22 



OHIO FOSSILS 



The animal population of the seas remained as high in Mississippian as in Devonian 

 time. This is not always evident in the Mississippian rocks of Ohio for some of the sandy beds 

 of our section yield few fossils. Glimpses of the abundant life of the sea in this time are given 

 us in the limy and shaly parts of our section in which brachiopods and pelecypods are especially 

 abundant. Many Devonian forms persisted into the Mississippian and were joined in time by 

 newly-evolved forms. 



Ohio's Mississippian seas were not as clear as those of the Devonian so coral reefs and 

 even individual corals were not as common; their place was taken by mud-loving brachiopods, 

 pelecypods, and gastropods with a sprinkling of bryozoans. 



The characteristic brachiopods of the Mississippian and of the succeeding Pennsylvanian 

 and Permian are the productids (see figs. 242, 246, 247) whose shells bore spines which are 

 sometimes preserved but ordinarily only the broken spine bases can be seen on the shell. 



Maxville limestone 



Logan sandstone 

 & shale 160' 



£'£$i$(i-ij Black Hand sandstone 



Cuyahoga sa 'jtone 

 & shale 340' 



=s=HC Sunbury shale 20' 



Berea sandstone 35' 



Bedford shale 85' 



Fig. 23 Mississippian rocks of Ohio 



Some of the pelecypods of the Mississippian have 

 a surprisingly "modern" look. Scallops (see fig. 254) 

 are abundant in some beds. They are only distantly re- 

 lated to the living forms. Small, nut-shaped clams 

 (genus Nucula) are so much like the living species that 

 they are placed in the same genus. 



Cephalopods are rather scarce in our Mississippi- 

 an rocks; the few that have been found are about evenly 

 divided between ammonoids and nautiloids. The trilo- 

 bites are much rarer in Mississippian than in Devonian 

 beds but some of them are highly ornamented with knobs 

 and spines (see fig. 271). 



Some of the most interesting of our Mississippian 

 fossils are the tiny conodonts which are thought to be 

 the teeth of fish-like, primitive animals. They are 

 quite abundant in some of our Mississippian black shales 

 and are very useful to the geologist as index fossils. 

 They are seldom collected by anyone but professionals 

 because of their microscopic size; searching for them 

 is well worth while, both because of their variety of 

 form and their scientific value. 



Fishes of many different kinds were abundant in the 

 Mississippian seas. More than 400 species of ancient 

 sharks have been described, some of them very large. 

 Dinichthys and Cladoselache survived from the Devoni- 

 an and their remains are abundant in some Mississippi- 

 an formations. Another group of fishes, the ganoids, 

 with shiny plate -like scales, was also abundant in 

 Mississippian seas; they are related to the living 

 garpike. 



On land, amphibians existed and perhaps reptiles 

 also. No fossil remains of these two groups have been 

 found in Ohio; Mississippian amphibians have been 

 found in Europe and their tracks and footprints in 

 North America. 



The record of land plants becomes increasingly 

 abundant in the Mississippian. Even the most barren 

 beds of silts tone and sandstone bear fragments of land 



