538 Comparative Morphology of Chordates 



even larger than in reptiles, and contain a greater store of food (yolk). 

 The shell is calcified and hard in contrast to the flexible parchment-like 

 shell of most reptilian eggs. The protective, nutritive, and respiratory 

 embryonic membranes — amnion, yolk-sac, and allantois — closely 

 resemble those of reptiles. 



Early Birds 



Definitions of the Class Aves put such great emphasis on adapta- 

 tions for flight that other characteristics and exceptions are over- 

 shadowed. The mere mention of "bird" suggests something flying. 

 But, just as there are "vertebrates" without the vertebral column, so 

 the name "bird" is applied to some animals which cannot fly. The 

 ostrich and penguin have wings which are insufficient for flight. The 

 remains of the recently extinct gigantic moa of New Zealand show, in 

 some cases, no trace of pectoral limbs. Birds which are strong fliers 

 possess a complex of highly specialized features, but in flightless birds 

 these are, in varying degree, so reduced that they cannot be said to be 

 universally characteristic of birds, and their close equivalent may be 

 found in some reptiles. The one highly specialized thing which, without 

 any exception, is common to all animals which we call "birds" is the 

 feather. The ostrich does not fly, but ostrich plumes are extraordinary 

 examples of the feather. A bird without feathers can perhaps be im- 

 agined, but no such animal is known to exist at present. A feather 

 without a bird is equally foreign to our experience. 



About 1860, on a slab of fine-grained (lithographic) limestone ob- 

 tained from a quarry in Bavaria, was found what appeared to be the 

 impression of a single feather. Its identity was doubted until, about a 

 year later and in the same locality, there was found a nearly complete 

 vertebrate skeleton with which were associated unmistakable impres- 

 sions of feathers. Through the effort of Sir Richard Owen, this fossil 

 was bought and deposited in the British Museum. In 1863 Owen 

 published a detailed account of it. About 16 years later the original 

 locality yielded another and still better specimen (deposited in the 

 Berlin Museum) differing from the first in some details but evidently 

 representing a related genus or species. Since then no similar fossils 

 have been found anywhere. 



The two fossil skeletons represent animals of "about the size of a 

 crow." The skeleton is, in general, distinctly reptilian (Fig. 417). The 

 skull is more heavily built than that of a modern bird. The upper jaw 

 carried numerous well-developed conical teeth. Teeth were probably 

 present in the lower jaw, but less numerous. There were about 50 

 vertebrae, of which only about 10 were in the short neck. There was 

 no fusion of trunk vertebrae. The sacral region included 5 or 6 verte- 

 brae. The long tail contained some 20, which were all freely movable 



