... 

,. 

The Habits and 

Adaptation of the 

0 ligocene Saber Tooth 

Carnivore, Hoplophoneus 

By JEAN HOUGH 

SHORTER CONTRIBUTIONS TO GENERAL~ :GEOLOGY, 1949, PAGES 125-137 

GEOLOGICAL SURVEY PROFESSIONAL· PAPER 2.21-H 

.. A study of the anatomy and hunting habits of 

H oplophoneus, with comparisons to both fossil 

and present-day relatives 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1950 
. I 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

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

Washington 25, D. C. - Price 40 cents (paper cover) 

,., 

) 
.,. 

... 

CONTENTS 

Abstract __________________________________________ _ 

Introduction ______________________________________ _ 

Habits and adaptation of Recent Felidae _____________ _ Predation _____________________________________ _ 

Panther a _______________________________ -_--

J?elis ________ ------------------------------ Acinonyx _________________________________ _ 

Cranial variation ______________________________ _ 

Dentition _____________________________________ _ 

Structure of the limbs __________________________ _ 

The structure of I-lo1Jlophone·us ______________________ _ 

General characters _____________________________ _ 

Page 

125 

125 

126 

126 

126 

126 

127 

127 

127 

128 

128 

128 

Page 

The structure of Hoplophoneus-Continued 

Range of variation______________________________ 128 

Cranial characters_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 129 

Hoplophoneus primaevus primaevus Leidy______ 129 

I-1 oplophoneus primaevus latidens Thorpe_______ 130 

Dentition _____________________________________ ...; 130 

AJdal skeleton_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 130 

Appendicular skeleton___________________________ 131 

Mode of life of I-loplophoneus_________________________ 132 

Comparison of Smilodon and Hoplophoneus_____________ 133 

References cited____________________________________ 135 

ILLUSTRATIONS 

Page 

Pr.A'l'ES 26-28. Views of Hoplophone·us mentalis Sinclair----------------------------------------------------------- Fol. 137 

29. Fore limb bones of Hoplophoneus primaevus latidens Thorpe _____ ----------------------------·-------- Fol. 137 _. 30. Hind limb bones of I-loplophoneus p1·imaevus latidens Thorpe _________________________________________ Fol. 137 

31. Vertebral column of Hoplo7Jhoneus primaevus latidens Thorpe ________________________________________ Fol. 137 

III 
THE HABITS AND ADAPTATION OF THE OLIGOCENE SABER TOOTH 

CARNIVORE, HOPLOPHONEUS 

BY JEAN Houarr 

ABSTRACT 

Most restorations of the Oligocene saber tooth carnivore, HopZophonetts, depict it as very feline in pose and appearance. A 

detailed comparative study of the osteology seems to show that 

this Is erroneous. Actually, the head is large, the neck long 

and straight, the legs short. The radius, which is a short stout 

bone, articulates with the cuneiform as well as with the scapholunar. The shafts of the radius and ulna are thus held in an 

oblique position, with the elbow joint everted and the foot 

turned inward. The manus is pentadactyl, with divergent 

digits, and a sentiopposable pollew. 

The hindquarters slope abruptly, bringing the hind limbs forward under the body in a slinking pose. The tibia, which is 

the longest bone in the body of Fel,is, is shorter than the femur 

in Hoplophoneus. The knee joint, like the elbow, is everted; 

the hind foot, like the forefoot, plantigrade. · 

'l'he dentition is characterized by a reduction of the p·remolars 

and molars and carnassialization of the remaining cheek teeth 

t:s extreme as that of Felis. The upper canines are elongate 

sabers, the lower canines short and incisorlike. The lower jaw 

is very deep vertically, especially at the symphysis. A lobelike 

flange from the external, anterior border forms a sheath for 

the upper canine. 

The contours of the skull resemble those of Panthera. This 

combination of characters-pentadactyl scansorial feet with an 

extreme carnivorous dentition-is unlmown among modern carnivores and consequently difficult to interpret. It would seem, 

however, that the actual mode of attack, dropping on the back 

of prey, or using the long canines to pierce the throat in a head-on 

approach was similar to that of Fel'iS but that the more highly 

developed and typical feline habits, such as the stalk in ambush, 

and running leap at the victim so highly developed in Pantltera 

had not yet evolved. 

Although the saber teeth in all genera seem to have been 

used as stabbing weapons, the mode of their use must ha:ve difered widely. Especially, the habits and mode of attack of the 

gigantic Smilodon of the Rancho la Brea tar pits must have 

differed from the Oligocene hoplophoneids, most of which were 

not much larger than a big lynx. The sabers in Smilodon are 

extremely large in proportion to the slmll. size (index canine 

diameter: prothion-basion length is 14.4: 15.7), heavy and recurved. Evidently, the growth period was long. There is 

evidence that brealmge was frequent. The period when the 

canines were at their maximum efficiency was thus apparently 

very short. Even with all of the mechanical adaptations in 

the structure of the skull which made possible the use of such 

huge teeth, they must have been awkward weapons in an ordinary attack. It is suggested, therefore, that they may have 

been used primarily in sexual combat between males, and as 

a means of obtaining food only in unusual circumstances. One 

such situation existed at Rancho la Brea, where large numbers 

of the bigger herbivores were rendered helpless by miring in 

the asphalt. Under these conditions, with the victim unable 

to run away or put up a very violent struggle, a strike with the 

huge, unwieldly canines could be made at leisure and there 

880•!05-50 

would be no need for a quick withdrawal--difficult because of 

the length and recurvature of the teeth. It may have been 

that kills were made by animals with mature, fully effective 

canines and the food provided used by the young and aged 

individuals. 

'l'he role of Smilodon in the Pleistocene fauna was quite ditrerent from that of HopZophoneus in the Oligocene fauna. The 

former had to compete with Panthera atrow, the lynx, and the 

jaguar, all much more intelligent and highly evolved animals. 

Although the .machairodont still held its own. in numbers, it 

apparently did so only by a.n excessive specialization. 

There were no true cats, dogs, or modern carnivores of any 

sort in the Oligocene. H oplophonetts had no competitors higher 

in the evolutionary scale than itself. Stupid, slow, and awkward 

though it may have been in comparison. with modern cats, it was 

nevertheless the most active flesh-eater of the time. 

INTRODUCTION 

The various genera of Oligocene carnivores are near 

enough to modern forms, in an evolutionary sense, that 

the structure of the dentition, of the basicranium, or 

of the limbs, in almost every instance allies them with 

one or another of the present day families. The combinations in which these characters occur are different in 

all the genera .. In Daphoenus the auditory region _is 

extremely like that of the viverrid, Nandinia-the dentition and limb structure a mixture of canine and ursine 

characters. Zodiolestes has a procyonid type of auditory region although the dentition is mustelid. In 

Phlaocyon, on the other hand, the dentition is procyonid 

and the auditory and limb structure are canid. The 

saber tooth carnivores usually included in the Felidae 

. are no exception to this general rule. H oplophoneus, 

E'U87fllilis and Dinictis have a type of dentition which is 

feline, both in the reduction in the number of teeth and 

in the extreme carnassialization. The elongation of th~ 

upper canines is also, in a sense, an exaggeration of a 

feline specialization, because in all of the family the 

upper canines are relatively longer and stouter than 

the lower. However, in all Oligocene forms, especially 

in H oplophoneus, the details of the dentition are quite 

dissimilar to those of true felids. The other adaptive 

characters (shape and proportion of the skull, relative 

size of the head and body, limb structure and foot structure) are even more widely divergent. · 

These differences are obscured by the common assumption that the OHgocene saber tooth carnivores are 

"cats," primitive to be sure, but nevertheless true felids 

on their way to evolving into the modern forms. This 

125 
126 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 19 4 9 

is wholly untrue of H oplophoneus. In fact, the term 

"saber tooth tiger" applied to this genus is such an 

extreme misnomer that its use ought to be discouraged 

even for purposes of popular exposition. Dinictis is 

perhaps somewhat more "feline" but still far from typical, its habits and appearance more nearly approximating those of the cheetah, as Matthew (1910) suggested. Even so, the resemblance is analogous only, 

with no close correspondence in detail of the skull or 

limbs. 

