Plateosaurus

*Plateosaurus engelhardti*

* Jurassic Park Institute Artwork
* Robert F Walters Artwork

***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 animals occassionally.

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.

## JPInstitute.com Description

Plateosaurus is the earliest known member of the huge plant-eating, sauropod (long-neck) dinosaur family. These include all the great long-necked dinosaurs like Brachiosaurus, Diplodocus, and Mamenchisaurus. Compared to these huge monsters, Plateosaurus was small, but it was a giant compared to the other early dinosaurs.

Unlike its later relatives, Plateosaurus probably spent some time on its hind legs. These back legs were quite a bit stronger and larger than its front legs, which would have enabled it to rear up to get food or to defend itself. It had a large, sharp claw on each hand that would have made a formidable weapon. Plateosaurus also shows the characteristics that became so pronounced in later sauropods - a long neck, long tail for balancing, and great size. Its teeth were all the same size and shape - small and pointy. Bone ridges around its mouth indicate that it likely had cheek pouches that would have enabled it to keep gathering food into its mouth while it chewed.

Like Coelophysis, a great many Plateosaurus skeletons were discovered in one location, possibly the result of some local catastrophic event such as a flash flood. This has given scientists a good picture of the individual variations of this dinosaur.

Recently, some scientists are classifying the prosauropods, including Plateosaurus, as a separate group of creatures and not simply as the ancestors of the later Jurassic sauropods.

## Dinosaur Field Guide Description

Plateosaurus ("'flat lizard") is an early dinosaur from the Triassic Period. It was the first dinosaur that was much larger than a human, and the first with a long sauropod-like neck. Plateosaurus was heavily built, and its long muzzle was filled with teeth designed for chopping. The feet were clawed, and the hands had some grasping ability. The hand claw was relatively small compared to that of Massospondylus. Many outdated skeletons show Plateosaurus walking on two feet. But that is unlikely because Plateosaurus was big and front heavy and likely walked on all four feet. Plateosaurus has been studied many times, mainly by the German paleontologist Friedrich von Huene in the early 1900s and by Peter Galton in the late 1900s. Galton challenged the theory that Plateosaurus was an omnivore, or plant- and meat-eater. He showed that its teeth and jaw action were more like that of a true plant-eater, where the lower jaws meet the upper jaws like a nutcracker, with all the teeth coming together at the same time. In an omniore, the jaws come together more like scissors, with the teeth meeting first at the back of the jaw, then finally at the front of the jaw.

### Fun Facts

Over a hundred Plateosaurus skeletons have been found.

### Trivia

Plateosaurus was named in 1837, before the word "dinosaur" was coined!

## Links

http://web.archive.org/web/20040221045503fw\_/http://www.jpinstitute.com/dinopedia/dinocards/dc\_plate.html#
https://web.archive.org/web/20080706162458/http://kids.yahoo.com/dinosaurs/36--Plateosaurus

## References

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