454 



THE CHANGING GENERATIONS 



which are to be associated their warm blood, high metabolic rate, and 

 probably their nesting habits, the birds are little more than "glorified 

 reptiles." Feathers are their most distinctive feature, yet even these seem 



to have been derived from horny 

 reptilian scales in which the edges 

 have developed into a large number 

 of fine, interlocking subdivisions. 

 The fossil record gives conclusive 

 proof of their archosaur deriva- 

 tion. 



The oldest known birds. At 

 Solnhofen, in Bavaria, a very fine- 

 grained Jurassic limestone is 

 quarried for use in lithographic 

 printing. Many beautifully pre- 

 served fossils have been taken 

 from the quarries, and among 

 these are two primitive birds about 

 the size of crows, in which even 

 the outlines of the feathers may 

 be seen. Although placed in dif- 

 ferent genera, they are very similar 

 and are usually referred to under 

 the name Archaeopteryx. So rep- 

 tilian are their characters that if 

 the feathers had not been pre- 

 served they would doubtless have 

 been classified as small, primitive 

 ornithischian dinosaurs. Their 

 differences from modern birds are shown in the following tabular 

 comparison. 



Fig. 28.19. The earliest known 

 Archaeopteryx. (After von Meyer.) 



bird, 



Archaeopteryx 



Jaws with many sharp teeth 



Tail long, reptilian, with row of feathers 

 on each side 



Wings feeble, the 3 anterior fingers clawed, 

 projecting from front margin of wing; 

 digits not fused together 



Bones not hollow and air-filled; air sacs 

 presumably not developed 



Breastbone (and by inference the flight 

 muscles) weakly developed 



Pelvis of ornithischian type, bones show- 

 ing only incipient fusion 



Modern Birds 

 Jaws toothless, with horny bill 

 Tail short, with fanlike spread of feathers 



^'ings strong, the digits fused together, 



and claws lost (except in the primitive 



hoatzin) 

 Bones hollow and air-filled; air sacs in 



body, connected with lungs 

 Breastbone large and keeled for insertion 



of powerful flight muscles 

 Pelvis derived from ornithischian type, 



but fused with vertebrae into a rigid 



structure 



