62 



GENERAL ORNITHOLOGY. 



them than that among the members of any other classes of Vertebrates. Their likeness to 

 each other is strong, and their difference from any other Vertebrates is peculiar ; this 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, witli 

 reason, that Birds should not form a class Aves, but an order, or at most a sub-class, of Saurop- 

 sida, and thus be compared not with a class Beptilia collectively, but with other Sauropsidau 

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

 convenience of starting with a "class" Aves, however, is so great, that such classificatory 

 value will 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 " ; 

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

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

 Mammals were developed from any such creature as a Bird has come to be, nor that Birds 

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

 lar misunderstandings of the Theory of Evolution, to imagine that all the lower forms of ani- 

 mals 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 ape. The theory simply requires all forms 



of life to be developed from some ante- 

 cedent 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 either of 

 these existing creatures. All Mammals 

 are similarly the modified descendants 

 of some more primitive stock, from which 

 stock sprang also all Smtropsida, n^.edi- 

 ately or immediately ; therefore, a Mam- 

 mal is not a modified Bird, though higher 

 in the scale; and, though 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 

 are not the Pterodactyls, or Flying Rep- 

 tiles (Pterosatiria) , as might be sup- 

 posed ; but of that remarkable order, the 

 Ornithoscelida, comprising the Dinosau- 

 rians, which "present a large series of 

 modifications intermediate in structure 

 between existing Reptilia and J.fes," 

 and are therefore inferentially in the 

 direct ancestral Hue of modern Birds. 



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

 trating also the art of lithography in the Jurassic period, 

 engraved by Archceopteryx lithographica. From the originnl 

 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 ornithichnites — the 

 fossils so called because supposed to indicate the presence of Birds by their foot-prints — were 

 discovered about the year 1835 in the Triassic formation in Connecticut. But the creatures 



