THE GEOLOGICAL RECORD 



297 



resemblance to mammals. One of the best known is the celebrated 

 Pjiriasaurus (Fig. 140), described by the late Professor Seeley 

 from the Karoo formation of Cape Colony. This animal attained 

 a length of some ten or eleven feet. 



The Sauropterygia or Plesiosauria (Fig. 141) were long- 

 necked lizard-like forms, sometimes of large dimensions, which 

 had become re-adapted to a marine life, and whose limbs, while 

 retaining the typical pentadactyl structure, gradually became 

 modified to form paddles. The group seems^ to have persisted 



FIG. 143. Skeleton of lyuanodon lernissartensis, as reconstructed by 

 Dollo. X g V (From British Museum Guide.) 



throughout the whole of the Secondary period and shows a gradual 

 evolution from the Trias onwards. 



The Ichthyopterygia or Ichthyosauria (Fig. 142), which also 

 range throughout the whole of the Secondary period, were more 

 completely adapted to life in the ocean and acquired a remarkably 

 fish-like form, like the whales, dolphins and porpoises amongst 

 existing mammals. 



The Dinosauria or Ornithoscelida formed an enormous group 

 of land reptiles which seems to, have arisen in the Triassic per/od 

 and reached its climax in Jurassic and Cretaceous times. 

 Some of them were carnivorous, others herbivorous ; some walked 

 on all fours and others on their hind legs, and they often attained 

 gigantic dimensions. The well Known Iguanodon(Fig.l43), from the 



