An Ultimate Guide to Plesiosaurus: The Near to Lizard

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Name Meaning“Near to Lizard”Height1 to 2 meters (3 to 6 feet)
PronunciationPlee-see-oh-SAWR-usLength2.87 to 3.5 meters (9.4 to 11.5 feet)
EraMesozoicJurassic PeriodWeight185 kg (408 lbs)
ClassificationSauropterygia,‭ Plesiosauria & PlesiosauroideaLocationEurope and North America

Plesiosaurus Pictures

Plesiosaurus | Sebastian Kaulitzki via GettyImages

The Plesiosaurus

Gage Beasley Prehistoric's Plesiosaurus Concept
Gage Beasley Prehistoric’s Plesiosaurus Concept

Plesiosaurus is a genus of large marine reptiles that lived in the Pacific seas of North America, Asia, and Australia during the Early Jurassic Period.

This reptile was alive about 200 million years ago and is one of the most fascinating creatures from the Mesozoic Era.

Plesiosaurus is known for its extremely long neck, streamlined turtle-like body, and short tail.

The forelimbs and hindlimbs of the marine reptile were modified to form two pairs of large elongated paddles.

Plesiosaurus was a plesiosaur, an order of marine reptiles that were alive between 228 and 61.6 million years ago. 

The group includes Plesiosaurus and the contemporaneous pliosaurs known for their shorter necks and thicker torsos.

Plesiosaurus, large marine predatory reptile from the Jurassic Era
Plesiosaurus, large marine predatory reptile from the Jurassic Era | CoreyFord via GettyImages

Discovered in the 19th century, Plesiosaurus was one of the first plesiosaurs ever described. 

As one of the most dominant marine reptiles of the Jurassic Period, Plesiosaurus is also one of the most studied members of its family. 

The discovery of numerous fossils of this marine reptile and subsequent studies have helped to clear up initial misconceptions about its appearance, ecological role, and possible behavior. 

In this article, we’ll discuss the Plesiosaurus and the fascinating life it lived in the Pacific Ocean millions of years ago.

Gage Beasley's Prehistoric Shirt Collection
Gage Beasley’s Prehistoric Shirt Collection
Gage Beasley's Prehistoric Plush Collection
Gage Beasley’s Prehistoric Plush Collection

Physical Characteristics

Plesiosaurus was a moderately-sized marine reptile. 

Although size estimates for this genus vary, the length of the Plesiosaurus was typically between 2.87 and 3.5 meters (9.4–11.5 feet), and it has a body mass of about 185 kg (408 pounds).

Gage Beasley Prehistoric's Dilophosaurus Size Comparison Chart
Gage Beasley Prehistoric’s Plesiosaurus Size Comparison Chart

Plesiosaurus had a broad, flat body with a short tail.

The general body plan of this reptile resembled a turtle without a shell. 

The most distinctive feature of the Plesiosaurus was its extremely long neck. The neck had at least 40 cervical vertebrae (neck bones). 

Despite having such a long neck, the Plesiosaurus’ neck is still not as long as that of some other plesiosaurs. 

The Elasmosaurus, for instance, had a neck with at least 76 vertebrae and was up to 13 meters (43 feet) long. 

The snake-like neck of the Plesiosaurus had a small narrow head at the end of it. 

The external nostrils of the Plesiosaurus were positioned on top of its head, closer to the eyes than the tip of the skull. 

The neck of the Plesiosaurus was notably flexible, allowing it to move its head in various directions.

Plesiosaurus with its barrel-shaped body
Plesiosaurus with its barrel-shaped body | Mark Garlick via GettyImages

The barrel-shaped body of this marine reptile was fully adapted to an aquatic lifestyle. 

It had four paddle-like limbs that functioned as flippers for swimming through the water. 

The hindlimbs were elongated but narrow. In adult Plesiosaurus, the hindlimbs were smaller than the forelimbs.

Habitat and Distribution

Plesiosaurus inhabited the ancient Pacific seas during the Early Jurassic Period, about 200 to 183 million years ago. 

Fossils of this marine reptile have been discovered from various locations in Europe (England, Germany, and France), North America (Western United States and Canada), Asia, and Australia. 

This suggests that the Plesiosaurus had an extensive geographic range. 

The widespread geographic range of the Plesiosaurus can also be explained by the fact that the continents were arranged into a single landmass known as Pangaea during the Early Jurassic Period when this reptile was alive. 

The Earth’s climate was also considerably different. 

It was warmer compared to today’s temperature.  

