Meet the plesiosaur: a gigantic aquatic reptile

There’s a common misconception that any kind of large prehistoric animal is a dinosaur – from a t-rex to the flying pterodactyl to the woolly mammoth.

When I first heard this, I couldn’t believe it. Did people really believe that a woolly mammoth qualified as a dinosaur? Obviously a woolly mammoth was covered in thick fur (hence the name), which makes it a mammal, even if you knew nothing else about it. They just aren’t reptilian like dinosaurs.

But flying prehistoric reptiles (like pterosaurs) and swimming prehistoric reptiles (like plesiosaurs) – those were just different types of dinosaurs, right?


Until recently, I didn’t realize that plesiosaurs and pterosaurs are not considered dinosaurs. I had mistakenly lumped them all together. True, they were all reptiles and they lived during the same geological time period (the Mesozoic Era), but they were sufficiently different from an evolutionary and biological perspective that they aren’t categorized as dinosaurs at all.

long necked plesiosaur underwater
meet the plesiosaur

Plesiosaurs were a group of long-necked marine reptiles that lived during the Mesozoic Era, from the late Triassic period, through the entire Jurassic period, to the late Cretaceous period (roughly 225 million to 80 million years ago). Some, but not all, types of plesiosaurs continued to exist until the end of the Cretaceous period, about 66 million years ago. This is approximately the same geologic time period as the dinosaurs.

While the name “dinosaur” means “terrible lizard,” the name “plesiosaur” means “close to lizard,” an appropriate name since they were admittedly similar in many ways to the dinosaurs.Β 

The world map looked extremely different hundreds of millions of years ago, but plesiosaurs were geographically distributed in many areas, throughout the Pacific Ocean and near what is now North America, Europe, Australia, and Asia.Β 

Early in their history, plesiosaurs split into two different lineages – pliosauroids and plesiosauroids. The latter had a longer neck that was very flexible. Interestingly, later on, plesiosaurs increased dramatically in size (up to 43 feet or so) and the neck reached extreme lengths. with half the total body length consisting of the neck and head. And the jaws had an estimated biting force of around 33,000 psi, possibly the largest known bite force of any animal!

plesiosaur skeleton

There is even some evidence that plesiosaurs may have been warm blooded and gave birth to live young, rather than laying eggs. Of course, there is significant debate about whether some dinosaurs were similarly warm blooded, but that is a topic for another post…

Further reading:


The Plesiosaur Directory



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