File:Image from page 125 of "Water reptiles of the past and present" (1914) (14586537807).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: snakes, not-withstanding their fish-likeform and habits. The ich-thyosaur ancestors were oncetruly land reptiles—of thatwe are as sure as we wellcan be. Some have thoughtthat those ancestors were theprimitive Rhynchocephalia,but most are now convincedthat they were among themost primitive of reptiles, abranch probably from thecotylosaurs or cotylosaurianancestors. Probably of allthe extinct forms that weknow the Proganosauriacome the nearest; indeed itis not impossible that they may have been the actual forbears ofthe ichthyosaurs. The ichthyosaurs varied in length from two to thirty feet, butthe different species, especially all the later ones, resembled eachother pretty closely in shape; the beak was more slender in somethan in others, and the shapes of the fins and paddles varied not alittle, as we shall see. The jaws were long and slender, providedwith numerous rather small but sharp and recurved teeth, espe-cially well fitted for the seizure and retention of slippery prey. The

Text Appearing After Image: Fig. 54.—Occiput of Baplanodon (Oph-thalmosaurus): pa, parietal; soc, supraoccip-ital; sq, squamosal; exoc, exoccipital; op.o,paroccipital; sta, stapes; st, supratemporal;qu, quadrate; qj, quadratojugal; pt, ptery-goid; bs, basisphenoid; sag, surangular; ag,angular; art, articular; pra, prearticular.(After Gilmore.) ICHTHYOSA URIA 115 teeth were inserted, not in separate sockets, as are those of thecrocodiles and many other reptiles, but in long, deep grooves, andwere easily lost, indeed so easily lost that one late American formwas originally described as edentulous, and it was not till a numberof years had elapsed that the teeth were found. The nostrilswere small, and situated far back on the sides of the face, near theeyes. The eyes were very large, not only in proportion to the sizeof the skull, but, in the largest species, actually attaining in some,perhaps, the size of a human head. The eyeball was surroundedin front by an extraordinarily large and strong ring of ossifications

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