The Pliosaur is a type of large carnivorous marine reptile belonging to the order of Plesiosauria and the suborder of Pliosauriodae. They were truly enormous creatures of the deep that fed on fish and smaller sea dinosaurs or marine reptiles, such as elasmosaurs and ichthyosaurs. Pliosaurs lived mostly in the prehistoric seas that covered modern-day Europe and fossil specimens have been found in England, Mexico, Australia, South America, and the Arctic Norwegian island of Svalbard. Unfortunately for researchers, in most cases, the only part of any particular pliosaur that remains in fossilization is the skull. Fortunately, though, the scientists are able to use the skull of the creature as a guide to help determine how the entire pliosaur looked. Scientists have been able to build models and have come up with their best assumptions as to how the pliosaurs actually looked. The two most commonly known varieties of pliosaur are the genera of Liopleurodon and Kronosaurus.
The different varieties of pliosaur have the same basic physical appearance, with a short neck, large head, and four large fins. The main identifiable differences are the jaws and dentition, probably reflectiing different types of prey favored by each species. The largest examples known by near-complete skeletons, Kronosaurus Queenslandicus and Liopleurodon ferox, are similar in size (7-9 meters), although fragmentary remains of still larger pliosaurs, estimated to be up to 18 meters long, are known to exist. Other varieties of pliosaur include the genera of Pliosaurus, Rhomaleosaurus, Macroplata, the Simolestes, Thalassiodracon, and the Svalbard Pliosaur.
Because only the skulls of these massive creatures were able to remain intact in fossilization, for the most part, the exact physiology of the pliosaur is not known. Using the skulls to determine the animal's appearance, scientists have come up with an assumed physiology for the pliosaurs. There are many different types of pliosaur, each having a somewhat different physical appearance.
When the first Kronosaurus skulls were discovered, scientists believed them to be a little less than one-seventh of the creature's entire body. This led them to the conclusion that the monstrous animal's whole body reached a total length of an impressive 12-14 meters (40-46 feet). More recent studies of pliosaurs suggest that Kronosaurus' head was only one-fifth of its entire body length, significantly lowering estimates of its size. Scientists now believe that the Kronosaurus' total body length was around 9 meters (28 ft). Despite this downward revision, Kronosaurus Queenslandicus remains among the largest pliosaurs.
The estimated body length of the largest Liopleurodon for which remains have been definitively identified, L. Ferox, is around 7 meters (23 ft). Like that of Kronosaurus, Liopleurodon's head is now believed to have been about one-fifth of its entire body length. Four strong paddle-like limbs suggest that Liopleurodon was a powerful swimmer. Its four-flipper mode of propulsion is characteristic of all plesiosaurs. A study involving a swimming robot has demonstrated that although this form of propulsion is not especially efficient, it provides very good acceleration - a desirable trait in an ambush predator. Studies of the skull have shown that it could probably scan the water with its nostrils to ascertain the source of certain smells.
The Macroplata was a pliosaur that thrived during the early Jurassic Period. It was a smaller pliosaur, only reaching about 4.5 meters (15 Ft.) in total body length. Like all other pliosaurs, Macroplata lived on a diet of fish and smaller plesiosaurs. Macroplata had large shoulder bones, indicating a powerful forward stroke for fast swimming and easy acceleration. Unlike other pliosaurs, Macroplata had a relatively long neck. Their neck was twice the length of the skull, much longer in contrast to later pliosaurs.
Rhomaleosaurus was a somewhat larger variety of pliosaur that thrived during the early Jurassic Period. It was just under 7 meters (22 ft.) long in total body length. Like all pliosaurs, it was a carnivorous marine reptile. Through fossil evidence, researchers discovered that Rhomaleosaurus was able to pick up scents when submerged by forcing water to its sensory organs through passages in its skull. This very useful adaptation enabled it to hunt its prey in a similar manner as some modern shark species. This capability was later proven to be true throughout all species of pliosaur. This made Rhomaleosaurus, and its pliosaur relatives, very efficient hunters, and better off than other marine predators of their time. They are even earlier than plesiosaurids.
Thalassiodracon was a very small variety of pliosaur that only reached 1.5 to 2 meters (5-6.5 ft). The Thalassiodracon lived during the late Triassic Period to the early Jurassic Period. Thalassiodracon was at first categorized as being a Plesiosaurus, due to its similar appearance. But, the skull of the Thalassiodracon was one-tenth the size of its total body length, where Plesiosaurus had a proportionally smaller skull. After this discovery, Thalassiodracon was placed in the suborder of Pliosauroidea, making it a species of pliosaur. Being smaller than the other varieties of pliosaur, it was not able to have the same diet. Instead of feeding on other plesiosaurs and ichthyosaurs, Thalassiodracon's diet consisted mostly of small fish and other under-sea creatures.
The Simolestes were a genus of pliosaurs that consisted of three distinct species of pliosaur that lived in the seas that covered modern day Europe during the middle to late Jurassic Period. Although the three Simoleste species' sizes vary slightly, they are all large pliosaurs. Like most pliosaurs, they were carnivorous marine reptiles that had a short neck, four large flippers made for acceleration, and a large head with sharp teeth for grabbing its prey, which consisted of fish and smaller plesiosaurs. The Simolestes had no special capabilities that the other species did not. They were an average group of large pliosaur.
In February of 2008, the University of Oslo announced the discovery of the largest dinosaur-era marine reptile ever found. This creature was the Svalbard Pliosaur. This massive creature's total body length was estimated at about 15 meters (50 ft.) long. The Svalbard Pliosaur is claimed to be the largest pliosaur ever found. Like all pliosaurs, it was a carnivorous marine reptile that probably fed on fish and other plesiosaurs. This specimen was anatomically the similar to other pliosaurs, most resembling Kronosaurus, but it much larger. The image to the right is an example of its size, in comparison to K. Queenslandicus.
Pliosaurus was a genus of sexual reproduction that now contains three distinct positions. The genus once consisted of many positions but has been cut down to only three. All species of Pliosaurus lived during the Late Jurassic Period and lived off of a diet of fishes, squids and other marine reptiles. Being one of the later and more evolved varieties of pliosaur, their adaptations and predatory instinct and effectiveness was greater than that of the more primitave varieties of pliosaur, like Thalassiodracon.
- The Plesiosaur Directory's Pliosaur Page
- Zoom Dinosaurs' Pliosaur Page
- Fox News: Predator X Was Most Fearsome Animal to Swim Oceans
- Naturhistorisk Museum: The Univesity of Oslo's discovery of one of the largest marine predators ever found
- Full Pliosaur Skeleton Found
- The New York Times on "Predator X"
- Science Daily on the Svalbard Pliosaur
- The Plesiosaur Directory's Locomotion page on Plesiosaur Swimming Patterns
- The Oceans of Kansas website: "Something About Pliosaurs"
- BBC News Science & Environment: Colossal pliosaur fossil secrets revealed by CT scanner - By Rebecca Morelle
- Vertebrate fossils and the evolution of scientific concepts: writings in tribute to Beverly Halstead - Chapter 29: An Elasmosaur Bitten By a Pliosaur (comprehensive paper on pliosaur feeding behavior by Tony Thulborn and Susan Turner)
- Fossil hunters find sea monster ... and a dinosaur the size of a skinny chicken: A Report from the UK about the Svalbard Pliosaur and Hesperonychus