. The origin and evolution of life, on the theory of action, reaction and interaction of energy. -blooded, scaly reptile istransformed into a warm-blooded mammal through a changewhich produced the four-chambered heart and complete sep-aration of the arterial and venous circulation. This changemay have been initiated in some of the cynodonts. This newconstant and higher temperature favors the nervous evolutionof the mammals but has no influence whatever upon the me-chanical evolution. As pure mechanisms the cold-blooded rep-tiles exhibit as great plasticity, as great diversity, and perhaps Fig.
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. -blooded, scaly reptile istransformed into a warm-blooded mammal through a changewhich produced the four-chambered heart and complete sep-aration of the arterial and venous circulation. This changemay have been initiated in some of the cynodonts. This newconstant and higher temperature favors the nervous evolutionof the mammals but has no influence whatever upon the me-chanical evolution. As pure mechanisms the cold-blooded rep-tiles exhibit as great plasticity, as great diversity, and perhaps Fig. 71. A South AfricanDog-Toothed Reptile. Head of one of the SouthAfrican Cynodonts or dog-toothed reptiles, related tothe ancestors of the mam-mals. Restoration for theauthor by W. K. Gregoryand Richard Deckert. ADAPTIVE RADIATION OF REPTILES 193 higher stages of perfection than the mammals. Nor does increas-ing intelligence, as we shall see, favor mechanical perfection. Turning our survey to the origin and adaptive radiation ofthe reptiles as a whole, we find that in Permian time all of the. ORIGIN AND ADAPTIVE RADIATION OF THE REPTILES v». k. c«ecci«y, 1 Fig. 72. Adaptive Radiation of the Reptilia. The reptiles first appear in Upper Carboniferous and Lower Permian time and radiate intoeighteen different orders, three of which—the Cotylosaurs, Anomodonts, and Pely-cosaurs—attain their full evolution in Permian and Triassic time and later becomeextinct. Six orders—the Ichthyosaurs, Plesiosaurs, Dinosaurs, Phytosaurs, Pterosaurs,and Turtles—are first discovered in Triassic time, while five of the orders—the Ich-thyosaurs, Plesiosaurs, jMosasaurs, Dinosaurs, and Pterosaurs—dominate the Cretace-ous Period and become suddenly extinct at its close, leaving the five surviving modernorders—Testudinata (turtles, tortoises), Rhyncocephalia (tuateras), Lacertilia (lizards),Ophidia (snakes), and Crocodilia (crocodiles). These great reptilian dynasties seemto have extended
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