LK Ammonite Schloenbachia IF-A-16-013

Schloenbachia trinodosa
Duck Creek Fm. (Lower Cretaceous - Albian)
Pecos County, Texas

This specimen is very good quality for the locality and is prepared on matrix.  It has a good suture pattern and excellent definition.  This is a very complete ammonite with the entire living chamber preserved.  It shows a perfectly preserved rostrum which is rarely seen in these specimens.  The shell is 10.5 inches across in its largest dimension. The inner-most whorl is restored.  
The genus is small to large-sized with evolute coiling and deep, narrow umbilicus. The inner-most whorls are restored.  The whorl section is taller than wide and is subrectangular or squarish.  The venter has a low keel and appears squarish rather than rounded. Ribs are straighter and more widely spaced just before the body chamber.  Three rows of course, equidistantly situated tubercles (nodes) occur:  Umbilical, lateral, and ventrolateral.  Nodate to clavate ventrolateral tubercles are particularly prominent.
In Pecos County the Duck Creek is about 20 feet thick and contains a prominent ammonite fauna dominated by Schloenbachia and Eopachydiscus.  The Duck Creek appears to be conformable to the underlying Kiamichi Formation.  The formation is a soft chalky, nodular, whitish, argillaceous limestone rich in fossils.  The basal ledge that caps the Kiamichi contains a prominent layer of fossil oysters and the echinoid Macraster.