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Cephalopods (Octopi and Squids)
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Cephalopods are molluscan animals that live in the sea. The group includes the modern octopi and squids as well as many fossil forms. The name cephalopod means "head foot" and it looks as though its feet (actually tentacles) are growing out of its head. The soft parts of the cephalopod animals are not fossilized, but the shell fossils are common in some strata. The inside of the fossil cephalopod shells are very similar to the internal parts of the modern Nautilus, a squid-like animal with a coiled shell. Because the shell structure is similar, we infer that the fossil cephalopods animals were similar to Nautilus when they were alive.
Cephalopod Shapes
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Cephalopods had a variety of shell shapes. Some were coiled and some were straight (orthocone).
This fossil straight-shelled cepahalopod above was found in the Pennsylvanian rocks of eastern Kentucky. The outer shell has been eroded away, showing the regularly-spaced internal walls (septa) of this cephalopod. The entire animal from tentacle tip to shell tip was probably only 10 inches long. Straight-shelled (orthocone) cephalopods are common in Ordovician limestones in the Bluegrass Region of Kentucky. Some incomplete orthocone fossils have been found along the Kentucky River Palisades that were four feet long; the living animal was probably eight feet long.
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Often the shell is not preserved, rather, a mold of the shell is preserved (see above).
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Some Typical Cephalopod Fossils From Kentucky
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typical fossil fragment of Ordovician orthocone cephalopod |
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broken Ordovician orthocone cephalopod |
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coiled and knobby Pennsylvanian Metacocera |
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fragment of Pennsylvanian cephalopod (a goniatite) |
