Page:Popular Science Monthly Volume 41.djvu/841

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these latter it is possible to find indications for an evolution which must have ended in the appearance of two divisions—the odd-toed and the even-toed ungulates. Most laborious anatomical researches were required for properly interpreting these rich materials. But the result of the work is that we already know with a great approach to certitude the genealogical trees of most ungulates; we can go back to the ancestors of the ruminants, the cameloides, the chevrotains, the horses, and even to the common ancestors of the whole group of ungulates; while the genealogy of other large groups of mammalia has also been worked out to some extent.

The just-mentioned discoveries in North America were soon supplemented by still more remarkable finds in South America, which finds follow each other with such a rapidity that anatomists will have to make strenuous efforts in order to keep pace with the paleontological work. The formation which D'Orbigny described as "formation guaranienne" proved to consist of marine Cretaceous beds, covered by immense land deposits, which, like the Laramie beds of North America, are of an intermediate age between Cretaceous and Tertiary. These last beds offer an immense interest, owing to their mammalian fossils (of much more specified types than those of the Laramie), which are mixed together with relics of gigantic Dinosaurians, some of the latter attaining lengths of more than one hundred and thirty feet. As to the more recent deposits of the Argentine Republic and Patagonia—partly Eocene and partly Pliocene—they are so rich in mammals that more than two hundred species, some of them of the most extraordinary types, have already been described by Dr. F. Arneghino,[1] Burmeister, and Moreno; and every number of the Re vista Argentina brings some new descriptions of new fossils both from the Argentine and Patagonia, which is now explored by Carl Arneghino. There are among them ungulates which, to use Mr. Lydekker's words, are "totally unlike any found in all the rest of the world put together,"[2] and which combine the characters of both the odd-toed and the even-toed ungulates. Of them, the Macrauchenia seems to be a direct descendant of a type which must have been a common ancestor to both divisions. Another huge mammal, one of the Toxodontes, which must have equaled in size the hippopotamus, also occupied an intermediate position between the two groups; while in the earlier Tertiaries there are types which, so far as can be judged from

  1. His chief works are: Los mamiferos f osiles de la America del Sud, Buenos Ayres, 1880; Contribución al conocimiento de los mamiferos fosiles de la República Argentina, 2 parts, forming vol. vi of Actas de la Academia de Ciencias de Cordoba, Buenos Ayres, 1889; and several papers in Kevista Argentina de Historia Natural, Buenos Ayres, 1891.
  2. Nature, vol. xlv, p. 608.