The type species, Brachauchenius lucasi, lived in the Western Inland Sea of North America around 93.5-89.3 million years ago, during the Turonian stage of the Cretaceous. An older specimen referred to Brachauchenius from the Barremian of Colombia represents the first re-occurrence of the non-rhomaleosaurid pliosaurs after a Berriasian-Hauterivian hiatus.
The first known (type) specimen (USNM 4989) was collected by Charles H. Sternberg from Ottawa County, Kansas in 1884. It had a skull length of about 90 cm. The species was named by S.W. Williston. A larger specimen (FHSM VP-321 - skull length 170 cm) was collected by George F. Sternberg in 1952 from the Fairport Chalk of Russell County, Kansas, and later described by Carpenter. Schumacher and Everhart (2005) reported on the age and locality of both Kansas specimens. This pliosaur grew to around 10 meters (30 ft) in length. Brachauchenius represents the last known occurrence of a pliosaur in North America.
- Williston SW. 1903. North American plesiosaurs. Field Columbian Museum, Pub. 73, Geological Series 2 (1):1-79. (29 plates)
- 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 Berlin 8 (1): 37-51.
- Everhart MJ. 2005. Oceans of Kansas - A Natural History of the Western Interior Sea. Indiana University Press, 320 pp. ISBN 780253 345479.
- Everhart MJ. 2007. Historical note on the 1884 discovery of Brachauchenius lucasi (Plesiosauria; Pliosauridae) in Ottawa County, Kansas. Kansas Academy of Science, Transactions 110 (3/4): 255-258.
- Williston SW. 1907. The skull of Brachauchenius, with special observations on the relationships of the plesiosaurs. United States National Museum Proceedings 32: 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. Paludicola 5 (2): 33-54.