Phosphorosaurus

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Phosphorosaurus is an extinct marine lizard in the mosasaur family. It lived in the Late Cretaceous, during the Maastrichtian stage, about 72 to 66 million years ago.

Classification and species
- Phosphorosaurus belongs to the Halisaurinae subgroup, closely related to Halisaurus, Eonatator, and Pluridens.
- There are two known species:
- Phosphorosaurus ortliebi, found in Belgium.
- Phosphorosaurus ponpetelegans, found in Hokkaido, Japan.
- For a long time, scientists debated whether Phosphorosaurus was a separate genus or the same as Halisaurus. Recent work supports it as a valid genus, though some studies in 2023 suggested its species might belong to Halisaurus or need a new name.

Size and appearance
- Phosphorosaurus was small for a mosasaur, but typical for the Halisaurinae group.
- The skull of P. ponpetelegans is about 50 cm long; the original P. ortliebi skull fragment is about 42 cm.

Discovery and naming
- The genus was defined by Louis Dollo in 1889 with the species P. ortliebi from Belgium.
- The species P. ponpetelegans was described in 2015. Its name blends ponpet (a creek in Ainu, the language of Hokkaido’s indigenous people) with elegant, referring to the well-preserved fossil and the place it was found.

What Phosphorosaurus was like
- It was a deep-water or night hunter, likely feeding on squid and bioluminescent fish.
- Its large eyes suggest good night vision and depth perception, helpful in dark waters.
- It probably hunted by ambush, lying in wait rather than swimming fast like larger mosasaurs.

Notes
- Phosphorosaurus is known only from the Maastrichtian of Europe and Japan. Its exact relationship to other mosasaurs is still discussed as new analyses emerge.