62 



GENERAL OBNITHOLOGY. 



closelj agreeing with one another in the peculiar sum of their pliysical characters. In compar- 

 ison with other classes of Vertebrates, all birds are much alike ; there is a less degree of 

 difference among them than that found among the members of any of the other classes of Verte- 

 brates : their likeness to each other being strong, and their kind of difference from any other 

 Vertebrates being peculiar, makes them the '"highly specialized" class they are recognized to 

 be. The structural difference between a humming-bird and an ostrich, for example, is not greater 

 in degree than that subsisting between the members of some of the orders of Reptiles ; whence 

 .Some hold, with reason, that Birds should not form a class Aves, but an order, or at most a sub- 

 class, of Sauropsida, and so be compared not with a class liepHUa collectively, but with other 

 Sauropsidan orders, such as Chelonia (turtles), Sauria (lizards), Ophidia (serpents), etc. The 

 practical convenience of starting with a ' ' class " Aivs, however, is so great, that such classificatory 

 value mil probably long continue to be ascribed, as heretofore, to Birds collectively. I have 

 spoken of Birds as a particular " side-issue " or lateral branch of the Vertebrate " tree of life " I 

 hence it is not to be supposed that they are in the direct line of genealogical descent. Thougli 

 they stand as a group next below Mammals in the scale of evolution, it does not foUow that 

 Mammals were developed from any such creature as a Bird has come to be, any more than 

 that Birds have been evolved from any such Reptiles as those of the present day. It is one 

 of the popular misunderstandings of the Theory of Evolution, to imagine that all the lower 

 fonns of animals are in the genetic line of development of the higher forms : that man, for 

 example, was once a gorilla or a chimpanzee — actually such an ipe. The theory simply 

 requires all forms of life to be developed from some antecedent form, presumably, and in most 



cases certainly, lower in the scale of or- 

 ganization. Thus man and the gorilla 

 are both descendants of some common 

 progenitor, more or less unlike eitlier of 

 these existing creatures. All mannnals 

 are similarly the ujoditied descendants of 

 some more primitive stock, from which 

 stock sprang also aU Sauropsida, medi- 

 ately or immediately; therefore, a Mam- 

 mal is not a modified Bird, though higher 

 in the scale ; and, thcjugh a Bird is a 

 modified Reptile, it is not a modification 

 of any such snake or lizard as now ex- 

 ists. The most bird-like reptiles known 

 arc not the Pterodactyls, or Flying Rep- 

 tiles {Pterosauria), as might be sup- 

 pciSed; Ijut of that remarkable order, the 

 Ornithoscelida, comprising the Dinosau- 

 lians, wliich "present a large series of 

 modifications intermediate in structure 

 between existing Septilia and Aves," 

 and are therefore inferentially in the 

 direct ancestral line of modern Birds. 



Fig. 14. —Oldest known ornitliological treatise, illus- 

 trating also the art of lithography in tlie Jurassic period, 

 engraved by Archceopteryx Htlmfiraphwa. From the original 

 slab in the British Museum ; after A. Newton, Ency. Brit. 



Geologic Succession of Birds. — 



Birds have been traced back in geologic 

 time to Cretaceous and Jurassic epochs 

 of the Mesozoic or Mid-Life period of 

 the world's history. The earliest ornith- 



