Chapter XIV: History of the Carnivora (2)

The mustelines have shortened jaws and a reduced number of teeth, the molars being 1/2 or even 1/1 and the premolars varying from four to two, though three in each jaw is the usual number. The cranium is generally very long and the facial part of the skull short, but the soft snout may add considerably to the length of the face. The tympanic bullæ are single-chambered and little inflated, and the lower lip of the entrance is extended; the hard palate is usually continued well back of the teeth. The body is very long and the tail variable and, in most of the genera, is short rather than long. The limbs are short, the feet, except in one genus, five-toed and plantigrade or semi-plantigrade, and the claws are non-retractile. Terrestrial, arboreal, burrowing, aquatic and marine forms are all represented in the family.

So far as North America is concerned, it is scarcely practicable to do more than catalogue the genera of the successive geological epochs. Pleistocene mustelines were very modern in character, differing little from those now inhabiting the continent, though in some cases with different ranges, according to climatic fluctuations. Badgers, martens, skunks and others occurred then very much as they do now and the Boreal Wolverene extended down to Pennsylvania. Little is known of Pliocene mustelines, the Blanco having yielded fragments of only one genus of uncertain affinities and though several genera occurred in the lower Pliocene, but one, a marten (_Martes_), can be identified. Unquestionably, North America had many more Pliocene members of the family, but the conditions of preservation were unfavourable.

Much the same is true of the Miocene stages. In the upper Miocene there were a marten (_Martes_), a weasel (_Mustela_) and two otters (_†Potamotherium_ and the modern _Lutra_), of which the marten and the more primitive otter went back to the middle Miocene. In the lower Miocene were several mustelines quite different from any now existing. One of those, _†Megalictis_, was truly gigantic, with a skull nearly as large as that of a Black Bear and having heavy, pointed claws. This and a similar genus, _†Ælurocyon_, were related to the Ratel (_Mellivora_) of India and Africa and, more closely, to the Wolverene. _†Oligobunis_, a much smaller animal, was apparently of the same group. This genus was also in the upper Oligocene, but there represented by a larger species, which was as large as a badger.

The White River beds have yielded but a single genus, _†Bunælurus_, which was the most primitive of American mustelines and had four premolars and two molars in each jaw, though the second upper molar was extremely small. The face was much less shortened than in the modern weasels and the tympanic bullæ were short and strongly inflated and had no tubular entrance, and were thus canine rather than musteline in form. The bony palate was not extended back of the teeth as it is in the modern genera. The same primitive group was much more abundant in the European Oligocene, migrating probably from Asia into Europe as well as into North America.

SOUTH AMERICAN FISSIPEDIA

The history of the South American carnivores is a comparatively brief one; the southern continent has representatives of the same five families as the northern, but most of the genera are different, the time since the great southward migration having been sufficient for the development of peculiar forms in the new environment. Among the dogs, there are to be noted the curious, close-haired, long-bodied and short-legged Bush-Dog (_Icticyon_) and the fox-like wolves (_Cerdocyon_), but there are no true foxes. Of the cats, the Puma differs little from that of North America, and the Jaguar (_Felis onca_) and Ocelot (_F. pardalis_) also range into the northern continent, but several small cats are confined to South America, which has no lynxes. There is but one bear (_Tremarctos ornatus_) of Andean range. Of the Procyonidæ, the northern _Procyon lotor_ is replaced by the Crab-eating Raccoon, _P. cancrivorus_, while the coatis (_Nasua_) and kinkajou (_Potos_) are chiefly Neotropical. Except for the otters, the genera of Mustelidæ are nearly all different; there are no badgers and a different genus of skunks (_Conepatus_) replaces the northern _Mephitis_; the Grison (_Grison_), Tayra (_Tayra_) and the Patagonian _Lyncodon_ are peculiar.

Even less can be done to trace the evolution of the South American genera than for the forms of the northern continent, whence migrated the more or less different ancestors of the former. The Pleistocene has yielded most of the modern genera, both existing and extinct species. An example of the latter was _Procyon †ursinus_ from the Brazilian caverns, a truly gigantic Raccoon, as large as a bear. The †sabre-tooth tigers (_†Smilodon_) and short-faced bears (_†Arctotherium_) were shared with North America. In the Pliocene a bear, a raccoon and a dog were the only known fissipedes, and in the Miocene none have been found, their place being taken by flesh-eating marsupials.

