Metacoceras clinocostatum, a cephalopod - Fossils of Parks Township

The extinct cephalopod Metacoceras clinocostatum is a species commonly found in Brush Creek limestone. Compared to other examples of the genus Metacoceras, it is very small in size. I was apprehensive about identifying these. In the past, I believed they were the inner whorls of larger specimens. But, these are small cephalopods.

Metacoceras clinocostatum

Scientific Classification

Kingdom:

Animalia

Phylum:

Mollusca

Class:

Cephalopoda

Order:

Nautilida

Family:

Tainoceratidae

Genus:

Metacoceras

Species:

clinocostatum

1982 Sturgeon et al.

The common local cephalopod genus, Metacoceras, lists twenty-seven species on Fossilworks, inside of the Paleobiology Database (as of 2021). But for whatever reason, M. clinocostatum is not listed as one of the species in the database. It was clearly defined as a new species by Sturgeon et al. in a research article published in November of 1982, ahead of the publication of Pennsylvanian Cephalopods of Ohio. Many of its specimens had earlier been identified as Metacoceras perelegans Girty (Miller and Unklesbay, 1942; Murphy, 1970). The authors separated them as a new species because of the oblique ribs on their flanks. The type locality is the Brush Creek Member at locality Aa-41, a cliff on the east side of Ohio Route 56, 0.4 miles south of its junction with Route 682, in Athens Township, Athens County, Ohio. Its name comes from two Latin words, clino, which means inclined, and costatus, which means ribbed.

The holotype is specimen OSU 28971-A. The specimen is 17 mm in diameter and has an 8 mm shoulder-to-shoulder umbilical diameter.

Dernov in 2021, citing the photos on this page, suggested that these specimens may belong to Gzheloceras and/or Pseudogzheloceras. He states that massive transverse ribs on the flanks are not typical for Metacoceras, and that ribbed species like this might instead belong to Foordiceras. I believe that Metacoceras in its current form is rather crowded and could use a review.

Photos of Metacoceras clinocostatum, CG-0169

I recovered this specimen from naturally chemical-altered limestone. This type of matrix is soft and readily preserves intricate details. After needing identification for quite some time, it is the first declared specimen in the catalog of M. clinocostatum. I based my identification on reported populations of specimens in the publication “Pennsylvanian Cephalopods of Ohio”, where the authors reported 114 specimens from the Brush Creek limestone. In reading the description, I found that the largest diameter paratype specimen was only 25 mm in diameter. Scale marks in the photo are 0.5 mm each. The specimen consists of 2/5 of a whorl. The umbilical depression is also sharply visible.

CG-0169, Metacoceras clinocostatum. 2/5 of a whorl with flank ribs easily seen. — CG-0169, *M. clinocostatum*. Flank view. 2/5 of a whorl with flank ribs easily seen.

Metacoceras clinocostatum dorsal view. Umbilical depression can be seen. — CG-0169, *M. clinocostatum*. Dorsal view. Umbilical depression can be seen, which is much smaller than the whorl.

Photos of Metacoceras clinocostatum, CG-0170

This is a specimen recovered from the Pine creek limestone. The specimen has 3-6 visible ribs on the flank. It consists of 1/2 of a whorl. There appears to be some shell material left. There is a well-defined umbilical shoulder. The specimen feels heavy and is likely embedded in an ironstone concretion.