56 MEMOIRS OF THE CARNEGIE MUSEUM 
acters of the Sauropoda. As already observed, Marsh has considered the elevated 
position of the anterior nares in Diplodocus as evidence of an aquatic life. But this 
evidence, although strongly presumptive, is by no means conclusive, for there are 
among living terrestrial vertebrates similar conditions, more especially among the 
mammalia accompanied by habits which are in no sense aquatic, while such essen- 
tially aquatic or amphibious reptiles as the crocodiles, alligators and gavials have 
the narial opening in its normal position at the distal extremity of the snout. In 
like manner Owen’s remark that, “These enormous Cetiosawri may be presumed to 
have been of aquatic and, most probably of marine habits, on the evidence of the 
coarse cancellous tissue of the long bones which show no trace of medullary cavity ” 
is not conclusive since some of the most strictly aquatic reptiia and mammalia, as 
for instance the Manatee among the latter class have exceptionally dense and heavy 
bones. However this exception is not so important, as it might at first glance seem 
to be, for it is a well-known fact that in the Manatee the bones have acquired greater 
density and increased specific gravity in order to aid these animals in retaining a 
submerged position while feeding on the aquatic plants found growing on the bot- 
tom of the shallow waters in which they live. It is clear that the feeding habits of 
the Sauropoda required no such modification of the osseous skeleton, and that if 
modified at all for aquatic habits, it was in the direction of a more open and cancel- 
lous structure even than that which obtains in the Cetacea and calculated not only 
to give greater buoyancy to these massive quadrupeds when in water but, in addi- 
tion, to give the greatest possible surface for muscular attachment compatible with 
the required rigidity and with the least possible weight. As Osborn, in speaking of 
the axial skeleton of Diplodocus, has truly remarked ‘“ It 1s a mechanical triumph of 
great size, lightness and strength.” Although the present writer cannot agree with 
Osborn in considering the chief function of the tail as that of a swimming organ, 
even in Diplodocus the most highly specialized member of the order, with the prob- 
able exception of Barosawrus; and while there seems to be no evidence whatever of 
the presence of a vertical fin on the tail of that genus as suggested by Osborn, I 
nevertheless believe that all the Sauropoda were aquatic to the extent that they fre- 
quented swamps, marshes, lakes and streams, that they were capable of swimming 
and that when moving about by that method the tail was a very efficient propelling 
organ. From the character of the modification of the chevrons of the mid- and 
posterior caudal regions in all the Sauropoda, however, I believe that when in a 
normal position, whether on land or in water, the greater portion of the tail rested 
on the surface of the ground, and I am not prepared to say that its function as a 
balancing, supporting, or defensive organ, was secondary to its function as a swim- 
