Cephalopod, Turtle Or What?

[Okie]

Keeping in mind that I'm a complete fossil novice, I was very excited to see this piece my brother found. Not a trilobite, right? Cephalopoda were invertebrates, right? This piece looks as though it has a spine or is that deceptive? Could it be a turtle?

Found in Murray Co., OK near Arbuckle Mountains. For decades my brother has picked up interesting 'rocks' laying on the ground and this is one so I can't tell you the geologic formation. Fossils from many ages have come from this area.

[John K]

unless I'm completely mistaken, you've indeed got part of a cephalopod. The "spine" that you see is actualy the animals siphon tube, or "siphuncle":

the siphuncle comnnected each of the chambers of the animals shell; it used these to maintain buoyancy while it swam through the ocean.

It looks like most of the fossil is a replacement mold of the original shell

that's a pretty cool find - cephalopod's are some of my favorites!

Edited August 9, 2013 by John K

[Okie]

John K., thank you! I can now see it in the light you've described and looking at the other fossil I posted in July, imagining it cut/broken differently. I couldn't get past thinking it was a 'spine'. Do you think it is a straight shelled Endoceras as was my July fossil? And, I really appreciate the drawing you included. Can you point out where on the drawing, my piece would be? Can the approximate size of the animal be determined from my specimen? So full of questions....sorry.

[FossilDAWG]

Your fossil is certainly a straight shelled nautiloid, but not Endoceras. The siphuncle in your specimen is distictly bead-like, expanding outward in each segment (camerae) of the shell, and has extensive internal deposits. Endoceras had a tubular siphuncle that does not bulge outward within the camerae. Your specimen is suggestive of a genus such as Armenoceras, but it is impossible to say for sure what it is without a close examination of the specimen to determine fine details of the structure such as the nature of the juncture between the septa (the part of the shell that separates camerae) and the siphuncle. It does not help that the age and source geological formation are unknown. You have to bear in mind that many hundreds of genera and thousands of species of straight-shelled Paleozoic nautiloids have been described, so accurate identification requires well-preserved specimens from known geological horizons, and usually involves the preparation of polished sections to establish details of the internal anatomy.

If your "July" specimen was the "plant or animal?" specimen, that was not an Endoceras either.

Don

Edited August 9, 2013 by FossilDAWG

[Okie]

FossilDAWG, please look at my July post of "Ok Arbuckle Mtn Area" and not the "plant or animal" post. Could "Ok Arbuckle Mtn Area" have been an Endoceras??? ......I understand your comment about not being able to specifically pin it down. Can't thank you enough for your looking at this and commenting.

[Okie]

Question...Is it possible to guesstimate the length and width of the living creature from this piece? The piece is 3-1/2" L x 4-1/2" W x 2-1/4" Thick. The one I posted in July titled "OK Arbuckle Mtn Area" was somewhat larger.