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Plateosaurus
Temporal range: Late Triassic
An artist's illustration of Plateosaurus engelhardti
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Superorder: Dinosauria
Order: Saurischia
Suborder: Sauropodomorpha
Family: Plateosauridae
Genus: Plateosaurus
Type species
Plateosaurus engelhardti
von Meyer, 1837
Referred species
  • Plateosaurus engelhardti
    (von Meyer, 1837)
  • Plateosaurus gracilis
    (von Huene, 1907–08) (originally Sellosaurus)
Synonyms
  • Dimodosaurus Pidancet & Chopard, 1862
  • Gresslyosaurus Rütimeyer, 1856
  • Pachysaurops von Huene, 1961
  • Pachysaurus von Huene, 1907–1908
  • Pachysauriscus Kuhn, 1959
  • Sellosaurus von Huene, 1907–1908

Plateosaurus was a large prosauropod dating back to late Triassic Europe. One of the bigger members of the prosauropod group, this dinosaur measured roughly twenty-eight feet in length, it was also the biggest dinosaur from the Triassic period. It shared it's environment with non-dinosaurian reptiles like pyhytosaurs, giant amphibian stegocephalians, first pterosaurs and primative theropod such as Liliensternus and Halticosaurus among others.

Plateosaurus was one of the last prosauropod dinosaurs that walked on its hind legs alone. Like other prosauropods it fed on plants, though it might've eaten small invertebrates as well.

It was falsely depicted as living in North America alongside Coelophysis, appearing right at the end and scaring away a flock the Triassic theropods, in the BBC special "Walking with Dinosaurs", not an impractical theory due to the connection of the continents at the time, but still incorrect. To make this correct, it would've instead been truly depicted as living in Europe alongside its natural enemy Liliensternus, with this being both dinos' own segment had Liliensternus not appeared exclusively in Walking With Dinosaurs - The Arena Spectacular.

Discovery and history

In 1834, physician Johann Friedrich Engelhardt discovered some vertebrae and leg bones at Heroldsberg near Nuremberg, Germany. Three years later German palaeontologist Hermann von Meyer designated them as the type specimen of a new genus, Plateosaurus. Since then, remains of well over 100 individuals of Plateosaurus have been discovered at various locations throughout Europe.

Material assigned to Plateosaurus has been found at over 50 localities in Germany (mainly along the Neckar and Pegnitz river valleys), Switzerland (Frick) and France. Three localities are of special importance, because they yielded specimens in large numbers and of unusually good quality: near Halberstadt in Saxony-Anhalt, Germany; Trossingen in Baden-Württemberg, Germany; and Frick. Between the 1910s and 1930s, excavations in a clay pit in Saxony-Anhalt revealed between 39 and 50 skeletons that belonged to Plateosaurus, along with teeth and a small number of bones of the theropod Liliensternus, and two skeletons and some fragments of the turtle Proganochelys. Some of the plateosaur material was assigned to P. longiceps, a species described by palaeontologist Otto Jaekel in 1914. Most of the material found its way to the Museum für Naturkunde in Berlin, where much of it was destroyed during World War II. The Halberstadt quarry today is covered by a housing development. P. engelhardti, collection number F 33 of the Staatliches Museum für Naturkunde Stuttgart, Germany, in dorsal view. The skeleton was kept in articulation as found at Trossingen by Seemann in 1933. It has the typical folded hind limbs of most Plateosaurus finds. Unusually, the anterior body is not twisted to one side.

The second major German locality with Plateosaurus finds, a quarry in Trossingen in the Black Forest, was worked repeatedly in the 20th century. Between 1911 and 1932, excavations during six field seasons led by German palaeontologists Eberhard Fraas (1911–1912), Friedrich von Huene (1921–23), and finally Reinhold Seemann (1932) revealed a total of 35 complete or partially complete skeletons of Plateosaurus, as well as fragmentary remains of approximately 70 more individuals. The large number of specimens from Swabia had already caused German palaeontologist Friedrich August von Quenstedt to nickname the animal Schwäbischer Lindwurm (Swabian lindworm or Swabian dragon). Much of the Trossingen material was destroyed in 1944, when the Naturaliensammlung in Stuttgart (predecessor to the State Museum of Natural History Stuttgart (SMNS)) burnt to the ground after an Allied bombing raid. Luckily, however, a 2011 study by SMNS curator Rainer Schoch found that, at least from the finds of Seemann's 1932 excavation, "the scientifically most valuable material is still available".

The Plateosaurus skeletons in a clay pit of the Tonwerke Keller AG in Frick, Switzerland, were first noticed in 1976. While the bones are often significantly deformed by taphonomic processes, Frick yields skeletons of P. trossingensis comparable in completeness and position to those of Trossingen.

