. The origin and evolution of life, on the theory of action, reaction and interaction of energy. Fig. 57. The EarliestKnown Limbed of Tliinopus anli-qiius Marsh, an amphibianfrom the Upper Devonian ofPennsylvania. Type in thePeabody Museum of YaleUniversity. Photograph ofcast presented to the Ameri-can Museum of Natural His-tory by the PeabodyMuseum. EVOLUTION OF THE AMPHIBIANS 177 %i:.-\. Form Evolution of the Amphibians A single impression of a three-toed footprint (Thinopusantiques) in the Upper Devonian shales of Pennsylvania con-stitutes at present the sole palaeontologic
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. Fig. 57. The EarliestKnown Limbed of Tliinopus anli-qiius Marsh, an amphibianfrom the Upper Devonian ofPennsylvania. Type in thePeabody Museum of YaleUniversity. Photograph ofcast presented to the Ameri-can Museum of Natural His-tory by the PeabodyMuseum. EVOLUTION OF THE AMPHIBIANS 177 %i:.-\. Form Evolution of the Amphibians A single impression of a three-toed footprint (Thinopusantiques) in the Upper Devonian shales of Pennsylvania con-stitutes at present the sole palaeontologic proof of the longperiod of transition of the vertebrates from the fish type tothe amphibian type. This transition was a matter of thousandsof years. It took place in Lower Devonian if not in UpperSilurian time. Under theinfluence of the heredity-chromatin it is now re-hearsed or recapitulated ina few days in the metamor-phosis from the tadpole tothe frog. As compared withfishes, the significant prin-ciple of the evolution ofamphibians, as the earliest terrestrial vertebrates, is their reac-tion to marked environmental change. Their entire life re-sponds to the changes of the seasons. They also respond tosecular changes of environment in the evolution of typesadapted to extremely arid conditions. The adaptive radiation of the primordial Amphibia prob-ably began in Middle Devonian time and extended
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