The type species, Brachauchenius lucasi, lived in the Western Inland Sea of North America around 100.5-89.3 million years ago, from the Cenomonian to the Turonian of the Cretaceous. An older specimen from the Barremian of Colombia was considered as part of this genus, representing the first re-occurrence of the non-rhomaleosaurid pliosaurs after a Berriasian-Hauterivian hiatus.[3] However, subsequent analysis of this Colombian specimen shows that it was enough distinctive to warrant a new genus and species, named as Stenorhynchosaurus munozi.[4]
The first known (type) specimen (USNM 4989) was collected by Charles Hazelius Sternberg from Ottawa County, Kansas in 1884.[5][6] It had a skull length of up to 1 m (3.3 ft).[7] The species was named by Samuel W. Williston.[1][8] The individual to which this specimen belongs would have measured 4–5 m (13–16 ft) long.[7]Brachauchenius represents the last known occurrence of a pliosaur in North America.
A larger specimen (FHSM VP-321 - skull length 170 cm) was collected by George Fryer Sternberg in 1952 from the Fairport Chalk of Russell County, Kansas, and later described by Carpenter.[9] Schumacher and Everhart (2005) reported on the age and locality of both Kansas specimens.[10] This specimen is now reassigned to its own genus and species, Megacephalosaurus eulerti.[7]
In 2013, Benson et al. referred a partial cranium from the Chalk Group of England (previously referred to Polyptychodon) to Brachauchenius indet.[11]
In 2015, a pliosaur mandible from Turonian deposits near Goulmima, Morocco were referred to the species Brachauchenius lucasi[2]
Classification
Brachauchenius lucasi holotype skull in dorsal, palatal and lateral views
The cladogram below follows a 2011 analysis by paleontologists Hilary F. Ketchum and Roger B. J. Benson, and reduced to genera only.[12]
^Hampe O. 2005. Considerations on a Brachauchenius skeleton (Pliosauroidea) from the lower Paja Formation (late Barremian) of Villa de Leyva area (Colombia). Fossil Record - Mitteilungen aus dem Museum für Naturkunde in Berlin8 (1): 37-51.
^Everhart MJ. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 320 pp. ISBN0-253-34547-2.
^Everhart MJ. 2007. Historical note on the 1884 discovery of Brachauchenius lucasi (Plesiosauria; Pliosauridae) in Ottawa County, Kansas. Transactions of the Kansas Academy of Science110 (3/4): 255-258.
^Williston SW. 1907. The skull of Brachauchenius, with special observations on the relationships of the plesiosaurs. United States National Museum Proceedings32: 477-489. (pls. 34-37)
^Carpenter K. 1996. A Review of short-necked plesiosaurs from the Cretaceous of the western interior, North America. Neues Jahbruch für Geol. Palaont. Abh. (Stuttgart)201 (2): 259-287.
^Schumacher BA, Everhart MJ. 2005. A stratigraphic and taxonomic review of plesiosaurs from the old “Fort Benton Group” of central Kansas: A new assessment of old records. Paludicola5 (2): 33-54.
^Benson RBJ, Evans M, Smith AS, Sassoon J, Moore-Faye S, Ketchum HF, Forrest R. 2013. A giant pliosaurid skull from the Late Jurassic of England. PLOS ONE 8(5):e65989 DOI 10.1371/journal.pone.0065989.
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