In line with the general notion that H oplophoneus 

was very catlike, skeletons are usually mounted with 

the feet in a digitigrade position and the back and neck 

arched in as feline a fashion as possible. A complete 

skeleton of the oldest known machairodont, H oplophoneus mentalis Sinclair, however, which has been 

skillfully mounted by John Clark and is now in the University of Colorado Museum at Boulder (pls. 26, 27, 28) 

was found articulated. This skeleton, together with 

another virtually complete one of the same species in 

the museum of the South Dakota School of Mines, 

and several articulated skeletons of the Brule subspecies, 

!1. primaevus latidens Thorpe, in the United States 

National Museum show that, in fact, the feet were 

plantigrade and the pose of the limbs very different 

from that of the modern Felidae. As no detailed comparative study of the limb structure of the various 

species has been published, and there is abundant material for such a study, a more complete description seems 

desirable. To emphasize the divergence in adaptation 

of Hoplophoneus from Felis or Panthera, descriptions 

of the habits of the modern genera are included. 

HABITS AND ADAPTATION OF RECENT FELIDAE 

The Felidae were designated by Cuvier as the exemplar or archetype of the Carnivora, a category which 

included the Carnivora of modern classification and also 

carnivorous marsupials. The idea of an archetype in 

the way the French naturalist used the term is, of 

course, outmoded, but in a broader sense the cats can· 

be said to be the ideal type of carnivorous mammal 

and to exemplify that habit in one of its most extreme 

adaptations. The "great" cats are the largest and most 

powerful predatory animals (with the possible exception of the bears) ; all of the Felidae are more exclusively flesh eating than the Canidae; of all of the Carnivora their dentition is the most uniformly specialized 

for that mode of life. To use the adaptive peak imagery, 

the Felidae, like the Canidae, may be said to be grouped 

around one major adaptive peak, the characteristics 

of which are determined by the method of securing 

prey. 

All the Felidae (except the cheetah) use essentially 

the same method of securing prey-from the lion to the 

lynx they capture their victims by a silent, gliding stalk 

from ambush followed by a swift dash and attack. The 

details vary from individual to individual and species 

to species, according to the necessities of the environment and the relative sizes of predator and prey. 

Panthera.-The large cats, especially the lion and 

the tiger, usually attack_ by leaping from the ground 

onto the back of the animal which is then gored through 

the throat or nape by the powerful canines. With these 

teeth embedded in the flesh the neck is broken by a 

wrenching twist and the victim brought to the ground, 

in part by its own struggles and in part by the weight 

of the attacker. Both lions and tigers prey on very 

large animals such as bison, buffalo, and even (Pocock, 

Peacock, Blanford, and others) adult cow elephants, as 

well as the less powerful artiodactyla such as deer, antelope, and wild pigs. With the largest animals hamstringing may be resorted to and the victim felled 

before the kill is made. The hunt may be social-that 

is, participated in by two or more individuals-two 

males, a male and female during the breeding season, 

or (most commonly) a female and half-grown cubs. 

The smaller species, lacking the size of the lion and 

the tiger, make the final leap from a rocky ledge or 

overhanging branch rather than from the ground. 

Gravity thus adds force to the weight of the cat. 

All of the Pq,nthera drag their kill to some place of 

concealment. A deer or antelope provides food for several days, or as long as it is eatable. If the carcass is 

very large it may feed a whole family. Therefore, 

size of prey is important not only with regard to ease 

of attack but also to amount of food furnished. It is 

difficult for a full-grown lion and impossible for a 

lioness with cubs to obtain enough small animals for 

subsistence unless they are very abundant and incapable 

of defense by flight. The capture of a· rabbit requires 

as much time and almost as much effort as that of a 

deer. Two rabbits a day are semistarvation diet, and 

hunting is almost continuous.. This is an important 

point in considering some of the reasons for the extinction of the extraordinarily large Pleistocene felids. 

The size of predator invariably declines with the size 

of the prey not only because larger size is not needed 

but because it is an obstacle in the way of. obtaining 

sufficient food. 

Felis.-The wild cats included in the genus Felis 

range in size from Prionai7Mrus ( 15 to 18 inches 

in length) to the puma, which may reach a head-andbody length of 5 feet. Thus, some species of Felis are 

as large as the smaller species of Panthera, but most 

are moderate sized or small. The habits vary not only 

from species to species but even among races of the 

same species. Some, such as the marbled cat, are 

strictly forest-dwelling, where they feed on small mammals such as squirrels and rats, or on pheasant and 

other birds. Others, such as Felis chaus, live in bush 

jungle and the long-grass reed banks near lakes and 

.... 

r 
THE HABITS AND ADAPTATION OF HOPLOPHONEUS 127 

marshes. A few, such as F. ( Q tocolobus) manul, and 

some species of lynx inhabit rocky districts. All of the 

environments have in common the presence of some sort 

of cover. Only the caracal inhabits really open country, in this respect resembling the cheetah but lacking 

the typical adaptations of that genus. 

These cats hunt in much the same way as Panthera. 

There is always the stalk or wait in ambush, the swift 

dash and attack. If the prey is larger than the predator, as is the case with the larger herbivora, there is a 

drop frmn a tree or rocky ledge and in some instances a 

head-on attack. Against small mammals and birds the 

kill is made by a "pounce" in which the victim is stunned 

by a blow from the paw. 

to sight prey while keeping the entire body and most 

of the head concealed, and are most highly developed in 

forms such as Acinonyx that habitually peers over rocks 

while waiting in ambush for its victims. . 

An exaggeration of this type of development is found. 

in Pallas' cat ( Otocolobus manul). The forehead in this 

species is exceptionally flat and the eyes are placed wide 

apart and practically at the top of the skull. This cat 

habitually lies stretched out on a large branch with the 

head resting on the forepaws and is virtually invisible. 

Among the smaller cats, Felis yagua'rwndi, an aberrant 

species not much larger than a domestic cat, and a native 

of South America and Mexico, is at the opposite extreme. 

The habits of this animal resemble those of a marten, 

and the head is elongate with almost musteline proportions, and very large in contrast to the short limbs. 

DENTITION 

A,cinonyw.-The cheetah or hunting leopard is the 

only felid that captures its prey by running it down. 

