The science of life : fully illustrated in tone and line and including many diagrams

THE EVIDENCE OF THE ROCKS

to us is only small and sluggish, but the demonstration is complete, with not a chink or loophole in it.

$5 “ Missing Links”

It would be possible to give a number of other evolutionary series, almost or quite as perfect as those we have described in detail. The Titanotheres, strange, horned, extinct mammals, rival the horses in fulness of record. So do the camels. The tapir and rhinoceros branches are not far behind. An _ extraordinary parallel to the later development of the horse-stock is afforded by the evolution of the Litopterna, a group of South American animals, all now extinct. Although many characters prove that they were not horses, and not even closely related to horses, they responded to the world-wide change of vegetation in the same way as the horses did. Evolving from a different five-toed ancestor, they gradually increased in size, lengthened their legs, reduced their outer digits and from three-toed became one-toed. They grew regular hoofs and their teeth became progressively longer and longer and of more complicated pattern. It is interesting that while their side toes were finally reduced farther than in any horse, to mere stubs of bone, their teeth remained less efficient, and never formed cement. Grassy plains developed in South as in North America, and since for long before the Pliocene (V D) the southern continent was wholly cut off from North America, no true horses could then invade it; but the Litopterna developed along a parallel line to fill the same niche in Nature.

The elephants, too, provide us with a fine evolutionary series, which is peculiar in that its trend was first towards the development of a four-tusked creature, with long, lower jaw. Later, however, with increasing bulk, the further

Ing. 127. A Reconstruction of Archeopteryx in the Jurassic woods.

Tt must have used its wing-claws to scramble among the branches.

LOR. Or ishiaell-

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