CHAPTER XIV

HISTORY OF THE CARNIVORA

The story of the hoofed mammals, as sketched in brief outline in the preceding chapters (VIII-XIII), is a curious mixture of relatively full and satisfactory paragraphs, with scanty, broken and unintelligible ones, not to mention those which have not yet been brought to light at all. With all its gaps and defects, which inhere in the nature of things, the history of the various ungulate series is the best that the palæontology of mammals has to offer and constitutes a very strong and solid argument for the theory of evolution. For the Carnivora the story is less complete and for obvious reasons. Individual abundance was a very large factor in determining the chances of preservation in the fossil state for any given species, and, as a rule, whole skeletons are found only when the species was fossilized in large numbers. In any region the Carnivora are less numerous than the herbivora upon which they prey, and while most ungulates live in larger or smaller herds, the carnivores are mostly solitary.

The Carnivora are divisible into three well-marked suborders, called respectively the Pinnipedia, Fissipedia and †Creodonta. The Pinnipedia, seals, walruses, etc., which are almost purely marine in habitat, are not dealt with in this book, since so little can be learned of them from the fossils, and the †Creodonta, an extremely ancient and primitive group, will be treated separately. The Fissipedia are chiefly terrestrial, though they include the otters, and their subdivisions, so far as the American forms are concerned, are shown in the following table, which, it should be observed, omits several genera. Unless otherwise noted, the genera are North American.

Suborder FISSIPEDIA. Land Carnivora

I. CANIDÆ, Dogs, Wolves, Foxes, etc.

_Canis_, Wolves, Pleist. and Rec. _Vulpes_, Red Fox, do. _Urocyon_, Grey Fox, do. _Cerdocyon_, fox-like wolves, S. A., do. _Icticyon_, Bush-Dog, S. A., do. _?Cyon_, Dhole, mid. and up. Mioc. _†Dinocynops_, S. A., Pleist. _†Ælurodon_, up. Mioc. and low. Plioc. _†Tephrocyon_, mid. Mioc. to low. Plioc. _†Borophagus_, up. Mioc. to mid. Plioc. _†Ischyrocyon_, up. Mioc. _†Amphicyon_, mid. Mioc. to low. Plioc. _†Daphœnodon_, low. Mioc. _†Enhydrocyon_, up. Oligo. _†Temnocyon_, up. Oligo. _†Mesocyon_, up. Oligo. _†Cynodesmus_, low. Mioc. _†Daphœnus_, Oligo. _†Cynodictis_, Oligo. _†Procynodictis_, up. Eoc.

II. PROCYONIDÆ, Raccoons, etc.

_Procyon_, Raccoons, N. and S. A., Pleist. and Rec. _Nasua_, Coatis, S. A., Pleist. and Rec., now extending to Calif. _†Cyonasua_, S. A., up. Plioc. _Bassariscus_, Cacomistle, low. Plioc. to Rec. _†Phlaocyon_, low. Mioc. _†Leptarctus_, up. Mioc. _Potos_, Kinkajou, Neotropical, Recent.

III. URSIDÆ, Bears.

_Ursus_, true Bears, Pleist. and Rec. _Tremarctos_, Spectacled Bear, S. A. _†Arctotherium_, †Short-faced Bears, N. and S. A., Pleist.

IV. MUSTELIDÆ, Martens, Weasels, etc.

_Mustela_, Weasels, mid. Mioc. to Rec. _Grison_, Grisón, S. A., Pleist. to Rec. _Tayra_, Tayra, do. _Martes_, Martens, up. Mioc. to Rec. _Gulo_, Wolverene, Pleist. and Rec. _†Canimartes_, mid. Plioc. _†Brachypsalis_, up. Mioc. _†Megalictis_, low. Mioc. _†Ælurocyon_, do. _†Oligobunis_, up. Oligo. and low. Mioc. _†Bunælurus_, low. Oligo. _Mephitis_, Skunk, Pleist. and Rec. _Spilogale_, Spotted Skunk, do. _Conepatus_, S. A. Skunk, Pleist. and Rec., N. A., Rec. _Taxidea_, Badger, Pleist. and Rec. _Lutra_, Otters, up. Mioc. to Rec., S. A., Pleist. and Rec. _Latax_, Sea-Otter.

V. FELIDÆ. Cats.

_Felis_, true Cats, N. A., low. Plioc. to Rec., S. A., Pleist. and Rec. _Lynx_, Lynx, Pleist. and Rec. _†Pseudælurus_, mid. and up. Mioc. _†Smilodon_, Sabre-tooth Tiger, N. and S. A., Pleist. _?†Machairodus_, mid. Mioc. to Plioc. _†Nimravus_, up. Oligo. _†Archælurus_, do. _†Hoplophoneus_, Oligo. _†Dinictis_, do. _†Eusmilus_, low. Oligo.

Two families, the hyenas (Hyænidæ) and civet-cats (Viverridæ), are omitted from the table because they apparently never reached the western hemisphere. The bears, of Old World origin, invaded America at a very late period and are not certainly known here before the Pleistocene. The other four families were well represented in North American history, though the great weasel tribe (Mustelidæ) went through the greater part of its history in the Old World. None of the families is indigenous in South America, and all of the five families which it now shares with North America came in in the series of immigrations, of which the first recorded effects are found in the Pliocene and continued into the Pleistocene.

The Fissipedia are adapted to a great variety of habits and modes of life and consequently there is considerable diversity of structure among them, though they all form a homogeneous, natural group. The dogs (Canidæ) are terrestrial, neither swimmers nor climbers; some, like the foxes, are solitary, others, like the wolves, hunt in packs and nearly all are strong, swift runners. The cats (Felidæ) which have a remarkable range of size, are terrestrial or arboreal; they take their prey by stalking and leaping upon it, not by running it down. The bears (Ursidæ) are mostly omnivorous, not very often killing prey, and largely vegetarian in diet. The raccoons (Procyonidæ) are chiefly arboreal and omnivorous. The very large and varied weasel family (Mustelidæ) have different habits, though nearly all are fierce and bloodthirsty. Otters and sea-otters are aquatic and prey chiefly on fish; minks and fishers are semi-aquatic; martens are arboreal, skunks terrestrial and badgers fossorial.