It inhabits open country-commonly grassy plains near 

low hills. When the prey is once sighted from behind 

cover of a rocky ledge the cheetah speeds after it, carry- The dentition of the Felidae represents the extreme 

ing the pursuit a much greater distance than usual with o~ carnassialization and is structurally adapted in a most 

cats, and making the final attack more in the manner of efficient way for their particular mode of attack. With 

a dog. The speed is very great. The cheetah is said to one exception,. the typical pattern prevails to some 

be able to cover 100 yards in 41;2 seconds which is "faster degree throughout the family, even in the smaller species 

than the fastest greyhound and twice the speed of the where the canines are reduced in size and can be no 

fastest ht.1man sprinter" (Pocock, 1939). Enlarged longer used as stabbing weapons. In all cats, but espenasal passages assure sufficient supply of air for this cially in the larger species, the upper canines are longer 

burst of speed but, because there are no physiological than the lower, stout, oval in cross section, and taper 

modifications for endurance, the maximum speed can be abruptly to a point. The edges of the incisors form a 

maintained for only a short time. E'ven in this one straight line at the extreme anterior margin of the jaw. 

"cursorial" cat, therefore, the adaptation is very imper- . The alveolar margin of these teeth is below the level of 

feet in comparison with that of animals in which the that of the canine. The forward position of the incisors 

habit is really well developed such as the Canidae and leaves a diastema in front of the canine, the loss of the 

swifter ungulates. Nevertheless, the cheetah does rep- first premolar and reduction of the second leaves a simiresent a felid which has "wandered," so to speak, from lar post-canine space. From this point the alveolar 

the adR.ptive peak representative of the family and is margin of the upper teeth curves downward. The edges 

well on its way to climbing another. of the lower incisors are raised above the level of the 

CRANIAL~V ARIATION 

In all felids the skull is broader and shorter than that 

of the Canidae or that of the Viverridae. The facial 

region is short, with a steep upper profile. · Generally, 

the crani n,l portion of the skull is also short and highly 

inflated. There is a strong flexure between the cranial 

and facial portions, resulting in the very characteristic 

upper profile. The muzzle is never as long and slender 

as that of the wolf, and among domestic breeds none 

show anything like the extremes of the Canidae. Nevertheless, there is some variation. The species of Pant hera 

have the longer, lower cranium, the longer muzzle, and 

the less abrupt cranial flexure, whereas the smaller 

species tend to have a shorter muzzle, broader palate, 

and more rounded cranium, and more sharply domed 

profile. These features are apparently intimately associated with the habits described in the preceding section. A domed skull and high orbits enable the animal 

cheek teeth and the alveolar margin of the lower 

dentition curves upward. The carnassials ·are high, 

trenchant teeth placed .at the angle of the jaw. M1 is 

reduced to a nonfunctional nubbin, M2 is absent. Th~ 

only point of. contact between the upper and lower teeth 

is thus between the carnassials at the extreme posterior 

of the jaw and the incisors and canines at the extreme 

anterior point. When the jaws are closed a wide gape 

remains between them. This gape together with the 

post-canine space is designed to give the greatest possible penetration and grasping power to the canines. It 

is present in all living felids except the cheetah but is 

especially well developed in Panthera. 

This specialization enables these cats, first, to pierce 

the skin of the large herbivores on which they feed, and 

second, to keep the teeth firmly embedded in the flesh 

during the neck-breaking process-no small feat considered that the victim is not standing passively waiting 

to be killed but is struggling desperately with all weapons it possesses: hoofs, horns. and muscular strength. 
128 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949 

In many of the smaller felines the canines are less 

well-developed, and the post-canine space is correspondingly reduced. Commonly, this is accompanied by a 

shortening of the muzzle. In the lynx, both the upper 

and the lower canines are very long, and the post-canine 

sp~ce is large. However, the alveolar margin of the 

upper and lower dentition is nearly straight, and there 

is little of the characteristic gape of the Panthera. 

In the cheetah, the canines are little longer than is 

common in most fissipedes, the tooth row is crowded anrl 

the post-canine space entirely lost. As there is little 

gape between the jaws the occlusion of the teeth resembles that of the Canidae. 

In one species of Panthera, the clouded leopard, the 

upper canines reach a length three times the diameter 

of the base, which is the same proportion as in some 

dinictids. This is the only example of anything 

resembling "saber" teeth in modern genera. 

The lower jaw of the clouded leopard also has points 

of resemblance with that of the machairodonts. The 

chin is described as "pronounced, flattish and nearly vertical in front, and the alveolus of the upper incisors is 

raised well above the socket of the canine so that when 

the mouth is ~losed the upper jaw is uptilted" (Pocock, 

1939, p. 247). As will be seen, this is very similar to 

the structure. of the lower jaw in H oplophoneus. 

. STRUCTURE OF THE LIMBS 

The limbs of the Felidae are less specialized than the 

dentition in contrast to those of son1e other carnivore . 

families. They are sometimes described as "primitive." 

If by primitive is meant generalized, this is not true. 

Living cats, with the exception of the cheetah, do not 

have the cursorial adaptations so characteristic of the 

Canidae. Nevertheless, the compactness, slende~ness, 

and mode of articulation of many of the bones do in 

many ways paralled that of the dogs. There is a much 

greater mobility and flexibility of the lower forefoot 

and paw, and these might be considered primitive features, but in the cats they are developed to such a 

degree of efficiency that they themselves constitute a 

specialization. The various devices that guarantee the 

retractibility of the claws also are specializations. In 

fact, it would be hard to find a forepaw other than 

that of the primates which is more specialized,o in the 

sense that the structural details are highly adapted for 

speed, precision, and strength. These structures form 

an important part of the eat's mechanism for offense 

and defense. A tiger is said to be able to crush a man's 

skull with one blow of the huge paw delivered so swiftly 

that defense against it is impossible. Even a very small 

kitten uses its claws more effectively than a puppy. 

Undoubtedly the playful antics of cats serve to perfect 

the· speed and coordination for which the structural 

details are so well adapted. 

The cushioning of the paw by the soft three lobed 

plantar pads also is a feline characteristic and is responsible for the silence and elegance of the "stalk." 

The hunting leopard alone among cats has lost-or 

never had-the greater part of these specializations. 

The short, stout, and almost straight cia ws are nonretractile, apparently because of the loss of an important 

part of the mechanism, the cia w sheath-but another 

part, the flexor tendons running to the base of the terminal flange of each digit, is still present. The webs 

which in other cats extend to the digital pads, binding 

the metacarpals into a compact unit, are little developed 

and the digits consequently more spreading. The plantar pads are hard and compressed, more doglike than 

catlike. These features, together with the long legs, 

powerful hindquarters, and small head, are cursorial 

adaptations which make possible the enormous speed. 

THE STRUCTURE OF HOPLOPHONEUS 

GENERAL CHARACTERS 

H oploplwneus, contrary to most restorations, was not 

very much like any of the modern Felidae. This is 

true of every important feature of the skeleton except. 

for the dentition and the shape of the skull. In fact, 

"saber tooth badger'' would come closer to describing 

the general aspect of the animal than "saber tooth 

tiger." 

The head is large. The neck is long and straight. 

The cervical vertebrae are inter locked in such a way 

that the double curvature of the Felidae would be impossible. The back is arched, with the apex at about 

the ninth rib. From this point, the hindquarters slope 

sharply downward. The pelvis is broad, with a strong 

oblique inclination (about 45° from the horizontal), 

and the acetabulum is so placed that the hind limbs 

have a straddling position and are incapable of being 

drawn forward under the body in the typical felid 

fashion. The upper part of the leg is longer than the 

lower, the reverse of felid proportions. The thorax is 

shallow in con1parison with that of Felis or Oanis. 

