Edgarosaurus was a 12 foot long short-necked plesiosaur which lived within the Mowry Sea during the middle Cretaceous Period 105-100 million years ago.

In 1993, a well-preserved fossil specimen consisting of the skull, neck, and one front flipper (collection ID code: MOR 751) was discovered near the village of Edgar, Carbon County, Montana within the Thermopolis Shale. The specific rock layer where the fossils were found dated to the middle of the Albian Stage of the middle Cretaceous Period about 105-100 MYA. Examination of the fossils showed that this animal belonged to a group of plesiosaurs called the “polycotylids” which included animals such as Polycotylus itself, Dolichorhynchops and Trinacromerum. Polycotylid plesiosaurs typically measured 8-12 feet long. In 2002, the partial skeleton was judged to be a new species and was named Edgarosaurus muddi, named after Edgar, Montana where it was found and the late Kevin Mudd of Bridger, Montana. Click here for Pat S. Druckenmiller’s 2002 article which named it.

In 1995, a partial skeleton belonging to an indeterminate species of polycotylid plesiosaur was found within the Wabiskaw Member of the Clearwater Formation of Alberta, Canada (click here to read article). These rocks are slightly younger than the rocks of the Thermopolis Shale, being dated to the early Albian Stage approximately 110 MYA. It’s possible that this polycotylid is another specimen of Edgarosaurus, but at the moment, this cannot be confirmed.

The teeth of Edgarosaurus are much larger than those seen in other polycotylid genera, and the points are rounded rather than being sharp. It’s possible that these teeth were better suited for punching through tough ammonite shells instead of grabbing slippery fish.

Edgarosaurus muddi. © Jason R. Abdale (May 25, 2024).

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Categories: Paleontology, Uncategorized

Tags: art, Cretaceous Period, Edgarosaurus, Mesozoic, Middle Cretaceous, Mowry Sea, North America, paleo-art, paleontology, plesiosaur, polycotylid, Polycotylidae, Prehistoric, reptile