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.* 
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, uzt:l 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 Zhe 
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. 
