Plesiosaurus: 6 Surprising Facts About The Real Life Loch Ness

constantly updated Christina Smith (Senior Editor)

The Plesiosaurus is one of the most famous marine reptiles and lived during the Jurassic period. You can recognize it by its long neck, small head, and its paddles. We’ve got everything you need to know, fascinating facts, a profile, and six key features.

Plesiosaurus is an extinct marine reptile that was related to the dinosaurs and lived at the same time. It grew up to 3.5 meters long and weighed about 500 kilograms. It became famous mainly through comparisons to the ‘Loch Ness Monster’.

Cool Facts About Plesiosaurus

Coming up, we’ll tell you where Plesiosaurus fossils have been found, what its name means, and the difference between dinosaurs and marine reptiles.

We’ll also cover a few types of marine reptiles and distinguish between plesiosaurs and pliosaurs. This will give you a good overview so you can better understand the features of the Plesiosaurus later on.

Discovery and Locations

Ammonite find in Lyme Regis (Great Britain)

Plesiosaurus was first discovered back in the 1820s by one of the first female paleontologists, Mary Anning. The find was made in a small town called Lyme Regis in Great Britain. Many other prehistoric remains of sea creatures, like ammonites or shells, were also found there.

The genus was first described by the British geologists Henry De la Beche and William Daniel Conybeare. Since Mary Anning’s discovery, this saurian genus was considered the archetype for plesiosaurs, which is why numerous species were attributed to it over time. The only recognized species today is Plesiosaurus dolichodeirus.

Most of the fossils have been found in Great Britain. This is also where the myth that the ‘Loch Ness Monster’ (Scotland) is a surviving Plesiosaurus originated, but more on that later.

Meaning of the Name

The term "Plesiosaurus" can be translated from Greek as "near lizard". The saurian genus was named in 1821 by the two British geologists Henry Thomas de la Bèche and William Daniel Conybeare.

Since Plesiosaurus was one of the early saurian discoveries, its name simply points to its genetic relationship to lizards. Dinosaurs were also not well-studied at the time and were only considered their own animal group starting in 1835. The species name "Plesiosaurus dolichodeirus" wasn’t established until 1824.

Differences: Dinosaurs and Marine Reptiles

Dinosaurs versus Marine Reptiles

The animal group of "saurians" refers to extinct reptiles from the Mesozoic Era. They can be divided into dinosaurs, pterosaurs (flying reptiles), and marine reptiles (ichthyosaurs and sauropterygians).

Dinosaurs lived on land and reached incredible sizes, which is why they are so famous today. Among them are predators like Tyrannosaurus or Velociraptor, medium-sized herbivores like Triceratops and Stegosaurus, and long-necked sauropods like Brachiosaurus and Brontosaurus.

Pterosaurs include species like Pteranodon or Pterodactylus. They had flight membranes that allowed them to fly. Ichthyosaurs ("fish lizards") are fish-like marine reptiles that were fully adapted to life in the sea.

Sauropterygians ("flippered lizards") also lived in the water and had paddles rather than fish-like fins to move around. This group includes the plesiosaurs, which Plesiosaurus itself belongs to.

Types of Marine Reptiles

Ichthyosaurus

Marine reptiles can also be roughly divided into fish-like, crocodile-like, and turtle-like categories. An example of fish-like marine reptiles is the Ichthyosaurus. They grew up to 3.5 meters long and looked similar to swordfish.

A crocodile-like marine reptile is Metriorhynchus. It grew up to 3 meters long and already looked similar to modern crocodiles. However, it had a tail fin and flippers instead of short legs. The Plesiosaurus belongs to the turtle-like category.

Another group of marine reptiles are those related to modern snakes and lizards. This includes, for example, the mosasaurs. They grew up to 18 meters long and had a snake-like shape with smaller side fins and a large tail fin. Other types of marine reptiles include:

• Ichthyosaurus (fish-like)
• Shastasaurus (fish-like)
• Coelacanth (fish-like, still alive today)
• Pliosaurus (turtle-like)
• Elasmosaurus (turtle-like)
• Liopleurodon (crocodile-like)
• Nothosaurus (crocodile-like, lived on land and in water)
• Mosasaurus (snake-like)

The Plesiosaur Group

The Plesiosaur Group

Plesiosaurs can be divided into "pliosaurs" and "plesiosaurs in the narrower sense". They existed as early as the late Triassic, 208.5 million years ago. They include many different genera and species of marine reptiles.