The specific environment in which Plesiosaurus lived was characterized by shallow seas and coastal regions. 

Although they mostly lived in shallow marine or freshwater environments, the Plesiosaurus likely ventured into the open seas occasionally.

Behavior and Diet

A school of Plesiosaurus looking for food in the deep waters
A school of Plesiosaurus looking for food in the deep waters | CoreyFord via GettyImages

One of the most debated facts about the Plesiosaurus is whether or not it lived on land. 

In the past, scientists believed marine reptiles like the Plesiosaurus were semi-aquatic, which means they could walk on land. 

Ancient art and reconstructions of the Plesiosaurus often depict the reptile’s long neck sticking out of the water. 

More recent studies have shown that this would have been unlikely. 

While the Plesiosaurus still had to raise its head above water to breathe air, its neck was too rigid to be raised completely out of water.

The limbs of the Plesiosaurus were also not useful out of water because they could not have supported the reptile’s weight and would have been too cumbersome to use on land.

Even if Plesiosaurus ventured out of the water, they would have been incapable of going far inland. 

This evidence suggests that the Plesiosaurus was fully adapted to an aquatic lifestyle. 

Plesiosaurus in deep waters | Mark Garlick via GettyImages

Their stiff flippers would have been very useful for maneuvering in the water, but their tails were too short to be useful for swimming. 

The Plesiosaurus were unique predators. 

While they didn’t have the notorious reputation of other marine reptiles like the Mosasaurus or ichthyosaurs, they were still adept hunters. 

They hunted fish but also fed on clams, snails and belemnites, fish, and other prey.

Mohamad Haghani
Plesiosaurus dolichodeirus hunting ammonites | Mohamad Haghani via GettyImages

The U-shaped jaws of the Plesiosaurus had sharp teeth effective for gripping and trapping fish. Their jaws were also strong enough to crush the shells of mollusks in the water. 

Plesiosaurus was a stealthy hunter. 

Experts think their long necks and narrow head aided them when hunting prey. 

The Plesiosaurus could easily approach schools of fish or other types of prey with its long neck while keeping the rest of its body hidden in the murky waters.

Life Cycle

Two Plesiosaurus going for the win with the female Plesiosaurus
Two Plesiosaurus going for the win with the female Plesiosaurus | CoreyFord via GettyImages

Plesiosaurus reproduced sexually, but whether they lumbered onto dry land to lay eggs or gave birth to live young in the water is unknown. 

This is one of the ongoing controversies about the life of this ancient reptile. 

The prevailing theory is that Plesiosaurus and other marine reptiles gave birth to live young. 

Scientists have discovered and studied a plesiosaur mother with the remains of an embryonic individual within it. 

While the individual studied was not Plesiosaurus, it is a closely related plesiosaur, and the finding answers some questions about the reproductive habits of the Plesiosaurus.  

Gage Beasley's Plesiosaurus Stuffed Plush Toy
Gage Beasley’s Plesiosaurus Stuffed Plush Toy

Experts think juvenile Plesiosaurus lived in estuaries in the early years. 

They developed rapidly in these shallow nurseries before moving out to the open ocean after attaining maturity. 

Fossil evidence of juvenile Plesiosaurus specimens suggests they had a different body proportion and skull structure compared to adult forms.

This indicates that the juveniles went through distinct growth stages as they matured into adults, with their long necks growing faster and longer than the rest of their bodies. 

Evolution and History

Plesiosaurus dinosaurs swim together in Jurassic seas to find their next prey | CoreyFord via GettyImages

Plesiosaurus was part of a larger group of marine reptiles known as plesiosaurs (order Plesiosauria). 

Members of this group were highly diverse and common during the Mesozoic Era. 

Plesiosaurus and their close relatives in the plesiosaur order evolved from a common ancestor. 

This was most likely a group of terrestrial reptiles that transitioned to an aquatic lifestyle at the beginning of the Mesozoic Era (Early Triassic Period)

The early ancestors of the Plesiosaurus were small semi-aquatic reptiles similar to modern lizards. 

The biggest of them were around 60 centimeters long, but they soon evolved into larger sizes and spread into a wide range of shallow marine ecosystems.

While many groups of aquatic reptiles evolved this way, most were wiped out during the Triassic-Jurassic extinction event, but the plesiosaurs survived. 

Plesiosaurus and Ichthyosaurus during the extinction event
Plesiosaurus and Ichthyosaurus during the extinction event | ZU_09 via iStock

The survivors soon branched off into the long-necked and small-headed plesiosaurs (more closely related to the Plesiosaurus) and the short-necked, large-headed pliosaurs (more closely related to the Pliosaurus).