The forelimbs are noticeably shorter than the hind, very 

stout, articulated in such a way that the elbow joint 

extends sideward and the lower part of the limbs and 

feet are turned inward. The pose is closely similar to 

tha.t of such plantigrade animals as lJ/ us tela or T amidea, 

especially the latter. Both fore and hind feet are 

strictly plantigrade. 

RANGE OF VARIATION 

The skulls of II oploplwneus are greatly varied in 

size and details of form but, as Leidy pointed out, this 

variation is not greater than among individuals of Felis 

concolor (which Leidy called Panthera). The cranial 

variation in Hoploph.oneus has been the subject of two l 

!· 
• 

' 

THE HABITS AND ADAPTATION OF HOPLOPHONEUS 129 

statistical studies (Simpson, 1941a, and Hough, 1949). 

These studies show that all specimens of H oplophoneus 

collected from the Brule clay belong to one species, 

B. primae't)us, which, however, has been subdivided into 

a number of geographic subspecies. These subspecies, 

which probably ranged over most of North America, 

include one or more of very large size, and at least one 

very small southern race. Two, occupying adjacent 

areas, are about the same size, but have clearly distinguishing ·cranial characters. The one, Hoplophoneus 

primae'l.''l.l8 prinwevus from South Dakota, included 

Leidy's original specimens, as well as the types of H. insolen.~ Adams, H. O'reodontis Cope, and H. robust'IJJS 

A.da'ms. The other, H. primaevus latidens Thorpe includes Thorpe's types of H. marsld, H. latidens, and 

11. molossus from Colorado and Nebraska and a series 

of skulls and skeletons in the United States National 

l\1useum from '\Vyoming. H oplophoneus primaevus 

latidens is closely allied to H. mentalis Sinclair from 

the Chadron formation, and is also primitive in having 

cranial characters nearer to those of the more generalized carnivores of the period, especially. the 

daphoenids. 

The variation in the proportions of the limb bones 

has not been so intensively studied. The work that has 

been done suggests that the amount of variation is not 

of great importance. Simpson (1941a) points out that 

in the specimens studied by him there is a general correlation (within a species) of the length and stoutness of 

limb bones in proportion to skull length. This is true 

o:f most Recent mammals. Small individuals tend to 

have relatively slender limbs but these limbs are shorter 

in proportion to skull length. The writer found this 

to be the case also for the United States National 

Museum specimens studied. 

However, in the Chadron species, H oplophoneus mentalis (insofar as ca,n be determined from the few a vailable specimens) there is positive difference in proportions, not correlated with size. The index, humerus 

length to femur length in H. primaevus is 85-87. That 

of H. 'mentalis is 94. In other words in the earlier form 

the fore and hind limbs are more nearly equal. 

CRANIAL CHARACTERS 

Hoz1lophoneu-s primaevu.r.: primaevus Leicly.-This 

type of skull was the one described by Leidy. He 

pointed out that the upper profile has about the same 

curvature as that in the skull of the puma, but the facial 

region is longer and .straighter, and the cranium shorter. 

The nasal openings are narrower and are placed higher. 

As Leidy said ( 1869, p. 54) : 

1-'he zygoma encloses a narrower space than in F. concolor, its 

posterior root has a deeper origin from the crantum and descends more in its outward course. Its anterior root below the 

orbit is shallow and thick. 

The greatest difference between the two types of 

skulls, however, is in the proportions: in H oplophoneus 

the muzzle is longer, narrower, and more tapering; the 

breadth across the postorbital processes is greater. 

There is a deep postorbital constriction with a narrow 

cranium so in dorsal vein the skull has a wasp waist 

curvature. The capacity of the cranium is hardly onethird that of the puma. In fact, in this respect all of 

the Oligocene carnivores are nearer to the carnivorous 

marsupials such as Thylaci'ri!Us or Dasyurus than to any 

of the placental families. 

The base of the skull is narrower in proportion to its 

length than in the puma. The glenoid articulation has 

nearly the same form and direction as in the puma but 

is much lower, fully one inch below the basispehnoid. 

The post-glenoid tubercle is nearly like that of Felis 

concolor; the anterior one extends farther media-laterally but is not as long or as distinct. 

The mastoid processes are highly specialized in relation to the saber tooth dentition. This was not emphasized by Leidy but has since been the subject of much 

discussion by Matthew ( 1910) and others. The mastoid 

is produced into a rugose knob that projects downward 

and forward over the external auditory meatus in such 

a way as to make a deep, narrow passageway quite in 

contrast to the open circular aperture of Felis. The 

degree of development of this feature . closely corresponds with the length of the canine teeth. When the 

sabers become very large, as in Eusmilis and Smilodon, 

the mastoid process extends so far forward as to be 

almost in contact with the base of the post-glenoid 

process. 

The details of the auditory region are typical and 

uniform in all hoplophoneids. The cavity is very deep 

and narrow. There are never more than fragments 

of bulla preserved, but in many specimens these fragments suffice to show that there was a small, undivided 

discoid bulla similar to that of certain undescribed 

specimens from the Valentine in the Frick collection 

which are probably machairodonts. The paroccipital 

process is distinct in all of the early members of the 

subfamily, being a lobelike process similar to that of 

Daphoenus. The cranial foramina are more canoid 

than feloid as has been pointed out by Scott (1936) ·and 

others. 

The mandible differs in many respects from that of 

modern cats. It js extremely thick and deep. Anteriorly, the depth is in remarkable contrast to that of 

Felis. The anterior face is a plane vertical surface 

44 mm. high in a skull188 mm. long. At the external 

corner of this vertical face the lobes for the protection 

of the upper canines project a distance of 13 mm. in 

the same skull. The ramus gradually narrows posteriorly, the least depth being just posterior to the last 

molar. The coronoid process is very low, lacking the 
130 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949 

backward extension of that of Feli8. It resembles that 

of the badger in general proportions but is relatively 

lower. 

The head-with the short facial region, huge canines, 

and enormous, highly proghathous lower jaw-must 

have been bizarre. These features are usually minimized 

in restorations which also give the impression that 

lloplophoneus and Smilodon (to say nothing of Dinictis and E~tsmilis) presented a very similar appearance. 

This could not have been the case. The contours of 

the skull are very different in all of these forms. In 

particular Smilodon and H oplopl~oneus differ in the 

size and shape of the lower jaw. 

Il oplophoneus primaevus latidens Thorpe.-In this 

subspecies the skull is typically much longer and lower. 

The upper profile is horizontal with the tip of the inion 

the highest point. The height is due mainly to the 

strong sagittal crest but the cranium is horizontal with 

no flexure between it and the cranial region. The latter is longer and straighter than in H. primae1Jus p1"imaevu,s, and the zygoma are stronger and deeper and 

more colesly pressed to the side of the skull. The muzzle 

is long, and narrower than that of any of the Felidae, 

although broad in comparison with that of the contemporary daphoenids or canids. In other respects, the 

proportions are very close to those of the larger specimens of Daphoenus vet~ts Leidy. The cranial capacity 

is very smalL The postorbital constriction.·is narrow 

and in some skulls, probably males, very posterior in 

position. 

The mandible has essentially the same characters 

as H. pri1naemt8 pri1naevtts but because of its greater 

length the disproportion seems less. 

