THE TRIASSIC PERIOD. 



229 



progression in the number of the joints as is observable in 

 living Birds that is to say, the innermost of the three toes con- 

 sists of three joints, the middle one of four, and the outer 

 one of five joints. Taking this evidence collectively, it would 

 have seemed, until lately, quite certain that these tracks could 

 only have been formed by Birds. It has, however, been 

 shown that the Deinosaurian Reptiles possess, in some cases 

 at any rate, some singularly bird-like characters, amongst 

 which is the fact that the animal possessed the power of 

 walking, temporarily at least, on its hind-legs, which were 

 much longer and stronger than the fore-limbs, and which 

 were sometimes furnished with no more than three toes. 

 As the bones and teeth of Deinosaurs have been found in 

 the Triassic deposits of North America, it may be regarded as 

 certain that some of the bipedal tracks originally ascribed to 

 Birds must have really been produced by these Reptiles. It 

 seems at the same time almost a certainty that others of the 

 three-toed impressions of the Connecticut sandstones were in 

 truth produced by Birds, since it is doubtful if the bipedal 

 mode of progression was more than an occasional thing 

 amongst the Deinosaurs, and the greater number of the 

 many known tracks exhibit no impressions of fore-feet. 

 Upon the whole, therefore, we may, with much probability, 

 conclude that the great class of Birds (Aves) was in existence 

 in the Triassic period. If this be so, not only must there 

 have been quite a number of different forms, but some of 

 them must have been of very large size. Thus the largest 



Fig. 156. Lower jaw of Dromatherlum sylvestre, 

 Trias, North Carolina. (After Einmons.) 



Fig. 157. a, Molar tooth of 

 Microlestes antiquus, magni- 

 fied ; b, Crown of the same, 

 magnified still further. Trias, 

 Germany. 



footprints hitherto discovered in the Connecticut sandstones 

 are 22 inches long and 12 inches wide, with a proportionate 

 length of stride. These measurements indicate a foot four 

 times as large as that of the African Ostrich; and the animal 

 which produced them whether a Bird or a Deinosaur must 

 have been of colossal dimensions. 



