Page:Popular Science Monthly Volume 12.djvu/696

676 such perfect preservation as to suggest a very recent period for their extinction. The Sloth tribe is represented by the huge Mylodon, Megatherium, Megalonyx, Cœlodon, Ochotherium, Gnathopis, Lestodon, Scelidotherium, and Sphœnodon; and among the Armadilloes were Chlamydotherium, Eurydon, Glyptodon, Heterodon, Pachytherium, and ''Schistopleurum. Glossotherium,'' another extinct genus, is supposed to be allied to the Ant-Eaters.

It is frequently asserted, and very generally believed, that the large number of huge Edentata which lived in North America during the Post-Pliocene were the results of an extensive migration from South America soon after the elevation of the Isthmus of Panama, near the close of the Tertiary. No conclusive proof of such migration has been offered, and the evidence, it seems to me. so far as we now have it, is directly opposed to this view. No undoubted Tertiary Edentates have yet been discovered in South America, while we have at least two species in our Miocene, and, during the deposition of our lower Pliocene, large individuals of this group were not uncommon as far north as the forty-third parallel of latitude, on both sides of the Rocky Mountains. In view of these facts, and others which I shall lay before you, it seems more natural to conclude, from our present knowledge, that the migration, which no doubt took place, was from north to south. The Edentates, finding thus in South America a congenial home, flourished greatly for a time, and, although the larger forms are now all extinct, diminutive representatives of the group still inhabit the same region.

The Cetacea first appear in the Eocene, as in Europe, and are comparatively abundant in deposits of this age on the Atlantic coast. The most interesting remains of this order, yet found, belong to the Zeuglodontidæ, which are carnivorous whales, and the only animals of the order with teeth implanted by two roots. The principal genera of this family are Zeuglodon and Squalodon, the former genus being represented by gigantic forms, some of which were seventy feet in length. The genus Saurocetes, which includes some small animals of this group, has been found in South America. The Dolphin family (Delphinidæ) are well represented in the Miocene, both on the Atlantic and Pacific coast. The best-known genus is Priscodelphinus, of which several species have been described. Several other generic names which have been applied to fragments need not here be enumerated. In none of the Tertiary species of this family were the cervical vertebræ anchylosed. The Sperm Whales (Catodontidæ) were also abundant throughout the Tertiary, and with them, in the earlier beds, various Ziphioid forms have been found. The toothless Balænidæ are only known with certainty as fossils from the later Tertiary and more recent deposits.