If you were among the dinosaur-loving hordes that helped Jurassic World to the biggest opening weekend in movie history, then you've already met the park's aquatic attraction: a massive ancient carnivore that would have cruised the world's oceans some 80 million to 66 million years ago.
Here's what we know about the mighty Mosasaurus.
1. Mosasaurs are not dinosaurs.
Dinosaurs are distinguished from other reptiles that once roamed the earth by, of all things, their hip sockets. The term "dinosaur" is actually very specific and describes only the land-dwelling descendants of the "ruling reptiles", the archosaurs. Mosasaurs, on the other hand, are more closely related to modern-day lizards.
2. It took a while to figure out what a mosasaur actually was
The first time a fragment of a mosasaur skull was found, in The Netherlands in 1764, it was mistaken for a fish. In the decades that followed, it was described as a giant crocodile and even a sperm whale. After French Revolutionary forces seized the skull while attacking the Fortress of Maastricht where it was held, French scientists argued over whether it was a crocodile, a whale or a giant monitor lizard.
It wasn't until 1822 that palaeontologist William Daniel Conybeare officially assigned the skull to a still-undescribed ancient reptile, which he named Mosasaurus.
3. It's taking a while to figure out what they're related to
As with a lot of things in science, their proper place in the tree of life is still being debated by palaeontologists. Originally, the ancient reptiles were thought to belong in the same order as snakes, given that they shared the trait of a double-hinged jaw. However, scientists later revised this theory, and mosasaurs found themselves reassigned to the same order as monitor lizards. Now, some scientists seem to be leaning towards the original snake theory once again.
4. They gave birth to live young.
Mosasaurs were reptiles, but some common mosasaur traits differ vastly from those you'd find in other marine reptiles. For example, most modern marine reptiles, like sea turtles and marine iguanas, lay eggs up on the shore. But mosasaurs would have given birth to live young in the water, and may even have given their offspring some parental protection.
5. There were lots of different mosasaurs
There were many species of mosasaurs. Smaller species were only around three metres long, but larger ones could grow to a gigantic 12-15 metres!
6. Some mosasaurs had shark-like tails
Until fairly recently, experts thought mosasaurs would have cruised through the water at a pretty leisurely pace, their whip-like tails (similar to those of eels or snakes) allowing for only brief bursts of speed to lunge at prey. But a 2013 study flipped what we know about mosasaur tails upside down, suggesting these aquatic predators had powerful, shark-like tails that would have allowed for high-speed hunting.
7. They ate EVERYTHING
Mosasaur fossils unearthed with other animal remains preserved where the stomach would have been have allowed scientists to conclude that these formidable hunters would have dined on fish, sharks, marine reptiles (including other mosasaurs), sea birds and any dinosaurs that got too close to the water.
8. They had countershading!
Thanks to a group of scientists led by Dr Johan Lindgren who discovered the pigment melanin in the fossilised scales of a mosasaur, scientists now think it's likely that these aquatic reptiles were light on their undersides and dark on top. This "countershading" is similar to what we see in sharks and whales, and is a handy form of marine camouflage.
9. They lived EVERYWHERE ... even in fresh water!
For a long time, experts believed mosasaurs lived only in marine environments. That's until scientists in Hungary collected over 100 bones of a new freshwater mosasaur species from a site that has produced no other marine or brackish-water animals or plants.
This new species was dubbed Pannoniasaurus inexpectatus, meaning "unexpected Hungary lizard". Mosasaur remains have been unearthed pretty much all over the globe – Europe, Asia, some parts of Africa, North America, South and Central America ... even some parts of Antarctica! They got around.
UP NEXT: Here’s how big the dinosaurs in Jurassic Park would be in real life
Join the conversation about this story »
NOW WATCH: This is how big dinosaurs actually were in real life