* * * * *

While the history of the Fissipedia, as outlined in the preceding pages, is sadly incomplete as compared with that of many ungulates, it is nevertheless highly suggestive. In each family the advance of specialization and adaptation to a narrow range of habits may be followed; generally speaking, the teeth were diminished in number and increased in size and were either simplified by the loss of parts, as in the cats, or complicated by the addition of new elements, as in the bears and raccoons. The brain grew larger and more convoluted and the cranium more capacious; in most of the families, the face was shortened, notably in the cats and mustelines, while in others, especially the dogs, it was elongated. In all of the early types there was a long and heavy tail, but in most series it underwent more or less reduction. There was little reduction of digits, and no fissipede has less than four. In modern dogs and cats there are five digits in the manus and four in the pes and the hyenas have four in each, as has one genus of mustelines; other modern genera throughout the suborder are pentadactyl.

It is significant that the more ancient members of the various families differed less than do the modern ones; the various groups, as they are traced back in time, would seem to be converging to a common ancestry, of which the lower Oligocene dogs were the least changed representatives, and it is probable that all the families of the Fissipedia were derived, directly or indirectly, from a single Eocene group of primitive flesh-eaters. The families, none of which is extinct, are not all of equal antiquity. So far as now appears, the dogs and viverrines are the most ancient, having become distinct in the upper Eocene; in the Oligocene were added the mustelines and cats; the raccoons branched off from the dogs in the lower Miocene, as did the bears in the upper Miocene. Finally, the hyenas appeared in the lower Pliocene, seemingly derived from the viverrines. The dogs passed through the greater part of their development in North America, where, during the Oligocene and Miocene, they were very abundant and varied, while at the same time they were comparatively rare in Europe and belonged chiefly to the phylum of the †bear-dogs. On the other hand, the remaining four families are of Old World origin, the bears and mustelines migrating to America, while the viverrines and hyenas did not.

SUBORDER †CREODONTA. †PRIMITIVE FLESH-EATERS

This group long preceded the Fissipedia in time, for they began their recorded history in the Paleocene and became extinct in the Oligocene. Through one family, the †Miacidæ, the †creodonts were broadly connected with the fissipedes, and it seems probable that that family was the ancestral stock from which all the fissipede families were derived. The other †creodont families died out without leaving descendants.

There is some difference of practice as to the number of families to be admitted; the table contains those listed in Professor Osborn’s book and also adopted by Dr. Schlosser. I should prefer a somewhat larger number of family groups, but the matter is one of secondary importance. Many genera are omitted.

I. †OXYCLÆNIDÆ.

_†Oxyclænus_, Paleoc. _†Deltatherium_, do.

II. †ARCTOCYONIDÆ.

_†Clænodon_, Paleoc. _†Anacodon_, low. Eoc.

III. †MESONYCHIDÆ.

_†Triisodon_, Paleoc. _†Dissacus_, do. _†Pachyæna_,
low. Eoc. _†Mesonyx_, mid. Eoc. _†Dromocyon_, do.
_†Harpagolestes_, mid. and up. Eoc.

IV. †OXYÆNIDÆ.

_†Palæonictis_, low. Eoc. _†Oxyæna_, do.
_†Patriofelis_, mid. Eoc. _†Limnocyon_, do.
_†Machairoides_, do. _†Oxyænodon_, up. Eoc.

V. †HYÆNODONTIDÆ.

_†Sinopa_, mid. Eoc. _†Stypolophus_, low. and mid.
Eoc. _†Tritemnodon_, mid. Eoc. _†Pterodon_, low.
Oligo. _†Hyænodon_, do.

VI. †MIACIDÆ.

_†Didymictis_, Paleoc. and low. Eoc. _†Viverravus_,
mid. Eoc. _†Miacis_, low. Eoc. _†Uintacyon_, low.
to up. Eoc. _†Oödectes_, mid. Eoc. _†Vulpavus_, do.
_†Palæarctonyx_, do.

The †Creodonta were an extremely varied assemblage, of carnivorous, omnivorous and presumably insectivorous habits, so that few statements, not subject to exceptions, can be made of them all. Only seven genera are known from skeletons, and several more from skulls, but most are represented only by jaws and teeth; limb- and foot-bones, however, give us a conception of the general structure of a considerable number. As a rule, the dentition was complete, according to the formula, _i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 3/3, × 2 = 44, but the first premolar or the last molar may be lost. The canines were always large, as was befitting for beasts of prey. In only one family, the Miacidæ, were the carnassial teeth confined to a single pair and those the same as in the Fissipedia, the fourth upper premolar and first lower molar; in all the other families there were either no sectorial teeth, or else there was more than one pair. In the Fissipedia the first is the largest of the lower molars, while in the †Creodonta (except the †Miacidæ) it was usually the smallest. The premolars were generally simple, compressed-conical teeth and the molars, with all their great variety, may be reduced to a common plan; those of the upper jaw were primitively tritubercular, with a triangle of two external and one internal cusps, and those of the lower jaw were in two distinct parts, an anterior, elevated triangle of three cusps and a low heel of two.

