16 



OHIO FOSSILS 



Fig. 14 An Ordovician trilobite 

 Calymene meeki 



Fig. 13 Ordovician sea bottom 



The trilobites ( see fig. 14 for a typical trilobite) of the Ordovician would naturally 

 attract attention. Most of them were small, 2 to 3 inches long, but they are abundant in 



some of the Ordovician beds around 

 Cincinnati. The largest of the Ordovician 

 trilobites (genus Isotelus) attained a 

 length of 18 inches. 



The majority of Ordovician tri- 

 lobites have little ornamentation; not so 

 for some of the rarer forms which have 

 abundant spines and tubercles. 



The most abundant forms of Ordo- 

 vician life might at first be mistaken for 

 clams; they are brachiopods, whose bivalve 

 shells are very abundant in some Ohio beds. For the difference between brachiopods and 

 clams (pelecypods), see p. 36. Unlike the puny Cambrian brachiopods, some of the Ordo- 

 vician ones attained fair size, as much as 2 inches across, and had sturdy, thick, limy 

 shells. They vary greatly in shape and ornamentation from the nearly flat strophomenoids 

 (see p. 50) to the ribbed Platystrophias (see p. 49) and the tiny, highly ornamented Rhyncho- 

 tremas. The brachiopods of the Ordovician are not equalled in variety and abundance in 

 any other rock unit in Ohio. 



The bryozoans first became abundant during the Ordovician. At times, the bottom of the 

 Ordovician sea in Ohio was covered with these microscopic animals in huge colonies occupy- 

 ing every available surface. 



Corals were abundant at times in the Ordovician but they did not form the massive reefs 

 characteristic of their present-day relatives. Most of them were solitary and formed a 

 horn -like cup - hence the name horn-corals - in which a single animal lived. There were 

 only a few colonial corals. 



The echinoderms (starfish and their relatives) were well represented in the Ordovician 

 seas. Complete specimens are rare because the dead animals were often washed to and fro 

 on the bottom of the sea and their fragments accumulated in groups in low spots. 



The vast hordes of larger marine animals of the Ordovician must have fed, as their 

 living relatives do, on microscopic plants and animals of all kinds. Microscopic animals 

 must have been extremely abundant in Ordovician seas but owing to their lack of hard parts, 

 they are not often preserved. 



Some of the animals and plants of the Ordovician have been preserved for us in another 

 way: their soft parts produced oil which has accumulated in the rocks and has been trapped 

 there. The Ordovician rocks of northwestern Ohio have produced large quantities of oil. 

 Maximum output was in 1896 when a total of 20, 757, 138 barrels was produced. Production 



