ART. 18 ON A NEW SKELETON OF DIPLODOCUS GILMORE 9 



the upward curvature of the vertebral cohimn both before and be- 

 hind the sacral region. In previous restorations of Diplodocus the 

 presacral region is depicted as extending nearly straight out from 

 the sacrum, the caudals forming a rapidly drooping tail. This idea 

 was carried out in the mounting of the original skeleton of D. car- 

 negii and its many replicas distributed over the world. The pres- 

 ent specimen shows an error in both of these respects. The articu- 

 lated presacrals in our specimen have a decided upward arcuation 

 of the column beginning with the vertebrae immediately in front 

 of the sacrum. That this is a natural arrangement seems to be 

 indicated by the peculiar character of the most posterior dorsals, 

 which have the tall spinous processes strongly inclined forward of 

 the vertical axis of the vertebrae as a whole. In other words, when 

 the tenth dorsal vertebra is in position the lower half is inclined back- 

 ward, which brings the forward leaning spine into a nearly vertical 

 position and thus the spines are evenly spaced ; whereas in both the 

 C^arnegie Museum and American Museum specimens there are wide 

 gaps between the sacrodorsal and the first free dorsal in front of it. 

 In the Carnegie specimen the spine was detached when found and in 

 restoring it was placed in a vertical position. Similarly in the 

 American Museum specimen the first free dorsal in front of the 

 sacrum which lacked the centrum was restored with the spine in a 

 vertical position. In both instances the wide gap between the tops 

 of the spines resulted when the bones were articulated. 



Forward of the mid-thoracic region the column starts the reverse 

 curve downward ; thus this part of the backbone has a more natural 

 arched curvature than has previously been given it. This upward 

 curve of the presacral region makes the mid dorsals the highest point 

 above the ground, whereas in the Diplodocus carnegii specimen the 

 sacral region is highest. 



In so far as the pose of the tail is concerned, the Pittsburgh author- 

 ities now recognize the incorrectness of the D. carnegii specimen, and 

 in the mounted skeleton of Apafosaurus in this same institution the 

 tail is carried far out from the sacrum before beginning to droop 

 toward the ground. This same result was attained by the articula- 

 tion of the actual bones in the present skeleton, brought about by the 

 decided V-shaped centrum of caudal 3, which is much shorter 

 above than below, and Lull ''' found that the same condition obtains 

 in Camarasaurns and Brontosaurus. The upward curvature of the 

 tail in the sauropodous dinosaurs bears a striking resemblance to 

 that of the large extant lizard Varanus homodoensis. 



It would thus seem that all the Sauropoda are so constituted. The 

 elevation of this part of the tail well outward above the posteriorly 



i^Amer. Journ. Sci., vol. 19, pp. 1-5, 1930. 

 120834—32 2 



