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same Order, which seem to be more nearly related to the Australian marsupials of other families; in fact, Ameghino has placed some of them in the (hitherto supposed to be) exclusively Australian family Dasyuridm.
The fossil Edentates of this formation are all of the American section of the group. The Perissodactyle Ungulates are represented by two families (ProterotheriidsB and Macraucheniid«)not very definitely connected with other Perissodactyles, and unknown elsewhere; and the Toxodonts (another group forming a distinct sub-order of the Ungulata) are also quite unrecognised outside South America, where, indeed, they appear to have existed for a short period only.
The Rodents of this formation all belong to the Hystricomorphine section of the order, and the Monkeys are all Platyrrhine, so that, except in the case of the Marsupials where the results are to a certain extent doubtful, no clue to the origin of the Neotropical fauna is shown by this extinct fauna. When these results are compared with the Eocene Mammal-fauna of the northern hemisphere, the absence of Artiodactyles, Insectivores, Bats, Carnivores, and Lemurs, is very striking.
The "Patagonian" beds contain a Mammal-fauna only to be distinguished from the previous "Santa Cruz" series by a further differentiation of genera belonging to the same orders without any traces of foreign admixture. When, however, we reach the more recent Araucanian formation, we find, in addition to the Edentates, Toxodonts, and other typical South American forms, a number of foreign intruders, such as Tapirs, Lamas, Elephants (Mastodon), and Wild Dogs (Canis), of an entirely different aspect. There can be little doubt that these animals had migrated
here southwards from North America, where their remains (or those of closely allied species) have been likewise found in the nearly contemporaneous formations of the United States.
Moreover, it would seem that in these bygone days, not only did the northern forms move southwards, but that also some of the southern forms emigrated northwards. This is evidenced by the fauna of the so-called "Equus-beds" and "Megalonyx-beds" of a slightly later date in the United States, which contain a composite Mammal-fauna of northern forms mixed with forms usually considered to be exclusively South American— such as the gigantic armadillo-like Glyptodon, the Capybara (Hydrochozrus), Toxodon, and others.
Finally, in the age of the "Pampas" beds, the peculiar South American Mammal-fauna seems to have reached its culminating-point, and to have far exceeded that of the present day both in number of species and in the size of the individuals. This great increase in size, which is, as a rule, accompanied by an extreme specialisation of individual organs, seems to have had a fatal effect on its possessors, as none of the larger Edentates or Toxodonts appear to have outlived the end of the pampas formation. Along with most of the larger arrivals from the north, such as Mastodon and Equus, they became extinct. All the conclusions to be derived from this much-abbreviated account of the extinct Mammals of South America, confirm in a remarkable way the evidence of the present fauna as to this history of the Neotropical Region. Up to the last period of the Tertiary epoch, South America was certainly isolated from the rest of the world, and the connections Avith Australia and with Africa, if they ever did exist, must have been previous to this
period. At the beginning of Pliocene time, during the deposition of the Araucanian formation in Argentina and the "Equus-beds" in the United States, a wide bridge between North and South America, affording an easy road to migrating animals, must have existed, and this again seems to have become considerably narrowed to form the present Isthmus of Panama.
List Of The Principal Authorities Referred To
(1) Allen, J. A.—"The Geographical Distribution of North American Mammals." Bull. Amer. Mm. N.H., iv., p. 199, 1892.
(2) Allen, J. A.—"On a Small Collection of Mammals from the Galapagos Islands, collected by Dr. G. Baur." Bull. Amer. Mm. N.H., iv., p. 47, 1892.
(3) Alston, E. R.—"Biologia Centrali-Americana, Mammalia. London, 1879-82.
(4) Chapman, F. M.—"Notes on Birds and Mammals observed near Trinidad, Cuba, with remarks on the Origin of West Indian Bird-life." Bull. Amer. Mm. N.H., iv., p. 279, 1892.
(5) Cope, E. D. —" Description of two large extinct Rodents from Anguilla, West Indies, with remains of human art associated." Proc Amer. Philos. Soc. Philad., xi., 1871, p. 183.
(6) Leidy, J.—" Remarks on Mylodon." Proc. Acad. Nat. Sci. ■ Philad., 1885, p. 49.
(7) Salvin, 0.—" On the Avifauna of the Galapagos Archipelago.' Trans. Zool. Soc., ix., p. 447 (1876).
(8) Sclater, P. L.—"Address to Section D. (Biology)." "Report of Forty-fifth Meeting of the British Association, at Bristol," p. 85 (1876).
(9) Thomas, 0—" On Some Mammals from Central Peru." P.Z.S., 1893, p. 333.
(10) Trotjessart, E. L.—" Note sur le rat musque' (Mm pilorides) des Antilles." Ann. Sci. Nat. Zool. (6), xix., No. 5 (1885).
(11) Wallace, A. R.—" The Geographical Distribution of Animals." 2 vols. London, 1876.
(12) Zittel, K. A. Von.—" The Geological Development, Descent, and Distribution of the Mammalia." S. B. k. bayer. Akad. Wiss., xxiii., p. 137, 1893. Translation in Geol. Mag. (3), x., p. 401 (1893).