HI LECTURES ON EVOLUTION 109 



We have had to stretch the definition of the 

 class of birds so as to include birds with teeth 

 and birds with paw-like fore-limbs and long tails. 

 There is no evidence that Compsognatlius possessed 

 feathers ; but, if it did, it would be hard indeed to 

 say whether it should be called a reptilian bird or 

 an avian reptile. 



As Compsognatlius walked upon its hind legs, it 

 must have made tracks like those of birds. And 

 as the structure of the limbs of several of the 

 gigantic Ornithoscelida, such as Iguandcn, leads 

 to the conclusion that they also may have con- 

 stantly, or occasionally, assumed the same attitude, 

 a peculiar interest attaches to the fact that, in the 

 Wealden strata of England, there are to be found 

 gigantic footsteps, arranged in order like those of 

 the Brontozoum, and which there can be no reason- 

 able doubt were made by some of the Ornithoscelida, 

 the remains of which are found in the same 

 rocks. And, knowing that reptiles that walked upon 

 their hind legs and shared many of the anatomi- 

 cal characters of birds did once exist, it becomes 

 a very important question whether the tracks in 

 the Trias of Massachusetts, to which I referred 

 some time ago, and which formerly used to be 

 unhesitatingly ascribed to birds, may not all have 

 been made by Ornithoscelidan reptiles ; and 

 whether, if we could obtain the skeletons of the 

 animals which made these tracks, we should 

 not find in them the actual steps of the evo- 