While there is thus much diversity of habit with corresponding differences of structure among the Fissipedia, there is a certain unity of plan recognizable among them all. With but few exceptions, the incisors are present in full number and the canines are formidable lacerating weapons. Especially characteristic of the dentition are the “sectorial” or “carnassial” teeth, always the fourth upper premolar and first lower molar, which form a pair of shearing blades, the premolar biting outside. In the bears and most of the raccoons the teeth are tuberculated, in adaptation to the omnivorous habit, and the carnassials have lost the shearing form, though clearly derived from that type. The skull has powerful jaws, and the crests and ridges for the attachment of the jaw muscles are prominent except in very small animals, and the stout, boldly outcurving zygomatic arches are very characteristic. The face may be elongate, as in the dogs, or extremely short, as in the cats, or of intermediate length; the brain-case is relatively capacious, and the orbits, except in the cats, are widely open behind. The neck is never very long, but the body often is, and the tail varies greatly in length, as do also the limbs. There is great difference, too, between the various families in the prominence of the processes on the limb-bones for the attachment of muscles, as expressive of the muscular development of the limbs, and also in the extent to which the fore foot can be rotated and used for grasping. In all existing Fissipedia the femur has no third trochanter, but many extinct genera possessed it. The bones of the fore-arm and lower leg are always separate and uninterrupted.

In the wrist (_carpus_) there is always a large bone, the _scapho-lunar_, which is made up by the coalescence of three elements, the scaphoid, lunar and central, a feature which, though recurring in a few other mammals, is essentially characteristic of the modern Carnivora. The feet are armed with claws more or less sharp, which in some families, notably the cats, are retractile and may be folded back into the foot. The gait may be plantigrade, as in the raccoons and bears, or digitigrade, as in the dogs and cats, or intermediate in character.

Throughout the Paleocene and most of the Eocene, there were no Fissipedia, the flesh-eaters all belonging to the extinct †Creodonta, and the first clearly recognizable fissipedes occurred in the upper Eocene or Uinta.

1. _Canidæ. Dogs, Wolves, Foxes, etc._

This family, which may with convenience be called simply dogs, is at present the most widely distributed of the families of Fissipedia, occurring in every continent, even Australia, and ranging through all climates almost from pole to pole. They are a singularly homogeneous family and show few differences of structure; such differences as there are affect chiefly the number and size of the teeth and external characters, such as the size of the ears, length and colouring of the hair, etc. The many domestic breeds are not here considered. Almost alone among the Fissipedia the dogs capture their prey by running it down, and they are endowed with remarkable speed and endurance. The entire organism, especially the limbs and feet, are adapted to cursorial habits.

For the purpose of comparison with the extinct genera of the family, some account of a wolf will suffice. The wolves, like most other members of the family, have a larger number of teeth than is usual in the suborder, as appears from the formula: _i_ 3/3, _c_ 1/1, _p_ 4/4, _m_ 3/3, × 2 = 42, that is to say, only the third upper molar has been lost from the typical number, though the third lower is very small and seemingly on the point of disappearance (Fig. 44, p. 93). The upper sectorial tooth, the fourth premolar, has its shearing blade made up of two sharp-edged cusps, one behind the other, and there is a small internal cusp carried on a separate root; the upper molars are triangular and tritubercular and are used for crushing. The lower sectorial, the first molar, has an anterior blade of two shearing cusps, with the remnant of a third, and a low, basin-like posterior “heel.”

The skull is characterized by the long face and jaws and by the structure of the auditory region; the tympanic bones are inflated into large oval bullæ, which are hollow and undivided, and the external opening of each is an irregular hole, without tubular prolongation. There is an alisphenoid canal for the passage of the internal carotid artery. The neck, body and tail are of moderate length and the vertebræ of the loins are not conspicuously large and heavy. There is no collar-bone. The limb-bones have a distinct, though superficial, resemblance to those of hoofed animals; the humerus has no very prominent ridges for the attachment of muscles and no epicondylar foramen, and the femur no third trochanter. The fore-arm bones are separate, but are so articulated together and with the humerus as to give the fore foot no power of rotation. The manus in all existing wild species has five digits, though the pollex or first digit is very small, a mere dew-claw; the four functional digits are arranged in two symmetrical pairs, very much as in the artiodactyls, a longer median pair, of which the metacarpals have a nearly square cross-section, and a shorter lateral pair (2d and 5th) of more trihedral form. All the metacarpals are closely appressed and almost parallel. The pes has four digits arranged in similar fashion. The claws are blunt and non-retractile, and are of little use in seizing or lacerating prey, but are useful in digging. The ungual phalanges have no bony hoods reflected over the base of the claw. All modern forms are digitigrade.

Materials are lacking for the construction of any such detailed phylogeny of the dogs as has been accomplished for many ungulates. Many of the extinct genera are known only from skulls, or even jaws, and the well-preserved skulls are too few to form distinctly defined and continuous series. On the other hand, there is every reason to believe that the canine genera of the successive geological stages did approximately represent the successive steps of development within the family, though it is difficult to distinguish between the phyla.

The Pleistocene dogs, for the most part, differed little from the Recent ones; there were some very large species like the _Canis †dirus_ (Frontispiece) of the Mississippi Valley and the Pacific Coast. Two very peculiar genera have been reported. One (_†Pachycyon_), from a cave in Virginia, had remarkably short, stout and strongly curved limb-bones, which suggest otter-like habits; the other (_†Hyænognathus_), from California, had a very short face and extremely massive lower jaw and very heavy teeth; it was probably like a hyena in appearance.

[Illustration: FIG. 255.—Skull of _†Cynodesmus thoöides_, a lower Miocene wolf. Princeton University Museum. Compare with Fig. 7, p. 62.]

As far back as the Blanco stage of the middle Pliocene, remains occur which are assigned to the modern genus _Canis_, though better preserved specimens would probably require their removal from that genus. In the lower Pliocene the phylum of the true wolves was represented by _†Tephrocyon_, which, so far as it is known, differed only in minor details from _Canis_, and _†Tephrocyon_ went back to the middle Miocene. What would appear to be its direct ancestor is _†Cynodesmus_, of the lower Miocene, which, in view of the long lapse of time involved, differed less from the modern wolves than one would have supposed, but the differences are significant, as pointing back to a far more primitive type of structure. _†Cynodesmus_ was a small animal, intermediate in size between a Red Fox and a Coyote. The dental formula was the same as in _Canis_, but the teeth were relatively smaller and more closely crowded, as the face and jaws were shorter and the cranium, though longer, had a less capacious brain-chamber. The cast of this chamber, which very perfectly reproduces the form of the brain, shows that the latter was not only smaller but less convoluted than in the modern animals, and this, in turn, denotes a lower grade of intelligence. The limb-bones were like those of wolves, but the feet were quite different. In the manus the first digit, or pollex, was much less reduced, though considerably shorter than the other digits, which were not in two symmetrical pairs, but were all of different lengths, not closely appressed, but arranged in radiating fashion; the metacarpals had not yet acquired the quadrate or trihedral form, but were more oval in cross-section. The pes was more modernized, but had five digits, which is not true of any existing member of the family. The claws were thin and sharp and were slightly retractile, a power which has been completely lost in all the modern canids. Such an animal could hardly have been preëminently cursorial.

