Plateosaurus
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[Photo] The Triassic prosauropod Plateosaurus. Sketch by Tim Bekaert, 2006 based on mounted skeleton.

Plateosaurus (meaning 'flat lizard' - Greek πλατυ??/platys "broad" or "flat" from πλατη/plat?? meaning "flat surface" and σαυρο?? meaning "lizard") is a genus of plateosaurid prosauropod dinosaur that lived during the Norian and Rhaetian stages of the Late Triassic period, around 216 to 199 million years ago in what is now Europe. There are two actually recognized species, P. engelhardti and P. longiceps, although others have been assigned in the past.

Plateosaurus is the best known of the prosauropods. Dozens of well-preserved skeletons have been unearthed in Triassic sandstones all over western Europe. In some locations, groups of complete individual fossils have been found. Herds travelled together through the Triassic desert landscape of Europe, searching for new feeding grounds. An alternative explanation for the groups of fossils, however, is that solitary individuals inhabited dry, upland areas. When they died, their bodies would have been washed away in periodic flash floods that are typical of desert environments even today. Many individual corpses could have piled up at the end of well-worn flood channels formed at the edge of desert basins.

Plateosaurus were bulky bipedal herbivores that dominated the European arid landscape along with another sauropodomorph dinosaur, Sellosaurus; the earliest known turtle, Proganochelys; and the tiny archosaur Procompsognathus. It had a small skull on a long neck, sharp plant-crushing teeth, powerful limbs, and a large thumb spike on each 'hand' probably used for defence and feeding.

Description
The skull of Plateosaurus was deeper than that of Coelophysis - i.e. a stronger, deeper head than most prosauropods, although still small and narrow compared to the size of its body. It had four sets of fenestrae (skull openings); these openings were for the naris and orbit as well as an infratemporal fenestra at the back of the skull and an antorbital fenestra between the eye and nose. It had a long snout and many small, leaf-shaped, socketed teeth and the low-slung hinge of of its lower jaw (to give the muscles greater leverage), suggest that it fed exclusively on plants. Its eyes were directed to the sides, rather than the front, providing all-round vision to watch for predators. Some fossil skeletons have preserved sclerotic rings.

Plateosaurus had numerous small teeth in both the upper and lower jaw. These teeth had serrated, leaf-shaped crowns suitable for digestion of plant material. It is thought Plateosaurus had narrow cheek pouches which kept food from spilling out when it ate.

Plateosaurus was the largest known dinosaur of its time, reaching 6 to 10 m in length and up to an estimated 700 kg in mass. A member of the group of early herbivores known as prosauropods, it was more powerfully built than that of similar animals such as Anchisaurus. Plateosaurus had a long neck, composed of around nine cervical vertebrae, a stocky body and a pear-shaped torso. It had a long tail composed of at least forty caudal vertebrae which served to counterbalance the front-heavy body and long neck.

Classification
Plateosaurus is the type genus of the family Plateosauridae, to which gives its name. It was proposed by Othniel Charles Marsh in 1895 within Theropoda. But later was assigned to Prosauropoda by Huene, and was accepted by most authors. For many years the clade only included Plateosaurus, but recently two more genus, Sellosaurus and Unaysaurus have been recognized.

Discovery and species
Plateosaurus is one of the most common dinosaur fossils found in Europe and has been found in over 50 locations on that continent and is also known as the "World's deepest dinosaur" found in a drillcore in the North Sea 2256 meters below the seafloor.

The first species, P. engelhardti, was described by the German palaeontologist Hermann von Meyer, from some vertebrae and leg bones discovered at Heroldsberg near Nuremberg, in Germany, in 1837. P. longiceps was described by Jaekel in 1914, and is the species to which the vast majority of fossil material belongs. P. engelhardti is known only from Bavaria, Germany, while P. longiceps is known from other areas of southern Germany, France, Switzerland, and Greenland.

P. longiceps had a longer snout and less massive hindlimbs than P. engelhardti.

A third species, P. gracilis lacks certain features of the genus Plateosaurus and has been placed in its own genus Sellosaurus.

In August 2007, an amateur paleontologist discovered wide bonebeds of dinosaurs, most of which were Plateosaurus individuals. The 'grave' was discovered near Frick, Switzerland and there is an estimated one dinosaur per 100 square meters.

Paleobiology
The natural environment of Plateosaurus was desert-like land in Europe.

Posture and gait
Like all prosauropods, Plateosaurus had forelimbs which were much shorter than the hind limbs and they had distinct digits ('fingers') and a spiked 'thumb'. A 2007 anatomical study of the forelimbs demonstrated that their range of motion precluded effective habitual quadrupedal gait. Like theropods, Plateosaurus and other related prosauropods could not rotate the hand so that their palms faced downward, and so would have been unable to use the front limbs for standing or walking. The study also ruled out the possibility of "knuckle-walking" and other forms of locomotion that would avoid the issue of the limited ability of Plateosaurus to pronate its hands. Thus, although its mass suggests a quadrupedal nature, it would have been restricted to its hind legs for locomotion. The forelimbs may have been used to rake trees for food, for grasping or for defence.

The hand bones of Plateosaurus were large, and bore five digits. The last two digits on each hand were very small.

Metabolism
A recent analysis of fossil deposits reveals there was considerable variation in size in individuals. Furthermore, growth rings in bone suggests periods of varying growth which may relate to the surrounding environment. The paper's authors propose that the metabolism of Plateosaurus may have been an intermediate between a reptilian and a warm-blooded one.

Popular culture
Plateosaurus was featured briefly in the opening sequence of The Land Before Time II: The Great Valley Adventure.

Plateosaurus featured briefly in the first episode ("New Blood") of the BBC television series Walking with Dinosaurs, to illustrate the success of dinosaurs.

Mounted Plateosaurus skeletons can be seen in the Institute and Museum for Geology and Paleontology, University of T??bingen, and the Humboldt Museum in Berlin, and the State Museum for Natural History in Stuttgart.

Plateosaurus is an adoptable animal in Zoo Tycoon: Dinosaur Digs.

http://en.wikipedia.org/wiki/Plateosaurus

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