A crescent shell indention showed up on the flat top of a piece of limestone. I thought maybe a large clam shell, but at this point I should know better. I hammered the rock for a while, thinking that maybe a piece would break off and reveal part of the shell. To my surprise, one final blow of the hammer had this pop out of the rock as a complete piece. Half of the fossilized shell material stayed behind.

This appears to be a large cephalopod of some sort. It’s much bigger than I anticipate Metacoceras can get, so this gets classified as one of the local giants. I have found about a half dozen of these so far, each one with some features and I’ve been able to identify only one. There is typically a raised line along the venter of the shell, however I’m not sure if this applies to all species. There is faint evidence of one on this specimen, but I’m skeptical.

I have identified this as a body chamber as there are missing septal lines.

Illustration on top of image showing possible venter line.
Showing a hint of a venter line along what would be the venter of the shell.

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Negative Rock

This specimen jumped out of the rock in one piece with a hammer blow. The rock it came from is shown below.