Post Oak Creek micros for ID

[old bones]

 

Exploring a nice sample of Post Oak Creek micro matrix was a new fossil adventure for me.

Each new matrix comes with an additional learning curve, and I have managed to identify most of the finds in this one with the help of the excellent collections of fellow TFF members: @ThePhysicist, @JamieLynn, @EPIKLULSXDDDDD, @Jared C, and the informed opinions of @Al Dente and @MarcoSr to name a few.

I am also an avid collector of PDFs regarding each new matrix that I explore.  I could use some help with these 4 finds. The scale is 1mm in every image.

I am having trouble deciding if they are Onchopristis dunklei or Ischyrhiza mira, or something else altogether…

 

 

 

 

 

Thanks for looking

[Tidgy's Dad]

Can't help, but those are super photos. 

Very interesting. 

[Jared C]

@EPIKLULSXDDDDD has a great guide for fauna of that age. From it, A seems to be Onchopristis denklei indeed. 

 

 

For B, compare here:

 

Not positive on C, but for D I perceive a possible dermal denticle. I'm not a shark specialist though, so take it with a grain of salt. 

[Mikrogeophagus]

The Sclerorhynchiformes of POC have always been a challenge for me, but maybe I can help with eliminating/narrowing down some names. The teeth from POC are mostly of the basal Atco which is early Coniacian to my knowledge. There's a useful paper on the Atco you should check out by Shawn Hamm that is publicly accessible.

 

Let's talk about Onchopristis dunklei first. Admittedly, tooth A does look pretty similar to some of the oral teeth from O. dunklei including the ones I had in my guide. Keep in mind though, O. dunklei is primarily known from Cenomanian and Albian deposits (the ones from my guide are Lower Bouldin Flags which is Cen). POC is significantly younger and I am not aware of any O. dunklei from the Coniacian. The iconic barbed rostral teeth of O. dunklei are never found in POC either. Instead, that oral tooth morphology is historically placed within the genus Ischyrhiza as a variety of species, usually either I. schneideri or I. mira. For a time, I. schneideri was considered a subspecies of I. mira, but it seems nowadays it's its own thing. I. mira oral teeth from younger sediments look pretty different, so I would comfortably consider your tooth A as I. schneideri. Here's some photos of I. schneideri from Cappetta & Case 1999:

 

 

Kiestus texanus is a Sclerorhynchiformes found in POC and only known from TX. It looks very similar to I. schneideri, but has some key distinctions. K. texanus has a shorter and wider lingual protuberance. Your tooth A has a long nose (long + skinny lingual protuberance) which I'd say is closer to I. schneideri. K. texanus, are also predisposed towards having lateral shoulder that develop into short cusplets which I do not see in tooth A. 

 

None of your teeth look like Ptychotrygon triangularis at all so I will toss that out. They are usually the most common tooth. None look like Cantioscyllium decipiens. The crown and root shapes are very different. None look like Sclerorhynchus priscus.

 

Texatrygon hooveri is what I'd go with for B and C. It's harder to tell because they were likely tumbling around in the creek for awhile and lost their ornamentation, but they fit the overall shape and have more robust shoulders. Tooth D is harder to tell because it's more damaged, but if I had to guess, I'd choose T. hooveri as well.

 

TLDR: A = I. schneideri (kinda rare); B, C = T. hooveri; D = T. hooveri?

 

 

 

 

[old bones]

@EPIKLULSXDDDDD Thank you so much for the thorough explanation. I have your guide bookmarked, and also have that paper. The reason that I was reluctant to label A is what you have said about the age difference. (It just looked so much like that! lol) So thanks for clearing that up. 

 

 I have all of my Ptychotrygon sp. labeled and will post them soon in the micro topic section. However, I did wimp out on trying to differentiate between Ptychotrygon and Texatrygon sp..

 I realize that the condition of these 4 made IDs difficult as does the fact that I did not obtain sufficient views of them. I am happy to be able to label A, and will settle for 'possible T. hooveri' for the other 3.

[old bones]

3 hours ago, Tidgy's Dad said:

Can't help, but those are super photos. 

Very interesting. 

Thank you, Adam!

2 hours ago, Jared C said:

@EPIKLULSXDDDDD has a great guide for fauna of that age. From it, A seems to be Onchopristis denklei indeed. 

 

 

For B, compare here

 

Not positive on C, but for D I perceive a possible dermal denticle. I'm not a shark specialist though, so take it with a grain of salt. 

Thank you for looking at these Jared! You can see why I was thinking Onchopristis denklei!   I hope that you will check out my post in the micros section which I will submit in a day or so.

[digit]

@EPIKLULSXDDDDD Wonderful explanation with detailed reasoning. This is the type of information that gets archived here on TFF which is helpful not only today but hopefully in years to come when others run into similar ID questions. Bare identifications with none of the reasoning behind eliminating or including taxa are not nearly as informative as understanding the thought process. This is a classic example of teaching a person how to fish.

 

 

Cheers.

 

-Ken

[Thomas.Dodson]

I would also be inclined to call B, C, and D Texatrygon hooveri.

 

I have found samples of species A before in POC and noted the similarity to Onchopristis dunklei but was always questionable for the reasons @EPIKLULSXDDDDD mentioned and assumed some Ischyrhiza. Didn't know about I. schneideri, very informative. The Kiestus texanus I've seen from POC (albeit just 2) both have the short lateral cusplets he mentioned.

