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What is a Plesiosaur?

Mary McMahon
Mary McMahon
Mary McMahon
Mary McMahon

A plesiosaur is a prehistoric creature from the order Plesiosauria. Although these creatures are often called “dinosaurs” by lay people, they were not, in fact, dinosaurs, and the two groups of animals were very different, with markedly different habitats and lifestyles. The plesiosaur is generally believed to be extinct, although apocryphal examples of living specimens occasionally crop up in the news.

The term “plesiosaur” means “almost lizard” in Greek, and these marine reptiles do indeed have several traits more closely associated with land-bound reptiles. It is assumed that they reproduced through eggs, possibly laying them on or near shore, and evidence suggests that these creatures died out during the Cretaceous-Tertiary extinction event, which claimed the lives of numerous and unusual plant and animal species who could not adapt to changing conditions on Earth.

Some people look at giraffes as an example of the way plesiosaurs could have evolved.
Some people look at giraffes as an example of the way plesiosaurs could have evolved.

Plesiosaurs lived in the ocean, with bodies specially adapted for swimming. The examples we have found in fossil form all have broad bodies, flipper-like limbs, and short tails, and biologists have suggested that they probably moved through the water much like penguins. Both short-necked and long-necked fossilized plesiosaur specimens have been discovered, although the long-necked variety is probably more famous. Some very fine examples of plesiosaur skeletons can be seen in many natural history museums.

The fossilized remains of plesiosaurs seem to indicate that the animals probably couldn't swim very rapidly, but they could swim well. Their four limbs would have acted like paddles, making it very easy for the creatures to rapidly swivel their bodies while seeking prey. Evidence suggests that plesiosaurs probably drifted below the surface, waiting for unwary victims to pass overhead, and then snapped them up with their extremely powerful jaws.

The long-neck plesiosaur is of immense interest to some fans of prehistoric creatures. In many drawings, the animals are depicted with raised necks, suggesting that they had very muscular necks and bodies. Biologists have suggested, however, that their necks may not have been as mobile as people believe; the sheer weight and size of the neck would have made it hard to move. Others point to giraffes, a land-based creature known for having an extraordinary neck, to demonstrate the possible ways in which plesiosaurs might have moved.

Frequently Asked Questions

What exactly is a plesiosaur?

A plesiosaur was a type of large marine reptile, not a dinosaur, that lived during the Mesozoic Era, about 203 to 66 million years ago. Characterized by their long necks, small heads, and broad, turtle-like bodies with flippers, plesiosaurs were adept swimmers and predators in ancient oceans. They are part of the order Plesiosauria, which includes two families: the long-necked Plesiosauridae and the short-necked Pliosauridae.

How big were plesiosaurs?

Plesiosaurs varied greatly in size, with some species measuring just a few meters in length, while others, like Elasmosaurus, reached lengths of up to 14 meters (46 feet). Their size made them formidable predators, with their long necks allowing them to strike swiftly at fish and other marine creatures.

What did plesiosaurs eat?

Plesiosaurs were carnivorous, feeding on a diet that primarily consisted of fish and cephalopods. Their sharp teeth and powerful jaws were well-suited for catching slippery prey. The long-necked varieties may have used their necks to reach into crevices or to perform quick, agile strikes, while the short-necked types were likely more powerful swimmers that could chase down prey.

Where have plesiosaur fossils been found?

Plesiosaur fossils have been discovered all over the world, indicating that they were widespread during their time. Notable locations include England, where some of the first plesiosaur fossils were identified, as well as North America, Australia, and Antarctica, reflecting their global distribution in ancient seas.

How did plesiosaurs swim?

Plesiosaurs swam using four large, paddle-like flippers in a manner unique among marine animals. Studies suggest that they moved through the water with a flying motion, similar to that of sea turtles, using their flippers in a coordinated, underwater 'flight.' This efficient locomotion allowed them to cruise through the Mesozoic seas with ease.

Are there any living descendants of plesiosaurs?

No, plesiosaurs do not have any direct living descendants. They went extinct during the Cretaceous-Paleogene extinction event about 66 million years ago, which also saw the end of the dinosaurs. Modern marine reptiles like sea turtles and marine iguanas are not descendants of plesiosaurs but have evolved similar adaptations for life in the sea.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Learn more...

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    • Some people look at giraffes as an example of the way plesiosaurs could have evolved.
      By: David_Steele
      Some people look at giraffes as an example of the way plesiosaurs could have evolved.