546 



THE AMERICAN NATURALIST 



[Vol. XL 



Pterosauria 



The y)ten)(liictyls were a nMnarkal)le group of rei)ti1ian forms 

 whose remains are known from the Mesozoie rocks, rangin<i from 

 the lUuetic to the Upper ( 1ialk. As yet we know nothing of tlieir 

 ancestry, for the first which appear are in ever^- way characteristic 

 of the group. 



Seelev p. 220) says: "There is no geological history of the 



rapi<l o"r gradual development of the wing finger, and although 

 the whig memi.rane may he accepted a^ the cau.e <.f if> existence 



" PterodactvK ^iiow singularly little variation in structure hi 

 their geological hi.torx . \Ve chronicle the loss of tlu> tail and the 

 loss of teeth. ^Phere" is also the loss of the outermost wing-digit 

 from the hind foot as a suj)p()rter of the wing membrane. \)ut 

 the other variations are in the length of the metacar])us, or of the 

 neck, or of the head." One might add to this an increase of size 

 as the huge pterodactyl I'teranodon and its allies are iunong the last 

 to appear. 



The a(la])tation of the pterodactyls for flight is a very i)erfect 

 one, im])lying not only the development of true wings, hut a spc- 



l 'ii.!-ilkr nHxhticaUon <,f the h.ain uhich is unlike that of an> other 

 tfptiic. 'Ihis i. M'cn r-~pr<'ialK in xhv ^^nhU of the h.Mi.ispheres 



