. The origin and evolution of life, on the theory of action, reaction and interaction of energy. uatic amphibia, reptiles,and mammals as one of the invariable effects of the coordina-tion of the mechanism of locomotion with that of offense anddefense. In each of these four or five great radiations of bodyform, from the swift-movingto the bottom- or ground-living, slow, armored types,there is usually an increase ofbodily size, also an increase of specialization, the maximum in both being reached just beforethe period of extinction arrives. Early Armored Fishes The armored Ordovician ostracoderm
. The origin and evolution of life, on the theory of action, reaction and interaction of energy. uatic amphibia, reptiles,and mammals as one of the invariable effects of the coordina-tion of the mechanism of locomotion with that of offense anddefense. In each of these four or five great radiations of bodyform, from the swift-movingto the bottom- or ground-living, slow, armored types,there is usually an increase ofbodily size, also an increase of specialization, the maximum in both being reached just beforethe period of extinction arrives. Early Armored Fishes The armored Ordovician ostracoderms are very littleknown. The Upper Silurian ostracoderms enjoyed a wide distribution in Europe andAmerica. They includeboth the fusiform, free-swim-ming type (Birkenia) andthe broadly depressed ray-like types {Lanarkia, etc.).Apparently they had notyet acquired cartilaginouslower jaws and were in alower stage of evolution thanthe true fishes. The armature is fromthe first arranged in shieldand plate form, as seen inPalceaspis, from the UpperSilurian Salina time of Schu-chert. In this epoch we. Fig. 47. The Antiarchi. Armored, bottom-living Ostracoderm type, Bo-///r/o/f/^w, from the Upper Devonian of Canada,with chitinous armature and a pair of anteriorappendages analogous to those of the euryp-terid crustaceans. This cluster of animals wasundoubtedly buried simultaneously whileheaded against the current in search of foodor for purposes of respiration. After Patten. i66 THE ORIGIN AND EVOLUTION OF LIFE obtain our first glimpses of North American land life in thepresence of the oldest known air-breathing animals, the scorpion spiders, also of the first knownland plants. There are indica-tions of an arid climate in manyparts of the world. In Upper Silurian time theostracoderms attain the slow,armored, bottom-living stage ofevolution, typified in the ptera-spidians and cephalaspidians,which were widely distributedin Europe, in America, and pos-sibly in the Antarctic regions,as indic
Size: 1617px × 1545px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookpublishernewyorkcscribnerss
