No less interesting in their own way are the remains of other hoofed forms that lead down to the elephants of to-day and to the mammoth and mastodon of relatively recent geologic times.  Common sense would lead to the conclusion that a form like a modern tapir was the prototype from which these creatures have arisen, and common sense would lead us to expect that if any fossils of the ancestors of the modern group of elephants occurred at all they would be like tapirs.  Thus a fossil of much significance in this connection is Moeritherium, whose remains have been found in the rocks exposed in the Libyan desert, for this creature was practically a tapir, while at the same time its characters of muzzle and tusk mark it as very close to the ancestors of the larger woolly elephants of later geological times, when the trunk had grown considerably and the tusks had become greatly prolonged.  Again the fossil sequence confirms the conclusions of comparative anatomy, regarding the mode by which certain modern animals have evolved.

The fossil deer of North America, as well as many other even-toed members of the group of mammalia possessing hoofs, provide the same kind of conclusive evidence.  The feature of particular interest in the case of their horns, is a correspondence between the fossil sequence and the order of events in the life-history of existing species,—­that is, between the results of palaeontology and of embryology.  Horns of the earliest known fossil deer have only two prongs; in the rocks above are remains of deer with additional prongs, and point after point is added as the ancient history of deer is traced upwards through the rocks to modern species.  We know that the life-history of a modern species of animals reviews the ancestral record of the species, and what happens during the development of deer can be directly compared with the fossil series.  It is a matter of common knowledge that the year-old stag has simple spikes as horns, and that these are shed to be replaced the following year by larger forked horns.  Every year the horns are lost and new ones grow out, and become more and more elaborately branched as time goes on, thus giving a series of developmental stages that faithfully repeats the general order of fossil horns.  Even Agassiz, who was a believer in special creation and an opponent of evolution, was constrained to point out many other instances, mainly among the invertebrata, where there was a like correspondence between the ontogeny of existing species and their phylogenetic history as revealed by the fossil remains of their ancestors.

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