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.

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