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Most of them fall into two large orders: the Condylarthra, the ancestral herbivores from which we shall find our horses, oxen, deer, elephants, and hogs gradually issuing, and the Creodonta, the patriarchal carnivores, which will give birth to our lions and tigers, wolves and foxes, and their various cousins.
It is highly probable that these three chief types have descended in as many distinct lines from the Creodonta, and that they were differentiated as early as the middle Eocene, but their exact degree of affinity is uncertain; bears and dogs are certainly closer together than either of them are to cats, and it is questionable if otters and weasels the Mustelidae, as they are termed and raccoons are really near of kin to bears.
Even to an uncritical eye, the differences between ungulates and carnivores of to-day are many and obvious, but as we trace them back into the past we follow on converging lines, and in our search for the prototypes of the carnivora we are led to the Creodonta, contemporary with Condylarthra, which we have seen giving origin to hoofed beasts, but outlasting them into the succeeding age.
They are then barely distinguishable from the Condylarthra and Creodonta, and seem only recently to have issued from a common ancestor with those groups. In the course of the Tertiary we find them especially in South America, which was cut off from the North and its invading Carnivores during the Eocene and Miocene developed into large sloths, armadilloes, and anteaters.
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