DEFINITION OF BIRDS. 63 
ichnites, — the fossils so called because supposed to indicate the presence of Birds by their 
foot-prints, were discovered about the year 1835 in the Triassic formation in Connecticut. 
But the creatures which made these tracks are now reasonably believed to have been all 
‘Dinosaurian Reptiles. The oldest ornitholite, or fossil certainly known to be that of a true 
Bird, is the famous Arch@opteryx, found by Andreas Wagner in 186] in the Odlitic slate of 
Solenhofen in Bavaria. This has a long lizard-like tail of twenty vertebre, from each of which 
springs a well-developed feather on each side; feathers of the wings are also well preserved ; 
Fie. 15.— Restoration of 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 Aves ; 
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- 
totorme and Odontolce, 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 
