DINOSAURS. 79 



As we remarked before, the carnivorous Dinosaurs were the 

 lions and tigers of the Mesozoic era, and, what with small mammals 

 and numerous reptiles of those days, it would seem that they were 

 not limited in their choice of diet. 



It is a question not yet decided whether Dinosaurs laid eggs as 

 most modern reptiles do, or were viviparous like quadrupeds ; but 

 Professor Marsh thinks there are reasons for the latter supposition. 



During the early part of the Mesozoic era, at the period known 

 as the Triassic (New Red Sandstone), Dinosaurs flourished 

 vigorously in America, developing a great variety of forms and 

 sizes. Although but few of their bones have as yet been dis- 

 covered in those rocks, they have left behind unmistakable 

 evidence of their presence in the well-known footprints and other 

 impressions upon the shores of the waters which they frequented. 1 

 The Triassic Sandstone of the Connecticut Valley has long been 

 famous for its fossil footprints, especially the so-called " bird- 

 tracks," which are generally supposed to have been made by 

 birds, the tracks of which they certainly appear to resemble. 

 But a careful investigation of nearly all the specimens yet dis- 

 covered has convinced Professor Marsh that these fossil impres- 

 sions were not made by birds (see Fig. 14). Most of the three- 

 toed tracks, he thinks, were made by Dinosaurs, who usually 

 walked upon their hind feet alone, and only occasionally put to 

 the ground their small fore limbs. He has detected impressions 

 of the latter in connection with nearly all the larger tracks of the 

 hind limbs. These double impressions are just such as Dinosaurs 

 would make ; and, since the only characteristic bones yet found 

 in the same rocks belong to this order of reptiles, it is but fair to 

 attribute all these footprints to Dinosaurs, even where no impres- 

 sions of fore feet have been detected, until some evidence of 

 birds is forthcoming. The size of some of these impressions, as 



1 Since the above was written, Professor Marsh has described, in The 

 American Journal of Science for June, 1892, several more or less complete 

 skeletons of Triassic Dinosaurs, lately found, and now in the Yale College 

 Museum. This is an important discovery. 