The skull was almost always very large in proportion to the size of the animal; the cranium, though long, was of small capacity and the face varied much in length in the different families. Primitively, the face and jaws were short in correlation with the small size of the teeth, and this primitive condition was modified in two opposite directions; in one the face and jaws were elongated, as the teeth enlarged, and in the other they were shortened still further. The zygomatic arches were stout and curved out strongly from the sides of the skull, making very wide openings, and, in almost all cases, the sagittal and occipital crests were very high, as would be necessary from the combination of powerful jaws and small brain-case (see p. 63). The tympanic bullæ were not ossified. The brain was extremely small, especially in the more ancient genera, and the convolutions were almost always few and simple, which indicates a low grade of intelligence and very marked inferiority to the Fissipedia.

In all the genera of which sufficient material has been obtained the body was long and had 19 or 20 trunk-vertebræ: in the lumbar and posterior part of the dorsal regions the processes by which the successive vertebræ were articulated together (zygapophyses) were cylindrical and interlocking, as in the artiodactyl ungulates (p. 360). To this general statement, the †Miacidæ formed a partial exception. The tail was very long and heavy in all the forms of which the caudal vertebræ are known, and this was probably true of all. The limbs were short and generally heavy; the femur had the third trochanter and the humerus, save in a few of the later genera, the epicondylar foramen, and the manus could, in nearly all, be freely rotated. Except in the most advanced forms of one family, the †Mesonychidæ, the feet were five-toed and plantigrade, or semi-plantigrade, and of decidedly primitive structure. The scapho-lunar bone of the Fissipedia (see p. 519) was not formed, its three elements, with very few exceptions, remaining separate. The astragalus nearly always had a shallow groove, or none at all. The claws were thick and blunt and the ungual phalanges cleft at the end, except in the †Arctocyonidæ and †Miacidæ, which had sharp claws and uncleft phalanges.

From this brief description, it is obvious that the †Miacidæ occupied a very isolated position among the †creodonts and, in my judgment, it would be better to transfer that family to the Fissipedia and include the others in a separate order.

Throughout the Paleocene and Eocene epochs the †Creodonta were numerous and varied, the first of the Fissipedia appearing in the upper Eocene. Till then the †creodonts were the only predaceous mammals in North America and Europe, and they were especially abundant in the former. Most members of the suborder and all the Paleocene forms were of small or moderate size, but some of the Eocene species were very large. In the Uinta the †creodonts were greatly decreased in numbers and in the White River there were only two genera of one family, the †Hyænodontidæ, and since the Oligocene the suborder has been extinct.

1. _†Miacidæ. Fissipede-like †Creodonts_

It is unfortunate that no member of this family is known from a complete skeleton, but the material collected is sufficient to give a fairly adequate conception of these most interesting animals. These were the only †creodonts with a single pair of carnassials, the fourth upper premolar and first lower molar, but in some of the genera the carnassials did not differ greatly from the other teeth. In the various genera the skull differed considerably in length and in the proportions of cranium and face; the brain-case was larger than in most other †creodonts and the brain more advanced, though smaller than in the fissipedes, and the sagittal and occipital crests were very prominent; the tympanic bullæ were not ossified. The humerus had the epicondylar foramen and the femur the third trochanter; in the wrist the scaphoid, lunar and central were separate, almost the only important difference from the Fissipedia and merely the primitive stage of the latter. The feet were pentadactyl and the digits were arranged in spreading fashion; the claws were small, sharp and partially retractile and the ungual phalanges not cleft at the tip.

Within the family several different phyla may be distinguished, one of which (_†Miacis_—_†Uintacyon_) led to the dogs, another to the †bear-dogs, or †amphicyons. A third phylum (_†Didymictis_—_†Viverravus_) is by several authorities regarded as ancestral to the civet family, or viverrines, of the Old World, and a fourth (_†Oödectes_, _†Vulpavus_) as the forerunner of the kinkajous (_Potos_). Except for the connection with the dogs, the hiatus in time between the supposed ancestors and descendants is too great to permit any confident statements. It seems very probable, however, that the †Miacidæ represented the common stock, from which the fissipede families were all derived, directly or indirectly, though for most of them the details of the connection remain to be learned.

We find thus a group separating itself from the other †creodonts in the older Paleocene and gradually assuming fissipede characteristics, at the same time dividing into several phyla. In the upper Eocene this group passed almost imperceptibly into the Fissipedia, more obviously into the dog family, which, as we have seen, represents the central line of fissipede development.

