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Selmasaurus
''Selmasaurus'' is an extinct genus of medium-sized plioplatecarpine mosasaur from the Late Cretaceous of the United States.
==Discovery==
First recognized by geologist Samuel Wayne Shannon in his 1975 Master's thesis, "Selected Alabama Mosasaurs", the taxon remained a ''nomen nudum'' until it was officially described in 1988 in an article coauthored by Wright. 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 of this genus 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. The species was named in honor of paleontologist Dale A. Russell, for his extensive work on mosasaurs. The holotype and only known specimen of ''S. russelli'' was collected from an unknown location in western Alabama, and for decades, uncertainty surrounded the precise stratigraphic horizon from which the specimen had been recovered. Then in 1998, Caitlín R. Kiernan extracted chalky matrix from the basilar canal of the basiocciptal and identified calcareous nanoplankton that indicated GSATC 221 had originated from basal Campanian beds within the lower unnamed member of the Mooreville Chalk Formation (Selma Group). In her study of Alabama mosasaur biostratigraphy, Kiernan placed ''S. russelli'' within the ''Clidastes'' Acme Zone, though it was the rarest element in the fauna, accounting for only 0.3% of the biozone's assemblage (one specimen).〔Kiernan, Caitlin R. 2002. Stratigraphic distribution and habitat segregation of mosasaurs in the Upper Cretaceous of western and central Alabama, with an historical review of Alabama mosasaur discoveries. ''Journal of Vertebrate Paleontology'' 22 (1): 91–103.〕
A remarkably well preserved and nearly complete ''Selmasaurus'' skull and partial postcranial skeleton was discovered by Steve Johnson and family in 1996, from the Santonian or Campanian marine horizon in the Niobrara Formation of Niobrara Chalk, western Kansas. Recovered in 1997 and donated to the Sternberg Museum of Natural History in Hays, Kansas, in 2001, the remains were determined to be a new species of ''Selmasaurus'' in 2008 after over a decade of study by Polcyn and Everhart.〔 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 Plioplatecarpinae. The holotype and the only known specimen is housed at the Sternberg Museum of Natural History under catalog number FHSM-VP-13910.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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