The life of the Miocene is in all respects a great advance upon that of the Eocene and Oligocene. The Grasses greatly multiply and take possession of the open spaces, producing a revolution in the conditions of food for the herbivorous animals. The vegetation of North America, as far north as Montana, perhaps even to northern British Columbia, still bore a southern character. In the Upper Miocene tuffs of the Yellowstone Park and contemporary strata of Oregon are found such trees as Poplars, Walnuts, Hickories, Oaks, Elms, Maples, Beeches, noble forms of Magnolias and Sycamores. One species of Aralia had leaves 2 feet long by 3 inches wide. Curiously enough, the Breadfruit (Artocarpus) flourished in Oregon, and probably on the Yellowstone also. Conifers were numerous and varied. At Florissant the plants are of a similar warm-temperate character, with very few palms, but with Sequoia, the California Redwood, abundant.

Fig. 308. - Rhus Sp, A sumach from the Florissant Shales.

In Europe the Lower Miocene flora was quite like that of modern India; over the central and western regions Palms continue to flourish, together with Live Oaks, Myrtles, Magnolias, Figs, etc.

In the latter part of the epoch a change is noted, and such trees as Beeches, Poplars, Elms, Maples, Laurels, and the like become dominant.

Marine Invertebrates belong almost entirely to genera which still live in the seas, and many of the species persist to our own day. In Europe the older Miocene has numbers of shells such as now live only in warm seas, like Cyprcea, Mitra, Purpura, Strombus, etc. (See PI. XVII, p. 765.) The Miocene of our Atlantic coast was evidently a time of cooler waters, and a similar change took place in Europe in the Upper Miocene. A very characteristic shell of the Atlantic coast Miocene is Ecphora quadricostata (Fig. 309).

The terrestrial Vertebrates of the interior are of much interest. Little is known of Miocene Birds in this country, but in Europe they are abundantly preserved and are of distinctly African character. Parrots, Indian Swallows, Secretary Birds, Adjutants, Cranes, Flamingoes, Ibises, Pelicans, Sand-grouse, and numerous Gallinaceous birds, were mingled with birds of European, type, such as Eagles, Owls, Woodpeckers, Gulls, Ducks, etc.

Fig. 309. - Ecphora quadricostata Say, X 2/3, Yorktown, Va.

The Lower Miocene {A rikaree) Mammals of the interior have only lately been discovered and are not yet fully described. In general, these animals are a continuation of the John Day fauna, in a higher stage of advancement, without admixture of exotic elements. The Ancylopoda, a very curious group of hoofed animals in which the hoofs had been converted into huge claws, and of which a few traces have been found in the White River and John Day, assume great importance in these beds.

In the Middle Miocene {Deep River) came a renewed migration from the Old World, bringing in the first of the elephant group (Proboscidea) which had simpler teeth than the modern elephants and a pair of tusks in the lower jaw, as well as in the upper. The genus is Tetrabelodon. The first of the true Ruminants to appear in North America came in with this migration and were, in a measure, intermediate between deer and antelopes, while European Rhinoceroses accompany them. Of the native stock, the Horses and Camels deserve particular mention as having increased in size and in variety and having made great advances toward the modern standard. The Oreodonts in a variety of bizarre genera, some of them aquatic, are very common.

The Upper Miocene {Loup Fork) Mammals resemble closely those of the Deep River stage, rather more advanced and modernized. The true Cats and a number of weasel- and otter-like Carnivores came in from the Old World, while the Wolves, Panthers, and Sabre-tooth Tigers were very numerous. Besides the true Ruminants, the American type of Camels and Llamas continued to flourish in such genera as Procamelus, Pliauchenia, and others. One very remarkable camel, Alticamelus, had nearly the same proportions as the giraffe. The extraordinary four-horned genus, Protoceras, of the White River, is represented by Syndyoceras, in which the four horns are much increased in length, but the tusks are reduced. The Loup Fork Horses {Protohippus and Hipparion) are much more modern in character and larger in size than their predecessors, but still have three toes on each foot. The Rhinoceroses are very abundant, and form a peculiar American genus (Aphelops) of massive, hornless animals. The Peccaries, or American swine, were commoner in the Loup Fork than in the earlier Miocene stages.

The Atlantic coast Miocene has yielded numbers of Dolphins, Sperm and Whalebone Whales.

In Europe the Upper Miocene mammals were, in general, like those of North America, but a salient difference is in the much greater number of early types of Deer and Antelopes which are found there, together with various forms of Swine and ancestral Bears. Besides the Mastodons, which were common to both continents, Europe had in Dinotherium a remarkable kind of elephant; this animal had a much flattened head and a pair of massive, backwardly curved tusks in the lower jaw. The weasel and otter tribe of Carnivora was much more abundant and varied in Europe, and the Civet-cats, which were also common there, did not migrate to America.

Little is known of the Miocene Mammals of other continents except South America, where a magnificent assemblage has been preserved in the Santa Cruz tuffs of Patagonia. This fauna is so entirely different from that of the northern hemisphere that it seems to belong to another world. It contains no Carnivora, Proboscidea, Artiodactyla, or Perissodactyla. The flesh-eaters were carnivorous Marsupials, like those of Australia, and another family of Marsupials like the Australian Phalangers, was also present in addition to the American Opossums. The Rodents, of which there were very many, all belong to the great porcupine group (Hystricomorpha) and closely resemble modern South American types, but among them are no rats or mice, squirrels, marmots, beavers, hares, or rabbits. Edentates are extraordinarily numerous and varied, Armadillos, Glyptodonts, and Ground Sloths forming one of the most conspicuous elements of the fauna. Hoofed animals were present in multitudes, but though having a certain likeness to those of the northern continents, they are but remotely related to them.

The Toxodontia (Nesodori) were slow and massive animals, and the little Typotheria had a superficial resemblance to Rodents. The Litopterna had one group which imitated the horses in a surprising manner and another which had some likeness to the llamas (see Fig. 310). The Homalodotheria were a parallel to the northern Ancylopoda and the Astrapotheria, largest of Santa Cruz mammals, were not altogether unlike Rhinoceroses.

Fig. 310. - Theosodon lydekkeri Amegh. One of the Litopterna from the Santa Cruz beds of Patagonia. On the right are two examples of Borhyama, a carnivorous Marsupial. Restoration by C. R. Knight, under the direction of the author.

The climate of the early Miocene was much like that of the Olig-ocene and decidedly warmer in Europe than in North America, though it was mild even in the latter. The difference seems to have been largely due to the manner in which Europe was intersected by arms and gulfs of the warm southern sea. In the Upper Miocene the climate became distinctly cooler on both sides of the ocean.