The appearance of H. primaev~ts latidens and H. 

mentalis both must have been more canine than feline. 

Very probably neither had the whiskers and cleft rhinarium with which they are often pictured. It is mueh 

more probable that the muzzle resembled that of a 

musteline. 

DENTITION 

The large saberlike canines are the most prominent 

feature of the dentition. The length ranges from three 

to four times the basal diameter. In Hoplophoneus, in 

contrast to Srrvilodon or to Eusrrvilis, there is little recurvature. The cross section at the base is a narrow, 

compressed, oval, tapering gradually to a point at the 

tip. The sabers are not as compressed or scimitarlike 

as those of Eusmilis, but are longer, thinner (and taper 

less abruptly) than those of Dininctis. Both length and 

width of l;>oss section are varied but, strangely enough, 

not so much as in the modern felids. 

The lower canines are small teeth that differ very little 

from the lateral incisors. They shear against the upper 

lateral incisors rather than against the upper canines, 

which they barely touch. The incisors, upper and lower, 

are stout, sharp, semiprqcumbent teeth, arranged in a 

semicircle, and in some species, pointed-in contrast 

with the straight comblike arrangement in Dinictis and 

Felis. 

Between the canines and the first premolar present 

(which is a minute nonfunctional tooth) there is a long 

post-canine space-much greater, of course, in the 

longer-jawed forms. The alveolar margin of the cheek 

teeth is almost straight, but the sockets are raised in 

such a way that when the mouth is closed the upper 

jaw is uptilted. The upper and lower jaws of the 

clouded leopard have similar relations. 

There are only two functional cheek teeth, P4 and 

one other premolar in the upper jaw, M1 and one premolar in the lower jaw. The upper molar is a rudimentary tooth. Both functional cheek teeth are shearing 

teeth with the posterior one the principal carnassial. 

The anterior one is smaller but placed in line with the 

other in such a way that they present one shearing surface. Both teeth have a strong backward inclination. 

The roots are stout and recurved. With age, the upper 

teeth tend to rotate inward and the lower teeth outward. 

This insures a type of wear that keeps the edge always 

sharp. There is nothing of this sort in Felis. In the 

latter, too, the premolars anterior to the sectorial are 

grasping teeth used for holding-food in the mouth. The 

incisors are weak and ineffective. The opposite is true 

in H oplophoneus. 

AXIAL SKELETON 

In general, all of the elements of the axial skeleton 

of H oplophoneus closely resemble those of Smrilodon 

(pl. 31). However, the atlas is more like that of Daphoenus. The transverse processes in Smilodon are 

greatly extended posteriorly, tapering to a rounded 

edge. In H oplophonerus the posterior extension is not 

so great, and the ends are truncated. Both in Smilodon 

and in H oplophoneus the processes differ from those 

of Felis in lacking the anterior breadth which gives 

them a rectangular shape. In all specimens there is an 

atlantar foramen on one side and not on the other. 

The axis vertebra resembles that of Smilodon, but 

the neural crest is proportionally higher and is extended 

into a longer, sharper spine. The anterior projection 

is less developed than in Felis. The opening of the 

neural canal is triangular, narrowing dorsally much 

more than in Felis. A deep, narrow groove is present 

on the under side of the neural spine where it projects 

over the posterior opening of the canal. The anterior 

articulating surfaces are close together and face more 

forward. The postzygapophyses ·are also closer together and face obliquely upward and laterally. In 

Felis their orientation is almostly directly downward. 

The odontoid process is relatively stout. The anterior 

face slants obliquely upward. The transverse processes 

are broader and extend laterally and ventrally. 

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THE HABITS AND ADAPTATION OF HOPLOPHONEUS 131 

The cervical vertebrae behind the axis. closely resemble those of Smrilodon, even in detail. There is a 

general likeness to Felis. The dorsal surface is broad; 

the neural spine of Cervical III is very low (lower than 

in Felis), and that of Cervical IV pointed and tapering. 

In this vertebra there is a suggestion. of bifurcation of 

the long and stout transverse processes that increases 

until in the sixth cervical a distinct dorsal and ventral 

process is formed. Such a bifurcation may be present 

also in SmJilodon (Stock, 1932). 

The thoracic vertebrae closely resemble those of Smilodon and do not differ markedly from Felis. The 

spines are somewhat longer and narrower than those of 

the Pleistocene genus but proportionally stouter than 

those of Felis. The centra are also somewhat broader 

and he a vier. 

The lumbar series in H oplophone~ts, as in Smilodon, 

is more firmly interlocked than in Felis, making the 

section more rigid. This is effected in part by the inward curvature of the zygapophyses, but principally by 

the position of the anapophyses. The latter are long 

and project 'Qackward, overlapping the metapophyses 

one-half to one-third of their antero-posterior breadth. 

1\ferriam and Stock (1932) pointed out this feature in Smilodon, and it is much more striking In 

Ff oploplwneus. · 

The very sturdy sacrum closely resembles that of 

Smilodon. It is much narrower than in Felis, particularly toward the posterior where the zygapophyses are 

very close together. The spines are broader and higher 

than those of Felis, and are slightly inclined backward. 

In true felines the spines are much more slender and 

inclined forward. 

There are 21 caudal vertebrae in Il oploplwneus mentalis. Probably, the number was varied. Most felines 

have 18 or 19, although there may be as many as 24. 

Ifowever, the tail in H oplophoneus was shorter and 

more slender than in such forms as the puma, not only 

because there are fewer vertebrae, but because the individual vertebrae (especially those in the posterior 

half of the tail) are proportionally much shorter. The 

tail must have been a less mobile and important appendage in H oploplwneus than in typical felines. 

APPENDICULAR SKELETON 

The scapula is narrower and more angular than that 

of Felis, and the vertebral border is sharply convex 

(pl. 29). The notch at its lower end (just below the 

coracoid process) is broad and shallow. The coracoid 

process is a rounded lobe, relatively larger than that of 

Felis. The a.xillary border is straight in its lower portion, but curves downward to form the process for the 

insertion of the teres major muscle. This process in 

H oplophoneus is short and broad, much more like that 

of the American badger ( Taxidea tar»us) than Felis. 

The spine is of almost even height throughout its 

length. The metacromion and acromion are not separate as in Felis, but confluent as in TaJIJidea. The 

glenoid fossa is an elongate oval, also resembling that 

of the badger rather than Felis. 

The humerus of H oplophoneus is very different from 

that of a cat; it is short and extraordinarily thick because of the enormous development of the deltoid and 

supinator crests. In Felis and Oanis the shaft of the 

bone is long and slender, with an oval cross section. 

The deltoid crest is a triangular flattened area extending a little more than a third the length of the bone. 

The supinator crest is a slight ridge along the external 

condylar surface. In H oplopl~oneus the deltoid area is 

two-thirds the length of the shaft and is extended into 

a process approxim·ately 5-mm. above the body of the 

bone. The supinator crest extends from a point on the 

external condylar side about on a plane with the termination of the deltoid crest and forms a wing-like 

process to the external condyle. The prominence of 

these muscle attachment areas makes the humerus look 

like the peculiarly crooked humerus of the badger. 

