Selmasaurus is a genus of medium-sized plioplatecarpine mosasaur

Mosasaur

Mosasaurs are large extinct marine lizards. The first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764...

 from the Upper Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 Mooreville Chalk Formation

Mooreville Chalk Formation

The Mooreville Chalk Formation is a geological formation in North America, within the U.S. states of Alabama and Mississippi. The strata date back to the early Santonian to the early Campanian stage of the Late Cretaceous. The chalk was formed by pelagic sediments deposited along the eastern edge...

 (Campanian

Campanian

The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...

) of western Alabama

Alabama

Alabama is a state located in the southeastern region of the United States. It is bordered by Tennessee to the north, Georgia to the east, Florida and the Gulf of Mexico to the south, and Mississippi to the west. Alabama ranks 30th in total land area and ranks second in the size of its inland...

 (United States). First recognized by geologist

Geologist

A geologist is a scientist who studies the solid and liquid matter that constitutes the Earth as well as the processes and history that has shaped it. Geologists usually engage in studying geology. Geologists, studying more of an applied science than a theoretical one, must approach Geology using...

 Samuel Wayne Shannon in his 1975 Master's thesis, "Selected Alabama Mosasaurs," the taxon remained a nomen nudum

Nomen nudum

The phrase nomen nudum is a Latin term, meaning "naked name", used in taxonomy...

until it was officially described in 1988 ("A new plioplatecarpine mosasaur (Squamata

Squamata

Squamata, or the scaled reptiles, is the largest recent order of reptiles, including lizards and snakes. Members of the order are distinguished by their skins, which bear horny scales or shields. They also possess movable quadrate bones, making it possible to move the upper jaw relative to the...

, Mosasauridae) from Alabama", Journal of Vertebrate Paleontology, Vol. 8, No. 1, 31 March 1988) in an article coauthored by Shannon and paleontologist Caitlin R. Kiernan

Caitlin R. Kiernan

Caitlín Rebekah Kiernan is the author of many science fiction and dark fantasy works, including seven novels, many comic books, more than one hundred published short stories, novellas, and vignettes, and numerous scientific papers.- Overview :Born in Dublin, Ireland, she moved to the United States...

. The type specimen, formerly reposited at the Geological Survey of Alabama and cataloged as GSATC 221, was transferred in 2005 to the Alabama Museum of Natural History (Tuscaloosa). The holotype consists of a very well preserved but incomplete and disarticulated skull, the left atlantal neural arch, atlas centrum, and a single neural arch from a cervical vertebra. Preserved skull elements include the frontal, parietal, left ectopterygoid, left jugal, supratemporals, basioccipital and basisphenoid, and quadrates. This species S. russelli, was named in honor of paleontologist Dale A. Russell, for his extensive work on mosasaurs.

A remarkably well preserved and nearly complete Selmasaurus skull and partial postcranial skeleton was discovered by Steve Johnson and family in 1996. Recovered in 1997 and donated to the Sternberg Museum of Natural History in Hays, KS in 2001, the remains were determined to be a new species of Selmasaurus in 2008 after over a decade of study by Polcyn, Everhart, Kiernan and others. Named S. johnsoni after its discoverer, the skull is one of the most complete mosasaur skulls recovered and thus provides new anatomical information for Selmasaurus, a better understanding of plioplatecarpine ingroup relationships, extends the geographic and temporal range of the genus, and documents further diversity within Plioplatecarpine. The specimen is housed at the Sternberg Museum of Natural History under catalog number FHSM VP-13910.

Relationship to other mosasauroids

Shannon and Kiernan classified Selmasaurus as a member of the mosasaur family Plioplatecarpinae, which also includes the genera Platecarpus, Plioplatecarpus, and Ectenosaurus, largely on the "basis of the mode of circulation through the basicarnium." The genus may be most closely related to Ectenosaurus, though it possesses a much shorter, stouter skull. Additional specimens would greatly expand our understanding of Selmasaurus russelli.

Cranial kinesis

The mosasaur Selmasaurus is notable in that its skull is unusually akinetic. Most mosasurus have skulls which possess "coupled kinesis" (mesokinesis and streptostyly), that is, parts of the jaw can open widely to accommodate large prey.