REPTILES IN GEOLOGY 145 



Hkptilks in Geology 



Except the Taatera all our modern reptiles be- 

 long to families that are comparatively recent. The 

 crocodilians, however, had ancient representatives. 

 If this order were not one of the families of the old 

 order of Dinosaurs^ it was close to them. They 

 occur just above the coal — after the age in which the 

 Reptiles all came in. It is probable that they are 

 now (and were then) a slightly degraded form, and 

 got the hole between the two great heart arteries by 

 going back to the water after having been once 

 more terrestrial. 



The tortoise-forms are not found farther back 

 than the rocks which are just below man — the so- 

 called Tertiary times. They are evidently just lizards 

 with shells on the back. As noted, many lizards show 

 bones on the back nnder the skin, and other lizard- 

 forms have in the abdomen bones which are not 

 p .rt of the breast-bone; some have beaks quite like 

 those of the turtles, but the teeth are still present. 

 One turtle, however, shows a tooth or two in its very 

 young. Finally, a small fossil burrowing lizard has 

 been found by Professor Cope which had a shell on top 

 only. A giant fossil turtle was found out West thir- 

 teen feet long and it had flippers which measured from 

 tip to tip about fifteen feet. Like the sea- turtle its 

 ribs were flattened but were not grown to the shell. 



Snakes are found in the lowest Tertiary — perhaps 

 a little older than the tortoise-forms. They are but 

 lizards with the leijcs lost and the chin loose-iointed. 



