TRIASSIC PERIOD. 



413 



Fig. 725. 



There were two groups : one, in which the hind feet were three-toed, 

 and undistinguishable in the tracks they made from those of birds; 

 and a seco?id, in which the hind feet were four-toed or Jive-toed, and 

 much resembled those of the Labyrinthodonts. In each, the fore-feet 

 were four-toed or five-toed, as is known from the occurrence occasion- 

 ally of impressions of these feet along with those of the hind-feet, and 

 also from skeletons of related species found in the Jurassic and Creta- 

 ceous rocks of the West. 



The Three-toed Dinosaurs were numerous, and some were of gigan- 

 tic size. The tracks were at first referred to birds, but the most of 

 them have been proved to be tracks 

 of Dinosaurs by the occurrence of 

 impressions of the fore-feet on some 

 slabs. Fig. 721 a represents the 

 track of the hind-foot of one of the 

 species of the Connecticut Valley, 

 and 721 that of the fore-foot. Fig. 

 725 shows the form of the largest 

 of the three-toed tracks, its length 

 in some specimens being nearly two 

 feet. It is the Brontozoum gigctn- 

 teum of Hitchcock. The depth of 

 the track, and the great length of 

 the stride, prove that it was both tall 

 and heavy ; fourteen feet has been 

 estimated for the height, but this is 

 a minimum. 



The four-toed or five-toed Dino- 

 saurs of the era, were of as gigantic 

 forms as the three-toed, and probably much exceeded them in the 

 magnitude of some species. They were as completely bipeds as the 

 preceding. Fig. 724 a gives the form of one of the hind-foot tracks, 

 the actual length of which was twenty inches ; the stride was three 

 feet. Eleven consecutive tracks have been observed on a single sur- 

 face of sandstone. The form of the fore feet, which were sometimes 

 brought to the ground, is shown in Fig. 724. The species is called by 

 Hitchcock Otozoum Moodii. No impression of a tail has been observed 

 on any of the slabs, and hence this part must have been short. Three 

 consecutive hind-foot tracks of a smaller species is represented in Fig. 

 719 ; the tracks were about three inches long. In one of these biped 

 species the tracks are but a fourth of an inch long. 



The idea that the four-toed bipeds were Amphibians was set aside by Professor Marsh 

 after the discovery of large four- toed Dinosaurs, as well as three-toed, in the Jurassic 



Brontozoum giganteum (X 



