Florida Beach Fossil Shell of Some Sort

[IndianRiverSonrise]

When I first picked this up I thought it was probably a mammal joint. That is the type of thing I mostly see at the location (same color etc.), but when I took it home and looked more closely it appears to me to be a shell.

I wonder if anyone would offer an opinion on the type and age. Thanks in advance.

[Harry Pristis]

This thing reminds me of a coprolite. Sharks have a spiral valve in their cloaca, but shark coprolites are not compacted longitudinally.

It could be that this is a land mammal coprolite and that the spiral is merely an accident of gravity.

Or, this may be a steinkern or internal cast of a gastropod.