Pluridens

''Pluridens'' ("many teeth") is an extinct genus of marine lizard belonging to the Mosasauridae. ''Pluridens'' is placed in the subfamily Halisaurinae with the genera '' Phosphorosaurus'', ''Eonatator'' and ''Halisaurus''.Konishi, Takuya; Caldwell, Michael W.; Nishimura, Tomohiro; Sakurai, Kazuhiko; Tanoue, Kyo (2015). "A new halisaurine mosasaur (Squamata: Halisaurinae) from Japan: the first record in the western Pacific realm and the first documented insights into binocular vision in mosasaurs". Journal of Systematic Palaeontology: 1–31. doi:10.1080/14772019.2015.1113447. Compared to related halisaurines, ''Pluridens'' had longer jaws with more teeth, and smaller eyes. It also grew large size, measuring long and perhaps over in some individuals. The jaws in some specimens are robust, and sometimes show injuries suggestive of combat. The jaws may have been used for fighting over mates or territories.

''Pluridens'' lived in the shallow seas of West Africa during the late Campanian-Maastrichtian. Three species of are known, ''P. walkeri'', ''P. calabaria'', and ''P. serpentis.'' ''P. walkeri'' is known from the Maastrichtian of southwest Niger,T. Lingham-Soliar. 1998. A new mosasaur ''Pluridens'' walkeri from the Upper Cretaceous, Maastrichtian of the Iullemmeden Basin, southwest Niger. Journal of Vertebrate Paleontology 18(4):709-707. whereas ''P. calabaria'' is found in slightly older (late Campanian) deposits in Nigeria.Nicholas R. Longrich (2016). "A new species of ''Pluridens'' (Mosasauridae: Halisaurinae) from the upper Campanian of Southern Nigeria". Cretaceous Research. in press. doi:10.1016/j.cretres.2016.03.013. ''P. serpentis'' was found in Maastrichtian deposits in Morocco. ''Pluridens'' was briefly synonymized with ''Halisaurus'' by Lindgren and Siverson (2005),Lindgren J, Siverson M. 2005.'' Halisaurus sternbergii'', a small mosasaur with an intercontinental distribution. Journal of Paleontology 79 (4): 763–773. but subsequent studies rejected the synonymy.Michael J. Polcyn, Johan Lindgren, Nathalie Bardet, Dirk Cornelissen, Louis Verding, and Anne S. Schulp (2012) Description of new specimens of ''Halisaurus arambourgi'' Bardet & Pereda Suberbiola, 2005 and the relationships of Halisaurinae. Bulletin de la Société Géologique de France 183:123-136 doi:10.2113/gssgfbull.183.2.123 http://bsgf.geoscienceworld.org/content/183/2/123.abstract

Description

''Pluridens'' was a moderately large mosasaur at roughly in length if the proportions of the dentary and the rest of the animal matches that of ''Halisaurus''; the referred material suggests an even larger body size at more than in length. A feature that separates ''Pluridens'' not only from the rest of the Halisaurinae, but from the rest of the Mosasauridae at large is its unusually high tooth count, dentaries assigned to the genus preserve almost twice the amount of teeth found in most other mosasaur genera. Additionally, the dentary of ''Pluridens'' also has one of the slenderest profiles among the mosasaurs; the only genus having a similarly narrow dentary being the mosasaurine ''Plotosaurus''. This combination of features indicate a feeding niche and lifestyle unique among the mosasaurs.

The shallow dentary and small teeth of ''Pluridens'' was likely elongated relative to the rest of the head to allow for the massive battery of teeth. Due to force exerted by the lower jaw when biting against the upper jaw would decrease with the distance from the joint, the anterior teeth would have been ineffectual for biting and crushing. Lingham-Soliar (1998) likened the lifestyle and feeding of ''Pluridens'' with that of the ichthyosaurs, particularly early ichthyosaurs such as ''Temnodontosaurus'' and ''Leptonectes''.

Lingham-Soliar (1998) listed the following unambiguous character states for the genus: "Very long, slender dentary, anterior half cross-section almost circular extending to tip. Twenty eight-plus teeth in dentary, close-set. Tooth crowns short, no distinguishable carinae, broad, smooth anterior surface, hairline crenations posterior, slightly discernible broad facets, tips posteriorly recurved; teeth virtually uniform in size along most of the dental ramus; replacement teeth emerge medial to mature tooth crowns; resorption pits on mid-lingual side of tooth base".

Classification

The unusually high amount of teeth present in the dentaries of both species of ''Pluridens'' initially made it difficult to immediately assign a classification on the subfamily level. Lingham-Soliar (1998) remarked that the unique combination of features (e.g. the high tooth count and a unique tooth shape) would normally result in the creation of a completely new subfamily, but did not create a new subfamily due to the rather fragmentary nature of the remains. Lindgren and Siverson (2005) considered many of the unique features of ''Pluridens'' to be shared with ''Halisaurus'' and reassigned ''P. walkeri'' as "''Halisaurus walkeri''". The genus synonymy was rejected by later authors, though similarities between the genera and the discovery of distinctly halisaurine vertebrae in Niger allowed the genus to be firmly placed within the Halisaurinae. Thus, ''Pluridens'' is today considered a highly derived halisaurine.

Species and specimens

Three species are known, ''Pluridens walkeri'' from the early Maastrichtian of Niger, ''P. calabaria'' from the Campanian of Nigeria, and ''P. serpentis'' from the late Maastrichtian of Morocco.

The type specimen of ''P. walkeri'' is BMNH R14153, an almost complete dentary recovered from the Maastrichtian Farin-Doutchi Formation near Mount Ilatarda, Niger.

Lingham-Soliar (1998) also assigned BMNH R9804, a partial dentary with poorly preserved teeth (one out of which is almost complete) from the late Campanian of the Nkporo Formation near Calabar in southern Nigeria, to ''P. walkeri''. The Nigerian specimen BMNH R9804 was reassigned to its own species by Longrich (2016) as it lacks many of the derived features that characterize ''P. walkeri'', such as a high tooth count and extreme elongation of the dentary. The Calabar dentary also lack the extreme lateral protrusion and subcircular section of the dentary and the strong transverse expansion of the dental thecae, both of which are present in BMNH R14153. Longrich (2016) dubbed the new species ''Pluridens calabaria''. It may be a direct ancestor to ''P. walkeri''.

A third species, ''Pluridens serpentis,'' was described from the late Maastrichtian phosphates of Morocco in 2021. It is the most completely known species, being represented by two skulls and a number of jaws.
Longrich, N. R., Bardet, N., Khaldoune, F., Yazami, O. K., & Jalil, N.-E. (2021). ''Pluridens serpentis'', a new mosasaurid (Mosasauridae: Halisaurinae) from the Maastrichtian of Morocco and implications for mosasaur diversity. Cretaceous Research, 104882.

References

{{Taxonbar, from=Q23655541

Russellosaurins
Mosasaurs of Africa
Fossil taxa described in 1998
Campanian genus first appearances
Maastrichtian genus extinctions
Taxa_named_by_Nicholas_R._Longrich