Plicatula mullicaensis Pelecypod from the Corsicana formation

Here is an interesting Pelecypod from the Cretaceous sediments of Texas. It's Plicatula mullicaensis and the small shell has remnants of spines that coat the shell surface.  It comes from the Corsicana Fm. in Bexar County, Texas and is around 68 million years old which places it in the Maastrichtian stage of the Late Cretaceous.

The shell is roughly oval in shape and relatively flat. Although the flatness could be due to the shell being compressed during/after fossilization. Plicatula mullicaensis is considered an oyster although it does not look like the ones we see on our plates today. The genus is extant in the warm waters of the Gulf of Mexico but they look different than this fossil does and they are call "Cat's Paws".

Right valve

Left valve

I took these pictures a few years ago and I can't really remember which angle of the shell they are showing. The first picture is of the anterior I believe but the other shots may just be profile views. The shell is so flat it's hard to tell!

I purchased this fossil from a collector in Texas.

Linoproductus sp. brachiopod from Texas

These next two, giant brachiopod shells are Linoproductus sp. from the early Permian aged (Asselian stage to Sakmarian stage of the ICS, Wolfcampian stage in US stratigraphy) sediments of Callahan County, Texas. This genus is known for having some of the largest shells for brachiopods from the period. The pedicle valve is very convex and the brachial valve startes our flat but becomes concave as the animal got older. The margins of the two valves are often turned 90 degrees from the hinge and (at least in the two specimens I am blogging about today) become very elongated. The surface of  both valves are marked with fine striations that are slightly wavy. Occasional spines are present but appear to not be in any planned arrangement.

Specimen #1 - Pedicle valve (note the grooves and marks in the shell which may be indicative of a boring sponge called Clionolithes sp.)

Anterior

Brachial valve and shell margins

Posterior

Profile

Another view of the brachial valve and the shell pattern

Specimen #2 - Pedicle valve

Anterior

Brachial valve

Posterior

Profile

These specimens come from rocks near Putnam, Texas in Callahan County.

Peilinia quadriplicata pelecypod from Texas

Another pretty cool looking oyster that I found in the Texas creek I was exploring is Peilinia quadriplicata (also called Ostrea quadriplicata). This species is very easy to ID based on the look of the shell. I only found a left valve but it has the typical splayed look to it, kind of like a duck foot. While the shell started out with a relatively smooth margin, as the animal grew older it started to have some distinct "points" with flat, straight areas of margin between them. Overall the shell is subpentagonal in shape with some obvious, widely spaced growth lines. There is also some gentle undulations on parts of the shell. The interior of the valve is smooth with a scallop shaped indentation where muscles once attached.

Left valve, top view

Ventral view

Interior view

Dorsal view

Right profile

Left profile

I found the above specimen in a creek that cuts through the Duck Creek formation but P. quadriplicata is not found in those rocks. Likely this washed downstream from a higher, younger formation such as the Denton Clay or Paw Paw formation which are Cretaceous (Albian and Cenomanian stages respectively) in age.

Texigryphaea corrugata pelecypod from the Duck Creek formation of Texas

Here is a fossil oyster shell from the Duck Creek formation that I found as float in the creek gravels. It belongs to the Genera Gryphaea Texigryphaea and is somewhat narrow with two undulations on the left valve (all Gryphaea Texigryphaea type oysters have a convex left valve and flat to concave right valve). As is often typical for oysters there are a number of seemingly overlapping growth lines that are hardly ever regular or flat. In profile the left valve is strongly recurved to nearly coiled over the right valve and angles off to one side a little. The interior of the valve is smooth and I don't see any obvious muscle attachment scars. The specimen I show below is missing it's right valve.

