Plesiosaur

The Plesiosauria or plesiosaurs were an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. They first appeared in the latest Triassic Period, possibly in the Rhaetian stage, about 203 million years ago. Plesiosaurs became especially common during the Jurassic Period and thrived until they disappeared due to the Cretaceous–Paleogene extinction event about 66 million years ago. They lived in oceans all around the world, and some species might have also spent time in freshwater environments.

Plesiosaurs had a broad, flat body and a short tail. Their limbs evolved into four long flippers, which they used to "fly" through the water. These strong flippers were powered by muscles connected to wide bony plates on their shoulder and hip areas. Plesiosaurs breathed air and gave birth to live young, and there are clues that they might have been warm-blooded.

There were two main types of plesiosaurs. One type, known as "plesiosauromorph," had very long necks and small heads. These plesiosaurs moved slowly and ate small sea animals. The other type, called "pliosauromorph," had short necks and large heads. These were fast hunters and top predators, able to catch large prey. Some pliosauromorphs grew up to seventeen meters long! While scientists once divided plesiosaurs into two groups based on neck length, recent research shows that these traits might have been mixed among different species.

Unlike other ancient marine reptiles such as the Ichthyosauria and Mosasauria, the different groups of plesiosaurs are not part of the Dinosauria clade. Plesiosaurs were among the first fossil reptiles discovered, and since their naming in 1835, over a hundred valid species have been identified.

History of discovery

Main article: Timeline of plesiosaur research

Skeletal remains of plesiosaurs were among the first fossils of extinct reptiles to be recognized. Early scientists often mistook these bones for fish remains. One of the earliest known plesiosaur fossils was described in 1719 by William Stukeley. This partial skeleton was found in a quarry in Lincolnshire, England, and was originally thought to be the remains of a sinner from the Great Flood. Today, it is displayed in the Natural History Museum.

During the 1800s, many more plesiosaur fossils were discovered, especially in England. Scientists began to understand that plesiosaurs were a unique group of marine reptiles. In 1821, William Conybeare and Henry Thomas De la Beche named the genus Plesiosaurus. Fossils found by Mary Anning in Lyme Regis helped reveal how unusual these animals looked, with long necks and large bodies. As more fossils were found around the world, scientists learned about different types of plesiosaurs and their lifestyles.

Evolution

The Plesiosauria originated from the Sauropterygia, a group of reptiles that returned to live in the sea. During the Upper Triassic, they split into two groups. One group kept functional joints, while the other, the Pistosauria, became better adapted to life in the ocean. Their limbs changed into flippers, and they gave birth to live young.

From the earliest Jurassic period, plesiosaurs became very common. They were divided into long-necked and short-necked groups. Some grew up to ten meters long, while others, like the large Pliosauridae, reached up to seventeen meters. During the Early Cretaceous, the Elasmosauridae appeared, known for their extremely long necks. All plesiosaurs went extinct at the end of the Cretaceous period, about 66 million years ago.

Description

Plesiosaurs ranged in size from about 1.5 meters (5 feet) to over 15 meters (49 feet) long. Some were among the largest marine predators of their time, similar in size to large sharks, ichthyosaurs, and early toothed whales. Their bodies were broad and flat, with short tails. They had four large flippers used for swimming, which moved up and down through the water. Unlike fish-like swimmers such as ichthyosaurs, plesiosaurs used all four flippers to move, with their tail mainly helping to steer.

Plesiosaurs had a unique body plan with strong muscles attached to bony plates on their undersides. Their limbs were large and flat, turned into flippers with many small bones added for extra length. They had long necks and small heads or short necks and large heads, depending on the species. Their teeth varied from needle-like to conical, suited for catching prey in the ocean.

Paleobiology

Plesiosaurs had different eating habits based on their neck length. Long-necked plesiosaurs, known as "plesiosauromorphs," likely hunted fish and squid using their large eyes for spotting prey. They may have eaten creatures living on the ocean floor, too. Short-necked plesiosaurs, called "pliosauromorphs," were powerful hunters, able to chase and catch large animals.

Scientists have found stones in plesiosaur stomachs, called gastroliths. These might have helped with digestion or controlling how buoyant the plesiosaurs were in water.

Distribution

Plesiosaur fossils have been discovered on every continent, including Antarctica. These ancient marine reptiles lived in the oceans during the time of the dinosaurs, from about 203 million years ago to around 66 million years ago.

Main article: List of plesiosaur-bearing stratigraphic units

The list of rock layers that have produced plesiosaur fossils shows just how widespread these creatures were during their time on Earth.

In contemporary culture

Main article: Loch Ness Monster

See also: Sea monster

Plesiosaurs are sometimes mistaken for dinosaurs in movies and books, even though they are not dinosaurs. Some people think that old stories of sea monsters and modern sightings of strange creatures in lakes might be because plesiosaurs still exist today. Scientists, however, do not believe this because there is no real evidence to support it.

The famous Loch Ness Monster is often said to look like a plesiosaur, but there are many reasons why this is unlikely. For example, the lake where the monster is said to live is too small and too new to have supported such large animals. Because of this, many people think the sightings are caused by things like waves, floating objects, or tricks of the light. Still, many people connect plesiosaurs with the legend of the Loch Ness Monster.