The plesiosaurs were a group of marine reptiles that existed in the late Triassic and the late Cretaceous periods around 215 to 66 million years ago.

Unfortunately, these incredible creatures were heavily impacted by the apparent extinction event that occurred around 66 million years ago. This event is known as the K-T extinction.

They were within the order Plesiosauria and the suborder plesiosauroidea. The relatively recent classifications were founded in the early 1800s. Some of the most notable of these species were the Elasmosaurus, Liopleurodon, Cryptoclidus, Plesiosaurus, and Stenopterygius.


The general appearance of typical plesiosaurs was very unique to the marine animals we see today. It could be said that plesiosaurs were a mix of many modern-day creatures. We know this from the plesiosaur fossils that have been found throughout time. For example, some species, like the Elasmosaurus, had a long, flexible neck like a snake and the skin of a reptile or lizard yet resembled a turtle with its four large flippers. 

Plesiosaurs were not to be reckoned with, as they could reach over 15 meters, or 50 feet in length, and would weigh upwards of 45 tonnes, or 100,000 pounds. These staggering dimensions made it nearly impossible for other predators to attempt to take them down.

Data suggests that plesiosaurs were indeed the apex predators within their environment. Their sheer size and incredible predatory features allowed them to take their place at the top of the food chain.

Plesiosaurs had extremely powerful jaws with rows of sharp teeth
Plesiosaurs had extremely powerful jaws with rows of sharp teeth

However, different species did possess variations. Some would have far longer necks, while others evolved to have shorter necks. Some would also have a medium-long neck. However, they had a relatively short tail.

The shorter-necked plesiosaurs would fare far better in shallow waters. For example, the Liopleurodon had a short neck and a large body. In fact, they were one of the largest species within the group, sometimes measuring over 20 meters.

All these attributes of contemporary aquatic animals gave them advantages in the dog-eat-dog world of the Mesozoic Era. For example, their long necks and powerful jaws made them excellent hunters in deeper water bodies.

Plesiosaurs can sometimes be confused with longer-necked pliosaurs. Their pliosaurian cousins had a far more lizard-like appearance, stocky build, and longer necks.

The first plesiosaur skeletons were discovered by Mary Anning in 1823. The bones and vertebrae of the animal were found in rocks from the early Jurassic period. The cliffs of the Lyme Regis in England proved fruitful in finding fossils.


The habitat range of the Plesiosaur was expansive. They had many attributes that allowed them to live in every ocean on Earth. The ability to adapt to different aquatic environments contributed to the success of the species. They were found in the Pacific Oceans, tropical seas to the Earth’s northern, colder oceans.

Due to being reptiles, they were air-breathing animals, using their nostrils to take in air. This had a significant impact on how they interacted with their habitat. They would remain relatively near the water’s surface unless they needed to dive deeper to hunt.

They were also known to live in Jurassic lakes and lochs. One of the most extraordinary tales of the Plesiosaur is the myth and legend surrounding the Loch Ness Monster. This mystery has been ongoing for centuries.

Many people believe that Loch Ness, in Scotland, is still home to a plesiosaur today. Whether a breeding colony of plesiosaurs could exist in such a place is highly debatable. Although most likely stuff of fiction, many sightings of a long-necked beast have existed throughout the years. The shores of Loch Ness still attract visitors to this day.

Another exciting incident occurred off the coast of New Zealand when the Japanese fishing trawler Zuiyo Maru caught what looked like a carcass of a plesiosaur. A team of researchers and scientists then began to analyze the find. At first, the scientists declared it was a plesiosaur, but French scientists later suggested it could have been a basking shark. The comparative cranial anatomy of the carcass to a basking shark did not completely line up, leaving the plesiosaur theory still open to debate.

The legend of the Loch Ness Monster is theorized to be a living plesiosaur
The legend of the Loch Ness Monster is theorized to be a living plesiosaur


Like many modern reptiles, they were carnivorous hunters using their incredibly sharp jaws to kill their prey. The unfortunate prey consisted of fish, a variety of smaller marine creatures, such as squid and crustaceans, and soft-shelled animals. Given the size of a plesiosaur, even a giant squid would not have been off the menu. Plesiosaurs were also known to target Ammonites, a prehistoric extinct mollusk species.

In recent years, some people within the scientific community have suggested that plesiosaurs could have been bottom-feeders alongside hunters. If true, this adaptation might have been critical to their survival.

They were incredibly versatile creatures, targeting the whole water column, from the surface of the water to the sea floor. This would allow them to extract more resources from the environment and enable them to be more adaptable to habitat changes.


As the Plesiosaur is only truly known through fossil records, it is hard to know their exact reproduction method. However, scientists largely believe they were viviparous, meaning they gave birth. This development only occurred in 2011 after the discovery of a fossilized fetus. Prior to this, they might have been oviparous, meaning they lay eggs. This was previously based on information known about reptiles that are similar to the Plesiosaur.

Remarkably, plesiosaurs are most closely related to modern-day turtles
Remarkably, plesiosaurs are most closely related to modern-day turtles


As an apex predator of its time, the Plesiosaur didn’t have many direct threats from other aquatic creatures. Due to its size, it was hard for anything to target them as potential prey.

Other creatures did impact the Plesiosaur in that available resources were taken up by other large aquatic predators that roamed the oceans during the period.

However, its demise came from natural disasters, as it is believed that the extinction event occurred around the end of the Cretaceous period, alongside many other dinosaur species

Facts about the Plesiosaur

  1. Plesiosaurs were the apex predator of their environment
  2. They were believed to have been wiped out as a result of the widespread extinction event of the period
  3. They fed on a wide range of smaller marine animals and were even believed to bottom feed
  4. Some plesiosaurs could weigh over 100,000 pounds
  5. They were believed to be viviparous, giving birth to young


Why did plesiosaurs go extinct?

Plesiosaurs went extinct due to the mass extinction event of the Cretaceous period. Although some of the population might have been wiped out directly, it is likely that the majority disappeared due to the regulating reduction in food sources.

Where did plesiosaurs live?

Plesiosaurs lived within a very broad range, existing in almost all the Earth’s oceans. They were believed to sometimes inhabit lakes and freshwater water bodies; however, this was rare.

What is the closest living relative to the Plesiosaur?

Remarkably, despite being an apex predator of its time, the Plesiosaur is most closely related to the modern-day turtle.

Did plesiosaurs live in freshwater or saltwater?

For the most part, plesiosaurs existed mainly within saltwater environments but were occasionally seen in freshwater habitats. However, this was rare.

Were plesiosaurs predators?

Yes, plesiosaurs were incredible hunters and one of the apex predators of their era. With size, speed, and strong teeth-filled jaws, they were a scary proposition.

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