Help Id a fossil in Iowa

[all_atv]

I have had this for about a year, not knowing what it was exactly. Found in a creek while arrowhead hunting. Then last weekend at a rock show I saw the same one there, but the guy or nobody else at the show knew what it was. Mine is kinda amber-transparent on some parts, the other guys was not. The squiggly lines go all the wat through and fit together like a puzzle. (but they wont actualy seperate) Kinda looks like the lines where skull plates fit together on skulls. And it looks like it would have been disc shaped if whole with lots of these segments. Mine is 3 segments and the other is the same I think. Thanks for the look mine was found in SE Iowa, and his in NE Missouri.

 

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[Harry Pristis]

This is a section of an ammonite. The exterior shell is gone, but the "squiggly" lines represent the interior cross-partitions (septa) of the shell. Your example appears to have been filled in with calcite, a fairly common thing. (In life, the chambers between the septa were gas-filled.)

 

[mikusek]

It's neat looking.