[Illustration: FIG. 256.—Skull of primitive “bear-dog” (_†Daphœnus felinus_). White River stage. (After Hatcher.)]

Out of the crowd of dog-like creatures in the John Day Oligocene, it is not yet practicable to select one which is to be taken as the ancestor of the Recent wolves through _†Cynodesmus_, nor can this be done with better assurance of success in the White River, though the beginning (_†Daphœnus_) of the †bear-dogs in that formation probably closely represents the ancestral stage sought for. It is likely that several of the phyla into which the family was divided became blended in a common stock at that stage.

[Illustration: FIG. 257.—Upper teeth of _†Daphœnus felinus_. _p. 4_ = fourth premolar. (After Hatcher.)]

[Illustration: FIG. 258.—Right manus of _†Daphœnus felinus_. _Sl._, scapho-lunar. _Py._, pyramidal. _Ps._, pisiform. _U._, unciform. (After Hatcher.) Compare with Fig. 32, p. 82.]

A second phylum, now entirely extinct, is that of the †bear-dogs, which is not certainly recorded later than the middle Pliocene, though some have been doubtfully reported from the older Pleistocene of the Great Plains and the remarkable Californian genus, _†Hyænognathus_, may have been an offshoot of the same stock. The phylum was characterized by the unusually large size of the molars and by certain other features, which, however, are not known to have persisted through the entire series from first to last. In the middle Pliocene lived some very large bear-dogs, of the genus _†Borophagus_, the teeth of which had a strong likeness to those of the hyenas and probably the animals had hyena-like habits, feeding largely upon carrion and crushing the stoutest bones with their massive teeth. The same, or a very similar, genus lived in the lower Pliocene, but none of the species of that date is at all well known. In the upper Miocene occurred several species which have been referred to the European genera, _†Amphicyon_ and _†Dinocyon_. The latter was an enormous canid, equalling in size the largest of living bears, the great Kadiak Bear of Alaska, and, though probably having a long and heavy tail, was much like a bear in appearance. The teeth indicate a more exclusively carnivorous habit than that of the bears and these may well have been savage and terrible beasts of prey.

[Illustration: FIG. 259.—Lower Miocene “†bear-dog” (_Daphœnodon superbus_). Restored from a skeleton in the Carnegie Museum, Pittsburgh.]

_†Amphicyon_, which had three upper molars, continued down through the middle Miocene, but was replaced in the lower by _†Daphœnodon_, which may or may not have been its direct ancestor. The uncertainty as to the exact relationship between the two genera will remain until more complete material shall have been obtained from the middle Miocene. _†Daphœnodon_ was the largest dog of its time, the contemporary wolves (_†Cynodesmus_) having been hardly half so large, but was much inferior in size to the huge †bear-dogs of the middle and upper Miocene. The skull resembled that of a large wolf, but the tympanic bullæ were smaller and more loosely attached and the molar teeth were relatively much larger, a persistent characteristic of this phylum. The very long and heavy tail was a cat-like feature. The limbs were comparatively short and stout; the humerus had the epicondylar foramen and the femur retained a trace of the third trochanter, both of which are lost in the modern members of the family. The feet were not at all canine in type, but rather resembled those of the ancient and unspecialized flesh-eaters. There were five digits in manus and pes and were not arranged in parallel pairs, but diverging; the metapodials were of oval cross-section, not squared, and their lower ends, which articulated with the first row of phalanges, had hemispherical surfaces, not semicylindrical. The claws were sharp and a remnant of former retractility was to be observed. Such an animal could hardly have been a strong and enduring runner and its structure suggests that it captured its prey by stalking and leaping upon it. The wolf-like head, with cat-like body, tail and limbs, made a strange combination, not closely paralleled by any existing carnivore.

Through the Oligocene the phylum was carried back by the several species of _†Daphœnus_, assuredly the ancestor of _†Daphœnodon_ and decidedly more primitive in many respects. The Oligocene genus was a much smaller animal than its lower Miocene successor, the larger species hardly equalling a Coyote; the teeth were smaller and more closely set, but the molars were proportionately large, while the carnassials were less finished and effective shearing blades. The skull was less distinctively dog-like and had a smaller brain-case, with very prominent sagittal and occipital crests, a longer cranium and shorter face; the tympanic bones were very small and so loosely attached to the skull that they are rarely found, a very striking difference from all existing dogs. The backbone was remarkable for the unusually large size of the lumbar vertebræ, a point of resemblance to the cats and suggesting that _†Daphœnus_ had great powers of leaping; there was a long, heavy, leopard-like tail, and the caudal vertebræ were very like those of the long-tailed cats. The limbs and feet were similar in character and proportions to those of _†Daphœnodon_, but the astragalus was less grooved for the tibia, the claws were rather more retractile and the gait was probably more plantigrade. There were so many cat-like features in the skeleton of _†Daphœnus_, that the observer cannot but suspect that these resemblances indicate a community of origin, but, until the Eocene ancestors of the cats are found, the question of relationship must remain an open one.

The most ancient member of the bear-dog phylum yet discovered appears to be one of the †creodont family of the †Miacidæ, found in the Uinta Eocene.

A short-lived branch of the canine stock was that of the so-called “†hyena-dogs,” a peculiar American type, which abounded in the upper Miocene and lower Pliocene and then became extinct. Traced backward, this brief series of species would appear to have sprung from the true wolves (_†Tephrocyon_) of the middle Miocene. The upper Miocene and lower Pliocene genus _†Ælurodon_ had several species, which differed considerably in size; the commoner of these were large wolves with very modern type of body, tail, limbs and feet, but having short and massive heads. The premolars were extremely thick and heavy, with such a resemblance to those of the hyenas, that these animals have sometimes been mistakenly regarded as ancestral to that family. The especial characteristic, however, of the series was in the form of the upper sectorial tooth, which was much more feline than canine in construction and has given occasion for the generic name which means “cat-tooth.”

