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No idea what this fossil is. Found in Northwest Arkansas, where, I believe, it is part of the Boone Formation, Mississippian Period. I’ve checked my fossil ID book, and every scallop-shaped fossil I see has vertical ridges, rather than horizontal. The fossil is just under 2 inches wide (5.08 cm) and one inch tall (2.54 cm). At its deepest point, it has a depth of 1/2 an inch (1.27 cm). It has a deep ridge in the center and a circular spot at its deepest point (seen most clearly in the second to last photo). Thanks for your help! Addendum: Just discovered that the circular spot was some kind of sediment that washed away when I was trying to clean that area of the fossil. Under the sediment was a slightly deeper cavity, making the depth of that spot closer to 3/4 of an inch. Added two new pictures with the sediment washed away.

I have been revisiting some of my fossils from my collection I gathered during a two year period where I had the privilege of exclusively exploring hundreds of acres of land in NW Arkansas in and around the town of Eureka Springs. During that time, I was able to collect on friends private land that had never before been surveyed by the outside world. 99.99% of what I came across was of oceanic and inland sea origin when it came to fossils but a couple of fossils perplexed me and this is one of them. I came across this fossil, or pseudo fossil, or weird anomalous permineralized erosion, or “I have no idea,” in a Mississippian Deposit known as the St. Joe and Boone Formations. I found this early in my collecting and had little background or research study under my belt at the time of discovery. I thought it was interesting and set it aside and moved on. I know that the area it comes from isn't known for bone, but it really does appear to be permineralized shoulder bone and upon magnification it has the hallmark of having been biological in origin, but I AM NO EXPERT, and I don't like to give into to fantastical thinking especially when there isn't other supportive evidence to suggest that Arkansas has fossil bones of any kind. What else could it be? Under magnification the flip side of the fossilized bone shape has detailed scale or skin pores and textures that have been preserved through the amazing process of permineralization…but again, there could always be a more plausible explanation that is outside my own understanding, simply because Arkansas doesn’t have bone fossils, historically speaking, aside from the Arkansaurus toe bone that was found some 160 miles south of where this fossil was found. I bring this to the forum because I would love to be able to get feedback and answers. And for future notation, I have many more fossils to present to the group and am looking forward to all of your thoughts, suggestions, expertise, and recommendations! Sincerely, PESEBECHE

I did a long weekend of fossil hunting in Oklahoma and NW Arkansas. All of the formations, fossils and areas were completely new to me. I will have to post a trip report in the next few days. I found this specimen yesterday in a creek in NW Arkansas in the St. Joe Limestone Member of the Boone Formation, which is Carboniferous, Mississippian. I am totally new to the Mississippian. It was all marine stuff. I’d like to ID it before I start removing more matrix so I know what it looks like and don’t accidentally take off something I shouldn’t. I saw lots of brachiopods, but none came even close to the size of this one or was of this species. Most were under 1 inch. This is what it looked like when it was found. I think it is a steinkern. I just thought it was a maybe an inch wide or so from what I could see. It was in a fairly large rock conglomerate. So I attempted to split the rock so the thing could be popped out. Turns out it is 10 x 5 cm or 4 x 2 inches. It is still in the matrix after the first split. This is the negative (cavity) of where it split out of. As you can see part of it remained on the other half. It looks like there may be a little crinoid pice on it too. These are other shots of it. You can see the end where it broke off. I’m curious about the hinge part and what it is supposed to look like. Close up of the hinge parts. The one end appears to be fused with the matrix. The other end looks like it is basically free. Any help on the ID would be greatly appreciated. I wonder if @Ludwigia, @Herb or @fifbrindacier or anyone else might be able to help with the ID.

This is my first post in Fossil Forum...names PD, in the next couple of days I will do an introductory post in the "Introduction" section but I wanted to get started with one of my specimens that has brought me to a wall. Late Devonian - Early Carboniferous, loose find in a fossil contaminated area so identifying the exact formation it came from has been a bit difficult. Possibilities within a stones throw of find are Boone Formation, Penters Chert, Clifty Limestone, Chattanooga Shale and Pitkin Limestone. I have been calling this little guy Tholuslensia collisspongia ONLY until I can identify the actual genus and species. From my current research, I have an initial taxonomy as follows: Porifera | Demospongiae | Chaetetid | Poecilosclerida | AND THAT IS WHERE MY GIANT WALL BEGINS... As you might already be aware, Arkansas does not have a good public fossil record database (something that I am currently working on changing) and trying to identify this sponge down through family, genus and species has been like trying to find the pin cushion that the needle in the haystack came out of. The University of Arkansas focuses more on fossil fuels than actual fossils, they were quite friendly but unable to provide me with any assistance. Their Museum Collection is off limits to me because I am not a paleontologist, accredited institution or research facility. Even though I am not a paleontologist, I do believe myself capable of figuring this puzzle out. It is just one of many paleontology puzzles I am currently working on. I am not afraid of rabbit holes, big words or old paleontology text books so if you have any information or leads that can help me get past this "wall" then by all means, SHARE ;-). There is a possibility that it could have come out of the Ordovician period. The majority of exposure, sediment and specimens from this location are Devonian/Mississippian. There is one new exposure of Ordovician that has surfaced due to creek erosion. It rests below all other primary material and my collisspongia could have eroded out of that exposure based on sheer proximity to the specimens resting location. I have my doubts though because of the iron staining that has permeated the calcified sandstone.Based on the amount of orange tinting the outer surface displays, I would think that the specimen had to have eroded out and been sitting for some time now. New fractures from the Ordovician peek-a-boo seem to be lighter in color ranging from white to camel tan. This orange tint makes me believe that the Ordovician formation is not the host rock that produced my fossil. That being said, I am perfectly comfortable with the idea and most likely, the actuality of being completely and totally WRONG about everything. So long as I can get close to the truth, I am good with as many missteps as it will take. Thanks again for anything you have to offer and thank you for helping create this great resource and forum. Specifications: Length (Middle Lens Curve): 110 mm Width (Across Lens Curve): 100 mm Height (Stem to Top of Dome): 70mm Circumference (Lens Perimeter): 340 mm Substance: White chert, calcified sandstone, limestone present within folds and around bottom stem/base