Foraminifera of relatively enormous size abounded, and their shells make up great rock masses. Orbitolites is a conspicuous genus along our Gulf coasts, Nummulites in the Old World. Corals are completely modern in character. The Sea-urchins and especially the Irregulares are much the most important representatives of the Echinoderms. Of the Mollusca both Bivalves (PI. XVI, Figs. 2, 3) and Gastropods (XVI, 4, 5) increase greatly and are very rich in species. Nautiloid Cephalopods are more varied and widely distributed than now (XVI, 8), and in a few localities, particularly in India, Ammonites and Belemnites have been found, but these are mere belated stragglers from the Cretaceous and are much too rare to be at all characteristic. Among the Crustacea should be noted the increase of the Crabs, which are more numerous and varied than in the Cretaceous. The Fishes, both fresh-water and marine, differ only in minor details from modern fishes. The Reptiles are likewise essentially modern in character, the Choristodera having died out with the Paleocene, and only two groups, the Lizards and Snakes, are more numerous than they had been in Mesozoic times, though the venomous snakes had not yet appeared.
The Eocene beds of the West contained multitudes of large Crocodiles and a great variety of Turtles.
Fig. i, Ostrta virginiana, x 1/2, Miocene. 2, Pecten madisonicus, X 1/2, Miocene. 3, Car dita peraniiqua, Eocene. Whitfield. 4, Volutolithes sayana, X 3/4, Eocene, 5, Oliva caroli-nensis, x 3/4, Miocene. 6, Helix dalli, Miocene. White. 7, Planorbis convoluta,? Fort Union. Meek. 8, Aturia vanuxemi, x 1/4, Eocene. 9, Glyptostrobus ungeri, x 1/2, Eocene. Lesquereux. 10, Salix sp., x 3/4. Miocene. (Figs. 1-5, and 8, after Whitfield).
Eocene Birds are very much more numerous, advanced, and diversified than those of the Cretaceous; one characteristic feature of the times was the presence in Europe and America of extremely large, flightless birds, more or less like the ostriches in appearance. Of flying birds there were many kinds; Owls, Eagles, Buzzards, Vultures, Gulls, Waders, Woodcock, Quail, Ibis, and Pelicans are represented by ancestral forms, somewhat different from their modern descendants.
The Mammals have developed in a marvellous way since the Cretaceous, assuming in terrestrial life that dominant place which they have ever since held. Compared with the evolution of other animal groups, that of the mammals has been so rapid that each stage of the Eocene has its own mammalian fauna, differing from those of the preceding and succeeding stages. Besides these geological differences between the successive mammalian assemblages, there are often marked geographical differences between the faunas which are of approximately contemporaneous age, but widely separated in space. Comparing Europe and North America in this respect, we find that in the Eocene each continent had its own peculiarities, but that the land connection between them allowed intermigration and thus kept up a close general similarity in their mammals in the Lower Eocene, but this connection was interrupted and the faunas of the middle and later portions of the epoch diverge more and more in the two continents. The southern continents, on the other hand, had altogether different mammalian faunas, due to their long separation from the northern lands.
The change from the Paleocene mammals to those of the Wasatch was very abrupt, though no great time interval is involved, and in Europe the change was equally sudden, most of the archaic Mesozoic types going out and those of more modern character replacing them. Evidently this was due to an influx of mammals from some region still unknown, and hardly at all to a development of the Paleocene mammals. Rodents come in for the first time in North America. Perissodactyls make their first appearance with ancestral members of the Horse family (Hyracotherium), the tapirs (Systemodori), and other families now extinct. The Wasatch horse was a curious little creature, not larger than a domestic cat, with four toes on the fore foot and three on the hind, instead of having only a single functional toe, like the modern horses. The curious extinct group of hoofed animals called the Amblypoda greatly increases in numbers and in stature, and both in Europe and America the predominant genus is Coryphodon. Artiodactyls also appear for the first time in ancestral members of the Pigs (Eohyus), and the Ruminants (Trigonolestes). The Creodonts increase in numbers and in the size and strength of the individuals, Pachycena being as large as a bear.
Numerous Lemuroids and primitive types of Monkeys (Anaptomorphus) swarmed in the trees. The correspondence between the mammals of Europe and North America was never closer than in Wasatch times.
The Wind River fauna is a development of the Wasatch, apparently without the admixture of foreign elements by immigration, and there is no such complete change as at the end of the Paleocene. Noteworthy is the appearance of the first known member of the Perissodactyl family of the Titanotheres, a family which was destined to great expansion in the Upper Eocene and Lower Oligocene; also of the earliest true Carnivora.
The Bridger mammals represent a steady advance upon those of the Wind River. The Perissodactyls may be said to culminate in the Bridger; for though they afterwards reached much higher stages of development, they never again had the same relative importance. Horses, still of minute size, but more highly developed than those of the Wasatch, Tapirs, Rhinoceroses, and Titan-otheres (Palceosyops) are extraordinarily abundant. Corypho-don has vanished, but the wonderful elephantine, six-horned Uintatherium and Eobasileus (Fig. 305) take its place in North America, though not in Europe. Artiodactyls, Creodonts, Rodents, Tillodonts, and Lemurs were more diversified than ever, and Bats are found here for the first time. The remarkable discovery in the Bridger of such a distinctively South American type as an armadillo has already been mentioned.
Fig. 305.-Eobaslleus cornutus Cope. One of the horned Amblypoda of the Bridger. Restoration by C. R. Knight, under the direction of Prof. H. F. Osborn. (Copyright by American Museum Natural History, N.Y).
In the Upper Eocene seas great whale-like forms (Zeuglodon) of extraordinary appearance and structure had grown abundant.
The recently discovered Middle and Upper Eocene fauna of Egypt is of very great interest. The mammals differ much from those of Europe, but there are some forms common to both regions. The long-sought ancestors of the Elephants have been found in the Egyptian beds, and a very curious animal (Arsinoetherium), which might be described as a small elephant with a pair of huge horns upon its narrow head, accompanies them.