THE MAIN KINDS OF FOSSILS 



43 



Some of these flying reptiles attained a large wingspread, more than 26 feet in one form. 

 They lived in Jurassic and Cretaceous times. 



Also during the Mesozoic, a group of reptiles took to the sea. Some of these sea -going 

 reptiles were very large, about 50 feet long but they too are extinct. 



Theromorphs (fig. 48) are the mam- 

 mal-like reptiles and, to us, the most 

 important of the extinct reptiles for they 

 form a link between the reptiles and the 

 mammals. Theromorph reptiles have not 

 as yet been recorded from Ohio but they 

 may well have roamed the state in Per- 

 mian time. 



Class Aves . The birds are rare as 

 fossils; the earliest known birds are 

 Jurassic in age. These ancient birds, 

 although fully feathered, still retain 

 reptilian characteristics, such as teeth, 

 scales on the lower part of the legs (as 

 in modern birds), and a peculiar arrange- 

 ment of the tail feathers, which are in 

 two rows, one on each side of the long 



tail, instead of being arranged like a fan, Fig. 48 



as in modern birds. 



Fossil birds are unknown in Ohio except for bird bones sometimes found in Pleistocene 

 deposits. 



Class Mammalia . The mammals are warm-blooded animals that bear their young alive, 

 have a body-covering of hair, and breathe by means of lungs. There are a few exceptions 

 to these general rules. 



The mammals were scarce during Mesozoic time and did not come into their own until 

 the beginning of the Tertiary. During that time many strange and unusual forms evolved, some 

 of them of gigantic size. The development of the mammals culminated in Pleistocene time 

 with the appearance of man-like apes and man himself. 



Mammals are not found, nor are they to be expected, in the Paleozoic rocks of Ohio. 

 The Pleistocene mammals of the state include some spectacular forms such as the mammoth 

 and mastodon, the ground sloth, and the giant beaver, all extinct. They also include some 

 forms which are far to the north or south of their present range. Pleistocene mammals are 

 discussed in greater detail in chapter 10. 



