HISTORY OF MARINE MAMMALS—ABEL. 483 
this is connected the peculiar marine turtles, which were modified 
for living entirely in the sea, and possessed a long salamander-like 
body and fins, and a vertical caudal fin like the ichthyosaur. They 
ally themselves to the snake-like mosasaurs (fig. 10), which again 
exhibit other forms of body. 
RESTORATIONS OF KANSAS MOSASAURS. 
VENTEHOENN GS 
Fic. 10.—Restored skeletons of Mosasaurus from the Upper Chalk of Kansas. A. 
Clidastes velox Marsh. Length about 4 meters (12 feet). B. Platecarpus corypheus 
Cope. Length about 4.6 meters (14 feet). CC. Tylosaurus proriger Cope. Length 
about 7.5 meters (23 feet). After 8. W. Williston. 
Of all the marine reptiles, none can be the ancestor of the marine 
mammals. Without exception, all these marauders of the sea were 
representatives of separate branches of the reptile stock, which have 
entirely died out. 
The time of the extinction of the great marine reptiles does not 
coincide with that of the appearance of the marine mammals. One 
may not at all picture to himself that the extirpation of the marine 
reptiles which ruled the sea at the end of the Mesozoic was due to 
their. being supplanted and annihilated by the rising and flourish- 
ing mammals. <A long time elapsed between the destruction of the 
marine reptiles and the appearance of the first marine mammals. 
Ill. Tue ANcEsToRS oF THE MAaring MAMMALS. 
The Mesozoic is the time of the uncontested dominion of the 
reptiles on land, in the air, and in the sea. The mammals of this 
epoch are known only from very rare and insufficient remains. The 
dominion of the mammals begins with that division of geological 
time which we call the early dawn of the world, éos yaw7, or the 
Eocene. They first conquer the land and then take possession of 
the sea. 