In general shape and proportions the ulna resembles 

that of the badger rather than of Felis. It is stouter 

and less tapered than in the latter, and the olecranon 

process is proportionally longer. The greatest difference from Felis, however, lies in the size and shape 

of the articular surfaces. The greater sigmoid cavity is 

oblique, narrower, and much deeper. The upper bounding process and the coronoid process that forms the 

lower border are about the same size. The lesser sigmoid cavity is a deeply concave rim of bone in Felis, but 

a flat triangular surface like that of the badger in H oplophoneus. The bicipital groove is deep in Felis but very 

·faint in Hoplophoneus, and this, too, is a likeness to 

Tax idea ta[JJUS. 

The shaft of the radius resembles that of Felis, but 

·the head is narrower, and there is virtually no neck. 

The margin of the head is flat, without the marked "lip" 

of Felis. The articular 'surface is much less concave. 

The tuberosity is somewhat smaller and the shaft below 

it is a little less flattened. The distal end is relatively 

broad. The surface for articulation with the scaphqlunar is more concave and the styloid process larger and 

stouter than in Felis. There is a small facet for articulation with the cuneiform. 

The carpus resembles that of the badger but differs 

in the contacts of the bones and lacks the height and 

compactness of that of Felis. The scapho-lunar is proportionally large. It articulates with the trapezium, 

trapezoid and magnun1 in very broad contacts. The 

magnum is high, almost excluding the cuneiform from 

contact with the scapha-lunar. The contact of the 

cuneiform with the unciform is superior (or dorsal) 

rather than lateral as in Felis. There is a broad, concave 
132 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1949 

articular surface for the styloid process of the ulna and, 

medially, a smaller flattened facet for articulation with 

the radius. The shafts of the radius and ulna are thus 

held in an oblique position with the elbow directed outward. The unciform articulates with the fifth metacarpal, the magnum almost entirely with the fourth 

metacarpal, the trapezoid with the third metacarpal, 

the trapezium with the second and first metacarpal. The 

articulation with the first metacarpal is almost at a right 

angle with that of the second metacarpal so that the 

pollex is widely divergent from the other digits. The 

head of the pollex also articulates with the posterior 

palmar surface of the scapho-lunar. Therefore, in 

walking, the digits of the forefoot would be spread 

widely apart and the divergent thumb used to give a 

forward impetus to the gait. In climbing, the hand 

could encircle a small branch with the first digit opposing the others. Opossums, raccoons, squirrals, and other 

arboreal animals climb in this fashion. 

Like the carpals, the metacarpals are broad and 

spreading. Metacarpal III and IV are of almost equal 

lengths and are the largest of the series. Metacarpal 

II and V are also paired as to length. Metacarpal I is 

the shortest, but is a stout bone almost two-thirds the 

length of Metacarpal II. 

The claws are hooded, with the claw core about as 

large proportionately as that of Felis. Probably, the 

claws were long and beaklike as in Felis. The ungual 

phalanx closely resembles that of Felis both in general 

shape and structure of the articular surfaces. Probably, it was capable of being rolled back on the phalanx 

preceding it and the claws retracted in the same way 

that this action is accomplished in the modern cats. 

The general outline of the pelvic. girdle is like that . 

of Felis but the details are quite different (pl. 30). The 

ilium much more closely resembles that of the badger. 

The outer surface is convex rather than concave as in 

Felis, and the posterior spinous process is expanded and 

situated relatively near the acetabulum as in Tawidea. 

The spine of the ischium is a large hooklike process, 

however, closely resembling that of Felis. In the badger 

this process is very small. The shape of the pubis and 

ischium, and the size of the obturator foramen also are 

very feline. The acetabulum is longer and narrower 

than that of Felis, and also shallower and more posteriorly placed. tt is lower in position, and faces laterally 

and a little posteriorly. Because of this, the limbs when 

articulated are relatively wide apart and drawn under 

the body in a squatting pose. In Felis the acetabulum 

is high and faces forward so that the femora lie close 

t~ the body and in the normal running gait have a completely fore and aft motion. 

The femur is feline in character and not at like 

that of T awidea. The only significant differences from 

that of a cat are the presence of a large third trochanter 

and the deeper separation of the head and greater 

tuberosity. 

The tibia and fibula also are very feline. The surface of the distal end of the tibia which articulates with 

the tarsus is narrower and somewhat less concave but 

otherwise like that of Felis. The internal.maleolus in 

H oplophonews is somewhat longer. The fibula is stouter 

and straighter, and lacksthe sinuous curvature of Felis. 

The external maleolus is narrower than in Felis and 

as Scott ( 1936) points out there is no sulcus for the 

peroneal tendon. 

The calcaneum differs from that of Felis in general 

shape and also in detail. The tuber calcis is narrower 

proximally and expanded distally. The outer articular 

surface for the astragalus is short and flat. In Felis this 

surface is a long tonguelike facet and very convex. The 

outer articular surface is narrower and flatter than in 

Fel-is. It is placed at a greater angle to the external 

facet so that the two .are much farther apart than in 

Feli8. The body of the bone is not spool shaped (as in 

Felis and almost all living carnivores) but more nearly 

cylindrical. The neck.extends downward and laterally 

rather than postero-laterally. It is broader and less 

distinct from the head which is narrow and oval, rather 

than hemispherical like that of Felis. 

The shape of the body of the bone and the position 

of the head are much more as in Tawidea than as in Felis 

but in Tamidea the neck extends almost directly forward 

whereas in Hoplophoneus the head is extended laterally 

and downward. 

The facets for the articulation of the external and 

internal maleoli are more obliquely placed than in either 

Felis or Tawidea. Evidently the ankle of H opZophoneus 

was articulated in such a way that the foot tended to 

point inward in walking. In fact, the posture of the 

foot from the evidence both of the articulation of the 

separate bones and of an articulated foot found in 

position was strikingly like that of the scansorial viverrine, Arctic tis. The metatarsals in H oplophoneus are 

long and slender as they are in Arctictis and agree in 

relative length. Metatarsal I is the shortest but is almost 

as long as Metatarsal II. Metatarsal III and IV are the 

longest and almost equal in length, while III and V 

· (missing in the articulated foot) form a similar pair. 

MODE OF LIFE OF HOPLOPHONEUS 

The long, upper canines are the most conspicuous 

feature of H oplophoneus. They are so conspicuous that 

they have been the subject of almost endless discussion 

with little consideration of other features of the dentition and skeleton ... From the standpoint of interpreting 

the mode of. life, however, it is the combination of characters that is most important. In H oplophoneus, this 

combination is unusual. 

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THE HABITS AND ADAPTATION OF HOPLOPHONEUS 133 

The dentition is marked by an extreme-development 

of the shearing function of the cheek teeth. This specialization, which appea.rs in the earliest known forms, 

is certain evidence of an exclusively flesh diet. The 

lower Oligocene (Chadron) species have as elongate 

canines and as advanced a mechanical adaptation for 

their use as the middle and upper Oligocene (Brule) 

species; throughout the Oligocene there appears to have 

been little evolution in these features. 

The shape of the skull is specialized, but differs from 

that of the true Felidae only in detail. Compared with 

the contemporary daphoenids or canids the forehead is 

domed, the frontal region high, and the nasals short 

and steeply sloping. The orbits are large, and placed 

higher in the skull than are those of Daphoenus or 

Pseudocynodictis. The nares are also comparatively 

large and highly placed. These features are by no means 

developed to the extent that they are in the modern 

Felidae, nor even to the degree found in the later dinictids, but they appear in the Chadron species and indicate at least an approach to feline habits. In the specimens that constitute Leidy's hypodigm of the Brule 

subspecies H. primaevus primaevus they are notably 

more highly evolved. · 

Associated with this comparatively catlike shape of 

the skull and the extreme carnassialization of the cheek 

teeth, there is a battery of stout, projecting semi procumbent incisors unlike anything found an1ong the Felidae. 

