Some say Plesiosaurus looked like the legendary Loch Ness Monster.

The largest stomach stone found in a plesiosaur was a huge 8 x 6 x 3cm (3 x 2 x 1in) and the total weight of stones in its body would have been about 2.2kg (5lb)! Plesiosaurs would ingest gizzard stones to aid in the digestion of their tough prey, although it is also thought that they could have functioned as ballast in the water.

Plesiosaurus was a small plesiosaur, Mauisaurus reached a whopping 20m (66 ft) long.



"Near to Lizard"


Plesiosaurus is often mistakenly referred to as a dinosaur, when in fact it is a prehistoric marine reptile which lived at the same time as the dinosaurs. It had a long neck, four paddle-like flippers and a tail. 



Plesiosaurus lived during the Early Jurassic, 195 million years ago.

Extinct for about: 00,000,000,000 Days00 Hours00 Min00 Sec

How old are you?
00,00,00.00 of your lifetimes have passed since their extinction.

They Call it Home

Plesiosaurus would have roamed the vast seas of the Jurassic.








  • Lias Rock Unit (Southern England)

What We Heard About Their Hearing

Human Ear

Plesiosaurus is likely to have had similar hearing to that of the whales and dolphins of today.


What Big Teeth You Have

Dinosaur Tooth

The Plesiosaurus mouth was the perfect fish trap: it had simple needle-like teeth curved around its U-shaped jaw.


Nose Knowledge

Human Nose

The nostrils of Plesiosaurus were positioned closer to its eyes than the tip of its snout.



The Poop Scoop

Dinosaur Poop

We haven't discovered any Plesiosaurus poop.


The Most Fantastic Find

The most fantastic find was a plesiosaur uncovered in 1987. Its abdomen contained bones of an embryo, which proves the animal gave birth to live young. Plesiosaurs gave birth to just one individual, allowing us to make inferences on the degree of maternal care.

From The Expert

Plesiosaurus looks something like a swimming Brachiosaurus - a big animal with a long neck, tiny skull, and barrel-shaped chest. Both of these unusual animals probably used their long necks to reach otherwise inaccessible food items. The long neck of Plesiosaurus is supported by approximately 40 individual vertebrae. For comparison, a human has only seven neck vertebrae. 


Sizing it Up


Compare to:

1m / 3.28ft

Plesiosaurus was 1/3 the height of Liopleurodon

1 human
1 human
1 m / 3.28 ft


Number of people head-to-toe to reach the top of Plesiosaurus. (average human height 1.76 m / 5.7 ft)

Compare to:

3.5m / 11.48ft

Plesiosaurus was half the size of Liopleurodon. 

1 human
1 human
3.5 m / 11.48 ft


Number of people side by side touching finger tips to match this length (average arm span 1.7 m / 5.58 ft ).

Compare to:

449.96kg / 992.0lbs

Plesiosaurus was about the same weight as a bottlenose dolphin. 

plesiosaurus weight

Number of people weighing 70.31 kg / 155 lbs needed to match the weight of Plesiosaurus.


Dino On The Go!

Experts have not yet proposed a definite speed for Plesiosaurus, but it would have been slower than a whale or dolphin because it used flippers for propulsion.  

16.5kph / 10.25mph

  • Dolphin 34.9 kph / 21.7 mph
  • Plesiosaurus16.5 kph / 10.25 mph
  • Sailfish 110 kph / 68.3 mph

22.5kph / 14mph

The average human sprint speed.


Family Album

Family Album

Plesiosaurus is part of the order plesiosauria which is a group of extinct reptiles. Plesiosauroids were long-necked marine reptiles like Plesiosaurus and pliosauroids were short-necked marine reptiles with larger heads.  



Plesiosaurus Vision

Plesiosaurus' eyes were positioned to the sides of their head, looking upwards so they could ambush their prey from below.

Plesiosaurus Vision.

Human Vision

The human field of view is roughly 180 degrees.

Human Field of View

The Skinny On Their Skin


Plesiosaurs had smooth skin to reduce drag in the water.


What's In The Nest?

Plesiosaurus Egg

Plesiosaurs are known to have given birth to a single live offspring, just like us. An unborn plesiosaur would have been 1.5m (5ft) long, that's a whopping 1/3 of its mum.  



plesiosaurus brain size

Plesiosaurs had smaller brains relative to body size than most dinosaurs.


Quite The Bite

A plesiosaur could use its long neck to sneak up on its prey from a distance with little chance of being detected.



Good Eatin'

Plant Icon

From the stomach contents of the plesiosaurs, we can tell they fed on belemnites and ammonites as well as prehistoric fish.


Parental Guidance

Plesiosaurus Parent and Child

A plesiosaur fossil has been found with a single foetus inside its abdomen. Plesiosaur mums would have put all their effort into a single offspring, just like us. 


True Colours

Color Wheel

We can only guess what colour Plesiosaurus was.