38 THE STRUCTURE AND LIFE OF BIRDS chap. 



been bi-concave, i.e., the centra presented hollows 

 at either end. This is a form of vertebra found 

 in very primitive reptiles, e.g., in the Hatteria lizard. 

 It is also found in Ichthyornis, a 

 fossil bird of more recent date than 

 Archaeopteryx. And what is far more 

 strange, the Gull, a highly special- 

 ised, a thoroughly modernised bird, 

 has some of its dorsal vertebrae con- 

 cave behind, thus conforming to an 

 old reptilian type, "and one almost 

 fig. 16.— Vertebra of bi-concave, which thus carries us back 



Hatteria Lizard. . .1 r ,mi •,• 



. . to reptiles oi a still more primitive 



C, centrum ; it is am- L L 



phicoeious, i.e. con- form. 1 In teeth, as I hope to show 



cave at each end. x 



presently, there is nothing unavian. 



It would be very interesting to know how this 

 bird lived. Of one thing we may be certain — he 

 was a poor flyer. With its three long unconnected 

 fingers the wing must have been a weak one. Prob- 

 ably he fluttered, rather than flew, from bough to 

 bough, his long tail serving as a parachute, and his 

 claws may have been used when he was young, 

 as Mr. Pycraft has suggested, and also when he was 

 moulting, to aid him in climbing, as the young 

 Hoatzin uses his now. 



Since the discovery of Archaeopteryx the fossil 

 bones of many birds of far later date have been found 

 in the cretaceous rocks, and also in the rocks of the 

 most recent geological periods, the Tertiary and 



1 Sec \V. K. Parker on Opisthocomus Cristatus, Proc. Zool. 

 Society, vol. xiii. part 2. 



