Most people think of prehistoric times as the Time of the Dinosaurs. And it was…from about 250 million years ago to around 65 million years ago, dinosaurs did run the show…on land, that is. The air and the sea were quite a different story. The world’s skies, oceans, seas, rivers and lakes were teeming with prehistoric life, and if it lived its life in the water or flew through the air, chances are it was not actually a dinosaur.

But why should dinosaurs have all the fun, anyway? Today we’re going to look at some super cool creatures from ancient times who called the ocean their home, because they deserve the spotlight every now and then too. Let’s check ‘em out!

1. Ammonite

What's an Ammonite?

Way back before the time of the dinosaurs, over 400 million years ago, you’ll find the first entry in our list: the ammonite. Ammonites were molluscs, or more specifically, cephalopods, meaning they’re related to the octopus and squid of today.

However, unlike squids and octopuses, ammonites had a hard spiral shell. While they first appeared long before the dinosaurs, they died out around the same time, about 65 million years ago. Ammonites are known as “index fossils”, which means they can help paleontologists determine the age of the rocks around them depending on which species of ammonite they find there.

Not too much is known about ammonites since only their shells are usually left behind, but it is believed they had tentacles like their present-day relatives. They also may have squirted ink to evade predators, as preserved ink is sometimes found in fossil ammonites.

The name “ammonite”, if you were wondering, comes from the Egyptian god Ammon, who had horns like a ram. The spiral shape of their shells resembles ram’s horns, leading Pliny the Elder, a naturalist of Ancient Rome, to liken them to the horns of Ammon.

2. Dunkleosteus

What's a ?

Let’s jump ahead a bit now about 50 million years to the Late Devonian Period. If you were to go for a swim during this time period, you might want to watch out for Dunkleosteus, a huge fish that could grow up to 20 feet long!

Dunkleosteus was one of the largest of a group of fish known as placoderms, which had armored bony heads. Dunkleosteus didn’t have teeth, but it did have bony plates that ended in very sharp edges, and very strong jaws that it could use to clamp down on just about anything in its path, including our old friend the ammonite (sorry, little guy!).

Because only the armored skull areas of Dunkleosteus are usually left as fossils, scientists have had to make educated guesses about what the rest of this creature looked like, based on its more well-known relatives and its feeding habits.

What does “Dunkleosteus” mean? Well, the second part “-osteus” comes from the Greek word for “bone”, referring to its very bony armored head. “Dunkle” refers to David Dunkle, a paleontologist at the Cleveland Museum of Natural History, who studied prehistoric fish.

3. Liopleurodon

What's a Liopleurodon?

Jump way ahead to around 150 million years ago, and we find ourselves in the seas of the Late Jurassic Period. Here, you’ll want to be very careful you don’t end up in the jaws of the pliosaurs, a group of meat-eating marine reptiles with huge heads full of lots of sharp teeth!

Liopleurodon was one such pliosaur. It could grow over 20 feet long, and its skull alone was over five feet in length. It used its four paddle-like flippers to propel itself powerfully through the sea, using its strong sense of smell to sniff out its prey. As an apex predator, it could eat just about anything it wanted.

“Liopleurodon” means “smooth-sided teeth”, which, if we’re being honest, seems to sell this prehistoric monster a bit short. However, when it was named, its teeth were the only remains anyone had found so far!

4. Kronosaurus

What's a Kronosaurus?

Liopleurodon wasn’t the only pliosaur patrolling the prehistoric seas, and it certainly wasn’t the biggest. That honor goes to Kronosaurus, which may have grown as long as 40 feet! Its teeth could grow up to 12 inches long.

Kronosaurus lived a bit later than Liopleurodon, in the Early Cretaceous Period, around 120-100 million years ago. It preyed on large turtles, other marine reptiles, and possibly even giant squids!

“Kronosaurus” was named after Kronos, a Titan of Ancient Greek mythology, who was the father of the god Zeus.