Help! My Brachiopod Has An Identity Crisis!

[ClearLake]

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

 

 

 

 

[Fossildude19]

Sorry - Cretaceous is way out of my wheelhouse. 

[Thomas.Dodson]

Sorry, don't have much experience with Cretaceous brachiopods. I'd lean Terebratulid as well but that answer has little confidence.

[DPS Ammonite]

The only brachiopod that I have seen from the Austin Group (Plano, Texas) is probably a Terebratulina. A search of the literature for a clearer photo/drawing maybe helpful.

 

https://www.cretaceousatlas.org/species/terebratulina-guadalupe/

[ClearLake]

1 hour ago, DPS Ammonite said:

The only brachiopod that I have seen from the Austin Group (Plano, Texas) is probably a Terebratulina

Thank you for that info. I remember seeing that genus but missed the Texas connection. That is in the same family as the other genus I thought was most similar so I will take another look at that tomorrow and see how the detailed description compares. Thanks again. 

[Al Dente]

Gemmarcula?

 

 

 

 

[ClearLake]

6 hours ago, Al Dente said:

Gemmarcula?

Hmmm, interesting option.  The Treatise description says this has a strong median ridge in the pedicle valve which I don't think I see, but I'm going to look more closely as well as for the presence of a pedicle collar.  The general shape is close and I like the ornamentation match.  I'll go find that publication and read through it. Thanks for the suggestion.

 

14 hours ago, DPS Ammonite said:

The only brachiopod that I have seen from the Austin Group (Plano, Texas) is probably a Terebratulina

I took a closer look at the description for Terebratulina and pictures in the Treatise and the shape (more tear drop) and hinge line (not very straight) do not seem to match very well.  It also said the socket ridges are fused with the crural bases which is not the case with mine if I am interpreting this correctly.  I'm going to look for some other pictures as you suggested just to confirm.  Thanks for the suggestion!!

[erose]

At first glance this appears to be a Terebratulid. I don't think it is a Rhynchonellid.  I have no specimens from the Ozan.  I do have specimens from the Austin Chalk. The ribs of yours appear to be thicker and more ornamented(like a Plicatula).  I would start by trying to come up with a list of what brachs are known from the Ozan.

 

I have found references for Texas Cretaceous brachs limited. Good luck. And if you get this to genus I think you will doing well. 

[ClearLake]

1 hour ago, erose said:

I would start by trying to come up with a list of what brachs are known from the Ozan

Thanks for the comments.  Yes, perhaps I was not clear, but the list of established brachiopods from the Ozan as far as I have found in going through the literature is........zip, other than some unidentified (apparently at one time they were labelled Choristothyris plicata) forms.  I don't doubt that the common Kingena (Waconella) wacoensis can be found, but I have not even seen that reported.  I of course welcome any citations that others may have for Ozan brachiopods.

[erose]

16 hours ago, ClearLake said:

Thanks for the comments.  Yes, perhaps I was not clear, but the list of established brachiopods from the Ozan as far as I have found in going through the literature is........zip, other than some unidentified (apparently at one time they were labelled Choristothyris plicata) forms.  I don't doubt that the common Kingena (Waconella) wacoensis can be found, but I have not even seen that reported.  I of course welcome any citations that others may have for Ozan brachiopods.

Oops. missed that.  You'll have ton find lists for formations of equal age.  Maybe a bit of a challenge.

[Tidgy's Dad]

There were three orders of articulate rhynchonellate brachiopods in the Cretaceous. The one you missed out is the Thecideida which arose from a spire bearing ancestor in the Triassic and is still very much with us today. But your specimen isn't a thecideide nor a rhynchonellid, but is almost certainly a terebratulid.

Many Cretaceous terebratulids have ribs and quite a few have straight hinge lines. yuurs appears to be slightly curved, not all the posterior of these specimens is the hinge line, just where the shell fits together when closed. 

Your pink arrows just seem to point to the posterior margin rather than a cardinal process. 

But the red circles do show crural processes, I think, which might help with an id. 

 

I'm afraid I don't know what your specimens are. Very interesting and, as you say, could be undescribed as yet. I can't quite make out all the internal detail either, unfortunately. 

In some regards they resemble Choristothyris, which can be found in rocks of the same age in New Jersey, but not in Texas, as far as I know. 

In other ways they seem a bit like Argyrotheca, but this genus doesn't make an appearance til the Maastrichtian. 

But it doesn't quite match either of those. 

[ClearLake]

13 hours ago, Tidgy's Dad said:

Your pink arrows just seem to point to the posterior margin rather than a cardinal process. 

Yes, I was trying to point the the prominent (at least in person, maybe not so much in the picture) rectangular projection that extends from just inside the posterior margin and projects a bit beyond the margin.  Maybe I'll try to get a better picture, but I see it as a feature in numerous of the terebratulid groups.  My arrows were probably not well placed.

 

13 hours ago, Tidgy's Dad said:

In some regards they resemble Choristothyris, which can be found in rocks of the same age in New Jersey, but not in Texas, as far as I know. 

In other ways they seem a bit like Argyrotheca, but this genus doesn't make an appearance til the Maastrichtian. 

But it doesn't quite match either of those. 

Yes, I would agree, they do have similarities to both of those, but also some important distinctions.  Both of those genera have a median septum which mine do not appear to have.

 

Thanks for your observations, Adam, and my apologies to the Order Thecideida for omitting them.    For now, I will tag them as an unknown terebratulid and keep looking at the options and suggestions to see if I can even get close to a family.