DEFINITION OF BIRDS. 



63 



which made these tracks are now believed to have been Dinosaurian Reptiles. The oldest 

 ornitholite, or fossil certainly known to be that of a true Bird, is the famous ArchfEopteryx, 

 found by Andreas Wagner in 1861 in the Oolitic slate of Soleuhofen in Bavaria. This has 

 a long lizard-like tail of 20 vertebra?, from each of which springs a well-developed feather 

 on each side ; feathers of the wings are also well preserved ; bones of the hand are not fused 

 together, as they are in recent Birds ; and the jaws bear true teeth. This Bird has served as 

 the basis of one of the primary divisions of the class Aves ; though it has many reptilian char- 



FiG. 15. —Restoration oi JhspirorHia n-fjalis. After Marsh. 



acters, it is a true Bird. A Bird {Laopteryx prisons) believed to be also of Jurassic age was 

 discovered in 1881 in North America. The great gap between these ancient Avians and latter- 

 day birds has been to some extent bridged by the discovery in 1870-72 of Birds from Creta- 

 ceous formations of North America ; such genera as Ichthyornis and Hesperornis forming types 

 of two remarkable groups, Odontotormce and Odontolcce, or Birds with teeth in sockets, and 

 Birds with teeth in grooves. In both the tail is short, as in ordinary birds. In Ichthyornis, 

 though the wings are well developed, with fused metacarpals, and the sternum is keeled, the 

 vertebrse present the primitive character of being biconcave. In Hesperornis the vertebra3 are 



