mammals--intermediate in most ways between a
hedgehog and a pig--which flourished in very early Eocene times, and
had five toes on each foot, and "a typical dentition." Even the
elephants came from such a small ancestral form. The common notion
that the extinct forerunners of existing animals were much bigger than
recent kinds, and even gigantic, is not in accordance with fact. Some
extinct animals were of very great size--especially the great reptiles
of the period long before the Tertiaries, and before the chalk. But
the recent horse, the recent elephant, the giraffe, the lions, bears,
and others, are bigger--some much bigger--than the ancestral forms, to
which we can trace them by the wonderfully preserved and wonderfully
collected and worked-out fossilised bones discovered in the successive
layers of the Pliocene, Miocene, and Eocene strata, leading us as we
descend to more primitive, simplified, and smaller ancestors.

It is easy to understand the initial character of the foot of the
early ancestral mammals. It had five toes. By the suppression or
atrophy of first the innermost toe, then of the outermost, you find
that mammals may first acquire four toes only, and then only three,
and by repeating the process the toes may be reduced to two, or right
away to one, the original middle toe. There is no special difficulty
about tracing back the elephants in so far as this matter is
concerned, since they have kept (like man and some other mammals) the
full typical complement of five toes on each foot.

But I must explain a little more at length what was the "typical
dentition,"--that is to say, the exact number and form of the teeth in
each half of the upper and the lower jaw of the early mammalian
ancestor of lower Eocene times, or just before. The jaws were drawn
out into a snout or muzzle, an elongated, protruding "face," as in a
dog or deer or hedgehog, and there were numerous teeth set in a row
along the gums of the upper and the lower jaw. The teeth were the same
in number, in upper and in lower jaw, and so formed as to work
together, those of the lower jaw shutting as a rule just a little in
front of the corresponding teeth of the upper jaw. There were above
and below, in front, six small chisel-like teeth, which we call "the
incisors." At the corner of the mouth above and below on each side
flanking these was a corner tooth, or dog-tooth, a little bigger than
the incisors, and more pointed and projecting. These