Plateosaurus (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of Plateosauridae dinosaur that lived during the Late Triassic period, around 214 to 204 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal (early) sauropodomorpha dinosaur, a so-called prosauropoda. The type species is Plateosaurus trossingensis; before 2019, that honor was given to Plateosaurus engelhardti, but it was ruled as undiagnostic (i.e. indistinguishable from other dinosaurs) by the ICZN. Currently, there are three valid species; in addition to P. trossingensis, P. longiceps and P. gracilis are also known. However, others have been assigned in the past, and there is no broad consensus on the species taxonomy of plateosaurid dinosaurs. Similarly, there are a plethora of synonyms (invalid duplicate names) at the genus level.
Discovered in 1834 by Johann Friedrich Engelhardt and described three years later by Hermann von Meyer, Plateosaurus was the fifth named dinosaur genus that is still considered valid. Although it had been described before Richard Owen formally named Dinosauria in 1842, it was not one of the three genera used by Owen to define the group, because at the time, it was poorly known and difficult to identify as a dinosaur. It is now among the dinosaurs best known to science: over 100 skeletons have been found, some of them nearly complete. The abundance of its fossils in Swabia, Germany, has led to the nickname Schwäbischer Lindwurm (Swabian lindworm).
Plateosaurus was a bipedalism herbivore with a small skull on a long, flexible neck, sharp but plump plant-crushing teeth, powerful hind limbs, short but muscular arms and grasping hands with large claws on three fingers, possibly used for defence and feeding. Unusually for a dinosaur, Plateosaurus showed strong developmental plasticity: instead of having a fairly uniform adult size, fully grown individuals were between long and weighed between . Commonly, the animals lived for at least 12 to 20 years, but the maximum life span is not known.
Despite the great quantity and excellent quality of the fossil material, Plateosaurus was for a long time one of the most misunderstood dinosaurs. Some researchers proposed theories that were later shown to conflict with Geology and paleontology evidence, but have become the paradigm of public opinion. Since 1980 the taxonomy (relationships), taphonomy (how the animals became embedded and fossilised), biomechanics (how their skeletons worked), and palaeobiology (life circumstances) of Plateosaurus have been re-studied in detail, altering the interpretation of the animal's biology, posture and behaviour.
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.
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 taphonomy 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 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. Material referred to Plateosaurus has also been found in the Fleming Fjord Formation of East Greenland, but they were given the new genus name Issi in 2021.
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 syntype. 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 south of Heroldsberg.
The type specimen of Plateosaurus gracilis, an incomplete postcranium, is kept at the Staatliches Museum für Naturkunde Stuttgart, Germany, and the type locality is Heslach, a suburb of the same city.
The type specimen of Plateosaurus trossingensis is SMNS 132000, stored in the same museum as P. gracilis. Its type locality is Trossingen, within the Trossingen Formation.
The type specimen of Plateosaurus longiceps is MB R.1937, which is stored in the Museum für Naturkunde in Berlin. Its type locality is Halberstadt, located in Saxony-Anhalt and the Trossingen Formation.
Von Meyer's original short description from 1837 did not provide an etymology for Plateosaurus, but noted (as translated into English by British biologist Thomas Henry Huxley in 1870): "The bones belong to a gigantic Saurian, which, in virtue of the mass and hollowness of its limb-bones, is allied to Iguanodon and to Megalosaurus, and will belong to the second division of my Saurian system." Von Meyer later gave the formal name Pachypodes or Pachypoda ("thick feet") to his second division of "Saurians with Limbs Similar to Heavy Land Mammalia", but the group was a synonym of Richard Owen's Dinosauria from 1842.
