Meet the Prehistoric Animals that Ruled the Ocean

Welcome the Jurassic Park of the sea

When we think about the age of the dinosaurs, we often forget about what was swimming in the ocean during that period. At the end of Jurassic World, the Mosasaurus is nearly forgotten until it terrifyingly jumps out of the water scaring those on land. Global sea levels were high during the Mesozoic period in which dinosaurs ruled the earth. While the animals that delighted our childhood like the Stegosaurus or the Tyrannosaurus rex roamed the land, the sea was also teeming with cool and unusual life.

Hold onto your butts and take a ride through the depths of the prehistoric ocean.



 This is the one creature that made it in Jurassic World. The Mosasaurus ruled the ocean during the Cretaceous period and are closely related to snakes or monitor lizards we see today. They were fast in the water with powerful tails that propelled them and small flippers that allowed them to easily maneuver to find their prey. Mosasaurus was at the top of the food chain and would eat pretty much anything they found in the ocean: sharks, cephalopods, giant turtles, and even other mosasaurs.

The real Mosasaurus wasn’t quite as big as Jurassic World made it out to be—as always, real life fails to live up to the Hollywood hype. The Mosasaurus measured up to 59 feet long, bigger than a Tyrannosaurus rex and about the size of a humpback whale today. While that doesn’t measure up to the skyscraper-sized beast of the silver screen, the Mosasaurus shouldn’t be embarrassed about their fearsome stature. If a whale-sized predator capable of taking down dinos came slithering through the water at me, my first thought wouldn’t be “I’d thought they’d be bigger,” it would be “I hope I’m on a fast boat.”


Plesiosaur skeleton

Plesiosaurus is one of my favorite prehistoric creatures. They were massive with long necks that made up half the length of their bodies. They grew up to 43 feet, about the size of a very large bus, but their size didn’t stop them from flying through the water. They had four flippers, and we believe they moved through the water like penguins, their front limbs doing the work while the back limbs steered them on course. If the look of these creatures seems familiar, perhaps it’s because you’ve been monster hunting lately. They are thought to be the origin of legends like the Loch Ness monster, though there has been no evidence of these animals existing in modern times.

Plesiosaurs had no gills so they had to come up to the surface for air just like marine mammals do today. That isn’t the only thing they have in common with modern dolphins and whales. A fossil found of a pregnant plesiosaur gives us evidence to support that these creatures gave birth to live young. Unlike modern reptiles, plesiosaurs produced one or a few babies at a time, and they invested a lot in the care of their babies. They were much like modern dolphins in the way they gave birth and perhaps in the way they took care of their young as well. Call the makers of Jurassic Worldand tell them you want a cute pod of Plesiosaurus mamas herding their babies through the next movie. It could be the cutest thing since baby Yoda.

Speaking of mothers, the Plesiosaurus was discovered in 1823 by Mary Anning, also known as the mother of paleontology. She was ahead of her time, documenting fossils before the word “dinosaur” was even around, it wouldn’t be coined until 1842. She would search for fossils along the coasts near her home with her trusty dog Tray. She found her first ichthyosaur when she was just 12! Unfortunately, Mary Anning didn’t get the credit she deserved for her incredible discoveries because of sexism in the leading scientific institutions of her time. When we marvel at the incredible ancient Plesiosaur, we should thank her for bringing this bit of history to light.


Pilosaurus rendition

The Pliosaurus was another massive prehistoric ocean animal growing up to 40 feet long, around the size of some whales we see today. These creatures were fierce hunters, strong and fast, known for taking down large prey, even dinosaurs. They had powerful jaws with bites some paleontologists believe were as strong as a Tyrannosaurus rex, known for having the most powerful bite on land.



One of the weirdest looking prehistoric animals has to be the Helicoprion. If you start at the tail and move up, it looks like a normal shark right up until the top where its mouth begins. The lower jaw ends in a circular saw-like shape that makes it look like it belongs in a Bond villain’s lair. It’s hard to believe that this strange and terrifying creature once roamed this planet.

That weird spinning blade has been a scientific mystery for over a century. Ancient chondrichthyans, the class of animals that include sharks and rays, often leave little behind for researchers. Their bodies are mainly made of cartilage which is difficult to preserve. In the case of the Helicoprion, this means that researchers first discovered them through their confusing array of teeth. No one really knew where these chompers fit as there was little left of their overall bodies to give them clues about the rest of the animal. Paleontologists debated for years whether these fossils were defensive spines, a terrifying row of teeth waiting at the back of the throat, part of the tail on a backend no one wants to mess with, a nightmarish tongue or a protrusion curling underneath the mouth. It’s like a scientific version of “pin the tail on the donkey,” although I hope no one was handling a murder ball of teeth while blindfolded!

Researchers were finally able to solve this mystery using a CT scan to find bits of cartilage left behind. They were able to confirm that this spiral of teeth was part of the lower jaw. They also found that the Helicoprion had no other teeth other than it’s frightening lower jaw. The teeth would rotate outward when it opened its mouth and then turn backward like a circular saw once the mouth was closed to tear at its prey. This may have helped them slice up cephalopods and gotten them kicked out of dentist offices. Now, I’m just waiting for the inspired Helicoprion sequel to Edward Scissorhands: Henry Saw Mouth.

Bonus: Megalodon

If you’re a fan of Shark Week, then you are no stranger to the megalodon. This huge shark has been extinct for a million years but hasn’t failed to capture the imagination of shark enthusiasts and horror-movie writers alike. If you’re curious about this ancient fish, we’ve got you covered here: 7 Mega Wild Facts About the Megalodon.

Although these amazing animals are no longer roaming the ocean, not all prehistoric animals are extinct. Check out these prehistoric ocean animals that are still around today!

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