DEFINITION OF BIRDS. 63 



iclmites,—t\ie fossUs so called because supposed to indicate the presence of Birds by their 

 f(,ot-prints, were discovered about the year 1835 in the Triassic formation in Connecticut. 

 But the cxeatures which made these tracks are now reasonably believed to have been aU 

 Dinosaurian Reptiles. The oldest ornitholite, or fossil certainly known to be that of a true 

 Bird, is the famous ArchcBopteryx, found by Andreas Wagner in 1861 in the Oohtic slate of 

 Solenhofen in Bavaria. This has a long lizard-like tail of twenty vertebrje, from each of which 

 springs a weU-developed featlier on each side ; feathers of tlie wings are also weU preserved ; 



Fig. 15. —Restoration ot Hesperornis regalis. After Marsh. 



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 Avefs : 

 though it has many reptilian characters, it is a true Bird. The great gap between this ancient 

 Avian and latter-day birds has been to some extent bridged by Marsh's discovery and splendid 

 restoration of Birds from the Cretaceous formations of North America, such genera as 

 Ichthyornis and Hesperornis forming types of two other primary divisions of the class, Odon- 

 totornuB and Odontokce, or Birds with teeth in sockets, and those with teeth in grooves. In 

 both genera the tail is short, as in ordinary birds. In Ichthyornis, though the wings are 