They grew between 3 and 15 meters long. Some are even estimated to have reached a length of 20 meters ("Monster of Aramberri"). They achieved a bite force of an incredible 147 kilonewtons.

For comparison: Modern crocodile species reach a maximum of 40 kilonewtons. Even the largest prehistoric shark Megalodon with its 108 kilonewton bite force didn’t reach such values.

Plesiosaurus belongs to the plesiosaurs in the narrower sense and represents the archetype with a small skull, a long neck, a turtle-shaped body (without a shell), and paddle-like flippers.

The Pliosaur Group

Kronosaurus belongs to the pliosaurs

Pliosaurs are bulkier and usually larger than plesiosaurs in the narrower sense. They also had a shorter neck, a larger skull, and powerful teeth.

Examples include the Kronosaurus, the Liopleurodon, or the Pliosaurus. They lived from the end of the Triassic to the end of the Cretaceous period.

6 Characteristics of the Plesiosaurus

In this chapter, you’ll find the most important characteristics of the Plesiosaurus. This includes the classification of its genus and species, when and where it lived, as well as its body structure and movement.

We also have important information on its weight, size, lifestyle, and diet. Afterward, you’ll find the key points summarized again in a profile.

Classification of the Genus and Species

Plesiosaurus dolichodeirus is the only recognized species of the genus Plesiosaurus so far. It belongs to the family Plesiosauridae and the group of plesiosaurs.

Plesiosaurs belong to the so-called "flippered lizards" (Sauropterygia). A wide variety of extinct marine reptiles from prehistoric times can be assigned to them.

They descended from land vertebrates and are related to the dinosaurs (a sister group). However, their legs slowly evolved into paddles and flippers to adapt to a life in the sea.

When Plesiosaurus Lived

Plesiosaurus skeleton at the American Museum of Natural History (New York)

Plesiosaurus lived during the early Jurassic (Lower Jurassic) from 201.3 to 190.8 million years ago. The specific time frames range from the Hettangian (201.3 to 199.3 million years ago) to the Sinemurian (199.3 to 190.8 million years ago). In total, the genus probably roamed the seas for 10.5 million years.

Habitat

The fossils of Plesiosaurus were found in Great Britain. During the Mesozoic, there was a shallow sea there, which was also home to the marine reptiles Archaeonectrus, Ichthyosaurus, Leptonectes, and Temnodontosaurus.

Shells, ammonites, plants, and insects were also found at the site. The pterosaur Dimorphodon also lived near the shallow sea. Its remains were also found in Lyme Regis.

Body and Movement

Body and Movement

The body of the aquatic reptile was well adapted to its habitat. Its legs were four paddles, with the front two being slightly longer than the back two.

It had a long, slender neck and a small, flat skull. The neck was not particularly flexible. Movements upwards and to the side would have been rather difficult for it. The neck was more flexible downwards.

Its jaws contained sharp teeth. A unique feature compared to other plesiosaurs is its short skull with a broad snout that still tapers to a point.

For a long time, it was assumed that the Plesiosaurus moved through the water like a sea turtle, in a flying motion. But researchers have now found that it probably used a special flipper technique that no longer exists today.

They discovered that it could have effectively used the momentum from the front pair of flippers. This would have allowed the rear pair of flippers to benefit from the released energy, absorbing the momentum and providing better propulsion. The movements of the flippers would therefore have been wave-like.

Weight and Size

With a length of 3.5 meters, Plesiosaurus is one of the smaller marine reptiles. Its weight is estimated to be around 500 kilograms. Nothing is known about its speed yet.

Other plesiosaurs, and especially pliosaurs, grew significantly larger. Examples include the Kronosaurus at over 10 meters long and weighing 11 tons, or the Mosasaurus at 17 meters long and weighing about 14 tons.

