Central Texas Walnut Formation ID Help please! Crab, Bivalves

[JamieLynn]

Hello all! I recently found a new spot that turns out is Walnut Formation. Finding lots of nice stuff there...big Echinoids - Phymosomas, a Tetragrmma and some little Leptosalenia mexicanas. 

But I've found a few things that I can't ID.  @erose  - I relooked at the presentation on Albian crabs you did for the PSoA last month and thought this one was in there, but now I don't see it? I thought you had collected one like this..        Thanks for any help, y'all! 

 

This little Bivalve looks like a Plicatula but those are not found in the Walnut? (According to the Houston Gem and Mineral Society Bivalve Book)

 

And this other bivalve -  closest I can come up with is Lopha, but again, not listed in the Walnut

[erose]

Those are Plicatula IMHO. The species ranges in the HGMS books are incomplete. I have the same fossils from the Walnut. 

 

I also think they are both Plicatula and not a Lopha. Lots of variation in those little oysters.
 

I also have similar claws from the Walnut. Again we need to see these with a described carapace to nail ‘em down.

 

 

[JohnJ]

I agree with @erose.  

[JamieLynn]

okay, cool. I am getting more comfortable with labeling at least Genus even if it is not listing as being in that formation (a la HGMS book).  This confirms my thoughts. Thanks y'all! 

[JohnJ]

Although you probably have, check out Finsley's book too. 

[grandpa]

 

33 minutes ago, erose said:

I also think they are both Plicatula and not a Lopha. Lots of variation in those little oysters

 

Agree.  See http://www.idscaro.net/sci/01_coll/plates/bival/pl_plicatulidae_1.htm

c.f. P. gibbosa

 

Nice finds btw!

[JamieLynn]

thanks @grandpa !

@JohnJ - egad...i always forget to check the Finsley book!!!  Always cross reference....hahahah! Thanks for the reminder! 

[erose]

1 hour ago, JamieLynn said:

thanks @grandpa !

@JohnJ - egad...i always forget to check the Finsley book!!!  Always cross reference....hahahah! Thanks for the reminder! 

So when I start in on identifications I usually start with a more general source like Finsley's book and then from there hone in with more detailed publications.  So it might go from Finsley's Fossils of Texas to Index Fossils of North America to the HGMS books on bivalves and then from there to a scientific publication or paper if needed.  I usually sort out new finds and tackle all the bivalves, gastropods or echinoids in groups so I don't have to have my entire library on my desk at once.  On occasion I dig into my more obscure literature like the Treatise on Invertebrate Paleontology or old monographs with lithographic plates. 

 

By the way was this that Walnut site up north?  I have a few rare Plicatula specimens like these from the Bee Cave Member down here in Austin but many more from the younger Keys Valley and Upper Marl members that crop out in Bell, Coryell and points further north.  I have my specimens labeled as Plicatula sp. cf. subgurgitis.  But they could be a different species yet to be described or one not known from Texas.  

 

 

[JamieLynn]

Yes, this was from the north site.  I am just barely getting a hang of the formations, I am certainly not at "member of formations" level! So i have no idea what member I was in.  Lampasas County is the best I can do! 

[erose]

23 minutes ago, JamieLynn said:

Yes, this was from the north site.  I am just barely getting a hang of the formations, I am certainly not at "member of formations" level! So i have no idea what member I was in.  Lampasas County is the best I can do! 

In some areas the members within formations lose their definition and it is hard to say that you are in a distinct member.  I have a paper by Moore (1964) that includes Lampasas County. The top two members are Keys Valley and the Upper Marl in ascending order. That is capped by a thick section of Comanche Peak. 

 

All of this suggests why good location notes are so important.  If you can take take the time to write down what you see, take good pics, mark with GPS or Theodolite, etc. If a road cut appears to have different layers make note of where you found the specimen. Look for distinctive "marker beds" of fossils, changes in rock color or texture, flat vs rubbly bedding, etc. With that data you can go back later and evaluate the site when you get better maps or reports with stratigraphic descriptions. And as long as that locality info stays associated with the specimen it doesn't matter what formation you wrote down. Plus things change.

 

And to top that off I am going to email you that paper by Moore....

[JamieLynn]

@erose - thank you so much!!!