The limb structure is definitely scansorial. The pentadactyl, grasping forefoot, with its divergent pollex, is 

well shown in the view of the mounted skeleton figured 

in plate 27. Both the structure of the humerus with its 

heavy deltoid and supinator cre·sts, and of the foot structure are reminiscent of the Paleocene Olaenodon. 

Neither the appearance nor the gait of H oplophoneus 

could have been like that of a cat, even a very short 

legged one, and even less like that of a civet. The contours of the body must have been broad and the gait 

waddling, as indicated by the everted elbow and knee 

joints and inwardly directed feet. This type of limb 

structure combined with an extreme carnivorous type of 

dentition is extraordinary, and has no representation 

among modern animals. Apparently _it results from a 

phenomenon observable in the history of many early 

Tertiary carnivores-the rapid evolution and high 

specialization of one set of structures, associated with 

extreme conservatism in others. 

The mental capacity in all hoplophoneids must have 

been extremely low. The braincase in the Brule species 

is not much larger than that of the contemporary hyaenodonts, and in the Chadron species it was smaller. 

Therefore, H oploplwneus could not have had approached the true cats in speed, coordination, or cunning. Nevertheless with the formidable dentition, powerful forelimbs, and (probably) highly effective retractile claws, H oplophoneus must have been an active predator-probably the most active of its time. The ca:tlike 

dentition suggests that it killed in the same way, although there was nothing comparable to the wait in 

ambush, stalk, and dashing attack of the Felidae. The 

smaller subspecies may have been strictly arboreal, and 

they may have fed on rodents, birds, and reptiles much 

in the manner of the small species of Felis today. Prob· 

ably, the larger hoplophoneids attacked the larger her· 

bivores, especially the slow-moving, thick-skinned types 

(as Matthew suggested in1910). The attack may have 

been made by a head -on charge in which the victim was 

seized by the throat, or by a drop frmn a tree branch 

or rocky ledge. In any case the canines could be used 

very effectively. They are not long enough in any 

known hoplophoneid to be unwieldly; they are thin and 

knifelike- after piercing the skin and muscle they 

could be readily maneuvered into interstices between 

bones or the cartilage and tendon of joints. There is 

little recurvature so that withdrawal would be easy. 

With the wide gape of the jaws the neck of the victim 

could be almost encompassed, the canines thrust deeply 

into the throat or nape of the neck, the strong lower 

jaw pressed upward, and the animal choked to death 

very speedily. 

COMPA~ISON OF SMILODON AND HOPLOPHONEUS 

It is often assumed, implicitly at least, that the sabers 

of Smilodon were used in much the same manner as those 

of H oplophoneu-s arid that the method of predation and 

type of victim was the same. Obviously this could not 

have been the case. Little H oplophonew belli of the 

Sespe or even the smaller subspecies of H. primaevw 

primaevus could not have attacked the same animals 

in the same manner as the gigantic machairodont of 

Rancho la Brea. Moreover, the same type of herbivores 

did not exist in the early Tertiary as in the Pleistocene, 

so that the role of Smilodon in the latter fauna was quite 

different from that of H oplophoneus in the Chadron 

and Brule formations. 

There is a _vast amount of literature on the use of 

the saber teeth which it seems unnecessary to review 

here. The ·consensus among paleontologists who have 

studied the matter undoubtedly supports the stabbing 

theory; first presented by Matthew (1910) and ably supported by Simpson in his refutation of the slicing hypothesis of Bohlin (Simpson, 1949). There is also 

no doubt of the mechanical adaptation of the skull 

for the use of the teeth which in Srnilodon reach such 

extraordinary proportions. They are not overspecializations in the sense that because of them the animal 

starved to death or could not open its mouth or was 

unable to use them effectively in an attack. 

Nevertheless, as Merriam and Stock point out in their 

detailed and able discussion of the subject in the Felidae 
134 SHORTER CONTRIBUT'IONS TO GENERAL GEOLOGY, 1949 

of Rancho la Brea, there were certain limiting factors 

to their use. They required an extraordinary growth 

period. 

These teeth are found to be represented by crowns 65 mm. in 

length in a kitten in which there is no indication of the formation 

of the enamel for the crown of the permanent carnassial. The 

permanent canine was not erupted and in full function until 

the other teeth bad begun to show some evidence of wear. 

On the other hand, a large number of old animals 

show loss of one or both canines by breakage. Merriam 

and Stock therefore concluded (1912, p. 55) that the 

peculiar mechanism of the animal was in active operation a relatively short time and suggest that the 

degree of specialization exhibited was dangerously near the 

borderline of overspecialization or at any rate at a point where 

a slight change in environment might work a severe hardship. 

Regardless of the mechanical efficiency of the sabers 

their thickness and recurvature must have made them 

difficult weapons to handle. Specializations of the 

skull which permitted a wide enough gape and a quick 

enough recovery to position to allow the animal to 

strike effectively could, and quite apparently did, take 

place. Nevertheless, choosing just the right position 

at which to strike, and particularly withdrawing such 

thick, elongate, recurved structures n1ust have been a 

dangerous undertaking, except under certain favorable 

conditions. 

The canines of the "great" cats of today are sharp, 

short, tubular teeth which can be used with the speed 

and efficiency of daggers. If the first strike is not successful they can be withdrawn and a second more effective one made. The head in all of the P a;nthera is 

small, the neck flexible. Smilodon on the contrary had 

to maneuver with bayonets-turned the wrong way. 

The very specialization necessary for the use of the 

huge teeth made the head unwieldy and the neck stiff. 

The strike could be made but once and from one position. Once the sabers were embedded they were there 

to stay, until the victim died. Were an attack to be 

made in the manner of the lion or the tiger, the struggles of the victim, the forward momentum of both 

predator and prey, as well as the manipulation of the 

teeth themselves in the act of withdrawal must have 

resulted almost invariably in breaking the neck of the 

predator, or the sabers, or both. 

There are two situations, however, where these difficulties would be minimized. One is in sexual combat 

between males. Here the combatants are approximately the same size and use the same weapons. There 

is thus neither advantage nor disadvantage on either 

side. Moreover, the purpose of the attack is not to kill 

or fell the opponent but merely to drive him away. 

A severe blow, anywhere, on the top of the head for example, ·even if not lethal, would be sufficient to accomplish this. 

The other favorable situation was at the tar pits of 

Rancho la Brea where the victims, mired in the asphalt, could not run a way nor put up so violent a struggle as otherwise possible. They were also weakened in 

many cases by hunger, by thirst, by fright, and by 

wounds. The huge machairodonts could choose their 

own vantage point for an attack, taking all of the time 

necessary for the strike, and once the sabers were embedded, literally crush the animal until it bled to death. 

Merriam and Stock have described at some length an 

adaptation in the palate, which they think probably 

served to drain blood of the victim to the gullet of the 

attacker (Merriam and Stock, 1932, p. 36) . 

