CHAPTER 10. PLEISTOCENE FOSSILS 



Collecting Localities 



There is scarcely a county in Ohio where Pleistocene fossils may not be found. The old 

 beaches of Lake Erie in the northern part of the state have yielded some interesting fossil 

 plants, invertebrates, and vertebrates; extinct lakes, long since drained or choked up with 

 sediments, have formed marl and clay beds which contain abundant gastropods, pelecypods, 

 and ostracodes. One such deposit, in Madison County, has recently yielded the skeleton of 

 a mastodon associated with an abundant freshwater fauna. Abandoned river channels in sev- 

 eral places in the state have beds of gravel and dried mud which also contain fossils. 



The Commoner Fossils 



PLANTS. The plants of the Pleistocene, in most cases, are identical with living plants. 

 Fossil wood, leaves, and seeds from Pleistocene deposits are best identified from botany 

 manuals. Some of the lake beds contain great quantities of fossil pollen which, with the help 

 of a microscope, can be identified to genus, if not to species. It provides an indication of the 

 vegetation surrounding a particular lake or pond during Pleistocene time. 



The age of fossil wood from Pleistocene beds in Ohio has been determined by the carbon 

 14 method (see chapter 2). See Libby (1952) for carbon 14 determinations of Ohio fossil wood. 



INVERTEBRATES . The fossil invertebrates found in Ohio Pleistocene deposits nearly 

 all belong to species still living in the state. There is no better way to learn the genera and 

 species of these deposits than collecting the living invertebrates of the state and studying them. 

 This method has the advantage of applying to the fossil forms the rich store of information 

 derived from living animals studied in their natural environment. The Pleistocene fauna seems 

 less rich than the present one for only those animals with hard parts, for example a shell or 

 carapace, have been preserved. No record of freshwater sponges, jellyfish, bryozoans, or 

 soft -bodied arthropods exists for the Ohio Pleistocene. The record for the spiders and insects 

 is exceedingly scanty although these groups must have been as abundant then as they are now. 

 The most abundant record is that of clams, snails, and ostracodes. 



MOLLUSCA . The two classes represented in our Pleistocene deposits are the Pelecy- 

 poda (clams) and the Gastropoda (snails). The standard text for freshwater clams and snails 

 is Baker (1928); most of our freshwater genera and species are described in this text. A 

 more elementary guide is Goodrich (1932) which is as suitable for Ohio as for Michigan. The 

 best reference for land snails is Pilsbry's two-volume work (1939, 1940, 1946, and 1948) 

 which covers the subject thoroughly. One of us (La Rocque, 1953) has published a catalogue 

 which gives references for all species likely to occur in the Ohio Pleistocene. 



PELECYPODA . The Pleistocene freshwater pelecypods of Ohio belong to two families, 

 the Unionidae (freshwater mussels) and the Sphaeriidae (fingernail clams). They may be 

 distinguished by the following characters and the key to the commoner genera of Unionidae 

 which follows. 



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