Not A Leaf, Not A Trilobite, Possibly An Insect?

[Mohawke]

My son found this tonight in a fairly large rock in our front yard. They are about two inches long. I searched everywhere with no results. I'm very new to this so my knowledge is rather limited. i thought at first that they might be leaves, then a trilobite of some sort, but they look more like the tail end of a water bug. I don't see evidence of eyes, antenna, or legs and I'm assuming it's a water creature as opposed to land.

The rock was found in the ravine behind our home by a stream in Columbus, Ohio. It's about a twenty pound or more rock. If anyone can give me an idea of what it might be that would be great! Thank you!

[rejd]

Not an insect. It is a cross section of a shell that has been worn down. Welcome to the forum.

[Fossildude19]

Hello, and welcome to the forum.

Looks to me like orthocone cephalopods in cross section.

Regards,

[Diceros]

I guess Columbus, Ohio should be m. Devonian (about 350my) Columbus Limestone, and there are some fairly rounded nautiloids (most are fairly cylindrical) in the m. Devonian, so I'll bet that's what they are. A Paleozoic nautiloid specialist should be able to ID them exactly. They aren't that common by the Devonian (the straight nautiloids were big in the Ordovician).

Mohawke - I think what what was confusing you about the fossil was in thinking the fossils is just on the surface (as it'd be in a leaf or trilobite). As both rejd and Fossildude19 point out, these three fossils are all sections cut through three fairly thick fossils. The calcite fossils are of just about the same hardness as the limestone rock, so they wear at the same rate. As in their modern cousin, the chambered nautilus, what you're seeing is a shell divided by a series of parallel chambers separated by septa. The white parts are chambers filled with the mineral calcite. The two at rt. and at bottom have been worn at such an angle that you can't see the front chamber where the animal lived, the phragmocone. You can see it at left in the top left specimen. Another interesting feature can just barely be seen. Do you see the two small dark spots in the center-right of the lower specimen? I believe that's a bit of the siphuncle - a tube which runs through the middle of the shell, going right through each septum. There's also one in the chambered nautilus. It's used to regulate how much air is in the back chambers, allowing it to rise or fall in the water column (they lived in fairly deep marine waters). Another interesting bit in the upper right is a section through a fragment of a stalked crinoid (sea lily) stem.

It's a nice specimen. I'd call it beginner's luck.

[Mohawke]

Thanks so much everyone! I learned a lot, especially about understanding what I'm looking at. It certainly is logical that they'd be any direction and worn over the years. Great info.

[Mohawke]

I found an image that matched almost perfect; although, not as worn so I could see the full tapered shell. It was found in Ohio and he mentioned Treptoceras nautiloid cephalopod. It looked to be really close. I read up on all the information you guys gave me and I have a lot to learn! Thanks for the welcomes also.

[Auspex]

Acquiring 'mental CAT scan' vision is a big step in interpreting life in the rocks

[Gen. et sp. indet.]

Three cephalopods, all right. Above the right one there's a nice, small fossil - a tentaculitid, I presume.