Mystery shell in need of ID

[AsystolicRythym]

Hello, all! As my first submission for identification, let me present to you the first fossil(?) I collected from the field.

I feel I should apologize for several things right now: I have very little functional knowledge of local geography, especially as it relates to this specimen. In truth, I wasn't hunting for fossils when I found it; I was fishing for catfish.

Since childhood, my favorite fishing spot has been at the junction of a local creek (Indian Creek, if anyone happens to know the geography of South-West Iowa) and the Missouri River. Good spot for big catfish, and plenty of limestone boulders to brace against while fighting them. It's easily accessible via bicycle trails.

In July of 2018, I had hooked a sizeable fish when he snapped my line around a snag. Enraged (that was my dinner swimming away, after all), I hurled an apple-sized rock at one of the limestone boulders, hard enough to split it along a fracture line. Intending to release more frustration by reducing it to gravel, I yanked the crack open. Inside the fault, I saw this perfect-looking shell. I hadn't really thought it was possible to collect fossils locally, let alone find one with color. So, I gently pried it off the limestone matrix with the blade of my Leatherman, tucked it in my tackle box, and peddled home. 

When I got home, a cursory Google search of local fossil assemblages led me to believe I may have found either a brachiopod or some kind of oyster-like bivalve. Recognizing that the thin shell was brittle, I immediately applied a coat of 50/50 cyanoacrylate glue and clear nail polish (a mixture I now favor for finishing).

In summary:

The specimen itself measures roughly 36 mm wide by 24 mm deep. It is concave, with a deep fold to the midline. Slightly pinkish-brown with white speckles, which may be early (and incomplete) calcification. It was found at GPS coordinates 41.1890, -95.8741, encased in a limestone boulder. The boulder itself may have been deposited by the action of the nearby Missouri River, or washed out of the surrounding geography.

Any conjectural identification is welcome and appreciated.

 

Edited May 25, 2021 by AsystolicRythym

[Lone Hunter]

Brachiopod?

[Caaaleb]

The brachiopod looks like it could be from the order Spiriferida. Or maybe it's a pelecypod?

[Thomas.Dodson]

Spiriferid brachiopod, something along the lines of Neospirifer I'd think.

 

The outcrops in the area are mainly of the Dakota Sandstone (Cretaceous so can be ruled out) and the Lansing Group and the Kansas City Group, both dating to the Carboniferous. It may be possible to narrow it to the formation with more specific geologic maps and by evaluating outcrop characteristics. The following reference discusses the bedrock of the general area you mentioned. https://pubs.usgs.gov/pp/0472/report.pdf

[Fossildude19]

I would agree with Spiriferid brachiopod. 

 

   

[Mahnmut]

Hello Asystolic rythm  8(I hope you are well) and welcome to the forum.

Did I see that right, its a preserved shell without much matrix adhering? Cool.

Best Regards,

J

[Tetradium]

On 5/24/2021 at 9:12 PM, Thomas.Dodson said:

Spiriferid brachiopod, something along the lines of Neospirifer I'd think.

 

The outcrops in the area are mainly of the Dakota Sandstone (Cretaceous so can be ruled out) and the Lansing Group and the Kansas City Group, both dating to the Carboniferous. It may be possible to narrow it to the formation with more specific geologic maps and by evaluating outcrop characteristics. The following reference discusses the bedrock of the general area you mentioned. https://pubs.usgs.gov/pp/0472/report.pdf

Most likely river carried it from upstream. 

[Tetradium]

On 5/24/2021 at 10:14 PM, Fossildude19 said:

I would agree with Spiriferid brachiopod. 

 

   

Probably similar to Cyrtospirifer whitneyi. Extremely variable in shapes.