In 1997, workers of an oil platform of the Snorre oil field, located at the northern end of the North Sea within the Lunde Formation, were drilling through sandstone for oil exploration when they stumbled on a fossil they believed to be plant material. The drill core containing the fossil was extracted from 2,256 m (7,402 ft) below the seafloor. Martin Sander and Nicole Klein, palaeontologists of the University of Bonn, analysed the bone microstructure and concluded that the rock preserved fibrous bone tissue from a fragment of a limb bone belonging to Plateosaurus, making it the first dinosaur found in Norway. Plateosaurus material has also been found in the Fleming Fjord Formation of East Greenland.

The type series of Plateosaurus engelhardti included "roughly 45 bone fragments", of which nearly half are lost. The remaining material is kept in the Institute for Palaeontology of the University of Erlangen-Nuremberg, Germany. From these bones, German palaeontologist Markus Moser in 2003 selected a partial sacrum (series of fused hip vertebrae) as a lectotype. The type locality is not known for certain, but Moser attempted to infer it from previous publications and the colour and preservation of the bones. He concluded that the material probably stems from the "Buchenbühl", roughly two kilometres (1.2 mi) south of Heroldsberg.


Description

Plateosaurus had the typical body shape of a herbivorous bipedal dinosaur: a small skull, a long and flexible neck composed of 10 cervical vertebrae, a stocky body, and a long, mobile tail composed of at least 40 caudal vertebrae. The arms of Plateosaurus were very short, even compared to most other "prosauropods". However, they were strongly built, with hands adapted for powerful grasping. The shoulder girdle was narrow (often misaligned in skeletal mounts and drawings), with the clavicles (collar bones) touching at the body's midline, as in other basal sauropodomorphs. The hind limbs were held under the body, with slightly flexed knees and ankles, and the foot was digitigrade, meaning the animal walked on its toes. The proportionally long lower leg and metatarsus show that Plateosaurus could run quickly on its hind limbs. The tail of Plateosaurus was typically dinosaurian, muscular and with high mobility.

The skull of Plateosaurus is small and narrow, rectangular in side view, and nearly three times as long as it is high. There is an almost rectangular lateral temporal foramen at the back. The large, round orbit (eye socket), the sub-triangular antorbital fenestra and the oval naris (nostril) are of almost equal size. The jaws carried many small, leaf-shaped, socketed teeth: 5 to 6 per premaxilla, 24 to 30 per maxilla, and 21 to 28 per dentary (lower jaw). The thick, leaf-shaped, bluntly serrated tooth crowns were suitable for crushing plant material. The low position of the jaw joint gave the chewing muscles great leverage, so that Plateosaurus could deliver a powerful bite. These features suggest that it fed primarily to 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 (rings of bone plates that protect the eye).

The ribs were connected to the dorsal (trunk) vertebrae with two joints, acting together as a simple hinge joint, which has allowed researchers to reconstruct the inhaled and exhaled positions of the ribcage. The difference in volume between these two positions defines the air exchange volume (the amount of air moved with each breath), determined to be approximately 20 L for a P. engelhardti individual estimated to have weighed 690 kg, or 29 mL/kg bodyweight. This is a typical value for birds, but not for mammals, and indicates that Plateosaurus probably had an avian-style flow-through lung, although indicators for postcranial pneumaticity (air sacs of the lung invading the bones to reduce weight) can be found on the bones of only a few individuals, and were only recognised in 2010. Combined with evidence from bone histology this indicates that Plateosaurus was endothermic.

The type species of Plateosaurus is P. trossingensis. Adults of this species reached 4.8 to 10 metres (16 to 33 ft) in length, and ranged in mass from 600 to 4,000 kilograms (1,300 to 8,800 lb). The geologically older species, P. gracilis (formerly named Sellosaurus gracilis), was somewhat smaller, with a total length of 4 to 5 metres (13 to 16 ft).

