Mosasaurus (Meuse Lizard, for it was first found in a chalk quarry close to the Meuse river in Europe) is a genus of mosasaur that lived 82.7 - 66 million years ago, from the Campanian to the Maastrichtian stage of the Late Cretaceous Period. Its remains were found on all seven continents, and (along with some of its other large relatives), as one of the largest marine reptiles to ever exist, it was the apex predator of the oceans and seas it lived in.
There are currently at least five valid species of Mosasaurus. The one mostly shown on Prehistoric Planet is the largest species, Mosasaurus hoffmannii,[PhP 4] referred to as "Hoffmann's Mosasaur" in the fourth segment of Coasts,[PhP 1] with the species name honoring Johann Leonard Hoffmann, an army surgeon and amateur geologist who was involved in the animal's discovery. Prehistoric Planet also appears to show another species, Mosasaurus hobetsuensis of the Hakobuchi Formation in Hokkaido, Japan, though, given its dubious validity, it is possible that this is also Mosasaurus hoffmannii.
“ Mosasaurs were seagoing lizards. Think of a giant, swimming, whale-sized Komodo Dragon. Tapered snout, rough skin, four fins instead of normal limbs, and a long tail that would look a lot like a shark tail, but upside down. That's basically a mosasaur. ”
― Dr. Michael Habib, University of California
Mosasaurus is the last and the largest of the mosasaurs, massive marine lizards that eventually became the dominant predators of the oceans and seas during the Late Cretaceous Period. These animals are best described as being like monitor lizards mixed with orcas, possessing elongated, streamlined bodies and two pairs of flippers. It was originally believed that mosasaurs were eel-shaped and thus moved like an eel or a sea snake. Today, however, it is understood that the more advanced species of mosasaurs had crescent-shaped tail fins like those of sharks and ichthyosaurs, albeit upside-down, with the lower fluke being longer than the upper fluke.
Mosasaurus was originally thought to be 17 - 18 meters long, based on the idea that the body is ten times longer than the skull.[3][4] However, no explicit explanation has been given regarding this 1:10 estimate in the original 1967 study that brings the ratio up,[5] and today, lengths of 17 - 18 meters are considered to be overestimations,[6] with revisions bringing up a more plausible skull-to-body ratio of 1:7, resulting in a maximum length of 10 meters (33 feet) and a body mass of 10 metric tons (11 short tons),[2] and more recent calculations as of 2022 bringing up a maximum length of 13 meters (42 feet) and a maximum weight of 5.5 metric tons (6.1 short tons),[1] though Prehistoric Planet considers it to still be plausible that Mosasaurus reached lengths of 15 meters (50 feet) and weights of up to 15 metric tons (16.5 short tons).[PhP 1][PhP 2][PhP 3] Even with these revisions, however, the formidable Mosasaurus hoffmannii, along with some of its large relatives like Tylosaurus and Prognathodon, remain as the undisputed apex predators of the Late Cretaceous oceans and seas. Smaller mosasaurs like Phosphorosaurus and other inhabitants would hide whenever one Mosasaurus is on the prowl nearby. And while pods of Tuarangisaurus are willing to fight off medium-sized mosasaurs like Kaikaifilu, which is only 10 meters (33 feet) long and 3 metric tons (3.3 short tons) in weight, they all immediately flee once attacked by Mosasaurus, though, given the animal's tremendous speed, when it successfully launches an ambush, the force of its strike alone is enough to kill prey before they even know what happened.
Jaws, Dentition, and Senses[]
Mosasaurus being cleaned, exposing his forked tongue and the set of pterygoid teeth on the roof of his mouth
“ Mosasaurs are giant lizards, and have both a lizard's forked tongue, and, during the mating season, a lizard's colorful skin. ”
Like snakes, mosasaurs have double-hinged jaws and flexible skulls to swallow their prey whole. They also possess four types of teeth, with one set being on the pterygoid bone (which forms the palate, the roof of the mouth), which helped secure prey and even ratchet them further into the mosasaur's throat. Mosasaurus has teeth specialized for cutting up prey, with M. hoffmannii possessing two premaxillary teeth, 14 - 16 maxillary teeth, 14 dentary (lower jaw) teeth, and eight pterygoid teeth,[7][8] all bearing fine serrations (another species, M. missouriensis, also possesses finely-serrated teeth).[9] Like lizards today, mosasaurs likely had their teeth sunken into their gums, as is shown on Prehistoric Planet.