A fourth phylum of the Canidæ, which would seem to be represented in the modern world by the Indian Dhole, or Wild Dog (_Cyon_), and perhaps by the Brazilian Bush-Dog (_Icticyon_), was characterized by the lower sectorial molar, the heel of which was not basin-like, as in the typical dogs, but trenchant and consisted of a single sharp-edged cusp, the external one of the primitive basin. Although there is no inherent improbability in the view that the Dhole and the Bush-Dog are derivatives of this phylum, no positive statement can yet be made, for the gap in the history is too great to be bridged with any assurance. The fossil members of the series did not come down later than the middle or upper Miocene and it is quite possible that the trenchant heel of the carnassial was developed more than once. The middle and lower Miocene members of the series are still very imperfectly known and it is only from the upper Oligocene (John Day) that well-preserved skeletons have been obtained. These pertain to an aberrant member of the phylum, the genus _†Temnocyon_, in which not only does the sectorial have a trenchant heel, but the second lower molar also was trenchant, having lost the two inner cusps, while the upper molars were as large as in the †bear-dogs.

_†Temnocyon_ was a comparatively large animal and its skeleton had a mixture of primitive and advanced characters, the latter predominating, so that this genus was not only the largest but also the most specialized canid of its time. There was the long, heavy tail, which all of the known Oligocene carnivores possessed, but the limbs were long and the gait was, it would seem, thoroughly digitigrade. While the epicondylar foramen was retained by the humerus and the third trochanter by the femur, those bones were otherwise very modern in form. The feet were five-toed, but the functional metapodials were parallel, appressed and with something of the quadrate shape. In very notable degree, therefore, the feet of _†Temnocyon_ anticipated the characters which the true wolves acquired considerably later. The less specialized _†Mesocyon_, which was smaller, was the ancestor of the Miocene forms and was, in turn, very probably derived from the White River _†Daphœnus_.

Still a fifth phylum, that of the †short-faced dogs (_†Enhydrocyon_), is very imperfectly known and has, so far, been found only in the lower Miocene and upper Oligocene. These also may have been descended from _†Daphœnus_, but the connection is not clear, nor has the relationship of the American genus to the extremely †short-faced dogs of the European Pliocene been determined.

[Illustration: FIG. 260.—Small, fox-like dog (_†Cynodictis gregarius_) of the White River. Restored from a skeleton in the American Museum of Natural History.]

Finally, so far as North America is concerned, there was a phylum of very small fox-like canids, which ranged from the lower Miocene to the upper Eocene and were very abundant, relatively speaking, in the White River and John Day. The dental formula was the same as in _Canis_ and the skull was narrow and slender, though the brain-chamber was proportionately capacious, and the face was quite short. The tympanic bullæ were large and inflated. The body and tail were long and the limbs quite short and weak. The humerus had no epicondylar foramen and the femur no third trochanter. The five-toed feet had the spreading arrangement of the metapodials seen in the more primitive fissipedes generally and the claws were sharp. In proportions and appearance these animals must have been more like civets or weasels than like dogs and it is evident that they were not swift runners. The series had its earliest representatives (_†Procynodictis_) in the Uinta and was doubtless derived from the †creodont family †Miacidæ. The White River species are referred to the European genus _†Cynodictis_, those of the John Day and lower Miocene to _†Nothocyon_, and it has been suggested that this series gave rise to the foxes, a suggestion which may prove to be true, but the very long gap in time between these animals and the most ancient known foxes prevents any conclusion.

To determine the mutual relationships of the six phyla of Canidæ which, from the Eocene onward, inhabited North America in such numbers, is a task of great difficulty and only a tentative solution of the problem can be offered. The central stock would seem to be nearly represented by the White River _†Daphœnus_, leading through _†Cynodesmus_ and _†Tephrocyon_, of the Miocene, to the wolves. A short-lived series, apparently given off from _†Tephrocyon_, was that of the †hyena-dogs, which flourished greatly in the upper Miocene and lower Pliocene and then became extinct. Another branch, that of the †bear-dogs, was derived from _†Daphœnus_, through _†Daphœnodon_ to _†Amphicyon_, _†Dinocyon_ and _†Borophagus_, the gigantic Miocene and Pliocene forms, ending perhaps in _†Hyœnognathus_ of the California Pleistocene. A third branch, represented by _†Mesocyon_ and _†Temnocyon_, is believed to be continued to-day by the Asiatic Dhole and the Brazilian Bush-Dog. The †short-faced dogs (_†Enhydrocyon_) are still very obscure. The last phylum, that of _†Nothocyon_, _†Cynodictis_, _†Procynodictis_, had become distinct in the upper Eocene and possibly gave rise to the foxes, but this is highly conjectural.

2. _Felidæ. Cats_

The only other fissipede group whose development in North America may be followed for a long period is that of the _†Sabre-Tooth Tigers_, the subfamily _†Machairodontinæ_, which have been extinct since the Pleistocene; the history of the True Cats (Felinæ) is much more obscure. In most respects the two subfamilies agreed closely and, as they became separate at least in the early Oligocene, they furnish instructive parallel series. The †sabre-tooth cats were terrible beasts of prey, which in most of the Tertiary period ranged over the whole northern hemisphere and in the Pleistocene or late Pliocene extended throughout South America.

[Illustration: FIG. 261.—Skull of the Pleistocene †sabre-tooth tiger (_†Smilodon californicus_, after Matthew). _P. 4_, fourth upper premolar, sectorial.]

The Pleistocene genus _†Smilodon_ (Frontispiece) belonged to nearly the whole western hemisphere and its various species were distributed from California and Pennsylvania on the north, to the Argentine Pampas on the south. The most obvious and striking peculiarities of _†Smilodon_ were in the teeth, which were much reduced in number, the formula being: _i_ 3/3-2, _c_ 1/1, _p_ 2/2-1, _m_ 1/1. The upper canine was a great, curved, scimitar-like blade, eight inches or more in length, with broad inner and outer faces, but quite thin transversely, and with finely serrate posterior edge. It is difficult to understand how these great tusks, which would seem to have blocked the entrance to the mouth, could have been effectively used, unless the creature could open its mouth much more widely than any existing mammal, so as to clear the points of the tusks, and would then strike with them as a snake does with its fangs. There are great anatomical difficulties in the way of accepting this explanation and the problem, which is the same as that presented by the †uintatheres (p. 446), is still unsolved. It is, however, quite certain that no arrangement which was disadvantageous, or even inefficient, could have persisted for such vast periods of time. The lower canine was much diminished and hardly larger than an incisor. The two upper premolars were the third and fourth of the original series; the third was small, but the fourth, the sectorial, was a very large and efficient shearing blade. In addition to the two external trenchant cusps of the blade, which are present in the Carnivora generally, the cats have a third small, anterior cusp which in _†Smilodon_ was large; the internal cusp had almost disappeared. The single upper molar was very small and so overlapped by the great carnassial as to be invisible from the side. The third lower premolar was small and unimportant and most specimens had lost it, leaving only the fourth, which was larger and evidently of functional value. The single molar was the sectorial, a large, thin, flattened blade, consisting of only two cusps, one behind the other, the trenchant edges of which met at nearly a right angle, and there was no trace of a heel.

