Sea Dinosaurs! A Prehistoric Ocean Story for Kids

Meet Mosasaurus, Elasmosaurus, Kronosaurus and more, the giant reptiles of the prehistoric seas, and find out why none were dinosaurs. For kids 3–7+, free to preview.

Choose a Narrator

Hold your breath, dinosaur explorer — we're diving into the prehistoric seas! Long, long ago these oceans were far bigger than today's, warm and shallow and packed with life. And swimming through them were some of the biggest reptiles that ever lived. Down we go!

But here's the secret hiding in the water: even though everyone calls them sea dinosaurs, not a single one was a dinosaur! Dinosaurs walked on land. These giant reptiles swam. So if they weren't dinosaurs at all… what in the world were they?

The most amazing sea reptiles you could ever imagine — and no two of them built the same! One shaped like a dolphin, one with a neck like a fire-hose, one wearing a shell like a shield. Let's go and meet them all!

One shape zips past, quick and close. Another glides by slowly, far out in the blue. Which way?

Sea Dinosaur Names

Here are six amazing prehistoric sea reptiles, all in the story, and one big surprise: not a single one of them was a dinosaur. Dinosaurs lived on land. These were other kinds of reptiles that took to the sea.

Ichthyosaurus (ICK-thee-oh-SORE-us): shaped like a dolphin, with huge eyes
Elasmosaurus (ee-LAZ-moh-SORE-us): a tiny head on an enormously long neck
Mosasaurus (MOSE-ah-SORE-us): a giant sea-going lizard
Placodus (PLACK-oh-dus): a shellfish cruncher with webbed feet
Kronosaurus (KRONE-oh-SORE-us): a huge head on a short neck, and one of the strongest swimmers ever
Archelon (AR-kel-on): one of the biggest sea turtles ever found

What Happens in the Story

In Sea Dinosaurs!, your child dives into the prehistoric seas, chooses where to swim, and finds out what these giants really were. Four paths, over the reef, down to the sea floor, out into the open blue and down to the deep, each lead to a different creature.

More Sea Reptile Facts

Ichthyosaurs gave birth to live babies at sea instead of laying eggs.
Elasmosaurus swallowed stones, possibly to help it balance or digest its food.
Placodus had flat, pebble-like back teeth for crunching open shellfish.
The giant sea reptiles are all gone, but sea turtles, Archelon's relatives, are still swimming today.

Frequently Asked Questions

Were there any dinosaurs in the sea?

Not among the giants. None of the great prehistoric sea reptiles were dinosaurs, and a few dinosaurs, like Spinosaurus, spent lots of time in rivers. But here's a twist: birds are dinosaurs, so penguins are dinosaurs that swim in the sea today! Follow that river giant in Spinosaurus' Towering Sail.