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 1] 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 2] 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 3]
Most squamates are ectothermic, reliant on the environment to keep their body temperature stable (equivalent to the outdated concept of "cold-bloodedness"). By contrast, mosasaurs are likely endothermic, able to generate favorable body temperatures with their own internal bodily functions. With body temperatures similar to those of seabirds during their time (e.g. Hesperornis and Ichthyornis), mosasaurs were able to stay warmer than the surrounding waters, making them highly-active predators capable of short bursts of energy and speed, an advantage over ectothermic competitors and prey. This is one factor that led to them becoming the apex predators in seas and oceans all over the world during the Late Cretaceous, with their "warm-blooded" nature allowing them to conquer even cold, polar environments, like the López de Bertodano Formation in Antarctica.[10][11]
Mosasaurus accelerating upwards with the C-start technique
“ Mosasaurus is an ambush predator. This enormous animal uses its huge tail to accelerate with astonishing speed. ”
Mosasaurs likely relied more on ambush than long-term pursuit,[12] as indicated by their swimming style and adaptations for quick bursts. They primarily swam using the sub-carangiform style seen in some fish like modern-day mackerels. Their bodies stayed mostly stiff while they were quickly propelled by the very rear of their bodies and their rapid, oscillating, crescent-shaped tails, granting them great speed at the cost of maneuverability,[13] The fourth segment of Oceans even depicts Mosasaurus relying on the "C-start" technique, a reflex used by fish and amphibians today, mostly to quickly escape predators but potentially also for ambushing prey. As the name suggests, animals that use this technique first rotate their head about the center of mass towards the direction of where they plan to go (thus forming a C-shape), before suddenly rushing towards their target or destination.
“ Mosasaurs could reach 30 miles an hour in as little as one second. This is what makes them arguably the ultimate marine predator of all time. ”
With large, low pectoral girdles supporting large muscle attachments, mosasaurs can also use their paddle-like flippers to enhance their bursts of speed with breaststrokes.[14][15] The force of their swimming is so powerful that it can even damage their bones; the cap of the large ilium (pelvic bone) of specimen TSMHN 11208 was significantly separated from the stem, believed to be the result of tremendous amount of shear forces on the articulation joint due to the power involved in the rotation of the animal's limbs.[16] As brought up in the Uncovered segment "How Fast Was A Mosasaur?", mosasaurs are able to cover a distance equivalent to three-fourths of their body length every second. In essence, Mosasaurus can accelerate to a top speed of 48.3 kilometers (30 miles) per hour in a single second.[PhP 4]
“ Camouflaged against the dark canyon floor, the mosasaur can approach unseen, waiting for a young, inexperienced individual, the ideal victim. ”
Mosasaurs may have been further aided in ambush by their scales. While the lower halves of some mosasaur bodies have smooth scales, the upper halves of their bodies have non-reflective keeled scales to help them remain less noticeable to prey,[17] perhaps further supported by countershaded skin coloration, a trait seen in a large mosasaur that lived with (and possibly competed against) Mosasaurus, Tylosaurus. Microscopic analysis done on a Tylosaurus nepaeolicus reveals that its scales have high traces of eumelanin, giving it a dark coloration like that of a leatherback sea turtle. Aside from aiding in camouflage, dark skin coloration also aids in absorbing and retaining heat (which is important for "warm-blooded" animals like mosasaurs), as well as adding protection against ultraviolet radiation from the sun whenever the animal surfaces.[18] Given all these, Prehistoric Planet portrays Mosasaurus with a similarly-dark, countershaded skin pattern.
Prehistoric Planet depicts Mosasaurus with pebbly, dark brown skin and a white underside, since most animals, predator and prey alike, are known to rely on countershading to effectively camouflage themselves, blending in with darkness when seen from above, and blending in with light when seen from below. As seen in the fourth segment of Coasts, during the mating season, as it sheds its skin in flakes like other lizards do, Mosasaurus displays a tone of bright red on its back and face to attract females.
The skulls of two Triceratops, Quetzalcoatlus, Mosasaurus, and Barbaridactylus in the opening of the second season's episodes
“ Deep beneath the water’s surface, the world’s largest predator — the Mosasaurus — lies in wait to ambush unsuspecting prey. ”
― The official Apple TV+ episode synopsis for Oceans
Mosasaurus appears in the first segment of Coasts, pursuing a family of T. rexes as they swim through the open seas, eventually snatching one of the juveniles. Later on, in the fourth segment of that same episode, a male Mosasaurus relaxes in a cleaning station in southern Europe before fighting a younger male trying to take his territory. The massive oceanic predator is briefly seen in the first segment of Oceans, where its threatening presence ominously looms over a reef in Japan.[PhP 5] The danger Mosasaurus poses is made apparent in the fourth segment of Oceans, where it ambushes a pod of Tuarangisaurus in a quick burst of speed that kills its target outright. This speed is the main focus of the Uncovered segment "How Fast Was A Mosasaur?", which brings up various techniques for achieving such speed like the C-start, and, following a unique scientific study ran four times by Prehistoric Planet's research team, concludes that Mosasaurus can accelerate to 30 miles (48.3 kilometers) an hour in just one single second.