If Smtilodon did bleed prey to death in this way, it 

might explain the weakness of the lower jaw and lack 

of a protective flange for the upper canine. Because 

in this type of attack tbe lower jaw is simply dropped 

down to allow free play of the canine and does not 

close upward against the upper jaw, the depth and 

strength of the jaw as it is in H oplophoneus was not 

needed. A bony outgrowth, such as that of the flange 

to the mandible, develops ontogenetically by the mechanical stress exerted on the growing bone. The pressure of the elongating canine on the mandible, as that 

is forced up against it, would condition the growth of 

the flange. Thus, if no such pressure existed there 

would be no flange. 

The incisors in Smilodon (and in all machairodonts) 

are long, sharp, stout teeth that show wear with age. 

The lower canine shears against the upper lateral in-· 

cisor rather than the upper canine, especially in Smilodon. It seems probable, therefore, that the animal 

could tear flesh from prey by the use of these teeth 

alone without opening the mouth wide enough to allow 

full play <?f the canines. The food torn off by the incisors could be shifted back to the carnassail dentition 

without the aid of the canines. The peculiar wear of 

these teeth, which keeps them sharp even in old age, 

suggests that they played an important part in obtaining food. In youth, the relatively short canines could 

be used with the incisors, and as the period before the 

full eruption of the permanent canines includes a large 

part of the animal's life, this was the more common 

method of feeding. This same method could be continued, as pointed out above, even after the saber teeth 

reached full development. -

It may have been that in many cases the kill was 

made by a mature animal and then participated in by 

young individuals in which the canines had not yet 

reached their full development, with the carcass left 

for tbe feeble, the old, and the crippled. 

Of course, this mode of attack was not without its 

dangers. The predator was as frequently mired as the 

prey. Merriam and Stock point out that only an animal 

of t~e low mental capacity of Smilodon would have 

been so oblivious of the danger. 

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THE HABITS AND ADAPTATION OF HOPLOPHONEUS 135 

It should be ren1embered, also, that by the middle 

Pleistocene the true cats were making their competition felt. Smilodon was too large for effective ambush 

in trees, too stupid for the type of jungle stalking characteristic of the lion and tiger, and too slow to run down 

its victims. These modes of attack were being developed 

rapidly among the true Felidae: Felis atrow, the lynx, 

and the jaguar-remains of all of which are found at 

Rancho la Brea. It is evidence of the extraordinary 

adaptability of the machairodont stock and the effectiveness of the saber tooth mechanism that these animals 

were able to continue on in any habitat, under such stiff 

competition. Nevertheless, the balance was precarious 

and a shift of any sort in the environment, even the 

continued slow infiltration of the Felidae, would be 

sufficient to bring about extinction. 

The role of H oplophone~ts in the Oligocene fauna 

was entirely different. During the early Tertiary there 

were no true cats, no dogs, nor indeed any highly evolved 

carnivores of any description. H oplophoneus was unquestionably the most able and active predator in 

existence. Its only rivals were the small cynodictids 

whose role in the fauna was that of the mustelines of 

today-rather than the canids and the larger, but 

small-brained and ambulatory daphoenids with no particular equipment in the way of unusual strength or 

dental specialization or speed of limb. In fact, competition must have been largely between the saber tooth 

genera, H oplophoneus, Dinictis, and Eusmilis themselves, with Hoplophoneus by far the most successful 

throughout Chadronian and Orellan time. 

H oplophoneus was in no way a generalized animaL 

It was highly specialized for a particular role in the 

fauna of the time. Certain characters (such as the 

narrow cranium or the foot structure, which do not 

show any of the specializations characteristic of 1nodern 

Carnivora) may be considered generalized-but only in 

contrast with characters such as the dentition, that are 

more highly evolved. The combination of characters 

found in H oplopho·neus represents the culmination of a 

long evolutionary history from early creodont stock. 

It also represents the beginning of the machairodont 

phylum as is now known. This phylum in turn culminated in the Pleistocene saber tooth genera of North 

America and China. 

.REFERENCES CITED 

HouGH, JEAN, 1949, The s-ubspecies of H oplophonetts: a statistical study: Jour. Paleontology, vol. 23, no. 5, pp. 536-555. 

LEIDY, JosEPH, 1869, The extinct mammalian fauna of Dakota 

and Nebraska: Acad. Nat. Sci. Philadelphia Jour., 2d ser., 

VOl. 7. 

MATTHEW, W. D., 1910, The phylogeny of the Felidae: ~m. Mus. 

Nat. History Bull., vol. 28, pp. 289-316. 

MERRIAM, J. C., and STOCK, CHESTER, 1932, The Felidae of Rancho 

la Brea: Carnegie Inst. Washington Pub. 422. 

PococK, R. 1., 1939, The fauna of British India, including Ceylon 

and Burma. Mammalia, vol. 1, J3P· 323-330. 

Sco-:rT, W. B. and JEPSEN, GLEN L., 1936, The mammalian fauna of 

the White River Oligocene. Part I. Insectivera and Carnivora. Trans. Am. Phil. Soc. n. ser. vol. 25, pp. 1-153. 

SIMPSON, G. G., 1941a, The species of HopZophoneus: Am. Mus. 

Novitates 1123, pp. 1-27. 

--, 1941b, The function of saber-like canines in carnivorous 

mammals: Am. Mus. Novitates, no. 1131, pp. 1-27. 

.> 

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PLATES 26-31 

137 

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880405-50-2 
GEOLOGICAl, SURVEY PROFESSIONAL PAPER 221 PLATE 26 

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(Side \'icw of "kull aud lower ja\\. Colorado t· ni\'. Mus. 19163.) 
GE OLOG ICAL S R Y E \ PUOFE

SSIONAL PAPER 221 PLATE 27 

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PROFESSIONAL PAPER 221 PLATE 28 

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(Aut.ero-lateral Yiew of mOHiltt'd skeleton. Colorado Univ. M11~. 19163.) 
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PLATE .29 

Fore limb bones of I-loplophoneus primaevus latidens Thorpe 

(F. 8. N. :VI. 18184) T. 

FIGURE 1. Internal Yiew of seapula. 

FIGURE 2. External view of seapula. 

FwuRE 3. Posterior yiew of radiu:;. 

FIGUHE -t. Anterior view of radiu:;. 

FIGURE 5. Po~terior view of humerus. 

FIGUHE 6. AnteJ;"ior view of humerus. 

FIGURE 7. External view of ulna. 

FIGURE 8. Intemal view of ulna. 
PHOFESSIONAL PAPER 22l PLATE 29 

GEOLOmCAI• SURVEY 
PLATE 30 

Hind limb bones of Hoplophoneus primaevus latidens Thorpe 

[U.S.N. M. 18184] 

FIGURE 1. Posterior. view of femur. 

FIGURE 2. Anterior view of·femur. 

FIGURE· 3. Posterior view of tibia. 

FIGURE 4. Anterior view of tibia. 

FIGURE 5. Anterior view of fil>ula. 

FIGURE 6. Posterior view of fibula. 

FIGURE 7~ Dorsal view of hind foot. (The astragalus and calcaneum are rotated 

so that the lateral aspect is shown. 

FIGUHE. 8. External vie~ of pelvis. 
PROFESSIONAL PAPEH 221 PLATE 30 

GEOLOGICAL SURVEY 
(; EULOGI< 'A L , St:RVEY PHOFESSIONAL PAPER 221 PLATE 31 

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