Imagine swimming in the ocean and suddenly spotting a creature larger than any shark, faster than any human can sprint, and more vicious than any predator alive today. Meet the Mosasaurus, a marine ...

At the end of the Cretaceous Period, a type of giant reptile called mosasaurs occupied and dominated oceanic food webs. Mosasaurs had long bodies and were related to both snakes and monitor lizards.

An enormous sea snake from Norse legend that was fathered by the trickster god Loki and grew big enough to circle the globe is now the namesake for a different type of “monster” — a newly discovered ...