Plesiosauria

Artistic live representation of Plesiosaurus

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The plesiosaur (Greek: plesio - " almost adjacent "; saurus - " lizard": Fast- lizards ) are a group of extinct marine reptiles that lived from the late Triassic to the end of the Cretaceous and became extinct at the same time with the dinosaurs.

They have an elongated body having an elongated neck and four paddle-shaped fins. They were like today's lizards and snakes to the Lepidosauromorpha and are divided into two distinct taxa, the long-necked and small-headed actual plesiosaurs ( Plesiosauroidea ) and the Pliosaur ( Pliosauroidea ), for a short, strong neck and a large head with a long snout characteristic.

Description

Plesiosaurs were 3 to 15 feet long, but there are also undescribed fossils, which suggest a maximum length of more than 20 meters ( "Monster of Aramberri "). All plesiosaurs had a short body in the form of a flattened stem and a relatively short tail, which could be provided to control with a tail fin. The neck of the real plesiosaur was greatly prolonged ( up to 72 vertebrae) and movable, the head was very small and the dentition homodont ( uniform). The Pliosaur In contrast, a short neck ( maximum of 13 vertebrae) and a very large head (up to 4 meters), their dentition was heterodont, that consisted of differently shaped teeth. The legs were converted to paddle-shaped fins.

As the ichthyosaurs and mosasaurs to have been able plesiosaurs to keep their body temperature at a constant high, the same level warm 35-39 ° C ( endothermic ).

Way of life

Locomotion

Previously it was assumed that plesiosaurs have rowed with their fins. Rowing is a method of locomotion that is because of the water resistance is used to push yourself virtually in the water forward. For the legs must on the one hand have increased area (which in plesiosaurs as is ), on the other hand, straight edges and corners are cheap because they generate eddies that increase the water resistance. A good example of a rowing extremity are duck feet, which are magnified by the webbed and also still have claws. The fins of the plesiosaurs, however, have a shape that resembles a wing, they run at the end pointed together and have a teardrop-shaped cross-section. In addition, plesiosaurs have greatly enlarged pectoral and pelvic bones to which large muscle have scheduled. This together strongly suggests that plesiosaurs have practiced the underwater flight. This movement is now used by the penguins, sea turtles, and otters and basically works like flying in the air. By the shape of the paddles different pressure conditions are created above and below the paddle, that are used for propulsion. The movement of the paddle in the water a lot of strength, so the big muscles.

Although some modern animals fly under water, they are limited with the plesiosaurs comparable, because they always use only the forelimbs. In contrast, the plesiosaurs front - like hind limbs are well developed and were probably both used. The precise coordination of the legs - so if all four were moved simultaneously, or alternately, then behind, or even left front at the same time with the right rear, and vice versa - is not known. Is also likely that the mode dependent on the speed.

Plesiosaurs and Pliosaur are slightly different in shape and relative size of the paddle, suggesting that they have moved in different ways. Initially it was assumed that Pliosaur were capable than wait predator to short, strong and quick accelerations, while the plesiosaur had rather moved with moderate speed, but were very persistent. More recent comparisons of plesiosaur flippers suspect leave with bird wings, that it was rather the reverse. However, the comparison of fins with wings in science is not entirely uncontroversial.

Nutrition

Plesiosaurs probably had a wide range of food. Common to all is that there were predators - the teeth of plesiosaurs do not indicate any plant food. Many plesiosaurs were probably fish -eaters, the larger Pliosaur other hand, have probably more versatile also hunted squid, ammonites, sharks, ichthyosaurs and plesiosaurs smaller. In the stomach of plesiosaurs squid remains were found, and leg bones of smaller plesiosaurs, there are bite marks that might belong to Pliosauriern. Plesiosaurs were also hunted himself, in a very large mosasaur from the Cretaceous of North America the remains of a Plesiosaur found.

The long neck of the plesiosaur has played determines a large role in food intake. The neck is not as flexible as it seems. Upward movements were only a very limited extent, also to the sides, the best was the mobility down. Plesiosaur could not bend to an "S" her neck, as it is often portrayed. The good mobility down could mean that plesiosaurs not only hunted, but also have picked up from the ocean floor food such as ammonites, clams, crabs and other small animals.

