CARDIOCERID AMMONITE JAWS FOUND IN GASTRIC CONTENTS OF A PLESIOSAUR FROM THE UPPER REDWATER SHALE (LOWER OXFORDIAN)

Remains of an ammonite were found in the gastric contents of a plesiosaur from the Upper Redwater Shale of the Late Jurassic Sundance Formation, of Hot Springs Co. Wyoming. Collection of vertebrate remains is always beneficial but identification of intact gastric material is a unique bonus. Gastric material in the form of coleiod tentacle hooklets, shark teeth, dorsal spine denticles, and a large portion of possible dermal denticles have been noted before but this is the first report of prey-predator relationships between Jurassic plesiosaurs and cardiocerid ammonites.

The plesiosaur skeleton consists of a partial limb, disarticulated ribs, several gastralia, and fragments of the pectoral or pelvic girdle and is housed at the Wyoming Dinosaur Center accessioned as WDC-SS-001. Two sections of disarticulated cephalopod jaw apparati indicate the cardiocerid ammonites of the Sundance seaway were a part of the diet of marine reptiles that lived in a nekto-benthic lifestyle.

Fragile parts of cephalopods such as hooklets and jaws are rarely preserved.Exceptional conditions are needed for the preservation of stomach contents, the hooklets and jaws could not have survived intact in the rough environment of the Jurassic Sundance seaway. No gastroliths were present. The matrix surrounding the bones does not contain larger than normal amounts of shell debris and belemnite guards of less than 3mm and it is doubtful that the material washed into the carcass by wave action or movement in the sediment.