THE EVOLUTION OF THE MAMMALIA. 233 
The first sub-order of the artiodactyls is the Suina (including 
the swine, peccaries, and hippopotamus), and is a very ancient 
branch, which had become distinct from the others as early as 
the Wasatch. In North America, only the peccaries are indig- 
enous, and, in spite of many resemblances, they must have been 
distinct from the true swine, at least since Eocene times. The 
Eocene ancestors of the peccaries are still very imperfectly known ; 
only fragmentary fossils having been found, though we may confi- 
dently regard them as the real ancestral forms, for the peccaries 
are typically developed in the White River, and from that time 
on the record is clear and unbroken. The changes are, however, 
comparatively few and slight, consisting chiefly in a reduction of 
the lateral digits to functionless dew-claws, the loss of the external 
toe of the hind foot, a very exceptional arrangement in this sub- 
order. The skull, teeth, and limbs also underwent some modifi- 
cations, and the stomach became complicated in a way that sug- 
gests the highly complex stomach of the ruminants. Like the 
tapirs, the peccaries were very common in North America during 
the Pleistocene, but the events of the latter part of that period 
drove them southward, and now they are not found north of 
Texas, though they are still abundant in South America. 
The true swine are an Old World group, and appear to have 
been derived from forms, which were very nearly allied to the 
early peccaries. They have simple stomachs, short limbs and 
feet, retaining four functional toes on each foot ; the upper tusks 
are turned outward and upward in a very characteristic way. 
The grinding teeth of the swine are much larger and more com- 
plex than those of the peccaries, and in the African wart-hog 
these teeth reach an extraordinary degree of complication, almost 
rivalling that seen in the elephant. 
An aberrant side branch of pig-like animals are the extinct 
elotheres, which are common in the White River beds and in 
the corresponding formations in France, and are remarkable for 
their great size. The large, conical front teeth and the very 
long and narrow skull, with its absurdly small brain case, have 
an almost reptilian appearance. The legs are proportionately 
