214 WATER REPTILES OF THE PAST AND PRESENT 



Perhaps all these characters may best be summed up in the 

 words of Professor Fraas, as translated: 



We recognize in Geosaurus an unusually slenderly built crocodile, in 

 appearance very different from all true crocodiles. The smooth, rounded 

 skull, with its greatly elongated and slender snout, and the deep-lying, small 

 eyes, reminds one most of the ichthyosaurs. The skull merges into the slender, 

 elongated trunk without a visible neck, and the body was provided neither 

 above nor below with horny or bony armor, but was, probably, as in the whales, 

 covered with a smooth, soft skin. The anterior extremities, attached far 

 forward, are developed as paddles, and served rather as organs of equilibration 

 than as a means of propulsion, which was the function of the elongated hind 

 legs and the extraordinarily strong and powerful tail, which supported at its 

 end a large fin. The entire impression given of the animal is that of an excellent 

 swimmer, with all the peculiar aquatic adaptations. In the skeleton, however, 

 all the characters of the original crocodiles are preserved. Most remarkable 

 are the laterally placed eyes, protected by the stout sclerotic bones, and the 

 overhanging bones of the orbits. So, too, the large temporal openings of the 

 skull, doubtless due to the absence of the bony plates in the integument, give 

 to the animal a strangely abnormal appearance for a crocodile. 



We have observed that all the truly aquatic air-breathing ani- 

 mals, save the plesiosaurs, have either lost the hind legs or else 

 have them greatly reduced in size, and the disproportionately large 

 size of these members in Geosaurus seems inexplicable. But an 

 explanation is not, I think, hard to find. In the adaptation to 

 water life the first to become modified for the control of the body are 

 the front legs. The hind legs never have any really important use 

 when the tail is a powerful propeller. The hind legs of the geosaurs 

 are still essentially legs and not paddles, and they were doubtless 

 used either occasionally for propulsion on land, or perhaps for 

 pushing the body about on the bottom of shallow waters. And the 

 presence of a well-developed ventral armor of bony ribs possibly 

 also indicates more or less of the terrestrial crawHng habit. As 

 soon as the hind legs cease to be used for crawling they take on only 

 a feeble use for the equilibration of the body, and speedily become 

 small, until finally they disappear. That the hind legs of these 

 creatures were of some use in the water is certain, because of the 

 modifications in their structure, and especially because of the loss 

 of the claws; but that they were of important use as propellers is 