2. _†Mesonychidæ_

This family displayed, in certain respects, the highest degree of specialization attained by any †creodonts, for they were the only ones which acquired cursorial limbs and feet. The †mesonychids were prevailingly, but not exclusively, a North American family and their range in time was through the Paleocene and Eocene.

The teeth, in the more advanced genera, had a curious mingling of primitive and specialized characters and none were sectorial in the proper sense of the word. The incisors were small, the canines large and bear-like and the premolars simple. The upper molars were very primitive, retaining the original tritubercular pattern, except that the two outer cusps were joined together, but the lower molars had lost all the internal cusps, which gave them a carnassial appearance; they were not sectorial, however, for their cusps wore directly against the upper teeth, not shearing past them, and were greatly blunted and worn down by use.

The last of the family was _†Harpagolestes_, of the Uinta and Bridger, one of the largest of the †creodonts. The skull, which was of disproportionate size, exceeded that of the Grizzly Bear; the upper profile of the skull had considerable resemblance to that of a bear in the steep forward descent at the fore head. The teeth were more reduced than in the other members of the family through the loss of the second premolar and third molar of the upper jaw. The skeleton is little known, but the humerus had a long and prominent deltoid crest and an epicondylar foramen.

In the middle Bridger stage were closely allied and very similar genera, _†Mesonyx_ and _†Dromocyon_ (Fig. 139, p. 269), which were like small, big-headed wolves, for the skull was as long as that of a Black Bear. Though the cranium was very long, the brain-chamber was very small and the sagittal crest enormously high, to afford surface for the attachment of the powerful jaw-muscles. The tympanic bullæ were ossified and had quite long, tubular entrances, a feature which has been found in no other †creodont skull. The face and jaws were also elongate, giving the head quite a wolf-like appearance. The neck and body were of moderate length, but the tail was extremely long, slender and whip-like.

The limbs and feet were more specialized than in any other †creodont and the changes were all in the direction of adaptation to swift running. The humerus was very smooth, with low ridges, and, alone among †creodonts, had in these genera no epicondylar foramen, though the femur retained the third trochanter. The radius was broad and so interlocked with the humerus as to prevent any rotation of the manus. The feet were four-toed and much resembled those of the modern dogs and hyenas. In each foot the metapodials were closely appressed and parallel, not spreading, but arranged in two symmetrical pairs, a longer median and shorter lateral pair, much on the artiodactyl plan; the ankle-bone (astragalus) also had an artiodactyl look, with its deeply grooved surface for the tibia and pulley-like lower end. The ungual phalanges were so short and broad as almost to suggest hoofs rather than claws. It is clear that the gait was as fully digitigrade as in a modern wolf and these were the only †creodonts of which this is known to be true. These were somewhat puzzling animals; the whole structure of the limbs and feet was that of cursorial types, but the broad, blunt claws do not suggest the running down and capture of prey, nor were the teeth those of savage killers. The speed may have been defensive, to escape from enemies, and the food may have been largely vegetable.

Ancestors of these Bridger genera have not been found yet in the Wasatch, a time when the family was represented by _†Pachyæna_, some of the species of which were very large, rivalling _†Harpagolestes_, which was descended from one or more of them. _†Pachyæna_ had extremely massive teeth and was not improbably a carrion-feeder of hyena-like habits, and it retained the epicondylar foramen of the humerus and pentadactyl feet.

Much more primitive was _†Dissacus_, of the upper Paleocene, which was very probably the direct ancestor of both the Wasatch and the Bridger genera. The upper molars were substantially as in the latter, but the lower molars had the internal cusp of the primitive triangle, though the heel was trenchant, and had lost its inner cusps. The feet had five well-developed digits, which were arranged in spreading fashion, and the gait was plantigrade. The claws were longer, more pointed and much less hoof-like than in the Bridger genera. The Puerco genus _†Triisodon_ may or may not have been directly ancestral to _†Dissacus_; at all events, it was very nearly what the desired ancestor must have been. The teeth were much less specialized than in _†Dissacus_; the tritubercular upper molars were broader and their external cusps were more separated, while in the lower molars the anterior triangle was made up of three nearly equal cusps and the heel was low and basin-shaped. The skull had an extremely narrow brain-case and a long, heavy sagittal crest.

The most interesting feature in the history of the †Mesonychidæ is the demonstrable derivation of the cursorial, digitigrade, four-toed and almost hoofed Bridger genera from the plantigrade, five-toed Torrejon genus, which had sharp claws. To all appearances, this family was the †creodont analogue of the hyenas.

