CHORDATA — VERTEBRATA — BIRDS 371 



since the close of Tertiary times by the semi-arctic winters 

 to the northward. Forced southward during winters into areas 

 already crowded, they returned into the northern regions of 

 less severe competition for the rearing of young. 



Derivation of name. — Latin plural of avis, a bird. 



Birds are exceedingly rare as fossils ; their remains falling 

 upon the surface of the land or water are quickly destroyed. 

 The earliest known bird, Archeopteryx, is known only from 

 two entire specimens and a single feather from the lithographic 

 stone quarries (Upper Jurassic) of Solenhofen, Bavaria (Fig. 

 160). These indicate a reptile-like animal covered with feathers, 

 and about the size of a small crow. It had sharp teeth, a short 

 neck, claws upon each of the three fingers terminating the wings 

 as well as the four toes of each foot, a small keel to the breast- 

 bone (hence it could fly), shoulder girdle exceedingly small (for 

 a flying bird) and a long tail composed of about twenty sepa- 

 rate vertebrae with a pair of feathers attached apparently to 

 each vertebra. During the remainder of the Mesozoic birds 

 became more modern in appearance through the shortening 

 of the tail by means of the consolidation of some of its verte- 

 brae, the nearly universal loss of the claws from wings and the 

 lengthening of the neck. 



Teeth did not disappear from the adult bird until the Tertiary. 

 Avian remains from the Cretaceous include Hesperornis regalis, 

 the three-foot high diving bird, and the small flying Ichthyornis, 

 both from Kansas (Fig. 161). One of the largest birds known 

 is the but recently extinct Dinornis maximus from New Zealand, 

 which stood twelve feet high. 



In the late embryo of most modern birds, the tail consists of 

 five to ten separate vertebrae which later coalesce. Teeth are 

 present in the embryo of certain species of parrot. A similar 

 repetition of ancestral characters is seen in the Hoadzin, a 

 native of the Amazon Valley. Directly after birth it makes 

 climbing expeditions by means of its beak, feet and the claws 

 upon its wings. These claws disappear in the adult bird. In 