Classification

Plateosaurus is a member of a group of early herbivores known as "prosauropods". The group is not a monophyletic group (thus given in quotation marks), and most researchers prefer the term basal sauropodomorph. Plateosaurus was the first "prosauropod" to be described, and gives its name to the family Plateosauridae Marsh, 1895 as the type genus. Initially, when the genus was poorly known, it was only included in Sauria, being some kind of reptile, but not in any more narrowly defined taxon. In 1845, von Meyer created the group Pachypodes (a defunct junior synonym of Dinosauria) to include Plateosaurus, Iguanodon, Megalosaurus and Hylaeosaurus. Plateosauridae was proposed by Othniel Charles Marsh in 1895 within Theropoda. Later it was moved to "Prosauropoda" by von Huene, a placement that was accepted by most authors. Before the advent of cladistics in paleontology during the 1980s, with its emphasis on monophyletic groups (clades), Plateosauridae was defined loosely, as large, broad-footed, broad-handed forms with relatively heavy skulls, unlike the smaller "anchisaurids" and sauropod-like "melanorosaurids". Reevaluation of "prosauropods" in light of the new methods of analysis led to the reduction of Plateosauridae. For many years the clade only included Plateosaurus and various junior synonyms, but later two more genera were considered to belong to it: Sellosaurus and possibly Unaysaurus. Of these, Sellosaurus is probably another junior synonym of Plateosaurus.

Basal sauropodomorph phylogeny simplified after Yates, 2007. This is only one of many proposed cladograms for basal sauropodomorphs. Some researchers do not agree that plateosaurs were the direct ancestors of sauropods.

Paleobiology

Practically every imaginable posture has been suggested for Plateosaurus in the scientific literature at some point. Von Huene assumed digitigrade bipedality with erect hind limbs for the animals he excavated at Trossingen, with the backbone held at a steep angle (at least during rapid locomotion). In contrast, Jaekel, the main investigator of the Halberstadt material, initially concluded that the animals walked quadrupedally, like lizards, with a sprawling limb position, plantigrade feet, and laterally undulating the body. Only a year later, Jaekel instead favoured a clumsy, kangaroo-like hopping, a change of heart for which he was mocked by German zoologist Gustav Tornier, who interpreted the shape of the articulation surfaces in the hip and shoulder as typically reptilian. Fraas, the first excavator of the Trossingen lagerstätte, also favoured a reptilian posture. Müller-Stoll listed a number of characters required for an erect limb posture that Plateosaurus supposedly lacked, concluding that the lizard-like reconstructions were correct. However, most of these adaptations are actually present in Plateosaurus.

From 1980 on, a better understanding of dinosaur biomechanics, and studies by palaeontologists Andreas Christian and Holger Preuschoft on the resistance to bending of the back of Plateosaurus, led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back. Many researchers were of the opinion that Plateosaurus could use both quadrupedal gaits (for slow speeds) and bipedal gaits (for rapid locomotion), and Wellnhofer insisted that the tail curved strongly downward, making a bipedal posture impossible. However, Moser showed that the tail was in fact straight.

The bipedal-quadrupedal consensus was changed by a detailed study of the forelimbs of Plateosaurus by Bonnan and Senter (2007), which clearly showed that Plateosaurus was incapable of pronating its hands. The pronated position in some museum mounts had been achieved by exchanging the position of radius and ulna in the elbow. The lack of forelimb pronation meant that Plateosaurus was an obligate (i.e. unable to walk in any other way) biped. Further indicators for a purely bipedal mode of locomotion are the great difference in limb length (the hind limb is roughly twice as long as the forelimb), the very limited motion range of the forelimb, and the fact that the centre of mass rests squarely over the hind limbs.

Plateosaurus shows a number of cursorial adaptations, including an erect hind limb posture, a relatively long lower leg, an elongated metatarsus and a digitigrade foot posture. However, in contrast to mammalian cursors, the moment arms of the limb extending muscles are short, especially in the ankle, where a distinct, moment arm-increasing tuber on the calcaneum is missing. This means that in contrast to running mammals, Plateosaurus probably did not use gaits with aerial, unsupported phases. Instead, Plateosaurus must have increased speed by using higher stride frequencies, created by rapid and powerful limb retraction. Reliance on limb retraction instead of extension is typical for non-avian dinosaurs.

Paleoecology

Plateosaurus gracilis, the older species, is found in the Löwenstein Formation (Lower Norian). P. trossingensis stems from the upper Löwenstein Formation (Upper Norian), and P. longiceps the Trossingen Formation (Rhaetian), and equivalently aged rock units. Plateosaurus thus lived probably from approximately 214 to 204 million years ago.

Popular Culture

  • Plateosaurus was featured at the end of the first episode of BBC’s Walking with Dinosaurs.
  • It also appeared in Fantasia.
  • Josef Augusta wrote about Plateosaurus in his book "The Vanished World".
  • Plateosaurus also appears in the opening scene in The Land Before Time II: The Great Valley Adventure where it browses from a tree.
  • Plateosaurus made an appearance in the ROBLOX game called Dinosaur Simulator.
  • Plateosaurus is set to be in the newest indie management simulation game Prehistoric Kingdom.

Gallery

  • See Plateosaurus/Gallery
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