3, 4. _†Arctocyonidæ and †Oxyclænidæ_

This second †creodont family which had no carnassial teeth has received the not very happily chosen name of †Arctocyonidæ, or “bear-dogs,” though they were not related to either bears or dogs. The family was a very ancient one and has been found only in the Paleocene and lower Eocene (Torrejon and Wasatch) of North America and Europe. The molar teeth were very low-crowned and quadritubercular, with numerous small tubercles in addition to the four principal cusps, a pattern which was rather pig-like than bear-like. The Wasatch genus _†Anacodon_, known only from jaws and teeth, had reduced premolars, both in size and number, while in the Torrejon genus, _†Clænodon_, the premolars, though small, were present in full number. The skull was like that of _†Mesonyx_ in the relative lengths of cranium and face, the very small size of the brain-case and the great prominence of the occipital and sagittal crests. The feet were pentadactyl and plantigrade and the claws were long, thin and pointed, and the ungual phalanges were not cleft at the tip, the only †creodont family, except the †Miacidæ, of which this was true.

Of the †Oxyclænidæ, very little is known and they may not have been †creodonts at all. They were quite small animals, with sharp-cusped tritubercular upper molars and lower molars with high anterior triangle and low heel. This is the type of dentition from which all the divergent †creodont types were doubtless derived. The family was Paleocene.

5. _†Hyænodontidæ_

This was the last of the †creodont families to survive, being quite common in the lower Oligocene of North America and Europe and in the upper Eocene of the latter also. The family became extinct in the upper Eocene of North America and the White River genera were not of native origin, but migrants from the Old World. One of the more abundant predaceous genera of White River times was the European _†Hyænodon_; it was represented by several species which ranged in size from a fox to a Black Bear. In this genus the dentition was somewhat reduced, the incisors often numbering 2/2 and the molars constantly 2/3; there were three pairs of carnassial teeth on each side, of which the pair formed by the second upper and third lower molar was the largest and most efficient, the other pairs being the first upper and second lower molar, the fourth upper premolar and first lower molar, the latter the smallest of the three. The upper molars had lost the internal cusp and the remaining, external portion consisted of a flattened-conical anterior cusp and a posterior trenchant ridge; the milk-teeth of _†Hyænodon_, as well as the permanent dentition of the ancestral genera, show that the anterior cusp was composed of the two external cusps of the primitive tritubercular tooth fused into one and that the trenchant ridge was a superadded element. The fourth upper premolar was a sectorial like that of the Fissipedia, but of an unfinished, ineffective sort. The third lower molar was very similar in shape to the carnassial of the cats and was composed of only two large, thin and trenchant cusps, which made a shearing blade, having lost the inner cusp of the primitive triangle and the heel. The first and second molars were like the third except in size and in retaining a vestige of the heel. The premolars were large and massive, almost hyena-like, which suggested the generic name. The canines were prominent and strong.

The skull, as in almost all †creodonts, was relatively very large, but in the various species there was considerable difference of shape; more commonly it was long and narrow, with elongate jaws, and was quite wolf-like in appearance, but in some of the species it was shorter and wider. The brain-case was more capacious and the brain more richly convoluted than in any other known †creodont, but the sagittal and occipital crests were very prominent. The neck was rather short, not equalling the head in length, the body elongate and the loins very muscular; the tail was fairly long and thick, but much less so than in most †creodonts. The limbs were short and, in most of the species, quite slender, though in some they were much stouter; the primitive features, such as the third trochanter of the femur, the epicondylar foramen of the humerus, the separate scaphoid, lunar and central in the carpus, were retained. The feet had five digits arranged in spreading fashion and were probably semi-digitigrade; the claws were so thick and blunt that they could hardly have served in seizing prey.

The restoration gives the animal quite a near resemblance to the modern hyenas and perhaps errs in making the likeness so close. From the whole structure of the skeleton and the form of the claws, it may be inferred that _†Hyænodon_ was not a swift runner or very efficient in the capture of prey. While probably savage fighters, they doubtless subsisted chiefly as carrion-feeders and scavengers.

Another doubtfully distinct genus, _†Hemipsalodon_, was so closely like, if not identical with, the much better known European _†Pterodon_, that the latter may be taken in place of it. _†Pterodon_ was similar in most respects to _†Hyænodon_, but distinctly less advanced, and though not the ancestor of the latter, serves to connect it with the older members of the series. _†Pterodon_ did not, so far as we know, penetrate North America south of the Canadian border, occurring in the lower White River of Alberta. In this genus the upper molars retained a large internal cusp, and the third molar, though small and not sectorial, had not been lost; the two external cusps were connate, but not completely fused together and the posterior ridge was not so well developed as in _†Hyænodon_, nor was the fourth upper premolar so nearly a carnassial. The lower molars were shearing blades, but distinct vestiges of the heel remained. So far as they are known, the skull and skeleton resembled those of _†Hyænodon_.

