In this age for the first time the highest flowering plants are abundant, and now for the first time also the highest orders of insects are abundant, such as bees, ants, butterflies, etc. On account of the greater warmth and moisture in the Tertiary period, insect and plant life were fuller then than now. That the climate was warmer in those times is shown by the following facts: In America, during the early Tertiary period, figs, evergreens and palms grew in Dakota, showing a temperature there at that time equal to the temperature in Florida at present. In the middle Tertiary period trees like the Redwood of California, and Magnolias, were abundant in Greenland. Although _Reptilian Mammals_ (_Multituberculata_) lived in the preceding era, true or typical Mammals first came to view in the earliest Tertiary times. They soon succeeded the vanished giant reptiles as the rulers of the world; so that this and the succeeding (Quaternary) period are known as the =Age of Mammals=. At this period, for the first time, appear generalized _primitive flesh-eating mammals_ (_Creodonta_), and _primitive grass-eating ones_ (_Condylarthra_ and _Amblypoda_); also _primitive Primates_ (_primitive Lemuroids_, and, later, _primitive types of Monkeys_, e. g., _Anaptomorphus_). The evolution of mammals, compared with that of other animal groups, has been so rapid that each stage of even the Eocene has its own mammalian fauna, differing from those of the succeeding and preceding stages. All through the Tertiary period, as through all the preceding ages, the species that are advancing in life are undergoing greater and greater specialization. Animals at first closely related finally become more and more separated from one another. This is well illustrated by a study of the hoofed animals. In the earliest Tertiary period all these animals seem to unite into one branch but now they consist of many widely separated sub-branches. As we trace the branch down to the earliest Tertiary period, we find that even in early Eocene times it divides into the even-toed and odd-toed ungulates. In the later Miocene times, each of these again separates,—the former, even-toed ones, into the hog and hippopotamus families with four toes, and the ruminant family with two toes; the latter, odd-toed ones, into the elephant family with five toes, the rhinoceros and tapir families with three toes, and the horse family with one toe. [Illustration: FIG. 14.—Illustrating genesis of horse’s feet. Fore-feet (a) and hind-feet (b) of Orohippus; fore-feet (c) and hind-feet (d) of Mesohippus; fore-feet (e) and hind-feet (f) of Miohippus; fore-feet (g) and hind-feet (h) of Protohippus; fore-feet (k) and hind-feet (l) of Pliohippus; fore-feet (m) and hind-feet (n) of Equus.]