On Lost Forms between Birds and Reptiles. 365 



Solenliofen slate, which record the life of a fraction of Mesozoic 

 time, should be the relics, the one of the most reptilian of birds, and 

 the other of the most ornithic of reptiles. 



And this conclusion acquires a far greater force when we reflect 

 upon that wonderful evidence of the life of the Triassic age, which 

 is afforded us by the sandstones of Connecticut. It is true that 

 these have yielded neither feathers nor bones; but the creatures 

 which traversed them when they were the sandy beaches of a quiet 

 sea, have left innumerable tracks which are full of instructive sug- 

 gestion. Many of these tracts are wholly undistinguishable from 

 those of modern birds in form and size ; others are gigantic three- 

 toed impressions, like those of the Weald of our own country ; others 

 are more like the marks left by existing reptiles or Amphibia. 



The important truth which these tracks reveal is, that, at the com- 

 mencement of the Mesozoic epoch, bipedal animals existed which had 

 the feet of birds, and walked in the same erect or semi-erect fashion. 

 These bipeds were either birds or reptiles, or more probably both ; 

 and it can hardly be doubted that a lithographic slate of Triassic 

 age would yield birds so much more reptilian than Archaopteryx, and 

 reptiles so much more ornithic than CompsognatJius, as to obliterate 

 completely the gap which they still leave between reptiles and birds. 



But if, on tracing the forms of animal life back in time, we meet, 

 as a matter of fact, with reptiles which depart from the general type 

 to become bird-like, until it is by no means difficult to imagine a 

 creature completely intermediate between Dromceus and Compsogna- 

 tJius, surely there is nothing very wild or illegitimate in the hypo- 

 thesis that the phylum of the class Aves has its root in the Dinosaurian 

 reptiles ; that these, passing through a series of such modifications as 

 are exhibited in one of their phases by Compsognathus, have given risQ 

 to the BatitcB ; while the Carinatce are still further modifications and 

 differentiations of these last, attaining their highest specialization in 

 the , existing world in the Penguins, the Cormorants, the Birds of 

 Prey, the Parrots, and the Song-birds. 



However, as many completely differentiated birds in all proba- 

 bility existed even in the Triassic epoch, and as we possess hardly any 

 knowledge of the terrestrial reptiles of that period, it may be re- 

 garded as certain that we have no knowledge of the animals which 

 linked Keptiles and Birds together historically and genetically ; and 

 that the Dinosauria, with Compsognathus, Archaopteryx, and the 

 struthious Birds, only help us to form a reasonable conception of 

 what these intermediate forms may have been. 



In conclusion, I think I have shown cause for the assertion that 

 the facts of Palaeontology, so far as Birds and Eeptiles are concerned, 

 are not opposed to the doctrine of Evolution, but, on the contrary, 

 are quite such as that doctrine would lead us to expect : for they en- 

 able us to form a conception of the manner in which Birds may have 

 been evolved from Keptiles, and thereby justify us in maintaining 

 the superiority of the hypothesis, that birds have been so originated, 

 to all hypotheses which are devoid of an equivalent basis of fact. 



[T. H. H.] 



