

well separated from the foramen lacerum posterius.

Discussion—The earliest procyonids have a very 

typical auditory region indistinguishable in essential 

features from that of the modern representatives of 

the family. In fact, the earliest procyonids, except for 

the smaller braincase are almost identical with Bassariscus. The evolution of Procyon and Nasua from these 

primitive forms presents no difficulty.

The relationship of the Ursidae is more obscure. 

However, their affinities as far as they are known seem 

closer to the Procyonidae than to the Canidae.

The early Mustelidae are clearly closely related to 

the early Procyonidae. There is a persistent tendency 

for the late Oligocene and Miocene carnivores with a 

procyonid type of bulla, such as Plesictis genetoides, 

to develop mustelid characters in the dentition. The 

more complex types of auditory region such as that of 

Taxidea taasus could be easily derived from a simple 

procyonid type. The family, however, is probably 

polyphyletic, with some addition of genera developed 

from later Canidae, which also show mustelid features 

in the dentition. A more exhaustive study of the fossil 

mustelids and their relation to the modern genera is 

needed before these affinities can be .properly evaluated.

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