Lifestyle and Diet

Lifestyle and Diet

These marine reptiles had to regularly come to the surface to breathe. Most of them gave live birth to their young and did not lay eggs. It’s believed that they had single, large babies that they then cared for over a longer period, similar to modern whales.

Plesiosaurs were all carnivores, or more specifically, piscivores. They fed on ammonites, squids, sharks, and smaller ichthyosaurs. Since they could bend their necks downwards well, they probably also collected food from the seabed. This could include things like crabs or shellfish.

Since the Plesiosaurus was a rather small specimen, a diet of smaller sea creatures is more likely. However, it was probably also hunted by larger aquatic reptiles itself.

Profile: The Plesiosaurus

Profile: The Plesiosaurus

In this profile, you’ll find the most important information about the Plesiosaurus summarized once again. This includes, for example, the classification of its species, its habitat, and key physical data like size and weight.

Afterward, you’ll find interesting facts about the extinction of marine reptiles and information about the myth of 'Nessie, the Loch Ness Monster,' which was once thought to be a Plesiosaurus.

• Genus Name: Plesiosaurus ("Near Lizard")
• Known Species: P. dolichodeirus
• Family: Plesiosauridae
• Subgroup: Plesiosaurs (Plesiosauria)
• Group: Flippered Lizards (Sauropterygia)
• Period: Jurassic (Lower Jurassic, 201.3–190.8 million years ago)
• Habitat: Great Britain (Europe)
• Diet: Carnivore and piscivore
• Physical Characteristics: Small head, long neck, four paddles, medium-length tail
• Length: 3.5 meters
• Weight: 500 kilograms

Extinction of the Marine Reptiles

The ichthyosaurs died out before the other marine reptiles

The marine reptiles belonging to the Sauropterygia group died out along with the dinosaurs about 66 million years ago. The reasons for this were changes in environmental conditions.

These included a drop in sea levels, several volcanic eruptions, and a giant meteorite that hit the Earth. These events caused about 20 percent of animal families and 50 percent of genera to go extinct.

The Ichthyosaur group died out suddenly 93 million years ago during the Late Cretaceous. The reasons for this have not yet been clarified.

There are theories that larger aquatic reptiles, which became more common in the Late Cretaceous, may have driven them out. Ichthyosaurs gave birth to only a few large, well-developed young, which consequently were more vulnerable than before.

Another theory suggests that the surface of the world’s oceans had less oxygen (Oceanic Anoxic Event). This could have led to a mass extinction, causing the ichthyosaurs to no longer find food.

Plesiosaurus as the Loch Ness Monster

Plesiosaurus as the Loch Ness Monster (Nessie)

Most people know the myth of 'Nessie', the 'Loch Ness Monster', from Scotland. The stories about the monster have been attracting many tourists for a long time, as alleged sightings began as early as the year 565 and continue to this day. We’ve compiled some of these events for you.

• 565: A monster from the River Ness is said to have attacked a Scotsman, who was saved by Saint Columba (mentioned in a biography of the Irishman Columba of Iona, written by Abbot Adomnán).
• 16th Century: Sighting of a monster on the shore of Loch Ness and an attack on three men.
• 17th Century: Report of "floating islands" for which Loch Ness was known.
• 1933: First reports in regional newspapers about sightings of the "monster".
• 1934: First photo of Nessie appeared (has since been exposed as a fake).
• 1977: A Japanese fisherman discovers a carcass that looks like a Plesiosaurus (identified as a basking shark after biological examination).
• 2007: A video of an eel-like creature surfaced.
• 2009: Alleged sighting on Google Earth (turned out to be a boat).

According to descriptions, the Loch Ness Monster, with its long neck, small head, and flippers, resembled the Plesiosaurus. However, some of the reports state that the sighted creature came out of the water. The Plesiosaurus, on the other hand, was adapted to a life in the water and probably would not have survived on land.

In any case, there would have to be many more credible sightings if Plesiosaurus had somehow survived in Loch Ness. There would need to be a whole colony to ensure the animal’s survival, and they would have to regularly come to the surface for air. Even cryptozoologists no longer believe in the Plesiosaurus theory.

The sightings can be explained by misidentifications, for example, with large eels, sturgeons, seals, currents, or 'standing waves' (seiches).

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