DEVELOPMENT OF REPTILES. 489 



They are believed to have affinities with Amphibians, Chelonians, and 

 Rhynchocephalia. Examples : — NotJiosaurus, Plesiosaurus, Mesosaurus. 



Order Ichthyopterygia. Large marine carnivorous Reptiles, re- 

 presented from the Trias to the Chalk, with long cetacean-like body, 

 without exoskeleton, with limbs adapted as paddles. They seem to 

 have some affinities with Labyrinthodonts and with Sphenodon. Some 

 measured thirty to forty feet in length. Examples : — Ichthyosaurus 

 (with some viviparous species), Mixosauncs, Opthalmosaurus, 



Order Dinosauria. Large terrestrial Reptiles, ranging from the 

 Trias to the Chalk, presenting distinct affinities with Crocodilians and with 

 Birds. Examples : — Camptosaurus, a type of those which have the shaft 

 of the pubis directed backward as in Birds ; Compsognathus, undoubtedly 

 hopped on its hind-legs, after the manner of a bird ; Iguanodon, 

 another which walked on its hind-legs, and had hollow limb bones; 

 Stegosaurus ; Megalosauius, a type of those in which the pubes sloped 

 forward ; Ceratosaurus, one of the horned Reptiles ; Atlantosaurus. 

 Some of the Dinosaurs were gigantic, thus Marsh estimates the total 

 length of Brontosaurus at upwards of fifty feet, and its weight at more 

 than twenty tons, — while the still larger Atlantosaurus immanis had a 

 femur measuring slightly over six feet. Many had small heads and 

 brains. Some were amphibious, and it is likely that many of them 

 browsed on succulent plants. 



Order Ornithosauria. Flying Reptiles, represented from the lower 

 Jurassic to the Upper Chalk, exhibiting many affinities withiCarinate 

 Birds, but still distinctly Reptilian. An expansion of the skin seems to 

 have been stretched on the much elongated outermost finger, and to 

 have extended backward to the hind-legs and the tail. Some are said 

 to have had an expanse of wing of nearly twenty-five feet ; others were 

 no larger than crows. Examples : — Pterodactylus, Hhamfhorhynchus ; 

 Pteranodon and some others were toothless. 



Pedigree of Reptiles. — -We know that some of the extinct 

 Saurians were generalised types, presenting affinities not 

 only with several of the extinct orders, but also with several 

 of the living types. It is likely that subsequent research will 

 unify the class of Reptiles. We also know that some of the 

 extinct forms have affinities with Amphibians, with Birds, 

 and with Mammals. Although we cannot with certainty 

 regard any of the extinct types of Reptiles as directly ancestral 

 to either Birds or Mammals, it is likely that the ancestors 

 of these two highest classes were among the ancient Reptiles. 



Development of Reptiles. 



The development of Reptiles has not been much investigated ; in 

 most ways the early stages agree with those observed in Birds. As the 

 latter will be discussed in the next chapter, only a few notes are here 

 necessary. 



