xviii. 4 CRETACEOUS BIRDS 513 



short distances only. There was a furculum and a small sternum. The 

 ribs were slender and had no uncinate processes. The pelvic girdle 

 and hind limb resembled those of archosaurs, with elongated ilium 

 and backwardly directed pubis. Only six vertebrae were fused to form 

 the sacrum (at least eleven in birds). The fibula was complete and the 

 proximal tarsals were free, but the distal ones were united with the 

 metatarsals. 



In the skull of *Archaeopteryx (Fig. 308) there were teeth in both 

 jaws. The shape was more reptilian than bird-like, with rather small 

 eyes and brain, and premaxillae and frontals much smaller than in 

 modern birds. There was a large vacuity in front of the eye and prob- 

 ably there were post-frontal and post-orbital bones. The condition 

 of the temporal region is unfortunately not clear on account of the 

 crushing of the material. The brain-case was large and many of the 

 bones were united, as in modern birds. The bones were not pneuma- 

 tized. The cerebral hemispheres were elongated as in reptiles and the 

 cerebellum was small. 



These very interesting fossils suggest that the birds arose from a 

 race of bipedal arboreal reptiles, living in forests and accustomed to 

 running, jumping, and gliding among the branches (Fig. 309). There 

 has been much controversy about the origin of flight, some maintain- 

 ing that the earliest birds were terrestrial and used the wings to 

 assist in running, leading eventually to a take-off, perhaps at first for 

 short distances. The claws and long tail of *Archaeopteryx speak 

 definitely against this view and in favour of a gliding origin for flight. 



4. Cretaceous birds. Superorder Odontognathae 



These Jurassic fossils are so distinct from other birds that they are 

 placed in a distinct subclass *Archaeornithes. All other known living 

 and extinct birds have a short tail, reduced hand, a sternum, and other 

 characteristics of the subclass Neornithes. A few fossils are known 

 from the upper Cretaceous in which certain reptilian characteristics 

 are still preserved. *Hesperornis probably possessed teeth. Another 

 Cretaceous bird skull (*Ichthyornis) was found associated with a toothed 

 jaw, but the latter is now believed to have belonged to a mosasaur. 

 However, the two birds are placed in a superorder *Odontognathae. 

 They were aquatic birds, and the former was a diver that had lost the 

 power of flight. 



Already in the Cretaceous there were some birds that had lost the 

 teeth and can be referred to orders found alive today. Birds are not 

 commonly found as fossils, however, and it is not possible to give 



