Sunday, May 10, 2020

Dipleura dekayi trilobite from the Moscow formation

Dipleura dekayi is the largest trilobite that I have found in middle Devonian aged rocks. At Deep Springs Road, in the Windom shale member of the Moscow formation, it is not uncommon to find dis-articulated pieces of this species.  Based on the characteristics of Dipleura I suspect it was a burrowing species more so than free swimming or walking on the surface of the sea bottom.  The exoskeleton is typically smooth and streamlined with no obvious spines. The only noticeable feature are small bumps or pits that cover the surface. These could have been sensory points with tiny hairs or other organic extension that allowed the animal to sense movement, electrical impulses, or perhaps smell it's prey.

Specimen #1 - An isolated cephalon which is mostly intact except for some distortion (likely incurred during burial and compression of the sediments) and one of the eyes missing.
You can see some of the small pinpoints that are present on the surface

Specimen #2 - An isolated pygidium that really shows off the pinpoint pits.

Specimen #3 - A dis-articulated, but complete exoskeleton. This is clearly a molt that was buried quickly as only the Cephalon has moved from it's original position.

Check out this specimen from the Mahantango formation (scroll to the bottom of the post) that shows only the cast of the exoskeleton. You can see the pits that are preserved on the above specimens are merely small columns or bumps. This is what leads me to believe there was some sort of organic connection from the soft body of the trilobite.

Another nice pygidium from the Windom shale that I found at Penn Dixie can be seen here.

And here is a post of some specimens of Dipleura dekayi from the slightly older Panther Mountain formation of New York.

These specimens were found at a borrow pit on Deep Springs Road in Madison County, NY which exposes the Windom shale member of the Moscow formation (middle Devonian in age, Givetian stage.) 

No comments:

Post a Comment