Pluridens

Pluridens serpentis. Credit: Andrey Atuchin.

*Pluridens* is an extinct genus of halisaurine mosasaurid that lived in Africa during the Late Cretaceous.

## Description

*Pluridens* means many teeth. Some specimens have robust jaws, sometimes sustaining injuries thought to have been gained in combat over other territories. *Pluridens* swam the shallow seas of West Africa in the Late Campanian-Maastrichtian. Three species have been named: *P. walkeri*, *P. calabaria* and *P. serpentis*. *P. walkeri* is from the Maastrichtian, southwest Niger, where *P. calabaria* remains are found in the Late Campanian of Nigeria. *P. serpentis* was collected in the Maastrichtian of Morocco, named in 2020. Lindgren and Siverson briefly merged *Pluridens* and *Halisaurus*, others rejecting this. *Pluridens* was somewhat large for a mosasaur, ~5 meters (16.4 feet) when given the proportions of *Halisaurus*. *Pluridens* has an abnormally high tooth count, differentiating the taxon not only from Halisaurinae, but Mosasauridae as well. Dentaries assigned to *Pluridens* show nearly twice the teeth found in most mosasaur genera. Additionally, the dentary has one of the most slenderest profiles among the mosasaurs; the only genus that compares is *Plotosaurus*. These features indicate a niche unique among the mosasaurs.

A shallow dentary and small teeth, characters observed in *Pluridens*, was a likely elongate relative for the head of the head, allowing a large battery of teeth. Force exerted by the lower jaw when biting against the upper jaw would have decreased when the distance from the joint did. The anterior teeth were ineffectual for biting and crushing prey. Lingham-Soliar (1998) compared its lifestyle (including feeding) to ichthyosaurs, especially with early ichthyosaurs, such as *Temnodontosaurus* or *Leptonectes*. Lingham-Soliar listed the following definite characters 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

*Pluridens* is assigned a halisaurine mosasaurid, alongside *Phosphorosaurus*, *Eonatator* and *Halisaurus*. *Pluridens* had longer jaws, more teeth and smaller eyes compared to other halisaurinae. Some individuals grew 8-9 meters long. The unusually large amount of teeth in the dentaries initially made it hard to assign it a subfamily. Lingham-Soliar (1998) states the unique character combination (such as a high tooth count and shape) would result in a new subfamily being erected, but did not do so since the remains were very fragmentary. Lindgren and Siverson (2005) considered many unique traits were shared with *Halisaurus*, merging the two. This was later rejected, however, with similarities of distinct halisaurine vertebrae from Niger allowed *Pluridens* to be firmly placed inside Halisaurinae. It is today considered highly-derived.

*P. walkeri* is known from  BMNH R14153, an almost complete dentary, from the Maastrichtian Farin-Doutchi Formation near Mount Ilatarda, Niger. Lingham-Soliar (1998) assigned BMNH R9804, a partial dentary with poorly preserved teeth (one is almost complete), from the Late Campanian Nkporo Formation, near Calabar, southern Nigeria to *P. walkeri*. Longrich (2016) assigned it a new species since it lacks the derived traits assignable to *P. walkeri* (such as many teeth and an extremely elongate dentary). It lacks an extreme lateral protrusion and subcircular section of the dentary and strong transverse expansion of the dental thecae, which are present in the first specimen. It was named *P. calabaria*, possibly being a direct ancestor to *P. walkeri*. *P. serpentis* was named from the Late Maastrichtian phosphates, Morocco in 2021. It is the most complete of the species, represented by two crania and several mandibles.

## References

1. ↑ https://www.syfy.com/syfywire/prehistoric-sea-monster-was-the-real-life-basilisk
2. ↑ https://www.researchgate.net/publication/351418084\_Pluridens\_serpentis\_a\_new\_mosasaurid\_Mosasauridae\_Halisaurinae\_from\_the\_Maastrichtian\_of\_Morocco\_and\_implications\_for\_mosasaur\_diversity
3. ↑ 3.0 3.1 https://en.wikipedia.org/wiki/Pluridens
4. ↑ https://www.sciencedirect.com/science/article/abs/pii/S0195667121001294
5. ↑ http://www.sci-news.com/paleontology/pluridens-serpentis-09652.html