Plesiosaurus Facts

The First Marine Reptile Discovered

Plesiosaurus was an extinct marine reptile that lived between 135 million and 120 million years ago, during the Early to Middle Jurassic Period.  Plesiosaurus was strictly a marine creature from the Sauropsida subcategory, although a study by William Conybeare made the claim that it was more of a reptile than a mammal. The Plesiosaurus and the Ichthyosaurus have been found in the same area of the Lias of England and Germany. It was first discovered by Mary Anning in 1821. It is known from several almost complete skeletons found over the years.

One of the most intriguing Plesiosaurus facts is that these reptiles were probably not very good at swimming. Of course, they did well enough to be able to swim, but they weren’t as good at adapting as Pliosaurs were. These reptiles were also smaller than Pliosaurs, with Plesiosaurus measuring only 15 feet long and weighing 1,000 pounds. That means they were twice the size of a modern horse and twice the weight of a modern hog.

The plesiosaur was not really a dinosaur. The creature was a sauropterygian. Many illustrations depict plesiosaurs attacking land animals, but a plesiosaur’s flippers could not support it on land. The modern loch ness monster myth is always described as a plesiosaurus.

What did they eat?

Since they lived in the sea they would mostly survive by taking in and consuming fish of all sizes or any other swimming animal in the ocean during that time period, due to their sharp teeth and incredibly strong jaws. It is even said to have eaten mollusks that lived along the prehistoric shoreline.

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This enabled them to feed not only on fish of all sizes, but also on any other swimming creatures that were present in the ocean at the time. Their powerful jaws and sharp teeth may have also enabled them to consume mollusks that lived along the prehistoric shoreline.


Studies show that the Plesiosaurus lived and behaved much like the present-day sea turtle. For the majority of their life, they lived in the water but would come to shore to lay their eggs as sea turtles do.

It has been argued that Plesiosaurus could walk on land. Early theories speculated it was possible, but more recent discoveries indicate that Plesiosaurus’ flippers could not have supported its weight for movement on land, but could have pushed the creature through shallow waters. Plesiosaurus would then move to shallower beach areas and lay eggs that would be land-bound except during tide. The geological indicators of fossil recovery support the theory that coastal regions were the primary location for brooding and feeding.

Physical Features/Characteristics

The most fascinating thing about Plesiosaurus is the fact that they looked like a combination of the characteristics of many animals. This included the serpent, a fish, a dinosaur and a turtle. The Plesiosaurus had necks that were like that of a snake. Long and serpent-like not to forget their small heads. The vertebrae of the animal were flat-ended which means that it seemed to be very stiff-necked. They would grow to a length of 11 feet. Their turtle-like bodies with two pairs of paddles on either side enabled them to navigate the waters. The Jaw of the Plesiosaurus was able to open very wide and had a lot of conical teeth that were in sockets.

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Recent Plesiosaurus fossil discoveries have led scientists to believe that it was a live-bearer of its young, completely contradicting the popular belief based on previous discoveries. Plesiosaurus has since been discovered in locations around the world, including North America and the Australian seas.

  • How many years ago did this dinosaur live? between 228 million and 61.6 million years ago
  • What class was this dinosaur assigned to? Sauropsida
  • What did this dinosaur eat? Animals
  • Live birth reproduction
  • Paleontologists discovered 938 different specimens.

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