Saturday, November 1, 2014

Amphistrophia funculata brachiopod from the Wenlock Fm.

Amphistrophia funculata is a strophomenid type brachiopod from the Silurian aged (Wenlock epoch, Sheinwoodian to Homerian stage), Wenlock formation, near Dudley, England. It has the typical arrangement of valves with the pedicle valve being convex and the brachial valve concave. To me this looks very similar to a Strophomena sp. brachiopods from the Ordovician. Fine radial ribs decorate the surface and the shell makes a sharp turn along the margin to grow perpendicular to the previous direction. The hinge line is straight with a very long and narrow interarea between the valves.

Pedicle valve
Anterior
Brachial valve
Posterior

Thursday, October 30, 2014

Leptaena depressa brachiopod from Wenlock Fm

An ubiquitous member of many faunal assemblages of the early Paleozoic is Leptaena. It must have been quite the generalist because I've found it in rocks from the Ordovician through the Devonian. The specimen below is Leptaena depressa from the Silurian aged (Wenlock epoch, Sheinwoodian to Homerian stage), Wenlock formation near Dudley, England. The shell is rectangular in shape with wavy growth lines and very fine radial ribs. Most specimens also have a feature where the pedicle and brachial valves are equal until the edge where they meet. At this point the valves make a sharp turn downwards all along the margin except at the hinge line. In some specimens this can be quite developed and the shell will have a triangular shape in profile.

My theory is that these brachs were attached to a hard substrate for most of their lives until they got too big and the pedicle muscle couldn't hold them upright. The shell them fell over onto the pedicle valve but the animal was still alive. Thus the shell kept growing "upwards" towards the current.

Pedicle valve
Anterior
Brachial valve
Posterior
Profile

I've found other examples of the genus in the Irondequoit limestone & Haragan Formation.

Tuesday, October 28, 2014

Dalejina hybrida brachiopod from the Wenlock Fm.

Dalejina is a Silurian aged brachiopod that, to me, resembles the genus Rhipidomella that is more commonly found in the Devonian. The specimen below is Dalejina hybrida from the Wenlock formation (Wenlock epoch, Sheinwoodian to Homerian), near Dudley, England. The shell is rounded but slightly oblong with fine raidial ribs on the surface and occasional growth lines. There is a small triangle shaped interarea at the posterior of the pedicle valve as well.

Brachial valve
Anterior
Pedicle valve
Anterior
Profile

I've found a small shell in the Waldron shale of Indiana that I think is Dalejina and you can see that blog post here.

Sunday, October 26, 2014

Anastrophia deflexa brachiopod from the Wenlock Formation

This is Anastrophia deflexa from the Silurian aged Wenlock formation, near Dudley, England. The shell looks very similar to Plecatrypa in size and shape but does not have the prominent growth lines. It has strong, coarse ribs, a shallow sulcus and lacks a visible interarea. I have posted before about a similar species from the Waldron shale: Anastrophia internascens.

Brachial valve
Anterior
Pedicle valve
Posterior
Profile

Friday, October 24, 2014

Plecatrypa imbricata brachiopod from the Wenlock fm.

Plecatrypa imbricata from the Silurian aged Wenlock formation (Wenlock epoch, Sheinwoodian to Homerian stage), near Dudley, England. The shell has a spirifer type shape with a wide hinge line and deep sulcus. It differs in that the pedicle valve does not have a triangular shaped opening for the pedicle muscle but rather a circular opening more typical of Rynchonellids. The shell also features strong, coarse ribbing and prominent growth lines. I have found this same genera in the Irondequoit Limestone of New York here.

Brachial valve
Anterior
Pedicle valve
Posterior
Profile