. Rettili d'acqua del passato e del presente . sasauri. L'estremità del muso ha una proiezione simile a un becco. I denti sono molto più lunghi, più appuntiti, e più ricorsi di quanto non lo sia la cassa con la maggior parte dei rettili di terra, indicando il loro uso per la cattura e la ritenzione di scivolosa, veloce-movente preda. Le costolette a testa singola sono corte, dimostrando che il corpo wasslender e senza dubbio cilindrico, più simile a quello di un serpente. I 136 RETTILI D'ACQUA DELLA coda PASSATA E PRESENTE non erano solo enormemente allungati, ma erano anche compressedati in un organo di propulsione piatto ed efficace nell'acqua. Spianatura della

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. Water reptiles of the past and present . sasaurs. Theextremity of the snout has a beak-like projection. The teeth aremuch longer, more pointed, and more recurved than is the casewith most land reptiles, indicating their use for the capture andretention of slippery, quick-moving prey. The single-headed ribs are short, proving that the body wasslender and doubtless cylindrical, more like that of a snake. The 136 WATER REPTILES OF THE PAST AND PRESENT tail was not only enormously elongated, but it was also compressedinto a flat and effective propelling organ in the water. Thisflattening of the tail is apparent from the skeleton, with its elongatedchevrons below and spines above, and it is also proved by the for-tunate preservation of the extremity of the tail of one specimen, showing not only the impressions of the scales in the matrix, butalso the outlines that the soft parts had in life. To quote fromLortet, in translation: The tail was covered wholly with smallscales, regularly hexagonal in shape, shining and nacreous, larger. Fig. 64.—Life restoration of Pleurosaurus on the under side than above. The upper border of the tail wassurmounted by a broad crest, extending to its extremity, and com-posed of large, oval scales. The body doubtless was whollycovered with scales, though it is not probable that the caudalcrest continued along the back. The limbs begin to show an aquatic adaptation, though notvery pronounced. They are much shorter and smaller than arethose of land-crawling reptiles; and the bones of the second series, that is, the radius and ulna, tibia and fibula, are relatively short, the beginning of adaptation to water habits. It is very probablethat the feet were webbed, though the fifth digit, as usual, is shorterthan the fourth. Doubtless on land the creature moved about PROTOROSA URIA 13 7 in a serpentine way, for it could not have progressed very rapidlyby the aid of its legs alone. The hind legs are longer than thefront legs, and they were connected

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• bookcentury1900
• bookdecade1910
• bookidwaterreptilesofp1914will