I am not familiar enough with the Gryphaea Texigryphea to ID this down to the species level. The excellent website North Texas Fossils lists two possible species for the Duck Creek formation: Gryphea corrugata (Say) and Gryphea washitaensis (Hill). I found another reference on Google Books in "The Lower Cretaceous Gryphaeas of the Texas Region" by Hill and Vaughan, USGS 1898. Even using the illustrations in that book I have a hard time deciding what I found as both species appear to be very similar looking to me. Indeed, the Authors have the same problem with specimens found in the Duck Creek formation (pg. 62) and postulate that the two species interbred with each other. So at this point I am going to call it Gryphaea Texigryphaea corrugata as that seems to be the most common species and also the "parent" species from which G. T. washitaensis developed.

Update 6/6/16: A vigilant reader pointed out that the genera Gryphaea is restricted to Europe and that the equivalent in the Cretaceous of Texas/Oklahoma is Texigryphea. He also recommended an old issue of "Oklahoma Geology Notes", Vol 35, No. 2 which has an paper by Robert Fay titled "The Type Species of Mortoniceras and the Holotype Specimens of the Lower Cretaceous Texigryphaea of the Southwestern United States". It has some helpful information and a key that may be used to ID specimens of Texigryphaea. The link above takes you directly to the paper but if you click here you can go to the Oklahoma Geological Survey site and look through all 74 volumes (up to winter of 2014). There are a lot of good publications and information on their website.

Left valve top

Left profile

Right profile

Interior of left valve

Ventral view

Dorsal view

The above specimen comes from the Duck Creek formation which is Cretaceous (Albian stage) in age.

Compare G. T. corrugata to a few other species from the lower Cretaceous of Texas: Texigryphaea navia, Texigryphaea marcoui and Ilymatogyra arietina

Macraster sp. echinoid from the Duck Creek formation of Texas

Not only does the Duck Creek formation have ammonites, it has some echinoids as well. I found a couple of nicely inflated specimens of the irregular echinoid Macraster. I sent pictures of my find to a friend in Texas, who is familiar with the Duck Creek formation, and he said they could be either M. elegans or M. washitae. Macraster has a suboval shaped test with a sub rectangular cross section. The adapical surface has the typical five arm imprint of the ambulacra which is where the feet of the animal would have extended from. There is a small oval shaped opening in the posterior of the test called the periproct which is where the anus of the animal would have been. On the underside, or adoral surface, is the opening for the animals mouth called the peristome.

When I was a kid I called echinoids with this shape "sea biscuits".

Specimen #1 is a little water worn.
Adapical surface

Posterior

Left profile

Anterior

Right profile

Adoral surface

Specimen #2 is missing some of the test on the adoral surface
Adapical surface

Posterior

Left profile

Anterior

Right profile

Adoral surface

The only other Echinoid evidence that I found was this isolated piece from a regular echinoid.

The above specimens come from the Duck Creek formation which is Cretaceous (Albian stage) in age.

Neithea texanus pelecypod from the Duck Creek formation of Texas

This is the pelecypod Neithea texanus from the Duck Creek formation of Texas. I found it in a creek in North Texas last fall. It looks very similar to a scallop but this particular specimen is missing the small "ears" that normally are present next to the beak and are part of the hinge line. Otherwise the shell has a triangular outline with a convex right valve and a slightly concave to flat left valve. There are strong, wide ribs on both valves and the rib pattern is reflected in the margin between the valves.

Right valve

Anterior

Left valve

Posterior

Profile

This specimen comes from the Duck Creek formation which is Cretaceous (Albian stage) in age.

Eopachydiscus sp. ammonite from the Duck Creek formation of Texas

I found another type of ammonite, in the north Texas creek bed I was exploring, called Eopachydiscus sp.   I found a large number of them, in fact, but as many were sizable and heavy I only packed out one. I saw some that were well over 18" in diameter, approaching 24"! The specimen I chose to keep is about 8-9" in diameter, 3" thick and had some of it's sutures showing as well as oyster spats glommed onto it. What I don't know is if the oysters colonized the actual shell surface or if the original shell had already fossilized, dissolved away and left a steinkern as a base for them.

This specimen comes from the Duck Creek formation which is Cretaceous (Albian stage) in age.