CHORDATA — VERTEBRATA — REPTILES 359 



and ulna) in the Triassic forms {e.g. Mixosaurus) are always 

 longer and more slender and hence less paddle-shaped than 

 in later forms {e.g. Ichthyosaurus ; Jurassic to Cretaceous) 



(Fig. 152). 



Order 5, Dinosaiiria 



Extinct land reptiles with elongate limbs adapted for 

 the habitual support of the body on land, while the long massive 

 tail suggests that they were also good swimmers. The surface 

 of the body was in some forms covered with scales, in others 

 with a bony armor, while in others it was probably naked. 

 Well-preserved external molds of the skin of various dinosaurs 

 {e.g. Trachodon) have been found in western North America 

 (Fig. 5). Some had sharp carnivorous teeth, others blunt- 

 crowned herbivorous ones. (Name > Greek deinos, terrible, + 

 sauros, a lizard.) ' 



The dinosaurs are known from the Triassic to the Creta- 

 ceous inclusive ; the earliest species, those from the Triassic, were 



Fig. 153. — A bipedal dinosaur, Fulicopiis lycllianus Hitchcock, known only from its 

 tracks preserved in the Triassic shaly sandstones of the Connecticut Valley. It 

 is here restored as though in the act of drinking. Th-e bones of the left fore and 

 hind foot are shown in place, and in the foreground their tracks in the mud. 

 Beneath the union of the pubis iPu.) and ischium {Is.) a callosity (Is.C.) is rep- 

 resented, which gave rise to the impression in the yielding mud beneath ; //., ilium, 

 (After Lull.) 



carnivorous, later many became herbivorous. The Dinosauria, 

 probably derived from the Rhynchocephalia of the Permian, 

 form an exceedingly variable order. One branch {Therop- 



