File:The dinosaur book - the ruling reptiles and their relatives (1951) (19777854154).jpg

Title: The dinosaur book : the ruling reptiles and their relatives
Identifier: bookruli00colb (find matches)
Year: 1951 (1950s)
Authors: Colbert, Edwin H. (Edwin Harris), 1905-2001; Knight, Charles Robert, 1874-1953; American Museum of Natural History
Subjects: Dinosaurs; Reptiles, Fossil
Publisher: New York : Published for the American Museum of Natural History by McGraw-Hill
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: IMLS / LSTA / METRO

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13 Sea Serpents lthough the dixosaurs were the undisputed rulers of the land in Mesozoic times, they never ex- tended their sway to dominance of the water. True enough, some dinosaurs were partially aquatic. The great sauropods spent much of their time in the muck and water of swamps and small lakes, while the hadro- saurs (the duck-billed dinosaurs) were ob- viously rather active swimmers. Yet even these most aquatic dinosaurs showed onlv partial adaptations to a life in the bounding waves. They were primarily land animals that spent their days along the shores of riv- ers or lakes, wading about in the shallows, escaping to the deeper waters when danger threatened, but alwavs coming back to the land—the environment to which they were firmly tied by the bonds of their heritage. True dominance in the waters of Mesozoic times was held by reptiles other than the dinosaurs. These belonged to four groups: the ichthyosaurs, plesiosaurs, mosasaurs, and marine crocodiles. The first two of these groups belonged to the reptilian sub- classes Parapsida and Euryapsida, respec- tively, containing those reptiles having a single upper opening in the skull behind the eye, groups which we have not yet discussed. The other two groups, the mosa- saurs and the marine crocodiles, of much less importance as aquatic or marine rep- tiles, were related to the dinosaurs—either distantly, in the case of the mosasaurs, or by a fairly strong bond, as in the case of the marine crocodiles. An early aquatic reptile, Mesosaurus
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The fishlike ichthyosaur, a perfectly streamlined and thoroughly aquatic reptile. Its ancestry can be traced back through a form possibly similar to Mesosaurus, to a typical land-living primitive cotylosaur like Seymouria Drawings by Margaret M. Colbert 104

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