CMNH 13573, Rusophycus
Age: Late Devonian (Famennian) Rock unit: Chagrin member, Ohio Shale formation
Locality: along the Ashtabula River in Plymouth Twp., OH
This is a trace or ichnofossil. Unlike body fossils, ichnofossils are not casts of the original organism but preserved evidence of the organism’s activity: in this case, a burrow. The ridge protruding from the top of this slab may look like the fossilized remains of an organism but it is actually sediment which filled in the semi-circular burrow. Invert the slab to see the proper perspective. Paleontologists aren’t sure what organism left this trace fossil, but they can infer it had a semi-circular shape similar to a horseshoe crab based on the burrow.
The darkened semi-circle on the cross-cut of the slab is evidence of another of these fossils, deposited in the opposite orientation above the specimen shown here.
Image by Jacob Kordeleski, CMNH Dept of Archaeology // Hawken School
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