It is difficult to find specimens of paleozoic cephalopod genus Domatoceras in local rocks. They can be found, but boththe genera Metacoceras and Pseudorthoceras dominate the cephalopod fauna. They are large cephalopods with a narrow venter. The younger whorls are only slightly or not impressed into the umbilical walls. Big shells are hard to find intact, and Domatoceras is no exception to that rule.

CG-0334 – Domatoceras sp.

Regardless, I have managed to find a few examples, with two nicer ones showing up recently from the Pine Creek limestone. The first specimen, CG-0334 is two-fifths of a whorl, with thick shell preservation on the umbilical shoulders. The ventrolateral shoulders feature a scalloped edge. The flanks are wide and show rapid growth in the oldest whorls. In what appears to be the aperture opening, there may be a preserved aperture edge viewable. I coated the entire specimen shell in paraloid to prevent breakage as I removed the attached matrix.

There are visible growth lines on the shell surface.

CG-0334 - Domatoceras
CG-0334 – Domatoceras sp., from the Pine Creek limestone in Kittanning, PA.
CG-0334 - Domatoceras
CG-0334 – Domatoceras sp., the underside of the shell. Specimen from the Pine Creek limestone in Kittanning, PA.
CG-0334 – Domatoceras sp., showing thin shell profile and scalloped ventrolateral shoulder.

CG-0362, a Specimen with a Unique View

This specimen provides a unique view into the shell architecture of Domatoceras. I found it face down in the talus, caked in mud and debris. The shell covering of the large body chamber eroded away, revealing a large flat portion of the inner shell wall. The juvenile whorls are deeply impressed into the umbilical wall, allowing you to see into the umbilical area.

Domatoceras sp., showing thin shell profile and scalloped ventrolateral shoulder.
CG-0362 – Domatoceras sp., showing thin shell profile and scalloped ventrolateral shoulder.

Last, I want to discuss a specimen, CG-0068, from the Brush Creek limestone. The venter is narrow and the flank is wide. At first, I thought this was another Metacoceras, but further study has this specimen properly under Domatoceras. Unfortunately, the thick Brush Creek limestone has prevented the further study of the details in the umbilical area.

Specimen CG-0068 from Brush Creek limestone.
CG-0068Domatoceras sp. from the Brush Creek limestone. Much of the shell was locked in a cement-like limestone.
Photo showing the ventrolateral shoulders on a cephalopod.
CG-0068Domatoceras sp. from the Brush Creek limestone. The arrows show the ventrolateral shoulders.

More Reading Online

References