Mosasaurus
Mosasaurus was a massive marine reptile that lived during the Late Cretaceous period, roughly 80–66 million years ago. It belonged to a larger group of ocean-dwelling reptiles called mosasaurs, which were highly successful and widespread. Fossils have been found on nearly every continent, including Europe, North and South America, Asia, Antarctica, and Africa. Before their extinction at the end of the Cretaceous, mosasaurs ruled the seas as apex predators, capable of eating virtually anything they encountered.
The name Mosasaurus means “lizard of the Meuse River” referring to where the first known specimen was discovered in 1764 in Holland. Currently, five recognized species fall under this genus: M. hoffmannii (the type species and largest), M. missouriensis, M. conodon, M. lemonnieri, and M. beaugei. Other species have been proposed as well.
M. hoffmannii grew to a length of around 10 - 12 m, making it one of the largest known marine reptiles. Other species were smaller, with estimates of around 7 - 10 m in length. Weight estimates for M. hoffmannii are around 10 tonnes or more. Even at its largest, though, it was still considerably smaller than the exaggerated version depicted in Jurassic World.
Not a Dinosaur
Mosasaurs coexisted with dinosaurs but belonged to a distinct group, separate from dinosaurs, called squamates – the group that includes lizards and snakes. It is thought that they primarily hunted in shallow environments such as near coastlines. While they would have been capable of diving and holding their breath for some time, mosasaurs, along with other marine reptiles like ichthyosaurs and plesiosaurs, were air-breathing and would have needed to come to the surface periodically to breathe like dolphins.Streamlined Swimmers
Mosasaurus was perfectly suited to life in the water. It had a long, streamlined body, four paddle-like limbs, and a tail that bent downward at the tip and ended in a crescent-shaped fin (fluke), which acted like a powerful paddle to propel it efficiently through the water. Unrelated marine animals like ichthyosaurs, fully marine crocodile relatives, and early whales, evolved similar crescent tail flukes independently - a case of convergent evolution that helped them all swim fast and efficiently. Fossilized skin impressions show that mosasaurs had small scales covering their bodies. Analysis of pigment in fossilized scales suggests that mosasaurs were likely countershaded (with the upper half of the body being dark and the bottom being lighter in color), similar to modern leatherback turtles and sharks, possibly helping to camouflage them.
Powerful Skull and Versatile Jaws
The skull of Mosasaurus was streamlined and cone-shaped, with a short snout that slightly extended past its front teeth. Its upper jaws were strong and deep, lined with small pits that likely held nerves. The lower jaw was long, straight, and flexible, and capable of a snake-like, double-hinged motion. The skull featured extra small teeth on the palate that helped grip prey securely. These features made Mosasaurus a formidable predator, capturing and swallowing a variety of marine animals, placing it at the top of the food chain.
Stomach contents found in a few specimens included turtles, fish, and possibly bird-like dinosaurs. It likely also fed on sharks, squid, ammonites, and even other mosasaurs. In one case, a Mosasaurus consumed a 1-meter-long fish—longer than its own head - indicating it tore apart larger prey into bite-sized pieces.
There is also fossil evidence of violent encounters between mosasaurs. Specimens of two Mosasaurus species – M. conodon and M. missouriensis – have been found with teeth from another member of the same species in their skulls along with other cuts, breaks, etc. The M. conodon specimen appears to have died from these injuries, with no evidence of healing, while the M. missouriensis survived.
Teeth Made for Tearing
Some mosasaurs appear to have been specialized feeders – Globidens was a mosasaur with highly rounded teeth that it likely used to crack mollusk shells. Mosasaurus, however, had teeth adapted for cutting prey, which were generally robust and in some species were serrated. The exact number and arrangement of teeth vary between species and individuals, but M. hoffmannii – the largest species – had around 40–50 teeth. The fossils also show thecodont dentition – which means its teeth were set in deep sockets in the jaw, similar to modern crocodiles. This gave the teeth a very strong attachment, allowing them to withstand powerful biting forces, and helping them to grip and crush their prey without easily losing teeth. Unlike many modern lizards with loosely attached pleurodont teeth, mosasaurs had a much more durable setup. The teeth were also constantly shed – a new tooth would grow inside the root of the old one, eventually pushing it out."Warm-Blooded" and Fast
Histological studies (looking at a section of bones under a microscope) have been used to estimate the growth rate of Mosasaurus and thus its resting metabolic rate. These studies suggest that while Mosasaurus does belong to the squamate group, which includes modern lizards and snakes, mosasaurs had a significantly higher metabolic rate than these animals and were essentially "warm-blooded" (endothermic). This would have helped it to survive in colder climates, and to pursue prey over larger distances. While speed is very difficult to accurately estimate for extinct animals, one study commissioned by Prehistoric Planet estimated that mosasaurs could reach top speeds of around 48 km/h(for more information on this, search for "Prehistoric Planet 2 — How Fast Was A Mosasaur?" on YouTube).Mosasaurus had strong vision, with large eye sockets. However, its sense of smell appears to have been relatively poor, which suggests it was likely not a scavenger. Its eyes were positioned more on the sides of its head, giving it limited 3D vision but excellent peripheral awareness - useful for spotting prey near the water's surface. It likely hunted by lurking in shallow coastal waters and ambushing prey with bursts of speed from its tail. While it mainly stayed near the surface, some evidence suggests that certain species might have hunted in deeper waters as well.
References & Attributions
Image: Life Restoration of M. hoffmannii - Jonagold2000, CC BY-SA 4.0, via Wikimedia Commons
Image: Reconstructed Skeleton of M. hoffmannii - Ghedoghedo, CC BY-SA 3.0, via Wikimedia Commons
Image: The Powerful Skull and Teeth of Mosasaurus - Wilson44691, Public domain, via Wikimedia Commons
