The age of dinosaurs was filled with fierce animals that weren't dinosaurs.
Take mosasaurs, for example. Their name translates to "river lizard" -- marine reptiles with whale-like flippers that lived some 96 million years ago. Different species of the animal ranged in size, from a few feet to nearly 60 feet long.
Their jaws, filled with sharp teeth, were double-hinged, like snakes. That let them open up and swallow prey in one big gulp. That feature comes to good use in this recreation of a dinosaur-era underwater battle, as our mosasaur mom fends off hungry sharks that have attacked her babies.
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Scientist used to think these creatures moved through the water like sea snakes, but more recent research suggests they got their undersea propulsion power primarily from their broad tails, using them in a fashion similar to sharks.
Visually, modern-day monitor lizards are reminiscent of these ancient reptiles, though mosasaurs were a bit more stretched out and streamlined for their aquatic lives.
Mosasaurs died off with the mass extinction event of 66 million years ago.