Many were plesiosaur with stomach stones found. Some birds have also stomach stones, which grind the food in the stomach. Birds do not have teeth and can not chew as well as mammals. A similar function is assumed by the stomach stones of the dinosaurs. In plesiosaurs - as in crocodiles, which also have stomach stones - it is not certain whether these were used for comminution of food or used as compensation for the buoyancy of the air-filled lung.

On the basis of 2008 to the Norwegian Arctic island of Spitsbergen by Jørn Hurum paleontologists discovered fossils of 15 meters long Plesiosaur Predator X ( "Monster of Spitsbergen " ) has a bite force of 147 kN was calculated. This is one of the highest pine forces in the animal kingdom.

Reproduction

The propagation of the plesiosaur was long known only insufficiently. Since they are reptiles, it was reasonable to assume that these animals laid eggs. But reptile eggs have to be laid on land, such as in turtles and plesiosaurs were so badly adapted to life in the sea, that it is unclear whether they ever came close to land or to have been at all capable. Beached whales die because their skeletons they no longer adequately supported without the buoyancy in the water, causing the lung is compressed and suffocating the animals. Because even with plesiosaurs the skeleton has adapted to the conditions in the water, it is conceivable that similar happened to them at a shore leave.

There are remains of ichthyosaurs and mosasaurs, their fetuses are received in the womb, which proves directly that these animals were also viviparous. The same is of Keichousaurus, Lariosaurus and Neusticosaurus, distant relative of the plesiosaur, and known since 2011, from a plesiosaur: The discovered in the abdomen of a 78 million years old fossil of Polycotylus latippinus skeleton of an immature young animal was having a length of 1.5 m already a third of the size of its 4.70 m long mother. Probably gave birth plesiosaur therefore only a single, relatively large young animal for which they operated parental care, much like today the whales. Very large species such as Kronosaurus, Elasmosaurus or Liopleurodon were certainly unable to come ashore to lay their eggs, which in turn the birth of live young conditional necessarily been due to their enormous mass.

Systematic Review

Plesiosaurs appear in the top Triassic. One of the first genera belong Thalassiodracon, Macro Plata and Microcleidus, the last two from the Rhaetian ( Thalassiodracon ) and Hettangian Britain. They belong to a group of swimming dinosaurs, the Sauropterygiern, known since the Lower Triassic.

Among the Sauropterygiern there are many different forms: some are very small, others larger and probably lived like crocodiles, still others had specialized in mussels as food. All these forms lived near the coast and were not as strongly adapted to life in the open ocean as plesiosaurs. Phylogenetic relationships of Sauropterygier to other reptiles are unclear, as is the exact ancestors of plesiosaurs within the Sauropterygier. As next of kin Pistosaurus and related forms are considered, which are known from the Upper Triassic of Europe and North America.

The plesiosaur itself be divided into two major groups:

The internal classification of plesiosaurs is shown below:

  • Plesiosauria Pliosauroidea Pliosauridae Archaeonectrus
  • Attenborosaurus
  • Brachauchenius
  • Hauffiosaurus
  • Kronosaurus
  • Liopleurodon
  • Marmornectes
  • Megalneusaurus
  • Pachycostasaurus
  • Peloneustes
  • Pliosaurus
  • Simolestes
  • Polyptychodon
  • Archaeonectrus
  • Borealonectes
  • Eurycleidus
  • Leptocleidus
  • Macro Plata
  • Maresaurus
  • Rhomaleosaurus
  • Sthenarosaurus
  • Umoonasaurus
  • Plesiosauridae? Attenborosaurus
  • ? Hydrorion
  • Plesiosaurus
  • ? Thalassiodracon
  • Elasmosauridae Albertonectes
  • " Alzadasaurus "
  • Callawayasaurus
  • Elasmosaurus
  • Eretmosaurus
  • Futabasaurus
  • Hydralmosaurus
  • Hydrotherosaurus
  • Libonectes
  • Microcleidus
  • Occitanosaurus
  • Styxosaurus
  • Terminonatator
  • Thalassomedon
  • Turangisaurus
  • " Woolungasaurus "
  • Cryptoclididae Aristonectes
  • Cryptoclidus
  • Kaiwhekea
  • Kimmerosaurus
  • Muraenosaurus
  • Pantasaurus
  • Tatenectes
  • Vinialesaurus
  • Tricleidus
  • Cimoliasauridae Kimmerosaurus
  • Cimoliasaurus
  • Dolichorhynchops
  • Edgarosaurus
  • Polycotylus
  • Thililua
  • Trinacromerum
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