[Illustration: FIG. 262.—Upper teeth of _†Smilodon_, left side. _P. 4_, fourth premolar. _m. 1_, first molar. (After Matthew.)]

The skull was in appearance closely similar to that of one of the great modern cats, such as the Lion or Tiger; with extremely shortened face, heavy and widely expanded zygomatic arches and very prominent sagittal crest. The tympanic bullæ were large and inflated, each divided by a septum into two chambers, but were not visible from the side, being covered externally by very large processes, which served for the attachment of some of the great muscles of the neck. The short, rounded, bullet-head of the true cats was thus repeated, but there were in the skull several interesting differences of detail, which it is not worth while to enumerate here. Suffice it to say, that some of these differences were due to the retention of primitive characters in the skull of _†Smilodon_, which have been lost in the modern felines, and others to special developments, in which the true cats did not share. The lower jaw had on each side a small, descending flange for the protection of the tusks, which, however, projected well below these flanges when the jaws were shut. The neck was heavy and the structure of its vertebræ was such as to suggest the presence of unusually powerful muscles; the back and loins were also uncommonly stout, in the larger species heavier than in the Lion or Tiger, but, in marked distinction from those modern forms, the tail was short. The limbs were shorter and much heavier in relation to the size of the body than in the great existing cats and must have been extremely powerful. The humerus usually had no epicondylar foramen, which all the true felines possess, though it was sometimes present. The feet also were very stout and armed with large retractile claws; the base of each claw was covered by a thin bony hood, an outgrowth of the ungual phalanx, which is very characteristic of the entire family. The hind foot had five digits, whereas no existing cat has more or less than four. The appearance of these animals must have been very much like that of the Lion or Tiger, aside from the unknown factors of mane and colour-markings, but differed in the great tusks, the short tail and the shorter and more massive legs and feet.

[Illustration: FIG. 263.—Skull of a †sabre-tooth tiger (_†Machairodus palmidens_) from the Miocene of France. (After Filhol.) _P. 4_, fourth upper premolar, sectorial tooth.]

On account of the very incomplete preservation of the material so far collected, little is known of the †sabre-tooth series in North America during the Pliocene and Miocene epochs. Remains of very large cats have been found in the lower Pliocene and upper Miocene, but it is uncertain whether they belong to the feline or the †machairodont subfamily. Some of the species have been referred to the genus _†Machairodus_, which ranged from the lower Pleistocene to the middle Miocene of Europe, and the reference may be correct, but is uncertain. However, the European representatives of that genus, which are much better known, will serve to show the developmental stage from which _†Smilodon_ was undoubtedly derived. The dental formula was the same as in the American genus, though there were generally two premolars in the lower jaw and in _†Smilodon_ generally but one; the individual teeth were formed on the same plan as in the latter, but were relatively smaller, and the very small, rudimentary upper molar was visible externally and was not overlapped and concealed by the great carnassial; the sabre-like tusk had not attained such great proportions. The skull of _†Machairodus_, the only part of the skeleton which is definitely known, was like that of _†Smilodon_ on a much smaller scale, but more primitive in several respects. It was longer and had a less capacious brain-case and less prominent sagittal and occipital crests. The large tympanic bullæ were conspicuous in the side-view of the skull, as the processes for the attachment of the neck-muscles had no such development as in _†Smilodon_. The descending flanges of the lower jaw were larger than in the latter.

The upper Oligocene (John Day) contained a large variety of cat-like forms, of which no less than five genera have been described; one of them (_†Pogonodon_), nearly as large as a Lion, would seem to have died out here without descendants, and two others, to which we shall return later, so combined the characters of true felines and †machairodonts as to be of uncertain reference. Two other genera, which are much commoner and better known, from the White River, will be described from specimens of that stage.

The White River, or lower Oligocene, had three highly interesting genera of †machairodonts, two of them known from nearly or quite complete skeletons. One of these (_†Hoplophoneus_), which was, it can hardly be doubted, the direct ancestor of the later typical †machairodonts, had several species, which are found in the various levels of the White River beds. The largest of these species was considerably smaller than _†Machairodus_, and the smallest and most ancient was inferior to the modern Wild Cat. The number of teeth was variable, but normally greater than in the genera above described, being _i_ 3/3, _c_ 1/1, _p_ 3-2/3-2, _m_ 1/1, × 2 = 28-32. The foremost premolar in each jaw was very small and often absent. The upper canine was a long and curved, but very thin, scimitar, finely serrate on both edges, while the lower canine was but little larger than the incisors. The carnassial teeth had a significant likeness to those of other fissipede families; the upper one, the fourth premolar, was relatively smaller than in _†Machairodus_ and its blade less effectively trenchant; the accessory antero-external cusp was present, though extremely small, and the internal cusp, which in _†Smilodon_ had almost disappeared, was quite large. The lower sectorial, the first molar, though already cat-like and consisting of two thin, broad and trenchant cusps in line, yet had vestiges of the heel and sometimes of the inner cusp. These vestiges were a connecting link between the highly specialized sectorial of the cats and the type usual among the Fissipedia, which is exemplified by the dogs. The small upper molar was less reduced than in the Miocene and Pliocene genera and plainly consisted of a larger external and smaller internal cusp.

[Illustration: FIG. 264.—White River †sabre-tooth tiger (_†Hoplophoneus primævus_). Restored from a skeleton in the American Museum. †Oreodonts (_†Merycoidodon_) in the background.]

Compared with that of other Fissipedia, the skull was short and broad, but in comparison with that of the modern cats and of _†Smilodon_, it was decidedly longer and narrower and the face was less abbreviated; the resemblance to _†Smilodon_ was very marked in the form of the cranium, but, of course, the skull of _†Hoplophoneus_ was distinctly more primitive in many respects. Thus, the orbit was much more widely open behind, the tympanic bullæ were but imperfectly ossified, and the perforations, or foramina, in the base of the skull, by which the nerves and blood-vessels communicated with the brain-chamber, were quite different and had more resemblance to those of the ancient dogs (_e.g._ _†Daphœnus_). In the classification of the Fissipedia much stress is laid upon the number and arrangement of these cranial foramina, and it is very significant to find the primitive dogs and cats agreeing so much more closely than do the modern members of these families. The lower jaw was relatively much stouter than in _†Smilodon_ and the anterior flanges much more prominent, projecting downward so far that, when the jaws were closed, the points of the tusks did not extend below the flanges. The animal could have made no use at all of the sabre-tusks unless the mouth could have been opened so widely as to clear their points.

