File:The chordates (1950) (19988973414).jpg

Title: The chordates
Identifier: chordates00rand (find matches)
Year: 1950 (1950s)
Authors: Rand, Herbert W. (Herbert Wilbur), 1872-1960
Subjects: Chordata
Publisher: Philadelphia : Blakiston
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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500 Comparative Morphology of Chordates along the body to the hindleg and tail (Fig. 389). This pair of integu- mentary membranes must have made possible not merely a gliding excursion through air but a positive flight and, judging by the mecha- nism, it was doubtless very effective flying. And so it came about that land, water, and air were dominated by reptiles. They existed in such diversity of forms as is indicated by the fact that their classification requires the making of 30 or more orders. Chief of the land types were the dinosaurs (Figs. 390,391). Some were no larger than cats and dogs; others ranged up to monsters 100 feet long and weighing 50 tons. Some, with long, strong hindlegs and very short forelegs, must have been bipedal in habit. Some were herbivorous; many were carnivorous. In the water were the externally fishlike ichthyosaurs (Figs. 392, 393), some of them 30 feet long, and even longer plesiosaurs having a long, slender neck and a very small head quite out of proportion to the broad, heavy body (Fig. 392). There is some evidence that ichthyosaurs were viviparous; skeletons of small ones are sometimes found inside the skeleton of a large individual. In various parts of the world were aquatic lizards, mosasaurs, up to 40 feet long. Some of the best speci- mens of them have been found in Kansas, which was at the bottom of a Mesozoic sea. Many of these large aquatic reptiles were carnivorous. The heavy coat of armor worn by the numerous "ganoid" fishes of the time must have been useful. The batlike flying reptiles, pterosaurs or pterodactyls, were abundant in the later Mesozoic, some measuring 25 feet across the spread wings. The Rhynchocephalia, Crocodilia, and Chelonia were well established in the early Mesozoic. The Sauria (Lacertilia) appear somewhat later and the Serpentes (Ophidia) not until the latter part (Cretaceous) of the Mesozoic. The skulls of ancient reptiles are of four types, as distinguished by differences in the structure of the posterior-lateral (temporal) region. In all cases there is a considerable space on each side between the lateral wall of the brain-case, including the auditory capsule, and
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Fig. 392. Plesiosaurs and ichthyosaurs. (From a painting by C. R. Knight. Copy- right, Chicago Natural History Museum.)

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