Plesiosaur
Fast facts
- Phylum
- Chordata
Scientific name
- Scientific name
- Plesiosauria
How to say it in other languages
- Japanese
- 首長竜目
Facts from Wikipedia’s “Plesiosaur” page and Wikispecies (CC BY-SA 4.0).
The plesiosaurs were an order of large, carnivorous marine reptiles. They flourished from 203 million years ago (mya) to 67 mya.
In 1719, William Stukeley described the first partial skeleton of a plesiosaur. The great-grandfather of Charles Darwin, Robert Darwin of Elston told him about it.
Mary Anning was the first to discover a fairly complete plesiosaur. She found it on the ‘Jurassic Coast’ of Dorset, England in the winter of 1820/21. The fossil was missing its skull, but in 1823 she found another one, this time complete with its skull. The name Plesiosaurus was given to it by the Rev. William Conybeare.
The earliest plesiosaur remains are from the Middle Triassic period. p128 The group was important through the Jurassic and Cretaceous. They had two large pairs of paddles, short tails, short or long necks, and broad bodies. They died out at the K/T extinction event, 65 million years ago.
Description
Plesiosaurs had many bones in their flippers, making them flexible. No modern animal has this four-paddle anatomy: modern turtles use their forelimbs for swimming. Plesiosaurs were mainly piscivorous animals. The most famous members of this family include Plesiosaurus, Elasmosaurus, Dolichorhynchops and Styxosaurus.
Pliosaurs
The pliosaurs were a group of mostly large submarine predators with short necks and large heads. Their sizes ranged from two to 15 metres, and they were predators of large fish and other reptiles. Their streamlined body shape suggests they swam and ate under water. Liopleurodon, Rhomaleosaurus and Kronosaurus are amongst the most famous members of this group.
Long-necked plesiosaurs
There were three families of long-necked plesiosaurs, who evidently had a different life-style from the pliosaurs. It was suggested by D.M.S. Watson that their method was as surface swimmers, darting down to snatch smaller fish which were feeding on plankton. It is hard to see the benefit of a long neck under water; aquatic mammals operating under water all have a streamlined torpedo-shape, as did pliosaurs and ichthyosaurs. All the longer-necked familiers were, from the setting of the teeth and jaws, eaters of small fish. However, some at least were bottom-feeders, consuming various prey. Digestion of shellfish was aided by gastroliths. These plesiosaurs included elasmosaurs, styxosaurs and plesiosaurs.
Gastroliths
Plesiosaurs have been found with fossils of belemnites (squid-like animals), and ammonites (giant nautilus-like molluscs) associated with their stomachs. But plesiosaurs could not crack shells. Instead, they probably swallowed them whole. In the belly of a plesiosaur were “stomach stones”, which are called gastroliths. These stones moved around in the plesiosaur’s stomach and cracked or crushed the shells of the animals it ate. One Styxosaurus fossil found in Dakota had 253 gatroliths weighing a total of 29 pounds.
Live birth?
Live birth has been proved for ichthyosaurs, but is uncertain for plesiosaurs.
False plesiosaurs
False plesiosaurs include Megacephalosaurus, Halisaurus, Tylosaurus, Mosasaurus and Thalassotitan.
Written for younger readers
Plesiosaur, in simpler words
This version comes from Wikijunior, a set of books written for children aged 8 to 11. It is shorter and uses plainer language than the article above.
From Wikijunior: Dinosaurs
The plesiosaur, more named correctly as Elasmosaurus, is not actually a dinosaur, but rather a large swimming reptile. The word plesiosaur is Greek for “nearer to the reptiles”. This name given to this creature because it resembles something that is part reptile and part fish. The whole group of these animals are called plesiosaurs, pliosaurs and elasmosaurs.
There were different types of plesiosaurs which were different from each other in size and in shape. The shortest were 2.5 metres long and the longest were 14 metres long! That is about as long as 8 adults lying in one long line! Some had long necks with small heads on the end, others had short necks with immense jaws (pliosaurs). Their stomachs were oval-shaped with two front flippers and two back flippers. They had long tails, though much shorter than their necks.
Scientists first thought that they swam close to the surface of the water (as the picture on the left shows). This way they could stick their head above the water and look down on fish. But because their eyes are placed facing slightly upwards, this is probably not true. They probably swam completely underwater and used their long necks to dart their heads towards fish. Plesiosaurs and their relatives were highly successful throughout the Mesozoic.
Their tooth structure and gut remains showed they ate mostly invertebrates, so things like cephalapods. They ate fish, squids, mollusks and other small sea creatures. Very recently, scientists have found evidence that the plesiosaurs may have also been “bottom-feeders”. That is, they would feed from the bottom of the sea - on things like clams and snails.
Rhomaleosaurus lived from the early Jurassic, while Elasmosaurus lived in the late Cretaceous. That is from about 220 million years to about 66 million years ago. Plesiosaurs, like dinosaurs, lived in the Mesozoic. Nobody is sure why the plesiosaurs went extinct on Earth.
Some people think that they could climb out of the water and crawl around on land, like seals. But other scientists disagree with this. Either way they would have spent a lot of their time under water. And because they were air-breathing animals, they would have to come up to the water surface for air every now and then.
Their fossils were found in England, Germany, Korea, Australia, New Zealand and USA. They also lived in Manitoba, Canada,and Mexico
The first plesiosaur was discovered in 1821 by Mary Anning, in England. Mostly found in the Benthic zone, they can also be found in the intertidal zones as well.
The most famous mysteries around these creatures is the Loch Ness Monster. There are a lot of stories of some large creature in the lake called Loch Ness in Scotland. Most descriptions of the monster are close to what the plesiosaurs must have looked like. Some of the sightings have been proven to be a hoax and at present there is no scientific proof of the existence of the animal but many people believe in it. The study and search for animals which fall outside of contemporary zoological catalogues has the name of Cryptozoology.
In 1977, some Japanese fishermen off the coast of New Zealand found a very rotten carcass of some large creature with flippers. It was so rotten that it was very hard to tell anything from it, but some people believed that it was a plesiosaur. Scientists however ascertained it was a basking shark, fallen to bits because it was so rotten.
- How flexible were their necks? Scientists don’t agree on this.
- Is there any truth to the stories around them?
Where this page comes from
The article above is adapted from “Plesiosaur” on Simple English Wikipedia, by its contributors. We removed reference markers, navigation boxes and tables, expanded measurement templates into readable numbers, and kept the prose otherwise intact. The simpler version is adapted from Wikijunior on Wikibooks.
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