222 HISTORICAL PALAZAONTOLOGY. 
as yet been detected in any Triassic deposit; but we have 
tolerably clear evidence of their existence at this time in the 
form of footprints. ‘The impressions in question are found in 
considerable numbers in certain red sandstones of the age of 
the Trias in the valley of the Connecticut River, in the United 
States. They vary much in size, and have evidently been 
produced by many different animals walking over long 
stretches of estuarine mud and sand exposed at low water. 
The footprints now under consideration form a double series 
of simgle prints, and therefore, beyond all question, are the 
tracks of a dzfed—that is, of an animal which walked upon 
two legs. No living animals, save Man and the Birds, walk 
habitually on two legs; and there is, therefore, a prima facie 
presumption that the authors of these prints were Birds. 
Moreover, each impression consists of the marks of three toes 
turned forwards (fig. 155), and therefore are precisely such as 
Fig. 155.—Supposed footprint of a Bird, from the Triassic Sandstones of the Con- 
necticut River. ‘The slab shows also numerous “‘ rain-prints.” 
might be produced by Wading or Cursorial Birds. Further, 
the impressions of the toes show exactly the same numerical 
progression in the number of the joints as is observable in 
living Birds—that is to say, the innermost of the three toes 
consists 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 
