Part III. 



SYSTEMATIC SYNOPSIS 



OP 



NORTH AMERICAN BIRDS. 



CLASS AVES: BIRDS. 



THIS CLASS OF ANIMALS, while sharply distinguished from Mammals, is so closely 

 related to Reptiles, that the presence of feathers in the former, and their absence 

 from the latter, is the most obvious if not the only positive character by which the two classes 

 are separable. 



Though the species of birds are numerous (some 10,000 are known), the structural diver- 

 sity of the Class is comparatively so slight, that the characters upon which the primary divisions 

 are based seem insignificant in view of those upon which the major groups of Mammals or 

 Reptiles may be founded. With strict regard for equivalency of taxonomic groups, based on 

 morphological considerations, the conventional "class" of Birds is scarcely or not of higher 

 value than an order of Reptiles, with which Birds are associated under the name Saurop- 

 SIBA. But it is not proven that a given structural character may not have classificatory value 

 in one case, different from that which may properly be attributed to it in another ; so that, 

 though the most diverse birds may be more alike than are extremes among Lizards for 

 example, we may still continue to speak of a class Aves, to be primarily divided into sub-classes 

 or orders. 



All known Birds, living and extinct, are divisible into the following primary groups, 

 which may be termed sub-classes : 



I. SaururyE. — Birds with teeth. Vertebrae biconcave (amphicoelous). Sternum 

 keeled. Wings small, with separate metacarpals. Tail longer than body, its 

 vertebrae not pygostyled, its feathers arranged in distichous series. (One species, 

 Archmopteryx UthograpMca, from the Jurassic of Europe. Pig. 14.) 

 n. Odontotorm^. — Birds with teeth, implanted in sockets. Vertebrae biconcave. 

 Wings large, with anchylosed metacarpals. Sternum keeled. Tail short. 

 (Typified by the genus Ichthyornis, from the Cretaceous of North America. 

 Fig. 16.) 