In 1855, von Meyer published a detailed description of Plateosaurus with illustrations, but again gave no details on the etymology. He repeatedly referred to its gigantic size ("Riesensaurus" = giant lizard) and massive limbs ("schwerfüssig"), comparing Plateosaurus to large modern land mammals, but did not describe any important features that fit the terms "flat" or "shaped like an oar." Researcher Ben Creisler therefore concluded that "broad lizard" is the most suitable translation, and possibly was intended to emphasise the giant size of the animal, in particular its robust limb bones.
Von Meyer had authored a popular audience book in 1852 Ueber Die Reptilien und Säugethiere Der Verschiedenen Zeiten Der Erde On based to two public lectures. In the book on page 44, he briefly described Plateosaurus, using the term "breit" broad for different features, including "broad, strong limb bones," noting that it had: "mehreren verwachsenen Wirbeln bestehende Heiligenbein, breite, starke Gliedmaassenknochen von 1 1⁄2 Fuss Länge mit einer geräumigen Markhöhle, zierliche Krystalle von Nadeleisenerz einschliessend, so wie Zehenglieder, welche ebenfalls breit und hohl waren...; es wäre diess der älteste bis jetzt aufgefundene Pachypode." a yet found.]
Yates has cautioned that P. gracilis may be a metataxon, which means that there is neither evidence that the material assigned to it is monophyletic (belongs to one species), nor that it is Paraphyly (belongs to several species). This is the case because the holotype of P. (Sellosaurus) gracilis has no skull, and the other specimens consist of skulls and material that overlaps too little with the holotype to make it certain that it belongs to the same taxon. It is therefore possible that the known material contains more species belonging to Plateosaurus.
Some scientists regard other species as valid as well, for example P. erlenbergensis and P. engelhardti. These claims are problematic since both P. erlenbergensis and P. engelhardti have undiagnostic type specimens.
All named species of Plateosaurus except the type species, P. gracilis, or P. longiceps have turned out to be junior synonyms of the type species or invalid names. Von Huene practically erected a new species and sometimes a new genus for each relatively complete find from Trossingen (three species of Pachysaurus and seven of Plateosaurus) and Halberstadt (one species of Gresslyosaurus and eight of Plateosaurus). Later, he merged several of these species, but remained convinced that more than one genus and more than one species of Plateosaurus was present in both localities. Jaekel also believed that the Halberstadt material included several plateosaurid dinosaurs, as well as non-plateosaurid prosauropods. Systematic research by Galton drastically reduced the number of genera and species. Galton synonymised all cranial material, and described differences between the of P. engelhardti and the Trossingen material, which he referred to P. longiceps. Galton recognised P. trossingensis ( P. fraasianus and P. integer are junior objective synonyms) to be identical to P. longiceps. Markus Moser, however, showed that P. longiceps is itself a junior synonym of P. engelhardti. Furthermore, a variety of species in other genera were created for material belonging to P. engelhardti, including Dimodosaurus poligniensis, Gresslyosaurus robustus, Gresslyosaurus torgeri, Pachysaurus ajax, Pachysaurus giganteus, Pachysaurus magnus and Pachysaurus wetzelianus. G. ingens has been considered separate from Plateosaurus, pending a revision of the material.
The skull of AMNH FARB 6810, the best-preserved skull of Plateosaurus that has been taken apart during preparation and is thus available as separate bones, was described anew in 2011. The authors of that publication, palaeontologists Albert Prieto-Márquez and Mark A. Norell, refer the skull to P. erlenbergensis, a species erected in 1905 by Friedrich von Huene and regarded as a synonym of P. engelhardti by Markus Moser. If the P. erlenbergensis holotype is diagnostic (i.e., has enough characters to be distinct from other material), it is the correct name for the material assigned to P. longiceps Jaekel, 1913.
Aside from fossils clearly belonging to Plateosaurus, there is much prosauropod material from the German Knollenmergel in museum collections, most of it labeled as Plateosaurus, that does not belong to the type species and possibly not to Plateosaurus at all. Some of this material is not diagnostic; other material has been recognised to be different, but was never sufficiently described.
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 mandible (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 (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 Bird lung-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 .