_†Hyænodon_ and _†Pterodon_ were evidently derived from a group of small †creodonts which, in the lower and middle Eocene, were spread all over the northern hemisphere, but it is not yet possible to select from the crowd of allied genera those which formed the actual steps of descent. These small animals were numerous and varied and are far better known in North America than in Europe and it is not at all improbable that some of the lower Eocene genera migrated to the Old World and there gave rise, among other forms, to _†Hyænodon_ and _†Pterodon_, which eventually returned to the land of their earlier ancestry. If confirmed, this will be an exceptionally interesting case of back and forth migration. However that may be, the American Eocene genera, _†Sinopa_ and _†Tritemnodon_, illustrate very well the ancestry of the Oligocene genera, as they must have been similar to the actual progenitors.

The first and most obvious difference from the Oligocene genera was the very much smaller size of the animals, few of the Eocene forms equalling a fox in height. The teeth were unreduced in number, and there were three pairs of carnassials. The first and second upper molars were not far removed from the primitive tritubercular form, but the two external cusps were close together and a small posterior cutting ridge was present; the third molar was progressively reduced in size. The three lower molars were carnassials of a rather imperfect kind and the first was the smallest of the series; the two outer cusps of the anterior primitive triangle formed the shearing blade and there was a basin-shaped heel. The skull was long, narrow and low and the cranial portion, despite the very small brain-case, was especially elongate, though face and jaws were also long; the sagittal crest was very prominent. The neck was of moderate length, the body long and slender and the tail extremely long. The short and delicate limbs were of very primitive character, but the radius had already lost the power of rotation; the feet had five spreading digits, armed with sharp claws. The †hyænodont relationships of these small animals are obvious in every part of their structure and yet, as would be expected, they were far less specialized. Probably, too, they were more active and successful hunters of prey, the smaller mammals and birds, less given to carrion-feeding. The line probably originated in the †Oxyclænidæ of the Paleocene.

6. _†Oxyænidæ_

The genera of this family had such feline characters that more than one writer has been misled into the belief that they were the ancestors of the cats. In this family there were two pairs of sectorial teeth, of which the larger pair was composed of the first upper and second lower molar, the smaller pair of the fourth upper premolar and first lower molar, as in the fissipedes. Of the three phyla within the family, the most specialized one ran a brief career, through the Wasatch, Wind River and Bridger, and then died out. The terminal member of this series, the Bridger genus _†Patriofelis_, had a skull as large as that of a lion, but the rest of the skeleton was not so large in proportion. The teeth were considerably reduced in number, the formula being: _i_ ?/2, _c_ 1/1, _p_ 3/3, _m_ 1/2, a loss of at least twelve from the primitive total of 44. The single upper molar was a large sectorial, which was formed much as in the †hyænodonts, the two external cusps connate, but not indistinguishably fused together, and a long, trenchant ridge behind, while the inner cusp had almost vanished. The second lower molar was very cat-like; its cutting blade was formed of two shearing cusps; of the inner cusp no trace was left, and of the heel merely a vestige. The first lower molar was smaller and less specialized, since it retained a small internal cusp and quite a large heel.

The skull was very large and massive, with elongate cranium and shortened face, the muzzle broad and abruptly truncate, not tapering; the brain-case was exceedingly small, with very long and prominent sagittal crest; the zygomatic arches were extremely heavy and curved outward boldly, so that the head was very wide, notwithstanding the absurdly small brain-case. The lower jaw was very deep and heavy and the chin abruptly rounded, with almost vertical front. The very unusual massiveness of the zygomatic arches and the great development of the crests and ridges for the attachment of the jaw-muscles, and the short, heavy lower jaw, all indicate a degree of power in the biting and shearing apparatus such as occurred in no other known †creodont.

The neck was of medium length, while the body, though actually elongate, was rather short as compared with most other †creodonts; the loins were very heavy and must have been extremely powerful in the living animal; in this region the articulations between the successive vertebræ were more complex than in any other member of the suborder; resembling the structure found in certain artiodactyls. The ribs were long and thick, the chest deep and capacious. Even for a †creodont, the tail was long and uncommonly thick.

The limbs, especially the anterior pair, were short and very stout; the humerus had an immensely developed deltoid ridge, which extended down for two-thirds the length of the shaft, and a very prominent supinator ridge; the fore-arm bones, particularly the ulna, were heavy and the radius had but a limited power of rotation. The feet were short and broad, with five complete, spreading toes, ending in thick and blunt-pointed claws.

