276 VERTEBRATE ZOOLOGY 



We would then have to suppose that some of the archaic diving 

 birds, such as the penguins, underwent a specialization of the prim- 

 itive wings, using them for under-water "flying"; that others, such as 

 the grebes, never developed them into fully effective organs of flight; 

 while still others, such as the loons, became good flyers though still 

 retaining their diving propensities. According to Dr. Coues, the 

 loon practically flies under the water, using the wings as well as the 

 feet as propellers. The strong flying sea-birds would then be derived 

 from ancestral diving types that had gradually perfected their flight; 

 while land-birds of all sorts would be derivatives of the sea-birds. 

 There are, in fact, many evidences that the sea is the ancestral home 

 of the birds and that they have invaded the land in comparatively 

 recent times. If one turns to page 289, where the orders of carinate 

 birds are listed, he will note that Brigade I (largely archaic birds) 

 consist abnost entirely of water birds, while Brigade II (largely 

 modern types) consists exclusively of land birds, with the arboreal 

 birds confined to the more highly specialized sub-orders. If this 

 classification represents an approximation to the phylogenetic order, 

 the arboreal birds, instead of being the most primitive (as the theory 

 of arboreal origin of fiight maintains), are a modern product, and hfe 

 in the trees is a modern habit. 



Archoeopteryx, of course, seems to militate against the diving 

 origin of flight, for it is assumed to be a climbing arboreal bird. But 

 might not climbing be equally appropriate as an aid in scaling cliffs 

 after diving and swimming in the water? Moreover, the teeth of 

 Archceopteryx would be of great service in seizing fish. On the whole, 

 then, the existence of Archoeopteryx is no more a barrier to the ac- 

 ceptance of the diving than to the cursorial origin of flight; while 

 other considerations appeal" to make the former more probable thari 

 the latter. 



Archaic Birds (Arch^eornithes) 



It is customary to divide all birds into two sub-classes: Archceor- 

 nithes, consisting of but one species {Archceopteryx lithographica) ; 

 and Neornithes, including all other birds living and extinct. 



It is highly probable that the period of avian evolution began not 

 later than the Triassic; hence the birds are the latest of the verte- 

 brates to have made their appearance in the world. The earliest 

 actual birds whose fossil remains have been found are not materially 



