An agatized pelecypod from the Genus Astarte from Morocco

Among the many examples of agatized gastropods, from the Eocene layers of the Dakhla region of Morocco, that are appearing on the market, I found two pelecypod specimens. They are small, about an inch (2.54 cm) in diameter and appear to be the same species. I don't have any literature that can get me an ID down to even the species level but it appears that they belong to the Genus Astarte. The closest Subgenus I could possible winnow them down to could be Laevastarte but beyond that I would need to see the interior of the shells.

Specimen #1- Right valve

Ventral view of both valves

Left valve

Anterior view of both valves

Dorsal view of both valves

Posterior view of both valves

Specimen #2 - Left Valve

Right Valve

Ventral view of both valves

Anterior view of both valves

Dorsal view of both valves

Posterior view of both valves

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.

Gibbirhynchia amaltei brachiopod from France

This internal mold of a brachiopod is Gibbirhynchia amaltei from the Marginatus zone of the lower Jurassic (Pliensbachian). It comes from a site near Tournadous in the Aveyron region of southern France. The fossil looks like a Limonite replacement (or maybe lining) of the shell interior and retains just a small amount of the calcitic shell. The fossil is broadly ovate with valves that are mildly convex. When viewed from the front or back it looks somewhat flat or squat. Both valves have numerous and regular plications with a gentle fold and sulcus that is most evident along the anterior margins.

Brachial valve

Anterior

Pedicle valve (note the cast of the channel where the pedicle muscle would have been)

Anterior

Profile

Placenticeras pseudoplacenta from the Mancos Shale of New Mexico

One last Ammonite from the Mancos Shale (Turonian stage of the Cretaceous) of Sandoval County, New Mexico: Placenticeras pseudoplacenta. This specimen is a little rough as it has fragments from several whorls attached. the left side is the most intact visibly and I may eventually try to remove the rest of the whorl pieces to make it look cleaner. By my estimations the full sized, intact specimen would have been 6-8" in diameter but only 3" of the current specimen is whole. P. pseudoplacenta is a narrow, flat, disc like shell with little ornamentation on the exterior of the shell. The suture pattern is very complex with a large number of nodes and lobes each with many smaller knobs.

Right side

Left side

Keel and cross section of a chamber

A closer view of the sutures

Thanks to Mike (PFooley on the Fossil Forum) for this fossil that he offered up as part of an auction to help defray some of the operating costs of the Fossil Forum website.

Prionocyclus hyatti (robust form) from the Mancos Shale of New Mexico

These large, bumpy ammonites are the robust form of Prionocyclus hyatti from the Mancos Shale (Turonian stage of the Cretaceous) of Sandoval County, New Mexico. None of the sutures are visible but the form of the shell is what helps to ID it. The robust form of the shell is wider than the normal form and has distinct, knobby ribs. There is also a noticeable raised keel. The cross section of the chambers is roughly square.

Specimen #1 still has part of the nodule, that once surrounded it, still attached. Ammonites in the Mancos shale are often found in nodules. Sometimes they are septarianized as well.

Right side

Left side

Keel

Closer view of the right side

Specimen #2 is larger than the previous specimen and does show some septarian features.
Right side

Left side

View of the cross section of the last chamber

Keel

Part of the fossil shows septarian features like the "seam" seen below.

The fossil had broken while in transit which allows a view of the calcite filling the interior.

Thanks to Mike (PFooley on the Fossil Forum) for this fossil that he offered up as part of an auction to help defray some of the operating costs of the Fossil Forum website.