Sea Dinosaurs & Prehistoric Sea Creatures
People call them sea dinosaurs and ocean dinosaurs but technically none of them were dinosaurs at all.
Mosasaurus, Megalodon, Liopleurodon, Kronosaurus, Elasmosaurus. These were marine reptiles and prehistoric sharks, a completely separate group that dominated the oceans for over 150 million years while dinosaurs ruled the land. Every bit as terrifying. Every bit as real.
Click any creature below to hear the exact pronunciation and see what it looked like.
Prehistoric Sea Creature Pictures
Aigialosaurus
ay-GEE-ah-lo-SORE-us
Clidastes
CLY-das-teez
Cryptoclidus
krip-TOE-klid-us
Cymbospondylus
SIM-bo-SPON-dih-lus
Elasmosaurus
eh-LAZ-moh-SOR-us
Eurhinosaurus
yoor-RY-no-SOR-us
Futabasaurus
foo-TAH-bah-sore-us
Globidens
GLOB-ih-denz
Hydrotherosaurus
HY-dro-thero-SORE-us
Ichthyosaurus
IK-thee-oh-SOR-us
Ichthyotitan
IK-thee-oh-TY-tan
Keichousaurus
KAY-chow-SORE-us
Kronosaurus
KRON-oh-SORE-us
Lariosaurus
LAR-ee-oh-SORE-us
Libonectes
lie-BON-ek-teez
Liopleurodon
LIE-oh-PLOOR-oh-don
Macroplata
MAK-ro-PLAH-tah
Mauisaurus
MAW-ee-SOR-us
Megalodon
MEG-ah-loh-don
Microcleidus
my-kro-KLY-dus
Mixosaurus
MIX-oh-SORE-us
Mosasaurus
MOH-za-SORE-us
Muraenosaurus
myoo-REE-no-SOR-us
Nothosaurus
NO-tho-SORE-us
Ophthalmosaurus
off-THAL-mo-SORE-us
Peloneustes
pel-oh-NOO-steez
Pistosaurus
PIS-toe-SORE-us
Plesiosaurus
PLEE-zee-oh-SOR-us
Pliosaurus
PLY-oh-SORE-us
Plotosaurus
PLO-toe-SORE-us
Rhomaleosaurus
ro-MAY-lee-oh-SORE-us
Shonisaurus
SHO-nee-SOR-us
Stenopterygius
sten-op-teh-RIJ-ee-us
Temnodontosaurus
tem-no-DON-to-SOR-us
Tethysaurus
TETH-ih-SAW-rus
Thalassomedon
thal-ASS-oh-MEE-don
Tylosaurus
TY-lo-SORE-us
Mosasaurus: The Ocean's Most Famous Predator
Mosasaurus pronounced MOH-zah-SORE-us is the most searched prehistoric sea creature on the internet by a wide margin. The name means lizard of the Meuse River, named after the location in the Netherlands where its fossils were first discovered in the 1700s making it one of the first prehistoric reptiles ever scientifically described.
Mosasaurs were enormous lizard-like predators up to 17 meters long with powerful flippers and a shark-like tail. They weren't related to plesiosaurs at all. Mosasaurs are actually more closely related to modern monitor lizards and snakes. You can tell by looking at their skull: they had a second row of teeth on the roof of their mouth for gripping slippery prey.
Tylosaurus was a larger relative of Mosasaurus that could reach 14 meters. Liopleurodon gets them all confused on the internet since its estimated size was once wildly exaggerated to over 25 meters in a BBC documentary. The real Liopleurodon was still massive at 6 to 7 meters but not quite the sea monster of television fame.
Plesiosaurs, Ichthyosaurs, and the Giants of the Deep
Plesiosaurs pronounced PLEE-see-oh-sores are what most people imagine when they hear "sea dinosaur." They had small heads, very long necks, and four large flippers. Elasmosaurus pronounced eh-LAZ-moh-SORE-us was the most extreme example with a neck so long it made up more than half its total body length.
Kronosaurus pronounced KROE-noh-SORE-us was a pliosaur the short-necked, big-headed cousins of plesiosaurs. At up to 10 meters long with jaws that could crush almost anything, it was one of the most feared predators in the ancient oceans.
Ichthyosaurs pronounced IK-thee-oh-sores were the dolphin-shaped ones. They weren't related to dolphins at all but evolution pushed them toward the same streamlined body shape over millions of years. Shonisaurus at up to 21 meters long is the largest ichthyosaur ever found, and possibly the largest animal that has ever lived.
None of these creatures were dinosaurs. They were air-breathing reptiles that had returned to the sea, gave birth to live young, and dominated the oceans while dinosaurs ruled the land.