Oyster identification

[Cgs928]

Hello all, 

Could anyone identify these oysters by name?

 

 

 

 

 

[abyssunder]

Maybe Pseudoperna congesta for the first ones.

[DPS Ammonite]

Pseudoperna congesta is a possibility for the first photo. Clearer photos of the oysters and a end on photo of the substrate that they are growing on will help with ID. Pseudoperna congesta grow on large flat bivalves such as Inoceramus. 

 

Are the oysters in the first photo from the Glen Rose Formation that is about 110 million years old? According to Fossilworks.org Pseudoperna congesta are not found in rocks older than 90 million years old. I have not heard or seen of Pseudoperna congesta occuring in the Glen Rose Formation.

[erose]

Yes, we need location/formation info. Are you still working on Glen Rose stuff?  If so Pseudoperna is most definitely eliminated.  There are quite a few types of oysters in the GR. Some will always be individuals, some in clusters and sometimes both. But these type of oysters are always difficult because the shape can vary. You need to look for the muscle and hinge scars. And you need to make sure you have some of both of the valves.  From there you can start to sort out the possibilities. These photos will not suffice considering all of that.

 

 

[Cgs928]

Hey! Yes I am still working in the Glen Rose Limestone. The ages are around 110 Ma so I guess it shouldn't be the Pseudoperna. There are a lot of Orbitolina texana forams within my outcrop so this time constraint is certain. The oysters that I have found grow individually and some in aggregates. I will include some more pictures below. I think there are several species of oyster present...

[Cgs928]

This one appears to have come into contact with something... Can anyone confirm the grid-like pattern.

[Tidgy's Dad]

An encrusting bryozoan by the look of it. 

[abyssunder]

I also wonder what might be the name of the encrusting oysters of specimen 9 / Plate 30 from here .

 

 

 

[DPS Ammonite]

The small oysters on the adult oyster in figure 9 are likely baby oysters of known varieties from the Glen Rose Fm. if Pseudoperna are not there. Many Texas Cretaceous oysters including Exogyra ponderosa and Cameleolopha bellaplicata are attached as babies but break free later in life. Look for adult Glen Rose Fm. oysters with attachment scars; they may be your best candidates. The oysters in figures 5 and 8 look like they may have attachment scars on their cup-like left valves.

 

Ceratostreon texanum (AKA Exogyra texana ) has giant attachment scars. See this good paper that talks about Cretaceous Texas oyster evolution: http://homepage.physics.uiowa.edu/~cnewsom/fossils/Oysters/ilymatogyra/Exogyra-plexa.html

[erose]

Although it is listed as occurring in the Glen Rose, Ceratostreon texanum is rare. It's cousin C. weathorfordensis* is found in the upper units of the Upper Member of the Glen Rose. But if you are finding the orbitolina forams you are too low.  I have seen oysters just like yours at various levels of the Glen Rose. I have also tried to identify them and it wasn't easy. I had to look closely at the hinge and muscle scars as well as the shell margins for tell tale details. And even then at best I had them down to genera.  Unfortunately in all of your photos I don't see any of that detail.  Can you go back and find better specimens? Maybe not complete but at least some pieces of both valves that preserve muscle scars and hinge point detail.

 

* A correction on what DPS said above. C. weatherfordensis is the species with a large attachment scar, not C. texanum. C. weatherfordensis will often have the entire lower valve attached while C. texanum will only have a small scar near the hinge. 

 

You should be looking at the various "Ostreas" such as Flemingostrea or Liostrea. Maybe a few other sub-genera as well.  As mentioned above there are a handful of these known to occur in the GR.

 

PS the bryozoan is a cool fossil. There has been some recent work on those and you can possibly identify that as well. PM me and I will see if I can scrounge up the paper.