THE FIRST MARINE REPTILE FROM THE AMERICAN WEST, A MOSASAUR: MOSASAURUS MISSOURIENSIS (HARLAN) 1834; ITS HISTORY, SOURCE AND OSTEOLOGY

Although the first marine reptile from the American West may have been the “45-foot long fish” that Lewis and Clark noted, the first described and surviving marine reptile is that of a mosasaur taken by Prince Alexander Philipp Maximilian of Wied-Neuwied from what is now South Dakota to Germany in the early 1830’s. The specimen was later named as Mosasaurus maximiliani in 1845. In the meantime, the snout of a marine reptile was named as Ichthyosaurus missouriensis in 1834. Evidently, the snout of the specimen taken by Maximilian had been sent earlier to the East Coast where it was thought to be an ichthyosaur. However, the snout matches perfectly with that of the skull in Germany and are therefore the same individual. Consequently, priority dictates that the specimen be considered as Mosasaurus missouriensis. The geographic source of the specimen was documented as the Big Bend of the Missouri River. However, the stratigraphic source of the specimen has long been in doubt and was considered to have come from a concretionary level within the Verendrye Member of the Pierre Shale. Invertebrate fossils associated with the skeleton commonly occur in the DeGrey Member, and geochemical analyses of concretionary fragments in which the original skull is encased indicate a DeGrey Member source. Moreover, extensive investigation of the Big Bend area has resulted in many additional specimens of the species, and most have been found in the DeGrey Member. Some specimens are exquisitely preserved and reveal additional characteristics of the osteology of the species. Overall, the first mosasaur from the American West came from the Big Bend of the Missouri River and was derived from the upper DeGrey Member of the Late Cretaceous Pierre Shale.