REPTILES. 



313 



Fig. 309. 



Restoration of Ichthyosaurus, 

 after Fraas. 



Ichthyosaurian coprolites (Fig. 41) show that these animals pos- 

 sessed a spiral valve, while the finding of embryos within the 

 fossil skeleton shows 

 that at least some 

 species were vivipa- 

 rous. 



Ichthyosaurians 

 were widely distribut- 

 ed, fossils having been 

 found in all parts of 

 the globe except 



South America. In time they ranged from the upper triassic 

 to the upper cretaceous. Some reached a length of 30 or 40 

 feet. Over 50 species have been described. Ichthyosaurus, 

 Mixosaurus, and Baptanodon (Jurassic of Wyoming) are the 

 best known. 



ORDER V. RHYNCHOCEPHALIA. 



Lizard-like, scaly reptiles with long tail ; amphicoelous verte- 

 bras with frequent intercentra ; ribs one-headed, with uncinate 

 processes ; abdominal ribs ; sternum and episternum present ; 

 two sacral vertebrae ; quadrate immovable ; supra- and infratem- 

 poral fossae present ; no procoracoid ; limbs pentadactyl, vent 

 transverse ; heart, lungs, and brain as in lacertilia. 



This order is represented to-day by but a single living- 

 species, Sphenodon (^Hatteria) punctata, from the New Zealand 

 region. While in general appearance it is lizard-like, it differs 

 much from them in structure, and finds its nearest relatives in 

 fossil forms which range from the trias to the present time. 

 From the fact that all the remaining groups of reptiles have 

 probably sprung from a rhynchocephalian ancestry, the order 

 becomes very important, despite its small size. 



The vertebrae are usually amphicoelous, and remains of the 

 notochord occasionally persist intervertebrally. Sometimes they 

 are flat, and in Proterosaicrus the cervicals are opisthocoelous. 

 Intercentra occur in the caudal and cervical regions, and occa- 

 sionally in the region of the trunk. A proatlas (p. 143) occurs. 

 The premaxillas are never anchylosed ; the jaws bear acrodont 



