Saturday, August 27, 2016

Lichenalia (Pinacotrypa?) stella bryozoan from the Hungry Hollow member at Arkona

The specimen today comes from the Hungry Hollow member of the Widder formation near Arkona, Canada (Devonian, Givetian stage). It's a bryozoan but I am not terribly sure of the name. It is a very detailed specimen with large mound like monticules and some star like features on the surface. Overall the individual zooids are small pin pricks but as a colony they look impressive.

Here is the specimen itself, Dorsal surface...
...Ventral surface. You can see that it covers both sides of the piece and in life may have been a vertical wall like feature.

Now some closer views of the surface...



As I am not an expert on Bryozoans I posted these photos to a group on Facebook that specializes in fossils from the Arkona region.  One of the members of the group is Michael Topor, who is very familar with fossils from the Widder and Arkona formations (since he spent much of his collecting career excavating and studying specimens from those rocks) said:
"Could be Lichenalia stellata. Not sure if that genus is still used."
Another local expert, Darrell Ellis, remarked:
"I believe Bassler placed Lichenalia stellata in the genus Pinacotrypa... though I'm not certain he had the final word on the matter. I've collected Pinacotrypa/Lichenalia from the top of the Encrinal Limestone. By appearance I believe your specimen is from there as well."
So I'm going with the experts and will label this as Lichenalia (Pinacotrypa?) stella.

As much as I dislike Facebook in general, it does allow a place for amateurs and experts alike to exchange and share information. Much like the Fossil Forum website!

Thursday, August 25, 2016

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

Monday, August 22, 2016

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.

Friday, August 19, 2016

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

Tuesday, August 16, 2016

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.