Fomil Mammalia.—The remains of mammalia are generally found in a fragmentary --condition; but there is a valuable compensation to the student of these higher oreanisms, for in them the parts are so differentiated that the smallest fragment--a tooth or a bone —often tells more to the comparative anatomist than the complete skeleton of some of the lower classes.
No relies of mammalia have been detected in the palmozoic rocks, the earliest we are Acquainted with belong to secondary strata. These are the remains of microlestes from the Keuper, unless the jaws of the dramatherium from an American coal-bed, which is probably of triassic age, be older. The microlestes, of which the teeth only have been found in Germany and in Somerset, is considered by Owen to have been allied to the small marsupial and insectivorous myrmecobius of Australia. The next remains of this .class have been found in the Stonesfield slate, a member of the oolite. They consist of teeth and lower jaws, which have been referred to four genera, three of which are thought to have been marsupial insectivora, while the other (stereognathus) was a placental mam mal, probably a hoofed, and consequently a herbivorous animal, allied to the eocene hyracotherium. 31r. Beckles has recently found the remains of twelve or thirteen species. belonging to eight or nine genera of marnmalia—placental and marsupial—in the Purbeck beds, the newest of the oolites. The great series of the chalk formations has hitherto yielded no mammalian fossils. We are certainly acquainted with only a small fraction of the mammals of the secondary measures. When more continued aud careful research is made, greater results must follow. 3Ir. Beckles recently uncovered 22 yards square
of the very thin dirt-bed of the Purbeck, from which previously the remains of only a single species had been obtained, and this very limited space yielded up to him the. remains of no less than twelve or thirteen new species.
As we rise through the tertiary deposits, the number of mammalia greatly increase. Nearly 60 species were described by Cuvier from the eocene strata of the Paris basin; and since his time, numerous additions have been made by Owen and others. They are chiefly pachyderms, belonging- to the genera palceotherium, anoplotheriunz, hyracotherium, etc.; but with them are associated the remains of an opossum and of several carnivorous animals. Not only do the number of species increase in the miocene beds, but they rep resent a larger number of orders. There have been discovered two monkeys, numerous proboscidian pachyderms, as the dinotherium, mastodon, and elephant, two or three ceta ceans, an enormous ant-eater, and several carnivora. The fossils of the pleiocene and pleistocene beds are still more numerous, and represent a race of animals not unlike the living fauna, but generally of a gigantic size. The elephants, elks, and bears of Europe were the contemporaries of immense sloths and armadillos in South America, and of huge kangaroos arid birds in Australasia. Associated with the bones of some of these extinct species have been found flint implements, and even the bones of man, but under circumstances that have caused great differeuce of opinion among observers as to their true age. See 3IA.x.