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Showing results for tags 'terebratulid'.
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From the album: Lower Carboniferous fossils of Ireland
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Terebratulid brachiopod & Productid brachiopod
Brian James Maguire posted a gallery image in Carboniferous
From the album: Lower Carboniferous fossils of Ireland
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I have a set of very small brachiopods from the Ozan Formation (Upper Cretaceous, Campanian) of north Texas (Fannin County, near the North Sulphur River). Some pictures have scale bars, others do not, but the largest of these shells is ~4mm (they are roughly equidimensional). They are not a rare shell in the matrix, but are small and are not abundant. I collected 57 pieces of them out of 3-4000 fossil items picked from the 12 mesh matrix fraction. I have not found a direct match in my literature and website searches so far, so I am looking for some help from our brachiopods gurus @Tidgy's Dad, @Misha, @Jeffrey P, @Thomas.Dodson @Fossildude19 and anyone else who might care to voice an opinion. Also our North (or even Central) Texas folks surely might have some valuable insight: @BobWill, @JamieLynn @ThePhysicist @JohnJ @erose, @grandpa, @Uncle Siphuncle just to call out a few. Maybe the Dallas Paleo Society has looked into these. I'll start with just a bit of background info first. These brachiopods are not new, but may be as yet officially unidentified, but that is what I hope to find out. Cretaceous brachiopods in Texas are not that common, other than Kingena (Waconella) wacoensis and these are clearly not that species. The 2019 version of the Fossils Collectors Guidebook to the North Sulphur River shows some similar looking specimens on Page 45 (Figure 8) but lists them as "small indeterminate rhynchonellid brachiopods". G.A. Cooper in a 1973 publication named a new terebratulid genus, Cricosia, which was found rarely in the Upper Cretaceous of Texas which bears some similarities and D.V. Ager, et al published a Journal of Paleontology paper in 1963 which discussed two genera (Cyclothyris and Lamellorhynchia) of rhynchonellid brachiopods which bear a passing resemblance (but have some major differences) and I have seen on other websites attributed to specimens from north Texas. As far as I know, that is about the extent of published brachiopods from the Cretaceous of Texas. If I have missed any others, perhaps that are too dissimilar from mine to have come across my radar, but if you are aware of others, please let me know. So my first question as I started looking for an ID, which Order of brachiopods do mine belong to? I thought this would be easy, I was wrong. While brachiopod diversity was very high in the Paleozoic, by the late Mesozoic (specifically Cretaceous) there were only two Orders of articulate brachiopods left, the Terebratulida and Rhynchonellida. That should be easy, only two to choose from. Unfortunately, the brachiopods in question don't fit nicely into the common forms of either one. I made a little table of the common features of the two orders based on information from the Treatise of Invertebrate Paleontology (Part H) and highlighted which features are present (check mark) or absent (no go sign) in the specimens in question. Probably the most important feature that distinguishes the two orders, is the support of the lophophore, (the internal feeding mechanism) and I don't have preserved features which make this obvious. On the outside, terebratulids are normally smooth with a curved hinge, mine are ribbed with a straight hinge. Rhynchonellids are normally very biconvex, have a strong fold and sulcus and the line where the two valves join is zig-zig due to very coarse ribbing, mine have none of these features. I can not see any punctae in the shells, but I always struggle with this and maybe the preservation in just not good enough to preserve this microscopic feature. One last thing I read is that rhynchonellids have strong hinge teeth and tend to be most commonly preserved as complete shells (both valves together). I have a couple of articulated specimens, but most of mine are isolated brachial or (less common) pedicle valves. So I am leaning to Terebratulid, but not positive. OK, enough yakking, lets look at them: The brachial valve interiors I think hold some of the most important features for determining an ID. In these you can see that the pedicle opening is not closed, but is an open triangular shape. On this one you can see that the ribbing is somewhat beaded and that the umbo area is somewhat smooth. You don't see that preserved on all of them. I know this is a lousy picture, but you can see the biconvex profile with the pedicle valve on the left and the pedicle opening at the top. In all cases the pedicle valve is quite inflated and the brachial valve is either flat or slightly convex. Here are two different shells in anterior view showing the straight line of junction between the two valves (sorry from the glob of sticky stuff on the top specimen). One is very biconvex, the other is planoconvex. Thee is no hint of a fold or sulcus. Here is a detailed view of the brachial valve interior with some lighting from the side to try and show the crura (right one is in red circle) which are paired processes that stick up and I believe were the base of the calcareous loop that supported the lophophore. So I am asking for any help in pinning a name to these. I'd be happy with a genus but will even settle for a family. Based on searching through the Treatise and reading several publications, I believe they are Terebratulids in the Family Cancellothyrididae. I believe the very distinct processes I see sticking up (red circles), the shape of the cardinal process and the lack of a median septum rule out any rhynchonellids, but I could be mistaken. The genus Cricosia is the closest I can find and it has been reported from Texas, but these are definitely different from Cricosia filosa (Conrad), which I believe is the only species described. Below are snippets from The 1973 Cooper paper of Cricosia and the one on the right is from the Treatise. You can see the shape is similar (straight hinge is very uncommon in terebratulids), the cardinal process is very similar, but the ornamentation is very different (the whole family is one of the few in terebratulida that has ribbing). Of course, my specimens are missing the whole loop feature that is so important, I only have the base of the feature (and is the Treatise diagram, those are reconstructed). Thanks for looking and I appreciate any insights. I can provide more info or other pictures if needed. Mike
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