Note 6 — Chapter VI

Mammals having the number and form of teeth which I have just described as typical—or such modification of it as can easily be produced by suppression of some teeth and enlargement of others—are called Typidentata. On the other hand, the whales, the sloths, ant-eaters, and armadilloes, as also the Marsupials, are called Variodentata, because we cannot derive their teeth from those of the Typidentate ancestor. They form lines of descent which separated from the other mammals before the Typidentate ancestor of all, except the groups just named, was evolved.