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.