The type species of Plateosaurus is P. trossingensis. Adults of this species reached in length, and ranged in mass from . The geologically older species, P. gracilis (formerly named Sellosaurus gracilis), was somewhat smaller, with a total length of .
Basal sauropodomorph phylogenetics simplified after Yates, 2007. This is only one of many proposed for basal sauropodomorphs. Some researchers do not agree that plateosaurs were the direct ancestors of sauropods.
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 Peter 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 Matthew 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. A recent study based on the cross-sectional geometry of long limb bones, comparisons with extant taxa and inference models also confirmed a bipedal posture and erect stance for Plateosaurus.
Plateosaurus shows a number of cursorial adaptations, including an erect hind limb posture, a relatively long lower leg, an elongated Metatarsal bones and a digitigrade foot posture. However, in contrast to cursors, the Torque of the limb extending muscles are short, especially in the ankle, where a distinct, moment arm-increasing tuber on the calcaneus 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.
So far, no fossil of Plateosaurus has been found with (gizzard stones) in the stomach area. The old, widely cited idea that all large dinosaurs, implicitly also Plateosaurus, swallowed gastroliths to digest food because of their relatively limited ability to deal with food orally has been refuted by a study on gastrolith abundance, weight, and surface structure in fossils compared to alligators and ostriches by Oliver Wings. The use of gastroliths for digestion seems to have developed on the line from basal theropods to birds, with a parallel development in Psittacosaurus.
Plateosaurus followed a trajectory similar to sauropods, but with a varied growth rate and final size as seen in extant reptiles, probably in response to environmental factors such as food availability. Some individuals were fully grown at only 4.8 metres' (16 ft) total length, while others reached . However, the bone microstructure indicates rapid growth, as in sauropods and extant mammals, which suggests warm-blooded. Plateosaurus apparently represents an early stage in the development of endothermy, in which endothermy was decoupled from developmental plasticity. This hypothesis is based on a detailed study of Plateosaurus long-bone histology conducted by Martin Sander and Nicole Klein of the University of Bonn. A further indication for endothermy is the avian-style lung of Plateosaurus.
Long-bone histology also allows estimating the age a specific individual reached. Sander and Klein found that some individuals were fully grown at 12 years of age, others were still slowly growing at 20 years, and one individual was still growing rapidly at 18 years. The oldest individual found was 27 years and still growing; most individuals were between 12 and 20 years old. However, some may well have lived much longer, because the fossils from Frick and Trossingen are all animals that died in accidents, and not from old age. Due to the absence of individuals smaller than long, it is not possible to deduce a complete ontogeny series for Plateosaurus or determine the growth rate of animals less than 10 years of age.
Comparisons between the sclerotic ring and estimated orbit size of Plateosaurus and modern birds and reptiles suggest that it may have been Cathemerality, active throughout the day and night, possibly avoiding the midday heat.
A different school of thought developed almost half a century later, with palaeontologist David Weishampel suggesting that the skeletons from the lower layers stemmed from a herd that died catastrophically in a mudflow, while those in the upper layers accumulated over time. Weishampel explained the curious monospecific assemblage by theorising that Plateosaurus were common during this period. This theory was erroneously attributed to Seemann in a popular account of the plateosaurs in the collection of the Institute and Museum for Geology and Palaeontology, University of Tübingen, and has since become the standard explanation on most internet sites and in popular books on dinosaurs. Rieber proposed a more elaborate scenario, which included the animals dying of thirst or starvation, and being concentrated by mudflows.
Pathologies affecting the chevrons of specimen SMNS 13200 have been hypothesized to be the result of capture myopathy, induced by a mud-miring trap.
Etymology
Valid species
Description
Classification
Palaeobiology
Posture and gait
Feeding and diet
Life history and metabolism
Palaeoecology
Taphonomy
Earlier interpretations
Mud-miring trap
Notes
External links
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