_†Patriofelis_ was by far the most formidable of the Bridger Carnivora and, with the exception of _†Harpagolestes_, the largest. Its appearance must have been very curious, judged from the modern standpoint, with its disproportionately large, broad and rounded, leonine head, thick body and long, extremely heavy tail. The short, powerful limbs and broad feet must have given it something of the appearance of an otter. As in the case of so many other †creodonts, the combination of characters in the skeleton makes the question of habits a very puzzling one. The teeth had a form suited only to seizing and devouring prey, but the short legs and feet were not at all adapted to the swift movements, whether by long-continued running, or by stealthy approach and sudden leap, which are required in capturing agile prey, while the blunt claws could have rendered no service in holding a struggling creature. The form of the humerus and fore foot suggests burrowing habits, but it seems most unlikely that so large an animal could have lived in any such fashion. Terrestrial, arboreal and aquatic modes of life have all been suggested, and, all things considered, perhaps the least improbable conclusion is that _†Patriofelis_ was more or less aquatic and preyed chiefly upon the fishes and turtles with which the Bridger waters abounded. This hypothesis of Dr. Wortman’s is supported by the otter-like form of the animal. Whatever the principal kind of food was, it must have been something that greatly abraded the teeth, which in old animals were mere stumps.

The Wind River representatives of the series are known only from fragments, which, so far as they go, are not separable from _†Patriofelis_. On the other hand, the Wasatch genus, _†Oxyæna_, is fairly well understood. This genus was very like its Bridger successor, but differed from it in just such ways as would be expected in an immediately ancestral form, that is to say, in smaller size and less advanced specialization. The number of teeth was not so far diminished: _i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 2/2, × 2 = 40; the carnassial teeth were the same, but they were less effective; the fourth upper premolar and first upper molar had large inner cusps, and in the latter the postero-external trenchant ridge was shorter. The second upper molar, lacking in _†Patriofelis_, was a transversely placed ridge, which engaged the heel of the second lower molar. The latter tooth, though larger than the first molar, was much less completely trenchant than in _†Patriofelis_ and retained a small internal cusp and quite large heel. The skull resembled that of the Bridger genus, but the face was not so much shortened, the zygomatic arches were not so widely expanded or so massive, the lower jaw was not so heavy, nor the chin so steep. The body was relatively longer and more slender, the ribs being thinner and the chest shallower; the tail was even longer, but not nearly so thick. The articulations of the lumbar vertebræ were less complex. Except for their greater length and slenderness the limbs and feet were nearly identical with those of _†Patriofelis_.

In appearance, _†Oxyæna_ must have been merely a smaller, lighter and less powerful variant of the Bridger genus, and, no doubt, its habits of life were substantially the same; but in the details of structure were many minor differences, all of them in the direction of greater primitiveness in the more ancient animal.

The second phylum of the family was represented in the Uinta and Bridger stages by a group of small species, which were survivors of still more ancient and primitive progenitors of the family. In the typical genus, _†Limnocyon_, the dental formula was the same as in _†Oxyæna_: _i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 2/2, but the first upper molar had its two external cusps well separated and a much lower posterior cutting ridge, while the inner cusp was much larger. The second upper molar, though transversely placed, had all the elements of the primitive tritubercular tooth, the pattern from which all the varied types of †creodont upper molars were derived by the addition or suppression of parts. The two lower molars were very primitive, having a high anterior triangle of three cusps, forming an imperfect shearing blade, and a low heel. This dentition was on nearly the same plan as that of the small, contemporary †hyænodonts, but the emphasis of development, so to speak, was differently placed. In the †hyænodonts there were three pairs of sectorials and the best-developed pair was made up of the second upper and third lower molar; while in _†Limnocyon_ the third molar was lost, and there were but two pairs of sectorials, of which the largest pair was the first upper and second lower molar, as was also true of _†Oxyæna_ and _†Patriofelis_.

The skull of _†Limnocyon_ had a much longer facial region, and more elongate and slender jaws than in the last-named genera, and the feet must have been quite different, with less spreading digits. _†Limnocyon_ thus tends to indicate a common origin for the †oxyænids and †hyænodonts, though these common ancestors are still unknown.

A very interesting genus of this series, _†Machairoides_, of the Bridger, shows another imitation of the cats, the flanges of the lower jaw indicating sabre-like upper canines.

