File:Image from page 158 of "Water reptiles of the past and present" (1914) (14772707532).jpg

Identifier: waterreptilesofp1914will Title: Water reptiles of the past and present Year: 1914 (1910s) Authors: Williston, Samuel Wendell, 1851-1918 Subjects: Aquatic reptiles Publisher: Chicago, Ill., The University of Chicago Press Contributing Library: Boston Public Library Digitizing Sponsor: Boston Public Library

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Text Appearing Before Image: ail also resemble those ofthe mosasaurs more than those of the monitors, but there is afirm attachment of the pelvis to the backbone, and the legs arelong and lizard-like, though not as long as those of land lizards.The feet were webbed in life, and the toes have no claws, conclu-sively demonstrating their water habits. The vertebrae indeedhave the same peculiar articulations, called zygosphenes, as inmost of the mosasaurs. The largest aigialosaurs were about sixfeet in length, that is, of about the size of the smallest knownmosasaurs. We have then in the aigialosaurs nearly every known inter-mediate character that we could wish for in a connecting linkbetween the mosasaurs and the monitors, lizards that were equallyat home on land or in the water, and there can be scarcely a doubtthat they were either the direct ancestors or closely akin to the SQUAMATA 147 direct ancestors of the strictly marine mosasaurs; and scarcelya doubt that they were the descendants of the actual forbears ■

Text Appearing After Image: s.vv.w 1910 Fio. 68.—Clidasles, an American mosasaur. Life restoration of the modern monitors, which, as we have seen, have acquiredpartial aquatic habits in escaping from their enemies. The 148 WATER REPTILES OF THE PAST AND PRESENT dolichosaurs we can now understand were a side branch from thesesemiaquatic aigialosaurs which, specializing in another direction,quickly came to grief, perhaps in competition with their moreagile and skilful short-necked kin. Taking all these facts into consideration it seems best to unitethe monitors, dolichosaurs, and aigialosaurs into one group ofthe Lacertilia, the Platynota, intermediate in place between thetrue land lizards and the truly aquatic mosasaurs. MOSASAURS At St. Pietersberg, a small mountain in the vicinity of Maes-tricht, Holland, there are immense subterranean stone quarries,which have been worked for more than a thousand years. Thestone quarried from them is a sandy limestone of Upper Cretaceousage containing many well-preserved rem

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