fossil sponge...coral...or what?

[colohank]

I found this little specimen in a box of treasures my maternal grandfather collected in his youth, most likely in the 1890s near his boyhood home in Huntington, WV. The collection consists of lithic tools, projectile points, potsherds, a few military buttons, some boars' tusks, mineral specimens, fossils, and other odds and ends. As oriented in the accompanying photo, the specimen is 15mm wide, 9mm high, and 5mm thick. It's bilaterally symmetrical, smooth and lustrous, and dotted with rather evenly spaced pores. The rear surface, however, is more planar and a bit rough, as if this tiny bit were broken off of something larger. If there are any paleontologists among us, I'd appreciate your help in identifying it. Image is about 2X, uncropped. Focus-stack captured with Nikon D810, reversed Nikkor 50mm f/1.8 lens, Nikon PB-6 bellows on StackShot. Illumination provided by two compact LEDs.

Hank

[BJ]

Hi,

my impression is that it might be part of a decapod carapace. The colour and preservation suggest to me that it is not that old - say Holocene (recent) or Pleistocene (ice age) . Mr G++gle suggests that there are freshwater Pleistocene deposits in the Huntington area.

BrianO

[MarkSturtevant]

You would have to consider the other fossils in the collection to maybe get some ideas about the range of ages here. There are tons of online groups in Facebook and elsewhere that would have people to ID fossils.
The dark color and luster could mean it was shellacked to help preserve it.

[Scarodactyl]

I'd ask on the fossil forum, they'll know: http://www.thefossilforum.com/
And while you're there, treat yourself to one of the greatest threads of all time on any forum (if you're a particular brand of nerd like me anyway) http://www.thefossilforum.com/index.php ... tructures/

[MarkSturtevant]

The thing is, the wavy form of the above fossil reminds me of a caste inside one of the chambers of a shelled cephalopod. There are ammonites, with coiled shells, and other kinds with straighter shells (can't think of the name).
Here is an example for context (from Wikipedia): https://en.wikipedia.org/wiki/Ammonoide ... ulated.jpg. The degree of wavey-ness will be different with different species.
What can happen with these is that since the shells can be quite thin, the shell can dissolve and leave a caste of the chambers. And the chambers can disarticulate. That is what this sort of looks like. But I don't know why it has the pores.

[rjlittlefield]

And while you're there, treat yourself to one of the greatest threads of all time on any forum (if you're a particular brand of nerd like me anyway) http://www.thefossilforum.com/index.php ... tructures/

Done, lovely! Following one of the links out to https://www.thisiscolossal.com/2018/06/ ... ink-fence/ was fun also.

Unfortunately I know nothing relevant to colohank's question. Interesting to read the comments, though!

--Rik

[colohank]

Per Scarodactyl's recommendation, I visited The Fossil Forum yesterday and posted the picture. By this morning, I'd received a number of replies, including one that I think nailed the ID. It's a tooth from a primitive shark of the genus Agassizodus, dating back to the Permian. The tooth is better suited to crushing than cutting. One of the respondents posted an almost identical picture.

Thanks, everyone, for your responses, comments, and suggestions.

Hank