“ Canyons in the atoll walls lead from the atolls to fresh feeding grounds. This deep water attracts not just the hungry elasmosaurs, but the predators that hunt them. The biggest in the ocean. Fifty foot-long Mosasaurus. ”
Initial studies have found that, in terms of depth and distance to the shore, Mosasaurus preferred to be close to the coast, within depths of 40 - 50 meters (131 - 164 feet).[16] However, more recent studies, involving the analysis of rare earth elements, indicate that Mosasaurus dwelled in offshore environments deeper than 50 meters (164 feet).[19]
“ In southern Europe, where the Atlantic meets the great Tethys Sea, coastal life perhaps reaches its greatest diversity. Rising sea level means that there are countless submerged islands covered with sponges, clams, and corals. Corals take advantage of the sunshine in these shallows, forming partnerships with algae that grow within their tissues. They collect tiny particles of food floating in the ocean currents. Myriads of these marine creatures encrust the solid rock. But one rock here appears surprisingly bare. Beyond is a sheer dropoff and the deep sea, home to oceanic predators, and danger for unwary reef fish. ”
Mosasaurus has been found in several sites all over the world. Fossils in the midwest and east coast of the United States and Canada show that it was present in the inland sea that splits the continent of North America in half. Brazil and Argentina have also yielded fossils of Mosasaurus. Evidence of its dominion in the Atlantic Ocean and Tethys Ocean is made apparent by remains found in Europe, Turkey, Russia, the Levant, and the African coastline from Morocco to South Africa. Fossils found in the López de Bertodano Formation indicate that Mosasaurus may have also prowled the cold waters of Antarctica,[10] though it has been theorized that these remains may actually be those of Moanasaurus, a slightly smaller mosasaur known from the Tahora Formation in New Zealand.[20] Having been present in several oceans with diverse ecosystems and wildly varying climates, from tropical to temperate, and even subpolar regions, Mosasaurus has proven to be a greatly-successful species and (along with the relatives it coexisted with) the true master of the ocean. At the height of its power, its superiority was only halted by the Cretaceous-Paleogene Extinction Event, which wiped out three-quarters of life on Earth 66 million years ago, including the non-avian dinosaurs, pterosaurs, plesiosaurs, and mosasaurs.
Hunting Tactics and Feeding Preferences[]
“ This mosasaur could probably clear 75% of its body length in one single second. That means if that mosasaur is 17 meters away from you, in one second, it will be 75% closer, and in the 2nd second, it would have surpassed you and probably eaten you along the way. ”
― Kiersten Formoso, University of Southern California
While Mosasaurus is able to cover great distances in a short amount of time,[12] its hunting strategy does not rely on the long-term pursuit of prey. Rather, this predator prefers to camouflage itself with its non-reflective, countershaded body,[17][18] stealthily ambush its prey and, in a short burst of speed, strike them with a sudden killing bite. This hunting tactic fits the generalist diet of Mosasaurus, which can choose to go after fish like Xiphactinus, sharks, turtles, smaller mosasaurs, and anything else that is within its reach. As with any predator, Mosasaurus is opportunistic, willing to chase and catch even a single juvenile T. rex that would barely satiate its hunger.
Agonistic Behavior[]
“ A rival, a younger male challenging for this territory. The old male is heavier, over 15 tonnes, but his rival is more nimble. When they are as evenly matched as this, these fights can be lethal. Mosasaurs have been found with the shattered teeth of rivals embedded in their skulls. ”
When it comes to competition, mosasaurs are highly territorial, and confrontations can become brutal and outright fatal, with some remains showing crushed skulls, broken necks, and even dismemberment. Mosasaurus also shared the oceans with other predators, and was thus involved in conflict with other species. The young could be eaten by sharks or the giant fish Xiphactinus, and some mosasaurs grew around 12 meters (40 feet) long, almost as big as Mosasaurus itself. Some battles can be prevented with niche partitioning. For example, Prognathodon was more suited for going after more robust prey like turtles, and while Mosasaurus is also capable of going after turtles, it had a more generalist diet and thus did not fully compete with Prognathodon. This is supported by the discovery of stomach contents from both, with Prognathodon containing hard prey like turtles and ammonites and Mosasaurus containing soft prey like fish.[21] Even so, competition cannot be fully avoided, as a fatal, concentrated blow to a subadult Mosasaurus skull is, at one point, interpreted to be due to an attack by Tylosaurus, which possesses a robust, arrow-shaped snout that was likely able to deal a coordinated strike and cause fractures like that.[22]
Grooming and Mating Habits[]
“ This is Hoffmann's Mosasaur, the ocean's deadliest predator, but he's not here to eat, he's come to be cleaned. ”
Despite its deadly nature, as a living being, Mosasaurus also has its more peaceful moments. Prehistoric Planet speculates that, as a lizard, it would have put on new hues of color or intensified preexisting displays during the mating season to help attract mates, as seen when the Mosasaurus in the fourth segment of Coasts turns its back and face bright red. They would have also likely benefited from cleaning stations, letting fishes and shrimps clean off scraps and shedding skin and just outright relaxing, with only other large mosasaurs able to capitalize on this moment of weakness and ambush them, though this is not a guaranteed means of bringing down a mosasaur, and may even backfire if the assaulted mosasaur is just as skilled as the attacker.
References[]
General[]
↑ 1.01.1The Princeton Field Guide to Mesozoic Sea Reptiles
↑ 17.017.1Kaddumi, H.F. (2009). "On the latest scale coverings of mosasaurs (Squamata: Mosasauridae) from the Harrana Fauna in addition to the description of a new species of Mosasaurus". Fossils of the Harrana Fauna and the Adjacent Areas. Amman: Eternal River Museum of Natural History. pp. 80–94.
