. Cold-blooded vertebrates: part I. Fishes. Fishes; Amphibians; Reptiles. PEDIGREE AND KINSHIPS remains of which have been recognized only in the Terti- ary formations. A second group of important fishes, known as chimae- roids, sharklike in character, appeared early in geological time, certainly as early as the middle Silurian, which greatly antedates the Carboniferous. These animals, havmg several living representatives, variously known as spookfishes, ratfishes, and elephant fishes, are generally. Fig. 7. One of the extinct Arthrodira, with heavy armor hinged at the neck. Ten to eighteen fe
. Cold-blooded vertebrates: part I. Fishes. Fishes; Amphibians; Reptiles. PEDIGREE AND KINSHIPS remains of which have been recognized only in the Terti- ary formations. A second group of important fishes, known as chimae- roids, sharklike in character, appeared early in geological time, certainly as early as the middle Silurian, which greatly antedates the Carboniferous. These animals, havmg several living representatives, variously known as spookfishes, ratfishes, and elephant fishes, are generally. Fig. 7. One of the extinct Arthrodira, with heavy armor hinged at the neck. Ten to eighteen feet long believed to have diverged from the sharks, although the association is not very close. A thick, round head which tapers gradually toward the pointed or filamentous tail usually distinguishes them. The skin is smooth and the paired fins are somewhat sharklike in character. The fin â on the back has a long spine and the skeleton is cartilagi- nous, both characteristics suggestive of the sharks. The cranium is a highly compact structure. The upper jaw is immovably fused with the cranium and the lower one is directly articulated with it, differing sharply in these respects both from the sharks and the bony fishes. The teeth are represented by dental plates, closely fused with the jaws and studded with sharp points. Chimaeroids, like the sharks, are very imperfectly represented in the rocks, probably because their skeletons were cartilaginous and decomposed before they could be- come covered and preserved. Little more than their dental plates and fin spines have been found. The struc- ture of the ancient chimaeroids, however, appears to have [â 51. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hildebrand, Samuel F. (Samuel Frederick), 1883-1949; Gilmore, Charles Whitney, 1874-; Cochran, Doris M. (Dori
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Keywords: ., bookcentury1900, booksubj, booksubjectfishes, booksubjectreptiles
