A New Plioplatecarpus from North Dakota

One of our current projects in the Paleo lab is the preparation, study and mounting of a large Plioplatecarpus mosasaur from the Cretaceous Pierre Shale, Griggs County, North Dakota.

The specimen was found in 1995 by two local fossil collectors, Mike Hanson and Dennis Halvorson. Mike and Dennis had been collecting fossils for a few years and had developed a keen interest in paleontology. This prompted them to contact John Hoganson, the paleontologist for the North Dakota Geological Survey. Because of earlier dealings with Dr. Hoganson, they knew that they had an important find, when they saw the lower jaws of a mosasaur eroding out of small knoll near the Sheyenne River.

A few days after Mike and Dennis talked with John, we headed out to check out the mosasaur find. Neither John, nor I were expecting anything more than a partial jaw, but to our surprise a little digging had exposed a lot more bones, and a lot more work than we were ready for at the time. It took about 4 weeks, spread over two years to collect the skeleton, but it was worth the effort!

The specimen is around 70% complete, missing only the flippers, pelvis, a few ribs and parts of the tail. It is the largest Plioplatecarpus ever found, 25% bigger, than the next biggest, (based on the quadrate) and a new
species.

The skeleton is 23 feet long, the near complete skull alone is 3 feet long. The specimen will be on display early 2000 at the North Dakota Heritage Center in Bismarck, North Dakota. Thanks to its donation to the state from Orville and Bev Tranby, the owners of the land it was found on.

Mosasaurs were large marine going lizards related to the modern monitor lizards. Mosasaurs ranged from about 3 meters long, to upwards of 12 meters. An average Plioplatecarpus would have been about 5 meters long. If you would like to read more about mosasaurs a good place to go is the Oceans of Kansas Web Page.

	Field sketch of mosasaur remains (ND97-115.1) Abbreviations: f = frontal; p = parietal; L.q. = Left quadrate; R.q. = Right quadrate; pm = Premaxilla; L.de. = left dentary; R.de. = Right dentary; L.m. = Left maxilla; R.m. = Right maxilla; L. j. = Left jugal; R.j. = Right jugal; L.s. = Left squamosal; R.s. = Right squamosasl; L.c. = Left coracoid; R.c. = Right coracoid; L.sc. = Left scapula; R.sc = Right scapula.
	*A dorsal view of the frontal and parietal of the Plioplatecarpus. Scale is in cm. (ND97-115.1). This and the following photos by Johnathan Campbell, NDGS.*
	A dorsal view of the premaxilla. (ND97-115.1)
	The left side of the premaxilla. (ND97-115.1)
	Lateral and medial views of the left quadrate. (ND97-115.1)
	The occipital condyle and part of the basioccipital (ND97-115.1)
	A medial view of the left maxilla (upper jaw) (ND97-115.1)
	The left jugal (supports a portion of the orbit of the eye) (ND97-115.1)
	Part of the right jugal showing evidence of scavenging by sharks (ND97-115.1)
	The scapula (ND97-115.1)
	The finished exhibit........ Background painting is by D. W. Miller
	..... with a detail from the above picture.
	Another view.

Copyright © 2000-2009 by Mike Everhart