Holotype and naming specimen of
B. lucasi (USNM 4989), as figured by
Samuel Wendell Williston in 1907 In 1884, a partial
skeleton of a
marine reptile was discovered by the owner of a quarry near
Delphos, in
Ottawa County, Kansas. News of this find thus reached
Charles H. Sternberg, who was then collecting fossils for
Othniel Charles Marsh. Sternberg then wrote several letters to Marsh seeking his permission and funding to exhume the specimen, which he allowed. After exhumation, Sternberg gave the specimen to the
Peabody Museum of Natural History for Marsh, but it turned out that Marsh would do little with it. The fossil was eventually transferred to the
United States National Museum of Natural History and subsequently given the code name USNM 4989. This same specimen consists of a nearly complete
skull measuring long, followed by thirty-seven
vertebrae and associated
ribs. Historical documentation from the museum where the specimen has since resided notes that Sternberg was allegedly helped by a certain "John Potts" in its exhumation. Williston chose this name because this specimen was considered the shortest-
necked plesiosaur ever described. The
specific name lucasi is named in honor of
Frederic Augustus Lucas for his notable contributions to American paleontology. but he does not, however, support any evidence for this assertion. A microscopic examination of the fossils published in 2005 revealed that the specimen came from either the upper level of the Greenhorn Limestone or the lower level of the Fairport Chalk Member of the
Carlile Shale, suggesting that the specimen dates to the early Middle
Turonian.
Formerly attributed specimens , which was briefly assigned to Brachauchenius'' in a 2013 study In 1860,
Richard Owen documented a partial skull having been discovered around an unspecified date by
George Cubitt in
Cretaceous sediments from the town of
Dorking, in the
county of
Surrey, England. Based on teeth characteristics, Owen referred this specimen to
Polyptychodon interruptus, a species of
pliosaurid that he himself had already named in 1841 from fossils dating from the same period which were discovered in the counties of
Sussex and
Kent. The following year, Owen cited that the specimen was discovered during the construction of a
railway tunnel through the
Chalk Group, near
Frome,
Somerset. However, this locality was most likely confused with those of other specimens assigned to this genus, and with multiple reported evidence, it seems more likely that the first locality originally mentioned is the most likely. This specimen has since resided in the
local museum of Dorking, where it is cataloged as DOKDM G/1-2. In a
phylogenetic study published in 2013, Roger B. J. Benson and colleagues recovered it as being close to several other specimens assigned to
Brachauchenius, and therefore suggested that it would be better to refer it to that genus as well, although without specific affiliation. In his revision of
Polyptychodon published in 2016, Daniel Madzia designates this genus as a
nomen dubium due to the lack of accessibility and diagnostics regarding the holotype tooth of the taxon, the latter having possibly even been lost. However, he considers it likely that DOKDM G/1-2 could be designated as the
neotype of this genus in order to maintain its
validity, but he refrains from doing so at this time since the descriptions provided by Owen are obsolete. In a 2017 conference, Madzia and colleagues judge the Dorking specimen to be potentially diagnostic despite its incomplete preservation.
, once considered as one of the largest specimens of Brachauchenius'' All recognized fossils of the related and contemporary genus
Megacephalosaurus were first interpreted as coming from
Brachauchenius. Shortly before the description made by Schumacher
et al., the phylogenetic study by Benson
et al. classified the taxon as
B. eulerti. When FHSM VP-321 was found to be a distinct genus, USNM 50136 was identified to be conspecific with it and was assigned to be its paratype. '', seen as the oldest known representative of the
brachauchenines. In 2000, a relatively complete pliosaurid skeleton, since cataloged as VL17052004-1, was discovered in the town of
Villa de Leyva in
Boyacá, Colombia, before being exhumed during 2004-2005. before being designated as the holotype of a new genus and species under the name
Stenorhynchosaurus munozi by María Eurídice Páramo and colleagues in 2016. ==Description==