1896.] of Birds and Dinosaurs. 207 



view. Nor is the descent of Birds from any known group of 

 Dinosaurs favoured by K. v. Zittel in his Handbuch der Palaeon- 

 tologie, or by Haeckel in his recent work Systematische Phylogenie 

 der Wirbelthiere. 



Nevertheless this notion of the Dinosaurian ancestry of, and 

 especially Iguanodont relationship of Birds has got hold of many 

 people's minds, thanks to various popular and not overcritical 

 writers. The picture of the Iguanodon, side by side with that of 

 a Dinorius or Moa, makes a powerful appeal. 



The oldest bird known is Archaeopteryx, from the Oolite of 

 Bavaria. Consequently all those Dinosaurs which are of Oolitic 

 and later date have to be excluded from the supposed ancestry, 

 and they happen to be those in which (as in Ceratosaurus, 

 Compsognathus, Iguanodon, Ornithomimus) the resemblances are 

 greatest. There remain only Anchisaurus of the Rhaetic, the 

 contemporary of the unknown Brontozoum which left its three-toed 

 footprints, and Anchisaurus disagrees from birds in its pelvis. 

 Zanclodon of the Keuper is also one of the Theropoda. Moreover 

 the most bird-like foot is either that of one of the Theropoda 

 (which are excluded by their pelvis) or of some of the latest 

 Ornithopoda. The upright walk, which has been assumed and 

 improved upon independently by members of both Theropoda and 

 Orthopoda, has produced the same, or nearly the same modifications 

 in them as in the birds. A splendid lesson in isomorphism, homo- 

 plasy, or convergent analogies. The common substratum from 

 which all the Dinosaurs and the Birds have sprung, have been of 

 course some pentadactyle, plantigrade, four-footed Reptiles. The 

 movable quadrate of birds, firmly fixed in Chelonia, Crocodilia, 

 Sphenodon, Dinosaurs and Theromorpha, hardly points in their 

 direction. 



Lastly, they who entertain the Dinosaurian ancestry of Birds 

 seem to forget, or at least they do not fully appreciate the enor- 

 mous differences between the forelimb of Archaeopteryx and that 

 of any Dinosaur with avine resemblances in the hindlimbs. The 

 forelimbs of these Dinosaurs are already developed in a direction 

 diametrically opposed to that from which a bird-like wing could 

 be developed. To reconcile the wing of a Bat with the foreleg 

 of a Cow, we have to go back to the indifferent pentadactyle type. 



The skull presents another difficulty, and here again Comp- 

 sognathus comes perhaps nearest to that of a generalised bird's 

 skull ; and that the Jurassic Archaeopteryx and the Cretaceous 

 Hesperornis have teeth in the anterior portion of the mandible, 

 seems to exclude the Orthopoda in which the toothless, padded, 

 front portion of the underjaw is such a universal feature. 



It can of course be assumed, for argument's sake, that the 

 ancestors of Birds were a group of Reptiles with an upright gait, 



