. The origin and evolution of life, on the theory of action, reaction and interaction of energy. ores, bats, lemurs, rodents, andthe edentates (armadillos and ant-eaters). Especially remark-able is the discovery in the Lower Eocene of the ancestors of Fig. 124. Two Stages in the EarlyEvolution of the Ungulates. Pantolambda {A), an archaic Palaeoceneform which transforms into Coryphodon(B), a Lower Eocene form of increasedsize, with greatly enlarged head, ab-breviated tail, and defensive transformation occupied a periodestimated at 500,000 years, nearly one-sixth of Tertiary time. Re
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. ores, bats, lemurs, rodents, andthe edentates (armadillos and ant-eaters). Especially remark-able is the discovery in the Lower Eocene of the ancestors of Fig. 124. Two Stages in the EarlyEvolution of the Ungulates. Pantolambda {A), an archaic Palaeoceneform which transforms into Coryphodon(B), a Lower Eocene form of increasedsize, with greatly enlarged head, ab-breviated tail, and defensive transformation occupied a periodestimated at 500,000 years, nearly one-sixth of Tertiary time. Restorationsin the American Museum of NaturalHistorv, bv Osborn and Knight. 26o THE ORIGIN AND EVOLUTION OF LIFE the modern horses, tapirs, rhinoceroses, and various types ofcloven-footed animals. A very general principle of mammalian evolution is illus-trated in Fig. 124 (.4, B), namely, the increase of size character-istic of all the herbivorous mammals, which almost withoutexception are in the beginning extremely small forms thatevolve into massive forms possessing for defense either power-. FiG. 125. A Primitue Whale from the Eocene of Alabama. Zeiiglodon cdoides exhibits a secondary elongate, eel-shaped body form analogous to thatof many of the aquatic, free-swimming, surface-dwelling reptiles, aquatic amphibians,and fusiform fishes. Restoration by Gidley and Knight in the American IVIuseum ofNatural History. ful tusks or horns. The most conspicuous example of veryrapid evolution which has taken place prior to the close ofEocene time is that of the great primitive whale Zeuglodoncetoides, discovered in the Upper Eocen,e of Alabama, and nowknown to have been distributed eastward to the region of theMediterranean. As described above (p. 241), as an example ofreversed adaptation and evolution, this animal had alreadypassed through a prior terrestrial phase and had reached astage of extreme specialization for marine life. These zeu-glodonts parallel several of the marine groups
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