Phosphorosaurus (Phosphate Lizard) is a genus of halisaurine 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,[PhP 1] meaning that Prehistoric Planet instead presented the second species, Phosphorosaurus ponpetelegans, which was found in a clean "ponpet" ("creek" in the language of the Ainu, the indigenous people of Hokkaido) called "Pankerusano-sawa", preserved in exceptional condition (hence "elegans", the Latin term for "elegant").[1]
Phosphorosaurus is part of a subfamily of mosasaurs known as halisaurinae, whose members range from 3 - 9 meters (10 - 30 feet). Phosphorosaurus is one of the smallest members of the family, and one of the smallest mosasaurs overall, with the holotype being a fragmented, incomplete skull around 42 centimeters (17 inches) long. Prehistoric Planet deliberately portrays a small individual in order to show how the sample sizes of fossilized specimens are not enough to reveal the full extent - much less the average - of variation in a population.[DN 1] 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.[1] This grants it depth perception (which most hunters need) as well as excellent scotopic (low-light) vision, indicating that it either hunted in deep water, during the night, or both. In such dark conditions, the show depicts Phosphorosaurus dilating its pupils until, like an owl, its pupils take up almost the entirety of its eyes, allowing it to gather all the light that it can from its surroundings.
Phosphorosaurus is also shown occasionally flicking its forked tongue out. As with other squamates, mosasaurs are believed to have forked tongues, which collect chemical particles from the environment to be inserted into the vomeronasal organ (also known as Jacobson's organ) by their palate,[DN 2] which contains a chemosensory system to help the user identify the source of these chemicals for a variety of reasons ranging from prey detection to the determination of the state of other organisms, be they aggressive rivals or individuals open to mating. 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.[DN 3] 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.[DN 4]
Prehistoric Planet's Portrayal[]
Prehistoric Planet's depiction of Phosphorosaurus was originally set by John Conway, who did the initial skeletal and muscular diagrams. Dr. Darren Naish, Prehistoric Planet's lead consultant, devised the mosasaur's striped tail and overall mottled look and countershaded coloring (a darker top contrasting with a lighter underside, meant to help camouflage both predator and prey species with environmental lighting), with the animal's facial markings emphasizing its head shape and large eye size.[DN 5] This concept was then improved by Gabriel N. Ugueto, who gave the mosasaur a brown color scheme with white accents, though this detail is mostly lost to the blue hue of the ocean it lived in.[PhP 3][DN 6]
Paleoecology[]
Paleoenvironment[]
The sun rises over the Hakobuchi Formation in Japan
“ 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... ”
Phosphorosaurus ponpetelegans lived in the shallow seas of the Hakobuchi Formation in 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. The segment Phosphorosaurus appeared in was filmed in the Grand Cayman Island (with the filming crew facing difficulties due to Hurricane Ida) and in an underwater studio.[PhP 1]
Paleofauna[]
“ As darkness falls, her underwater world transforms. Now, billions of creatures will begin to rise from the depths to feed near the surface. The largest mass migration on Earth occurs in almost-total darkness, and can only be seen by special night vision cameras. The most spectacular of these nighttime visitors are a type of lanternfish. ”
As depicted on Prehistoric Planet, Phosphorosaurus ponpetelegans lived alongside Mosasaurus (possibly Mosasaurus hoffmannii or its own species, 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.[1]
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. ”
The large eyes of Phosphorosaurus indicated that it thrived in conditions with poor lighting,[1] so it was likely a nocturnal predator, 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, which may also allow the animal to take advantage of other beings that emerge or events that occur during low-light conditions.
In the first segment of Oceans, taking place somewhere in Japan,[PhP 1] 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.
“ 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. ”
Swimming out in the open, with her eyes dilated greatly like an owl's, Phosphorosaurus sets out to meet her targets. In almost-total darkness, 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.
“ By the time dawn arrives, the migrating shoal has sunk once more to the depths, and Phosphorosaurus, too, must return to her daytime hiding place. The biggest mosasaurs are back on the prowl. She will have to wait 'til nightfall before it's safe to hunt again. ”
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.
Trivia[]
Phosphorosaurus and Tyrannosaurus rex (as well as Kuru kulla if one counts nest raiding as hunting) are the only animals depicted hunting at night on Prehistoric Planet.
Gallery[]
Initial Phosphorosaurus Concept Art by Dr. Darren Naish
Reworked Phosphorosaurus Concept Art by Gabriel Ugueto
