. The origin and evolution of life, on the theory of action, reaction and interaction of energy. onian time and extended throughthe great swamp, coal-forming period of the Carboniferous,which afforded over vast areas of the earths surface ideal con-ditions for amphibian evolution, the stages of which are bestpreserved in the Coal Measures of Scotland, Saxony, Bohemia,Ohio, and Pennsylvania, and have been revealed through thestudies of von Meyer, Owen, Fritsch, Cope, Credner, andMoodie. The earliest of these terrestrio-aquatic types have Fig. 58. A Primitive Amphibian. Theoretic reconstruction
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. onian time and extended throughthe great swamp, coal-forming period of the Carboniferous,which afforded over vast areas of the earths surface ideal con-ditions for amphibian evolution, the stages of which are bestpreserved in the Coal Measures of Scotland, Saxony, Bohemia,Ohio, and Pennsylvania, and have been revealed through thestudies of von Meyer, Owen, Fritsch, Cope, Credner, andMoodie. The earliest of these terrestrio-aquatic types have Fig. 58. A Primitive Amphibian. Theoretic reconstruction of a primitive sala-mander-like type with large, solidly roofedskull, four limbs, and five fingers on each ofthe fore and hind feet, such as may have ex-isted in Upper Devonian time. After Fritsch. 178 THE ORIGIN AND EVOLUTION OF LIFE not only a dual breathing system of gills and lungs, but a dualmotor equipment of limbs and of a propelling median fin inthe tail region. So far as known, the primordial Amphibia in their form werechiefly of the small-headed, long-bodied, small-Hmbed, tail-pro-. FiG 59. Descent of the Amphibia The Amphibia—in which the fin is transformed into a limb (Thinopus)—are believed tohave evolved from an ancestral ganoid fish stock of Silurian age through the fringe-finned ganoids. From this group diverge the ancestors of the Reptilia and the sala-mander-like Amphibia which give rise to the various salamander types, also to branchesof limbless and snake-like forms (Aistopoda, modern Coecilians). The other greatbranch of the solid-skulled Amphibia, the Stegocephalia, was widespread all over thenorthern continents in Permian and Triassic time (Cricotas, Eryops), and from thisstock descended the modern frogs and toads (Anura). Prepared for the author byW. K. Gregory. pelled type of the modern salamander and newt. The large-headed, short-bodied types (Amphibamus) were precociousdescendants of such primordial forms. In Upper Carbonifer- EVOLUTION OF THE AMP
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