husband found this fossil in a load of gravel

jwhittecar

My husband found this fossil in a load of gravel that was delivered to our home here in northwest Nebraska. Can't say for sure, but gravel is probably from this area or maybe southwest South Dakota.

The fossil is 5 1/2" along outside curve and 1 3/8" in diameter. You can see in the photos light spots and those are very shiny, almost look like glass. The color in photos isn't accurate, the color is tan.

Sitting on the knobs it looks like a giant caterpillar to me.

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Ophiolite

It appears to be a fragment of an ammonite. The ammonites were chambered creatures which added new chambers in a spiral pattern as they grew. The abandoned chambers were used to control floatation by varying gas pressure within them. In most ammonites the later chambers overlay the earlier ones. Some forms did not overlap - evolute rather than involute - and this appears to be such an example.

I'm going to take a wild guess - based on dimly remembered data from five decades ago - that this is Triassic in age. Unfortunately the real diagnostic feature is the suture line between chambers and this is not visible in your specimen.