EOCENE PERIOD 135 



tortoises, at the present time, are known only south of the 

 equator. 



The move to marine hfe initiated by some Jurassic 

 tortoises, and further developed by Cretaceous forms, con- 

 tinued without serious check. And sea-tortoises, or turtles, 

 were now becoming a power in the seas. Leathery turtles 

 (so-called from the leathery skin which does duty on the 

 carapace for the ordinary bony plates) were in existence : 

 and some large forms were enjoying life on the site of London 

 {Eosphargis). 



Lizards were now decidedly more recognisable as such lizards 

 than in earlier times. Not only iguanas, but monitor lizards, 

 and creatures of chameleon type basked in the Eocene sun- 

 shine (Jguanavus, Tinosaurus, Chamceleontidce). 



Snakes were also in being. These had probably sprung snakes 

 from some ancient lizard-like forms that had more or less 

 lost their limbs. Those ancestral creatures, it may be sup- 

 posed, had found it more advantageous in obtaining food, 

 and for self-preservation generally, to move along by the aid 

 of their ribs ; and as the result of disuse the limbs became 

 atrophied. Pythons, it may be mentioned, retain vestiges of 

 hind-limbs. 



The Eocene snakes of which remains have been found seem 

 to have been of aquatic habits, and closely related to the 

 pythons of our own time (PalcBophis, etc.). In Egyptian 

 waters some of the animals were nearly thirty feet in length 

 (Gigantophis garstini). No venomous snakes, it would seem, 

 had as yet appeared. 



The long-languishing ranks of amphibians were now amphibians 

 recuperated by the appearance of little creatures in a tail- 

 less condition. At least they were probably so as adults, 

 having, in juvenile days, used their tails, first for swimming 

 purposes, and then as food for the body. 



These, the first-known of the frog fraternity, seem to have 

 been much of the stamp of certain small frogs now living in 

 India (Oxyglossus). 



Fishes had meanwhile been developing into a decidedly 

 modern aspect. Shark-life was being further diversified sharks 

 by the evolution of forms to which the blue-sharks of our own 



