The discoveries of very rich deposits of mammalian remains in various parts of the United States have thrown great light on the relations of the faunas of very distant regions. North America now makes a near approach to Europe in the number and variety of its extinct mammalia, and in no part of the world have such perfect specimens been discovered. In what are called the "Mauvaises terres" of Nebraska (the dried-up mud of an ancient lake), thousands of entire crania and some almost entire skeletons of ancient animals have been found, their teeth absolutely perfect, and altogether more resembling the preparations of the anatomist, than time-worn fossils such as we are accustomed to see in the museums of Europe. Other deposits have been discovered in Oregon, California, Virginia, South Carolina, Texas, and Utah, ranging over all the Tertiary epochs, from Post-Pliocene to Eocene, and furnishing a remarkable picture of the numerous strange mammalia which inhabited the ancient North American continent.
Insectivora.—The only indications of this order yet discovered, consists of a single tooth of some insectivorous animal found in Illinois, but which cannot be referred to any known group.
Carnivora.—These are fairly represented. Two species of Felis as large as a lion; the equally large extinct Trucifelis, found only in Texas; four species of Canis, some of them larger than wolves; two species of Galera, a genus now confined to the Neotropical region; two bears, and an extinct genus, Arctodus; an extinct species of racoon (Procyon), and an allied extinct genus, Myxophagus—show, that at a very recent period North America was better supplied with Carnivora than it is now. Remains of the walrus (Trichechus) have also been found as far south as Virginia.
Cetacea.—Three species of dolphins belonging to existing genera, have been found in the Eastern States; and two species of Manatus, or sea-cow, in Florida and South Carolina.
Ungulata.—Six extinct horses (Equus), and one Hipparion; the living South American tapir, and a larger extinct species; a Dicotyles, or peccary, and an allied genus, Platygonus; a species of the South American llamas (Auchenia), and one of a kind of camel, Procamelus; two extinct bisons; a sheep, and two musk-sheep (Ovibos); with three living and one extinct deer (Cervus), show an important increase in its Herbivora.
Proboscidea.—Two elephants and two mastodons, added to this remarkable assemblage of large vegetable-feeding quadrupeds.
Rodentia.—These consist mainly of genera and species still living in North America; the only important exceptions being a species of the South American capybara (Hydrochœrus) in South Carolina; and Praotherium, an extinct form of hare, found in a bone cave in Pennsylvania.
Edentata.—Here we meet with a wonderful assemblage, of six species belonging to four extinct genera, mostly of gigantic size. A species of Megatherium, three of Megalonyx, and one of Mylodon—huge terrestrial sloths as large as the rhinoceros or even as the largest elephants—ranged over the Southern States to Pennsylvania, the latter (Mylodon) going as far as the great lakes and Oregon. Another form, Ereptodon, has been found in the Mississippi Valley.
Marsupialia.—The living American genus of opossums, Didelphys, has been found in deposits of this age in South Carolina.