Another genus, _†Palæonictis_, of the Wasatch, found also in France, is sometimes referred to the †Oxyænidæ and sometimes made the type of a distinct family, but is too incompletely known for final reference. It had the same number of teeth as _†Oxyæna_, but the principal pair of carnassials was the fourth upper premolar and first lower molar, as in the Fissipedia, the first upper and second lower molar forming the subsidiary pair. The first upper molar was hardly sectorial at all; its two outer cusps were long, sharp-pointed cones, and the posterior cutting ridge was a mere tubercle. The skull had a short, cat-like face. The genus left no successors.

* * * * *

This concludes the long story of the Carnivora, so far as it has been recovered from the rocks. Incomplete as it is, and full of unsolved problems, it yet enables us to follow, somewhat vaguely, but with a general kind of accuracy, the development of the various modifications which characterized the different families and genera of the group.

The more ancient and primitive suborder, the †Creodonta, made its first recorded appearance in the lower Paleocene and was, no doubt, derived from Mesozoic ancestors, which cannot yet be distinguished among the very imperfectly understood mammals of that era. In the upper Paleocene, if not before, the †creodonts had spread over the northern hemisphere and had begun to diverge into a number of families, which continued to diverge more and more widely throughout the Eocene epoch, as they became more specialized and adapted to different habits of life. From the most primitive group, represented more or less accurately by the †Oxyclænidæ, may be traced the several lines of diverging adaptations incorporated in the various families, some of which had become distinctly recognizable in the lower Paleocene, others in the upper, while all were in existence in the lower Eocene. In one series, the †Mesonychidæ, the upper teeth underwent comparatively little change, while the lower ones lost the inner cusps, but no carnassials were formed. The face and jaws were elongated and the limbs and feet became adapted to cursorial habits, and the more advanced genera had four-toed, completely digitigrade feet, with blunt, almost hoof-like claws. A second series, the †Arctocyonidæ, likewise failed to develop sectorial teeth, the molars becoming quadritubercular, with many accessory tubercles, and assuming a bear-like or pig-like pattern, while the premolars were reduced in size. The pentadactyl feet had sharp claws.

In the †Oxyænidæ two pairs of carnassial teeth were formed, of which the larger and more effective pair were the first upper and second lower molar, the smaller pair the fourth upper premolar and first lower molar. The teeth were diminished in number, first by the loss of the last molar, then the suppression of the first premolar and finally by that of the third incisor and second upper molar; the remaining teeth were enlarged. The upper carnassial molar (the first) was formed by the approximation and partial fusion of the two external cusps and the addition of a trenchant ridge behind these, and by the reduction and eventual loss of the internal cusp, thus becoming more exclusively shearing in function. The second lower molar also lost the inner cusp and the heel, becoming remarkably cat-like in form; the first was similar, but less simplified. The face and jaws were greatly shortened, which, with the widely expanded zygomatic arches, gave the head a very cat-like appearance. The body and tail were long, the limbs short and thick, and the feet had spreading toes and blunt claws. Save for a notable increase in size and muscular power, the †oxyænids showed but little change within the family.

The †Hyænodontidæ differed from the †oxyænids in the retention of all or nearly all the teeth and in having three pairs of sectorials, of which the largest pair was the second upper and third lower molar, but resembled them in the mode of forming these sectorials and in the cat-like form of the inferior ones. Although the actual line of descent was not through these genera, the series, _†Sinopa_—_†Tritemnodon_—_†Pterodon_—_†Hyænodon_, extending from the lower Eocene into the Oligocene, displays perfectly the successive steps in the transformation of the teeth. The skull underwent a corresponding series of changes, ending in long-faced, long-jawed, wolf-like forms, with larger brain-case than in any other †creodonts. The elongated form of body was retained, but the tail was reduced to moderate proportions. The limbs and feet did not change greatly, except in size and in the greater bluntness of the claws.

The †Miacidæ, if not actually referable to the Fissipedia, at least anticipated them in the mode of carnassial development. The upper molars changed very little from the primitive tritubercular plan, but the fourth upper premolar was enlarged and acquired a trenchant ridge behind the original single outer cusp. The lower molars were at first all alike, except in size, the first being the largest; they had the primitive pattern common to the earlier members of nearly all the †creodont families, of an elevated anterior triangle of three subequal cusps and low, basin-like heel. The first molar grew larger in the successive genera and, by the enlargement of the two external cusps of the primitive triangle and reduction of the inner one, gradually became an efficient sectorial, the fourth upper premolar keeping pace with it. In proportion as the first lower molar was elaborated, the second and third were reduced in size and the anterior triangle was lowered to the level of the heel, these teeth thus becoming tubercular. All the †Miacidæ were small animals, none attaining the stature of a fox, though some had heads as large. From this family, as was pointed out above, probably arose all of the Fissipedia, the history of which it is needless to repeat.