Period: Late Triassic
Order, Suborder, Family: Saurischia, Sauropodomorpha, Plateosauridae
Location: Europe (West Germany, East Germany, France, Switzerland, England)
Length: 23 feet (7 meters)
Plateosaurus is the best known of the early dinosaurs. It was among the largest of the Triassic dinosaurs, reaching an adult height of 15 feet when it stood on its back legs. An adult probably weighed close to a ton. It was the first Triassic dinosaur described. H. von Meyer named it in 1837; its name means "flat reptile."
Plateosaurus is the best-studied prosauropod dinosaur. The similarities between prosauropods and sauropods, their closest dinosaur relatives, are many. Both had massive trunks, long necks and tails, and small heads that were adapted to eating plants. However, adult prosauropods tended to be smaller. The smallest adult sauropods and the biggest prosauropods, such as Melanorosaurus, were about the same size.
One distinctive feature of Plateosaurus and of all prosauropods is their hands. They had small fingers and a huge thumb that had a large claw. This claw may have been used for plucking leaves from high branches, for digging roots, or for fighting. The front limbs were shorter than the back ones, but it walked on all four limbs.
The back legs of Plateosaurus were long and thick. Its legs were not made to run fast like Coelophysis. The feet of Plateosaurus had five toes, although the fifth (outer) toe was very small. The pelvis was short and massive, and the dinosaur had large, powerful leg muscles.
The prosauropods were unique among Triassic dinosaurs because they had long necks. This allowed them to reach leaves and branches high off the ground. Plateosaurus could reach even higher when it reared up on its back limbs, which it could have done while standing and maybe while walking.
The head of Plateosaurus was small. It was longer and flatter than the heads of the later sauropods. Its lower jaw curved down, as did the front of its snout; this made the animal look like it was smiling. It had simple, leaf-shaped teeth. They did not change shape from the front to the back of the jaw. Teeth in the upper jaw fitted between pairs of teeth in the lower jaw. This allowed it to chop the leaves as it ate. The jaws, muscles, and teeth of prosauropods were suited to a plant diet. Plateosaurus probably had fleshy cheeks. Dinosaurs may have stored food in these cheeks, and they kept food from falling out as the animal ate. To help its digestion, Plateosaurus may have had "gastroliths." These were stones in the stomach (swallowed by the dinosaur) that rubbed against one another and the food, slicing and grinding the leaves and plants.
Plateosaurus fed on high vegetation, such as the leaves of tree ferns. Prosauropods probably browsed in high tree branches much like sauropods did later in the Mesozoic and giraffes do today. A. W. Crompton and John Attridge noted that prosauropods were unique among Triassic herbivores because they had lightly built skulls, which suggests that they probably ate soft plants. To chew tougher branches and leaves, an animal's skull and jaw must be heavily built.
Dinosaurs did not become common until near the end of the Triassic. In Late Triassic European quarries, Plateosaurus is the most common vertebrate fossil. Michael Benton estimated that 75 percent of the skeletons from this age in West Germany belong to Plateosaurus.
In Halberstadt and Trossingen, West Germany, workers found mass graves of Plateosaurus and have removed dozens of skeletons from each. Trossingen contains one layer that has a herd of plateosaurs killed by a catastrophic event, possibly a flood. David Weishampel suggested that the reason Plateosaurus is so common in other layers of the quarry is because it was the most abundant animal at the time.
The sudden appearance and rise to dominance of Plateosaurus in the northern hemisphere, and other prosauropods elsewhere, is one of the most sudden and dramatic dinosaur success stories. Their great numbers could be because they were able to feed on high vegetation-this allowed them to find food that smaller herbivores could not reach.