With close general resemblance, allowing for the very inferior size, the skeleton of _†Hoplophoneus_ had many significant differences from that of _†Smilodon_. The neck was shorter and the body, especially the loins, longer, lighter and more slender and the tail very much longer, equalling that of the Leopard in relative length and surpassing it in thickness. The limbs were much less massive and somewhat differently proportioned, the upper arm being shorter and the fore-arm longer. The humerus, though far more slender than that of _†Smilodon_, was remarkable for the great development of the deltoid and supinator ridges, the latter, together with the shape of the radius, indicating very free rotation of the fore paw. The very prominent internal epicondyle was pierced by a foramen, and the femur had a distinct remnant of the third trochanter. The five-toed feet were comparatively small, but the claws were as completely retractile and as fully hooded as in any of the subsequent genera.

That _†Hoplophoneus_ was a fierce destroyer, is made evident by every part of its skeleton, and, like other cats, it no doubt subsisted upon warm-blooded animals, which it killed for itself, the size of the prey being determined by the size and power of the particular species of the †sabre-toothed genus. In view of the probable extent of the Oligocene forests, the restoration (Fig. 264) gives the animal a spotted coat and the general aspect is that of one of the modern spotted cats, but the protruding ends of the tusks and the relatively long head distinguish it from any existing cat. “The presence of long, knife-like canines is correlated with powerful grasping feet possessing highly developed retractile claws. With its powerful feet the animal clung to its prey, while it struck repeatedly with its thin, sharp sabres” (J. C. Merriam).

In the latter part of the White River stage lived one of the most highly specialized of the †machairodonts, so far, at least, as the dentition is concerned, for only the skull is known. This genus, _†Eusmilus_, which also occurred in the Oligocene of Europe, was apparently an example of premature specialization which led to nothing, for none of the subsequent genera could have been derived from it. The teeth were reduced to a minimum in number: _i_ 3/2, _c_ 1/1, _p_ 2/1, _m_ 1/1, × 2 = 24, one lower incisor and at least one premolar less in each jaw than had _†Hoplophoneus_. The canine tusk was very large and the flange of the lower jaw for its protection correspondingly elongated, being more prominent than in any other †machairodont. The American species, _†E. dakotensis_, was the largest carnivore of its time and not greatly inferior in size to the Lion.

Still another White River †machairodont, _†Dinictis_, differed in many interesting ways from its contemporary _†Hoplophoneus_, being more primitive and departing less from the ordinary fissipede type of structure. This is shown by the greater number of teeth, which was normally, _i_ 3/3, _c_ 1/1, _p_ 3/3, _m_ 1/2, × 2 = 34. The upper carnassial had a considerably larger internal cusp and the trenchant blade did not have the accessory anterior cusp, which is present in almost all other cats and was thus more dog-like than cat-like. The lower carnassial was more feline, but retained a remnant of the heel and of the inner cusp, but the latter was variable, being sometimes present in one side of the jaw and not in the other, a sign that it was on the point of disappearance. The upper molar was plainly a reduced form of the tritubercular tooth, in plan like that of the dogs, while the second lower molar was a very small, single-rooted tooth. No other American cat has such a primitive dentition as this, and, aside from the sabre-tusk, which was not nearly so long as in _†Hoplophoneus_, and the lower carnassial, it might almost as well have belonged to a dog or musteline.

[Illustration: FIG. 265.—Primitive †sabre-tooth (_†Dinictis felina_) from the White River. Restored from specimens in the American Museum and Princeton University.]

The skull was very like that of _†Hoplophoneus_, but was still longer and somewhat different in shape, owing to the higher forehead and lower occiput. The primitive features of the cranial base, such as the foramina, the imperfectly ossified tympanic bullæ, etc., were repeated in _†Dinictis_, but the lower jaw had much less prominent flanges for the protection of the tusks. The limbs differed considerably from those of _†Hoplophoneus_ in being relatively longer and more slender and retaining more primitive features, such as the larger third trochanter of the femur. The five-toed feet were decidedly small and weak, and the claws, though retractile, were less so than in the other genus and were not hooded. The gait was probably plantigrade or semi-plantigrade.

[Illustration: FIG. 266.—Skull of _†Dinictis squalidens_, White River. (After Matthew.) _p. 4_ = fourth upper premolar, sectorial.]

The relationships of _†Dinictis_ and _†Hoplophoneus_ are rather puzzling; none of the known species of the former could have been ancestral to the latter, for the two genera were contemporaneous. _†Dinictis_ was apparently the somewhat modified survivor of the ancestral stage and represented very nearly the common starting point of both the feline and †machairodont subfamilies. Dr. Matthew has propounded the bold theory that this genus was the actual ancestor of the felines, continuing the series through _†Archælurus_ and _†Nimravus_ of the John Day to the unmistakable felines of the middle Miocene. This view runs contrary to the supposed “law of the irreversibility of evolution,” a rule which many authorities look upon as well established. The theory postulates a different mode of development from anything that we have so far encountered in the series previously described and supposes that the upper canine first lost its original form, becoming a thin, elongate and scimitar-like tusk, while the lower canine was reduced almost to the proportions of an incisor and the lower jaw acquired a straight, flat chin and inferior flanges for the protection of the tusks. Then, after specialization had advanced so far, it was reversed and the original condition regained. This interesting hypothesis may possibly turn out to be true, though personally I cannot accept it, and, should it do so, it would necessitate a thoroughgoing revision of current opinions as to the processes of mammalian development.

[Illustration: FIG. 267.—Left pes of _†Dinictis felina_. _Cal._, calcaneum. _As._, astragalus. _Cb._, cuboid. Princeton University Museum.]

The only John Day cat which was assuredly derived from _†Dinictis_ was the large _†Pogonodon_, previously mentioned.

[Illustration: FIG. 268.—Skull of false †sabre-tooth (_†Nimravus gomphodus_) from the John Day. (After Matthew.) _p. 4_ = fourth upper premolar, sectorial.]

