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THE AMEBIC AN NATURALIST [Vol. XL V 



neath the water and move about. They are active 

 swimmers and it is possible that their movements along 

 the bed of the river or lake are to a considerable extent 

 due to the action of their feet against the water. They 

 have massive skeletons which have evidently been de- 

 veloped to bear them down in the water. Nevertheless, 

 it is to be questioned whether the animal exerts any con- 

 siderable pressure on the bottom. If the specific gravity 

 were any considerable amount above that of the water 

 the animal would have difficulty in coming to the surface 

 for air and to get a view of its surroundings. Tapirs 

 too are said to be great swimmers and divers and to run 

 along on the bottoms of streams; but these mammals 

 have no special modifications of the skeleton to enable 

 them to do this. Possibly they lay hold of the bottom in 

 some way with their hoofs, or, while running they may 

 incline the head and body downwards and forwards, like 

 a descending aeroplane. That the hippopotamus with 

 his heavy skeleton has a specific gravity little above the 

 water is proved by the following fact related in Brehm's 

 Thierleben: When a hippopotamus is killed he at once 

 goes to the bottom. Nevertheless, in many cases the 

 body comes to the surface within from 30 to 60 minutes, 

 a result of the development of gases within the cadaver. 

 Hence, it is extremely doubtful whether the animal can 

 exert much pressure on the bed of the stream. So too, 

 even if the sauropods did walk about at the bottoms of 

 streams, wholly submerged, they must have rested there 

 very lightly. 



Now what conclusions can we draw from the facts 

 above established! Dr. Matthew's strongest argument 

 in favor of the erect pose of the sauropods is derived 

 from the supposed resemblance of their limbs to those 

 of the elephant, the long straight femur, the short digiti- 

 grade feet, and the slight angulation of the limb. "Ob- 

 viously," says he, in describing rectigradism, "a special- 

 ization of this kind will occur only in an animal which 

 habitually rests its weight on the limbs." But we are 