Plesiosaurus was one of the earliest members of the plesiosaur group. 

Later members of this group, such as the Elasmosaurus, evolved even longer necks and were significantly bigger than basal forms like the Plesiosaurus

Plesiosaurus began to go extinct towards the end of the Jurassic Period. 

Still, some of its close relatives survived till the end of the Cretaceous when they died off along with the dinosaur population and other Cretaceous groups. 

Interactions With Other Species

Plesiosaurus swimming with the fishes
Plesiosaurus swimming with the fishes | CoreyFord via GettyImages

Plesiosaurus was one of the largest marine reptiles during the Jurassic Period, so it was probably one of the top predators of the ancient seas when it was alive. It mostly ate fish, mollusks, and squids.

They were big enough to be benthic predators, so they most likely targeted any animal they could find on the sea bottoms. 

The oceans of the Early Jurassic Period were also home to some other impressive predators. 

While there’s no direct evidence that the Plesiosaurus was preyed upon by other animals, larger predatory marine reptiles or some ancient sharks may have posed a threat to juvenile or weakened individuals. 

Additionally, some species of large marine reptiles, like the ichthyosaurs, may have competed with the Plesiosaurus for food and other resources. 

The Plesiosaurus’ position as a shallow marine predator would have helped partition their niche, limiting confrontation between these marine reptile groups.  

Cultural Significance

Antique illustration of the fossilized remains of Plesiosaurus dolichodeirus
Antique illustration of the fossilized remains of Plesiosaurus dolichodeirus | ilbusca via iStock

Plesiosaurus is also an important fossil to paleontologists because of its role in our understanding of the evolution of marine reptiles. 

Discovered early in the 19th century, the Plesiosaurus was one of the first plesiosaurs ever discovered, lending its name to the entire order. 

It was discovered just a few years after the Ichthyosaurus, at a time when knowledge about the world of marine reptiles was just starting to go mainstream. 

Expectedly, the discovery of the Plesiosaurus elicited significant excitement and interest in the scientific community of 19th-century England.

For many years after its discovery, several marine reptiles similar in appearance to the Plesiosaurus were simply classified into the genus.

Recent research has helped identify these incorrectly classified individuals and reassign them to the right genus. 

There are still a lot of ongoing controversies about the Plesiosaurus, including its habitat, diet, and whether or not it laid eggs on land or in the sea. 

Future discoveries and ongoing research may help settle these debates.  

Nessie, the famous Loch Ness monster commonly referenced in Scottish Folklore, is believed to be a Plesiosaurus

Ink hand-drawn vector sketch of Loch Ness ancient Nessie monster animal | Elena Smirnova via iStock

This mythical creature has been a subject of public interest across various cultures in Europe since the early 20th century, with several sightings, photographs, and mysterious sonar readings. 

Scientists have attributed these alleged sightings of the Loch Ness monster as mere hoaxes rather than an actual lake monster or the Plesiosaurus.

In addition to this mythical reference, Plesiosaurus has been featured in several books, documentaries, television shows, and movies. 


Plesiosaurus is a genus of extinct marine reptiles that lived during the Early Jurassic Period.

It was one of the first plesiosaurs to be discovered and remains one of the best-known members of the order. 

The Plesiosaurus is famous for its extremely long neck and turtle-like body. 

The marine reptile was relatively small compared to its other relatives in the plesiosaur family.

Still, it was big enough to be considered an apex predator in the marine ecosystem of the Jurassic Period.

It was fully adapted to an aquatic lifestyle, although there are speculations it may have ventured on land occasionally. 

Plesiosaurus fossils have been found all over the world. 

However, it is most common in Europe and often appears in European folklore.  


When was Plesiosaurus discovered? 

Plesiosaurus was first discovered by Henry De la Beche and William Conybeare in 1821. 

However, the first complete fossil of this marine reptile was discovered in 1823 by famous fossil hunter Mary Anning. 

The description of this reptile was based on the remains discovered by Anning.

Was Plesiosaurus a dinosaur?

No, it wasn’t.

Although Plesiosaurus lived around the same time as dinosaurs, they were not related.

It belonged to a separate group of reptiles that lived in the sea.

How did Plesiosaurus breathe underwater?

Plesiosaurus breathed air and had to come to the water’s surface to breathe. 

It is believed to have possessed a long neck that could extend above the water, and its nostrils were positioned above its head. 

This enabled it to breathe air while keeping most of its body submerged.


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