Also in the John Day stage lived _†Archælurus_ and _†Nimravus_, which, as was noted above (p. 249), have been called the “false sabre-tooths,” for in them the upper canine was not much larger than the lower and the latter, though smaller than in the felines, was yet very much less reduced than in the true †machairodonts. The skull closely resembled that of _†Dinictis_, but the lower jaw was without flanges. The limbs were long and slender and the feet long and digitigrade. The pes had only four digits, of which the median pair was elongated and the lateral pair shortened, so as to produce considerable resemblance to the pes of the dogs, and the claws were partially retractile. The proportions of the body, limbs and feet were suggestively like those of the Cheeta, or Hunting Leopard (_Cynælurus jubatus_) of India, the generic name of which means “dog-cat,” and it is quite possible that the Cheeta may have been derived from some member of this “false †sabre-tooth” series, though the connecting links are unknown. These cursorial cats quite displaced the leaping †machairodonts of the _†Hoplophoneus_ type, at least in the Oregon region at a time when, it will be remembered, that region had a remarkable variety of dogs. In other parts of the continent, of which we have no record, the true †machairodonts must have been thriving, as may be inferred from their comparative abundance in the later formations.

Concerning the habits of these cursorial cats, Professor Merriam says: “When the canines are not developed to the dagger-like form for stabbing, the premolar teeth serve a more definite purpose in the destruction of prey and would be less subject to reduction. The view suggested above finds support in that such evidence as we have indicates that during the deposition of the Middle John Day beds this region was in the main a country of open plains, offering advantages to running types of carnivores, and that during this epoch the _Archælurus-Nimravus_ type of feline was by far the most common form [_i.e._ of cats].” The derivation of these cats is still obscure, but their likeness to certain forms of the European Oligocene suggests that they were immigrants.

The true cats of the subfamily Felinæ include the great variety of living forms, large and small, from the Lion and Tiger at one extreme to the Domestic Cat at the other. There is great difference among naturalists with regard to the nomenclature of the Recent cats; some make a considerable number of separate genera, while others include all the species, except the lynxes and the Cheeta, in the genus _Felis_. For the purposes of this book the latter practice is the more convenient and will be followed. In _Felis_ the dental formula is: _i_ 3/3, _c_ 1/1, _p_ 2-3/2, _m_ 1/1, × 2 = 28-30; the canines are large and strong, of oval section, and the upper one is but little larger than the lower; there are two large and functional premolars in each jaw, and an additional very small one may or may not be present in the upper jaw. The upper sectorial has a large shearing blade, with well-developed anterior accessory cusp, and the inner cusp, which in _†Smilodon_ had almost disappeared, is quite large and carried on a separate root. The lower sectorial is composed of two cusps only, all traces of the heel and of the inner cusp having disappeared. The single upper molar is very small and usually concealed by the sectorial. The skull is very short and broad, and the shortening of the jaws gives great power to the biting muscles, because of the more favourable leverage. The zygomatic arches are very stout and curve out boldly, contributing much to the rounded shape of the head; the orbits are almost encircled in bone. The large tympanic bullæ are two-chambered and there is no alisphenoid canal, but in several other respects the base of the cranium differs markedly from that of _†Smilodon_. The lower jaw is without flanges and there is no angle between front and sides.

[Illustration: FIG. 269.—Dentition of Lynx (_L. rufus_), left side. _i. 3_, external upper incisor. _i. 1_, first lower incisor. _c._ = canine. _p. 3_, _p. 4_, third and fourth premolars. _m. 1_, first molar.]

[Illustration: FIG. 270.—Upper teeth of Puma (_Felis concolor_), left side. _p. 4_, fourth premolar. _m. 1_, first molar.]

The neck is short, the body long and the tail is long in most of the species, but short in the lynxes. The limbs are relatively longer and less massive than in _†Smilodon_, and there are five toes in the manus, four in the pes; the claws are hooded and retractile.

The western hemisphere at the present day contains none of the very large species, the Puma and Jaguar being the largest; but this was not true of the Pleistocene, where a huge cat (_Felis †atrox_), surpassing the Lion in size, ranged over the southern half of North America. Enormous cats also lived in the lower Pliocene and upper Miocene of the Great Plains region, but are not sufficiently well known for reference to either subfamily.

[Illustration: FIG. 271.—Skull of Puma (_Felis concolor_). _p. 4_, upper carnassial. The upper molar is concealed.]

The history of the true felines has been but partially deciphered, and can, as yet, be traced back only to the middle Miocene, the genus _†Pseudælurus_ representing the series both in Europe and North America. In this genus the dental formula was nearly the same as in _Felis_, but there was frequently an additional small premolar in the lower jaw and the sectorials were more primitive, the upper one having the accessory anterior cusp in a merely incipient stage and in the lower one there was a vestige of the heel. The upper canine was considerably longer than the lower, thinner and more blade-like than in _Felis_, which, so far as it goes, is in favour of Dr. Matthew’s theory (p. 541). What little is known of the skull and skeleton of _†Pseudælurus_ agrees with the modern cats.

[Illustration: FIG. 272.—Left manus of Domestic Cat (_Felis domestica_, after Jayne). The horny claws are left in place, covering the ungual phalanges.]

While it is not feasible to trace the series of true felines to an earlier stage than the middle Miocene, there can be no doubt that the subfamily was derived from the same stock as the †machairodonts and it is probable that the White River _†Dinictis_ nearly represents the common starting point for both series; the resemblances between _†Dinictis_ and such primitive dogs as _†Daphœnus_ are suggestive of a common origin.

3. _Procyonidæ. Raccoons, etc._

An almost exclusively American family of Fissipedia is that of the raccoons, which includes not only the latter (_Procyon_), but also the coatis (_Nasua_), curious animals, with long, flexible, pig-like snouts, the cacomistles (_Bassariscus_) and kinkajous (_Potos_). In addition to these American forms, there is an outlying Asiatic genus, the Panda (_Ælurus_) of the southeastern Himalayas, the last of a series which goes back to the European Pliocene.

The Procyonidæ are animals of small and moderate size, largely arboreal in habits and subsisting upon a mixed diet of fruit, eggs, insects and the like; the teeth are adapted to this diet and the sectorials have mostly lost their shearing form and the molars are tuberculated for crushing and grinding. The species generally have long tails, except in the raccoons proper, in which the tail is of medium length, and five-toed, plantigrade feet, with naked soles. Fossil members of this family are very rare in Tertiary formations and its history is therefore but scantily known; in the lower Pliocene have been found fragmentary remains with less specialized teeth, which appear to belong to the direct ancestor of _Bassariscus_. The upper Miocene genus _†Leptarctus_ was an undoubted member of the family, and, while it would seem not to have been in the direct line of any of the modern forms, it was near to the common ancestry of the American genera, so far as the imperfect specimens enable us to judge.

[Illustration: FIG. 273.—Dentition of Raccoon (_Procyon lotor_), left side. _i. 3_, external incisor. _c._, canine. _p. 4_, fourth premolar. _m. 1_, first molar.]

