Phosphorosaurus

## PhosphorosaurusPhosphate Lizard

* **Binocular Field of View** of 35 degrees
* Has the largest eyes of any mosasaur in terms of proportion

***Phosphorosaurus*** (Phosphate Lizard) is a genus of mosasaur that lived 72 - 66 million years ago, during the Maastrichtian stage of the Late Cretaceous Period. The type species is *Phosphorosaurus ortliebi* from the Craie de Ciply Formation in Belgium. However, official press notes reveal that the first segment of Oceans takes place in the Hakobuchi Formation of Hokkaido, Japan, meaning that Prehistoric Planet instead presented the second species, *Phosphorosaurus ponpetelegans*.

## Paleobiology

### Size and Physique

***“ Taking refuge in the reef is Phosphorosaurus. She too is a mosasaur, one of the smallest, at less than ten feet long. ”***

― **David Attenborough**, *Oceans*
*Phosphorosaurus* is part of a subfamily of mosasaurs known as halisaurinae, whose members range from 3 - 9 meters (10 - 30 feet), with *Phosphorosaurus* being one of the smallest, with the holotype being a fragmented, incomplete skull around 42 centimeters (17 inches) long. Halisaurines are believed to be ambush hunters, not as efficient in swimming as their larger relatives, with *Phosphorosaurus* being no exception.

### Senses

Despite its small size, *Phosphorosaurus* possesses the largest eyes of any mosasaur in terms of proportion, giving it a binocular field of view of 35 degrees. This is unusually high for non-snake squamates, which typically exhibit a binocular field of view of 10 - 20 degrees, and is higher than those of other measured mosasaurs by at least 5 degrees. This grants it depth perception (which most hunters need) as well as great vision in low-light conditions, indicating that it either hunted in deep water, during the night, or both.

*Phosphorosaurus* is also shown occasionally flicking its forked tongue out. Mosasaurs are believed to have forked tongues, much like lizards and snakes, which collect chemical particles from the environment with their tongues and insert them into the voremonasal organ (also known as Jacobson's organ) by their palate. This feature still works very well for sea snakes, so it would also work just fine for mosasaurs. While usually depicted as long, slim and deeply-forked like those of snakes, Prehistoric Planet instead modeled their tongues after the shorter, thicker, and less-mobile tongues of anguimorph lizards, since mosasaurs are believed to be part of the anguimorph group themselves. However, while this means that mosasaurs are in the same group as varanids (monitor lizards), they do not seem that close to them, and mosasaurs may possibly not be anguimorphs at all.

## Paleoecology

### Paleoenvironment

***“ The ocean. The largest habitat on the Prehistoric Planet, and home to one of the biggest predators that has ever lived, a giant mosasaur. But not all mosasaurs are ferocious, 50 foot-long monsters... ”***

― **David Attenborough**, *Oceans*
*Phosphorosaurus ponpetelegans* lived in the shallow seas of modern-day Hokkaido, Japan during the earliest part of the Maastrichtian Stage of the Late Cretaceous Period, unlike *Phosphorosaurus ortliebi* which lived in the seas of Belgium throughout the entirety of the Maastrichtian Stage, 72 - 66 million years ago. As depicted on Prehistoric Planet, *Phosphorosaurus ponpetelegans* lived alongside *Mosasaurus hobetsuensis* and lanternfish. Other organisms include the sea turtle *Mesodermochelys* as well as what appears to be bioluminescent squids. The presence of these light-flashing organisms lends further credence to the theory that *Phosphorosaurus* evolved to hunt down bioluminescent prey in the dark.

The segment *Phosphorosaurus* appeared in was filmed in the Grand Cayman Island and in an underwater studio.

### Hunting Tactics and Feeding Preferences

***“ She spends the daylight hours hiding from danger. But once or twice an hour, she has to dart to the surface to grab a breath. Like all of her kind, she is air-breathing. She's dwarfed by the biggest mosasaurs. But she too is a deadly predator. And she doesn't always hide in the shadows. When the time is right, she becomes a hunter. And that time is when the sun sets. ”***

― **David Attenborough**, *Oceans*
As mentioned before, the large eyes of *Phosphorosaurus* indicated that it thrived in conditions with not much light, so it was likely a nocturnal hunter, a deep-sea hunter, or both. These could be interpreted as adaptations to avoid larger predators or other threats that are active during the day, or as a means to take advantage of other beings that emerge or events that occur during low-light conditions.

## Appearance

The first segment of Oceans, taking place somewhere in Japan, a massive *Mosasaurus* swims close to a reef, prompting several of the area's inhabitants to scamper and hide. Even so, the point of the segment was to prove that not all mosasaurs are alike. In the maze of rocks and corals, a female *Phosphorosaurus* makes her way through as her bigger relative patrols the waters just outside her hideout, occasionally coming up to the surface to breathe. However, it is during the night, when her underwater world changes, can she truly show off her capabilities. In almost-total darkness, a massive shoals of lanternfish migrate, flashing their lights to confuse and disorient any predators that want to feast on them. But with her large eyes, *Phosphorosaurus* can visualize the dazzling display before her very well, charging several times through the shoals of fish to grab as many as she can.

***“ Their faint, eerie light is produced by a chemical reaction inside their bodies. A flash of this bioluminescence can be used to confuse predators. And when seen from below, the glow enables them to blend with - and hide against - the ocean's moonlit surface. But they can't hide from Phosphorosaurus. For her size, her eyes are the largest of any mosasaur, allowing her to see through the illusion and pick out her prey. ”***

― **David Attenborough**, *Oceans*
By dawn, as the lanternfish shoals descend back to the depths and the massive mosasaurs come out, once again prowling the reef, *Phosphorosaurus* returns to hiding in her sanctuary amongst the coral-encrusted rocks, waiting for nightfall to hunt once more.

## References

### General

1. ↑ 1.0 1.1 1.2 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

### Dr. Darren Naish

1. ↑ Openings on mosasaur palates may reveal the location of the Jacobson's organ, a palatal structure that lizards and snakes use in collecting chemicals from the environment via the tongue.
2. ↑ The tongues of the mosasaurs were based off of the shorter, thicker, and less-mobile tongues of anguimorph lizards.
3. ↑ Mosasaurs being close relatives of monitor lizards isn't really true. Assuming that mosasaurs are part of same group as monitor lizards, it appears that they don't seem particularly close, and it is possible that mosasaurs may not even be anguimorphs to begin with.

### Prehistoric Planet

1. ↑ As stated in Oceans.
2. ↑ 2.0 2.1 2.2 I Know Dino: The Big Dinosaur Podcast, Episode 446: Dinosaur-era Oceans and Darren Naish from Prehistoric Planet 2