[old bones]

15 minutes ago, Thomas.Dodson said:

I would also be inclined to call B, C, and D Texatrygon hooveri.

 

I have found samples of species A before in POC and noted the similarity to Onchopristis dunklei but was always questionable for the reasons @EPIKLULSXDDDDD mentioned and assumed some Ischyrhiza. Didn't know about I. schneideri, very informative. The Kiestus texanus I've seen from POC (albeit just 2) both have the short lateral cusplets he mentioned.

Thank you for looking and for the confirmation,Thomas. I sure do appreciate all the input I've received on this matter. 

[ThePhysicist]

6 hours ago, EPIKLULSXDDDDD said:

The teeth from POC are mostly of the basal Atco which is early Coniacian to my knowledge.

Don't mean to divert the topic at hand, but where did you come by this knowledge? 

[Mikrogeophagus]

@ThePhysicist I know there has been argument in the past concerning this with some people saying it may be Turonian. I got that the basal Atco was early Coniacian from Shawn Hamm's Atco article in which he cites the presence of fragments of indicative early Coniacian ammonite species. In the basal Atco there are also Ptychodus species that indicate Coniacian age including P. mortoni and the Coniacian-morphotype of P. whipplei. Though, this information is also based off of a Shawn Hamm publication so my logic might be a little circular here.

 

I surmised that POC is mostly basal Atco because of my previous experience working with micros from there and other sites in TX. POC is rich with Ptychotrygon triangularis, Texatrygon hooveri, Kiestus texanus, Ischyrhiza schneideri, Coniacian-morphotype Ptychodus whipplei (larger than Turonian), etc. All or most of these species I have only come into contact with in a couple basal Atco sites, one from Austin and the other in DFW. None of these species I have seen in the Turonian of Austin or DFW. I know there are older fossils mixed with the Atco stuff at POC, but I would assume it's a much smaller fraction.

[DPS Ammonite]

11 hours ago, EPIKLULSXDDDDD said:

The teeth from POC are mostly of the basal Atco which is early Coniacian to my knowledge.

Upstream from the Travis St. Bridge in Sherman, the creek cuts through fish tooth and clam rich yellowish sandstone  layers. I always thought that is where most of the teeth in POC came from. I also thought that the sandstone was part of the Eagle Ford. Does anyone have an opinion as to what formation these sandstones are in? I wish that I had found a single outcrop at POC that had the Eagle Ford, Atco and Austin all stacked in order so I could clearly see where the fossils were coming from. In other areas of north Texas (including Plano), I noticed that there are several teeth rich sandstone layers with typical Eagle Ford dark shale on top and bottom. 

[LSCHNELLE]

On 9/18/2023 at 1:29 AM, DPS Ammonite said:

Upstream from the Travis St. Bridge in Sherman, the creek cuts through fish tooth and clam rich yellowish sandstone  layers. I always thought that is where most of the teeth in POC came from. I also thought that the sandstone was part of the Eagle Ford. Does anyone have an opinion as to what formation these sandstones are in? I wish that I had found a single outcrop at POC that had the Eagle Ford, Atco and Austin all stacked in order so I could clearly see where the fossils were coming from. In other areas of north Texas (including Plano), I noticed that there are several teeth rich sandstone layers with typical Eagle Ford dark shale on top and bottom. 

@DPS Ammonite-do you have a picture of the sandstone layer or the area interspersed with dark shale?

[DPS Ammonite]

I may have a fossil somewhere. I won’t be able to get at it for a week.

[LSCHNELLE]

On 9/23/2023 at 12:27 PM, DPS Ammonite said:

I may have a fossil somewhere. I won’t be able to get at it for a week.

Correction - do you have a picture of the yellow sandstone that you're speaking of from the Sherman area? I reread your text and I'm not interested in the one that's interspersed with dark shale from the Eagle Ford.

 

People may not be aware that in certain locations there are two different condensed zones (shelly "sandstones" or "conglomerates") near the top of the Eagle Ford. One is associated with the Eagle Ford and has fossils that coincide with that formation. The other is associated with the Austin Atco member and has fossils associated primarily with the Coniacian. It is possible that there may be some of Turonian fossils mixed in with the upper condensed layer. But, that situation is probably much less likely.

 

My experience is that the Eagle Ford upper condensed zone has much better preserved fossils. This is in comparison with the Atco condensed zone, which can have very high energy depositional processes. The high energy forces frequently separate the roots of regular shark's teeth from their crowns. Ptychodus often survive the process with the root intact - but not always.

[Mikrogeophagus]

@LSCHNELLE Earlier this year I hunted a creek site that included a little basal Atco conglomerate and exposed a decent amount of upper Kef phosphatic sandstones. These sandstones were very different in color/composition to the basal Atco. They had some teeth, but not the richest and in very hard matrix so I didn't bother to take any home. The sandstones preserved ripple beds and intermittently had massive nodules. Didn't keep too many pics from the site, but here are a couple from that sandstone:

 

 

Not much to take home from the place, but I was happy as the discovery confirmed that the site I eventually took you to was in fact basal Atco.

[LSCHNELLE]

Thanks for the pics EPIK. I've seen these type of strata in both the Upper Cenomanian and Upper Turonian of the Eagle Ford. Usually, a limey sandstone or sandy limestone material due to the marine influence. The strata can be very dense and hard to break. But, I have also seen basal Atco strata that can be split with a chisel down along a two to three foot length.