By far the most primitive representative of the family yet discovered is the lower Miocene genus _†Phlaocyon_, which connected the Procyonidæ with the Oligocene genus of dogs, _†Cynodictis_ (p. 529). The dentition resembled that of the latter, with several differences, which were all changes toward the Procyonidæ. All the cusps were lower and blunter than in _†Cynodictis_; the premolars were small, thick and closely crowded together and the upper sectorial, while still trenchant, had a postero-internal cusp, which is found in none of the Canidæ and was a first step toward the tuberculated pattern of the raccoons, and the lower sectorial had a very low cutting blade and large heel; the other molars of both jaws were low, wide and of subquadrate shape. The skull was short and broad, with the face as much shortened and the orbits as far forward as in _Procyon_, but the brain-case was narrower, less capacious, and the lower jaw had the curved form and much the same character as in the modern genus. The limbs were relatively more slender than in the latter and the five-toed feet were more canine than procyonine in the proportions of the digits.

The discovery of _†Phlaocyon_ by Dr. Matthew was an event of capital importance, as showing the highly probable derivation of the raccoons from _†Cynodictis_ and thus bringing another fissipede family into relationship with the dogs.

4. _Ursidæ. Bears_

The present distribution of the bear family is all but exclusively northern, as there is but one African species, confined to the northwestern corner of that continent, and one in the Andes of Peru and Ecuador, all the others belonging to Eurasia and North America.

[Illustration: FIG. 274.—Dentition of Black Bear (_Ursus americanus_). _i. 3_, external incisor. _c._, canine. _p. 1_, first premolar. _p. 4_, fourth premolar. _m. 1_, first molar.—Below is a view, on a larger scale, of the grinding surface of the fourth premolar and first molar, upper jaw.]

Structurally, the family is very distinct and the dentition is quite peculiar. The incisors and canines resemble those of other Fissipedia; the three anterior premolars are very small, single-rooted and often shed early; the carnassials have lost their trenchant character; and the molars, which are usually longer than wide, are tuberculated, somewhat resembling those of pigs. Almost all the bears live principally upon vegetable food, and even the Polar Bear, which feeds upon fish and seals, will eat grass and berries in the brief Arctic summer; thus, the shearing teeth of the strictly carnivorous types are unnecessary to these animals. The skull is not unlike that of the dogs in shape, but the tympanic bullæ are much flattened and the entrances to them are long, bony tubes, while the cranial foramina are nearly as in the dogs. The body is very heavy and the tail always short. The limbs are short and thick; the humerus has lost the epicondylar foramen in all existing species except the South American Spectacled Bear (_Tremarctos ornatus_). The plantigrade feet have naked soles (except in the Polar Bear) and each foot has five well-developed and functional digits, armed with very long, sharp and non-retractile claws.

[Illustration: FIG. 275.—Restored head of the †Short-faced Bear (_†Arctotherium bonæerense_). From a skull in the National Museum, Buenos Aires.]

The Pleistocene representatives of the family in America included species of the true bears (_Ursus_) and of the very large †short-faced bears (_†Arctotherium_) which ranged over both North and South America. In _†Arctotherium_ the dentition was less modified; the larger premolars were very closely crowded together and the molars were nearly square; the lower jaw was almost as much curved as in the raccoons. The humerus retained the epicondylar foramen. The family, which was of Old World origin, may have reached America in the lower Pliocene, but was rare until the late Pleistocene. _†Arctotherium_ has not been found in the eastern hemisphere, but that, of course, is no proof that the genus was not an immigrant from Asia. On the other hand, it may have been a peculiar American development from Pliocene immigrants. In the Old World, bears were first distinguishable in the upper Miocene, and may be there traced back to forms which were unmistakably derivatives of the early dogs.

5. _Mustelidæ. Mustelines_

The last fissipede family, which has, or has had, representatives in the western hemisphere is that which includes a great variety of small carnivores, such as minks, martens, skunks, badgers, otters, etc., and was likewise of Old World origin, though now of universal distribution, except in Australia and Madagascar. These are fierce and bloodthirsty beasts of prey, most of them strictly carnivorous and often killing in mere wantonness more than they can devour. Though now quite numerous and varied in North and South America, they are decidedly less so than in the eastern hemisphere and comparatively few peculiar types have originated here. Owing to the small size and fragility of the skeletons, they have not been well preserved as fossils, and little can be done as yet in tracing out the genealogy of the various phyla.

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.

[Illustration: FIG. 276.—Upper teeth, right side, of _†Mesonyx obtusidens_, showing the grinding surface.]

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.

[Illustration: FIG. 277.—_†Hyænodon horridus_, a White River †creodont: in the background, _†Leptomeryx evansi_. Restored from skeletons in the American Museum of Natural History.]

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.

[Illustration: FIG. 278.—Skeleton of _†Hyænodon_. American Museum.]

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.

[Illustration: FIG. 279.—Lower teeth, right side, of †hyænodontids. _A_, _†Sinopa_. _B_, _†Tritemnodon_. _C_, _†Pterodon_. _D_, _†Hyænodon_. _X_, _Oxyæna_. The dotted line connects the first molar of each, lost in _†Pterodon_. See explanation of Fig. 280. (After Matthew.)]

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_.

[Illustration: FIG. 280.—Upper teeth of †hyænodontids, right side, showing the grinding surface. _A_, _†Sinopa_, Wasatch and Bridger. _B_, _†Tritemnodon_, Bridger. _C_, _†Pterodon_, upper Eocene and lower Oligocene of Europe. _D_, _†Hyænodon_, White River. The dotted line connects the first molar of each. For comparison is added _X_, _†Oxyæna_, one of the †Oxyænidæ. _C_ and _D_ are much larger than the others, but all, except _X_, are reduced to the same length. (After Matthew.)]

_†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.

[Illustration: FIG. 281.—_†Tritemnodon agilis_, a primitive †hyænodont, Bridger stage. Restored from a skeleton in the American Museum.]

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.

[Illustration: FIG. 282.—_†Patriofelis ferox_, Bridger stage. Restored from a skeleton in the American Museum.]

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.

[Illustration: FIG. 283.—Right pes of _†Patriofelis ferox_. _Cal._, calcaneum. _As._, astragalus. _Cb._, cuboid. _N._, navicular. _Cn. 1, 2, 3_, internal, middle and external cuneiforms. (After Wortman.)]

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.

[Illustration: FIG. 284.—_†Oxyæna lupina_, Wasatch stage. Restored from a skeleton in the American Museum.]

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.