344 CLASSIFICATION OF VERTEBRATES. 



of a crow, the other considerably larger. Laopteryx, known 

 from a few fragments from the Jurassic of Wyoming, may be- 

 long here. 



ORDER II. ODONTORM^:. 



Extinct carinate birds with normal avian tail (pygostyle) ; 

 teeth thecodont ; presacral vertebrae amphicoelous ; quadrate 

 with a single articular facet ; rami of lower jaw united by 

 cartilage. 



To this order belong a few birds arranged in the genera 

 Ichthyornis and Apatornis, pigeon-like in size, found in the 

 middle cretaceous of Kansas and Colorado. They had very 

 large skulls, strong wings, and small legs, while the succession 

 of the teeth was vertical as in the dinosaurs. This and the fol- 

 lowing order are frequently united as odontornithes or toothed 

 birds. 



ORDER III. ODONTOHOLC^E. 



Extinct ratite birds with teeth in alveolar grooves ; vertebral 

 centres saddle-shaped ; quadrate with one articular facet ; skull 

 dromaeognathous ; rami of lower jaw united by cartilage; wing 

 reduced, only the humerus retained. 



The birds belonging to this order occur in the same beds 

 as do the odontormae. In general appearance they were some- 

 what like grebes. The cranial bones were firmly united, the pre- 

 maxillary bone was without teeth, while the teeth of the maxillae 

 and lower jaw had a lateral succession as in the pythonomorphs. 

 There was no true pygostyle, but the caudal vertebrae were 

 broadly expanded, forming a paddle-like tail, only a few of the 

 distal bones being fused. The clavicles were not united into 

 a wish-bone ; the acetabulum resembled that of the crocodiles ; 

 ilia, ischia, and pubes were not united posteriorly ; and the feet 

 were apparently fitted for swimming only. Here belong Hes- 

 perornis and Lestornis. H. regalis was about six feet long ; 

 L. crassipes considerably larger. 



