42 OHIO FOSSILS 



abundant and sometimes spectacular specimens of this group, including complete skeletons. 

 Collecting is still possible in favored localities and will probably yield new forms of this 

 group of fishes. 



Class Chondrichthyes. Modern representatives of this class are the sharks, skates, and 

 rays. They all have skeletons made of cartilage which contains less lime than true bones. 

 The geologic range of the class is Devonian to present. 



True sharks have been found in the Paleozoic rocks of Ohio but they are far overshadowed 

 in size and numbers by the Placoderms. 



Class Osteichthyes. These are the bony fishes, characterized by the possession of jaws 

 and a skeleton of true bone. The majority of them are covered with scales but there are 

 some exceptions (e.g. the catfish). It is from one group of these fishes that the Amphibians 

 developed in Devonian time. The range of the class is Devonian to present. 



Devonian and later Paleozoic rocks of Ohio have yielded several kinds of bony fishes but 

 they are not generally common in the rocks of our state. 



SUPERCLASS TETRAPODA . 



General . The most advanced chordates are those with two pairs of limbs; they include 

 the amphibians, reptiles, birds, and mammals, each described separately below. 



In Ohio, fossil amphibians and reptiles are found sparingly in Upper Paleozoic rocks. 

 Mammals and rare bird bones are found in Pleistocene deposits. It is unfortunate in a way, 

 that the rocks of Ohio do not contain dinosaurs, for that group includes some of the most 

 spectacular land animals that ever lived. They undoubtedly roamed across what is now Ohio 

 during the Mesozoic but there are no deposits of this age in Ohio and therefore no record of 

 dinosaurs. 



Class Amphibia . Living representatives of the amphibians are the frogs, toads, and 

 salamanders. They are cold-blooded animals, that is, their blood is at about the same tem- 

 perature as the air or water around them. They undergo metamorphosis, a change from a 

 swimming, fish-like animal with gills to an air-breathing land animal. The early amphibians 

 include a group called Labyrinthodonts because the enamel of their teeth was folded into com- 

 plex patterns. They are sometimes called Stegocephalians , which means " roof -headed, " as 

 the larger ones had heavy bony armor plates on their heads. Some were only a few inches 

 long, but others were as big as crocodiles. The range of the class is Devonian to present. 



Fossil amphibians have not yet been recorded from the Devonian or Mississippian rocks 

 of Ohio but footprints and trails of some of the rarest and most interesting forms of the class 

 have come from the Pennsylvanian rocks of the state. There are no Permian records and 

 Pleistocene records are of amphibians like those of the present. 



Class Reptilia . Reptiles are cold-blooded, like the amphibians, but they do not undergo 

 metamorphosis. Reptile eggs are more complex than amphibian eggs and the embryo develops 

 into an air-breathing land animal before hatching. The living reptiles, odd as they may some- 

 times seem, are much less diverse than the Paleozoic and Mesozoic representatives of the 

 class. Four extinct groups deserve special mention though we do not find them fossilized in 

 Ohio. The class as a whole ranges from Pennsylvanian to present. 



The dinosaurs appeared in Triassic time and were extinct by the end of Cretaceous time. 

 Some of them were sluggish amphibious forms of huge size, others were peaceful plant- 

 eaters with bizarre armor. Large flesh-eating dinosaurs preyed on their less aggressive 

 relatives. 



During the "age of dinosaurs" (the Mesozoic) some reptiles developed the ability to fly. 



