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Plateosaurus
Temporal range: Late Triassic (Norian), 227–204 Ma
Mounted skeleton of P. trossingensis (GPIT "Skelett 2"), consisting of two individual specimens from the Trossingen Formation, museum of the Institute for Geosciences (GPIT) of the Eberhard-Karls-University Tübingen, Germany
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: †Sauropodomorpha
Family: †Plateosauridae
Genus: †Plateosaurus
von Meyer, 1837
Type species
†Plateosaurus trossingensis
Fraas, 1913
Other species
  • †P. gracilis (von Huene, 1907–08 [originally Sellosaurus])
  • †P. longiceps Jaekel, 1913-14
  • †P. engelhardti von Meyer, 1837 (nomen dubium)
Synonyms
  • Dimodosaurus Pidancet & Chopard, 1862
  • Sellosaurus von Huene, 1907–1908

Plateosaurus (probably meaning "broad lizard", often mistranslated as "flat lizard") is a genus of plateosaurid 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) sauropodomorph dinosaur, a so-called "prosauropod". 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 bipedal 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 4.8 and 10 metres (16 and 33 ft) long and weighed between 600 and 4,000 kilograms (1,300 and 8,800 lb). 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 geological and palaeontological 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.

Discovery and history

[edit]
Map of important Plateosaurus localities. Red = likely type locality Heroldsberg, black = important sites with many and well-preserved specimens. Other localities in blue.[A]

In 1834, physician Johann Friedrich Engelhardt discovered some vertebrae and leg bones at Heroldsberg near Nuremberg, Germany.[2] Three years later German palaeontologist Hermann von Meyer designated them as the type specimen of a new genus, Plateosaurus.[2] Since then, remains of well over 100 individuals of Plateosaurus have been discovered at various locations throughout Europe.[3]

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.[4] 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.[3] 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.[3] Some of the plateosaur material was assigned to P. longiceps, a species described by palaeontologist Otto Jaekel in 1914.[5] Most of the material found its way to the Museum für Naturkunde in Berlin, where much of it was destroyed during World War II.[4] The Halberstadt quarry today is covered by a housing development.[4]

Photograph of an articulated skeleton missing the head and tail, seen from above. The animal has the limbs strongly folded in a squatting posture, the arms are spread out with the palms facing up and inward. The body and neck curve to the right, with the body making a 40° curve and the neck a 110° curve. The trunk is compressed, which can be seen from the shoulder blades sticking straight up and the ribs being folded backwards. All sediment that is not necessary to keep the bones of the body and neck connected has been removed.
P. trossingensis, 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.[3]

The second major German locality with Plateosaurus finds, a quarry in Trossingen in the Black Forest, was worked repeatedly in the 20th century.[4] Between 1911 and 1932, excavations during six field seasons led by German palaeontologists Eberhard Fraas (1911–1912), Friedrich von Huene (1921–23),[6][7] 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.[4] 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).[B] 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".[C]

The Plateosaurus skeletons in a clay pit of the Tonwerke Keller AG in Frick, Switzerland, were first noticed in 1976.[3] 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.[3]

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.[10] 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,[10] making it the first dinosaur found in Norway. Material referred to Plateosaurus has also been found in the Fleming Fjord Formation of East Greenland,[11] but they were given the new genus name Issi in 2021.

The type series of Plateosaurus engelhardti included "roughly 45 bone fragments",[D] of which nearly half are lost.[E] The remaining material is kept in the Institute for Palaeontology of the University of Erlangen-Nuremberg, Germany.[F] From these bones, German palaeontologist Markus Moser in 2003 selected a partial sacrum (series of fused hip vertebrae) as a lectotype.[G] 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.[H]

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.[I]

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.[14]

Etymology

[edit]
Outdated 1912 life restoration by Otto Jaekel showing tripodal pose

The etymology of the name Plateosaurus is not entirely clear, as the original description contains no information and various authors have offered differing interpretations.[J] German geologist Hanns Bruno Geinitz in 1846 gave "(πλᾰτῠ́ς, breit)" [English: broad][K] as the origin of the name, with von Meyer's Latin spelling Plateosaurus evidently derived from the stem of πλᾰτέος (plateos), the genitive case of the masculine adjective platys in Ancient Greek. In the same year, Agassiz proposed that the name derives from the Ancient Greek πλατη (platê – "paddle", "rudder"; Agassiz translates this as Latin pala = "spade") and σαυρος (sauros – "lizard").[L] Agassiz consequently renamed the genus Platysaurus,[M] probably from Greek πλατυς (platys – "broad, flat, broad-shouldered"), creating an invalid junior synonym. Later authors often referred to this derivation, and the secondary meaning "flat" of πλατυς, so that Plateosaurus is often translated as "flat lizard". Often, claims were made that πλατυς is supposed to have been intended as a reference to flat bones, for example the laterally flattened teeth of Plateosaurus,[N] but the teeth and other flat bones such as the pubic bones and some skull elements were unknown at the time of description.[19][O]

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."[20] 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.[21]

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."[P][19] 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.[19][23][24]

Von Meyer had authored a popular audience book in 1852 Ueber Die Reptilien und Säugethiere Der Verschiedenen Zeiten Der Erde [On the Reptiles and Mammals from the Different Time Periods of the Earth] 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: "das in 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 sacrum composed of several fused vertebrae, broad, strong limb bones 1 1⁄2 feet long with an ample medullary cavity enclosing finely formed crystals of Goethite iron ore, as well as toe phalanges, which were also broad and hollow...; it would be the oldest pachypode [dinosaur] yet found.][25]

Valid species

[edit]
Skull cast of P. gracilis

The taxonomic history of Plateosaurus is "long and confusing" and a "chaotic tangle of names".[Q] As of 2019, only three species are universally accepted as valid:[26] the type species P. trossingensis, P. longiceps, and P. gracilis, previously assigned to its own genus Sellosaurus. Moser performed the most extensive and detailed investigation of all plateosaurid material from Germany and Switzerland, concluding that all Plateosaurus and most other prosauropod material from the Keuper stems from the same species as the type material of Plateosaurus engelhardti.[1] However, this is problematic due to the undiagnostic state of the lectotype.[27] Moser considered Sellosaurus to be the same genus as Plateosaurus, but did not discuss whether S. gracilis and P. engelhardti belong to the same species.[R] Palaeontologist Adam Yates of the University of the Witwatersrand cast further doubt on the generic separation. He included the type material of Sellosaurus gracilis in Plateosaurus as P. gracilis and reintroduced the old name Efraasia for some material that had been assigned to Sellosaurus.[13] In 1926, von Huene had already concluded the two genera were the same.[S]

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 paraphyletic (belongs to several species).[T] 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.[U]

Some scientists regard other species as valid as well, for example P. erlenbergensis and P. engelhardti.[28] These claims are problematic since both P. erlenbergensis and P. engelhardti have undiagnostic type specimens.[27]

Photograph of the skull in side view, with a partial neck composed of seven vertebrae extending from it, seemingly articulated. However, the vertebrae are at a right angle, i.e. their neural spines point to what is to the left for the skull. Among each other they are articulated, forming a 110° curve, which the cervical ribs follow. Next to the fossil are explanatory signs, including a schematic drawing showing the skull openings and giving their names. The name shown is Plateosaurus quenstedti, a junior synonym of P. engelhardti.
P. engelhardti skull and neck (MB 1927.19.1) previously assigned to P. quenstedti and P. longiceps, at the Museum für Naturkunde, Berlin

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.[1][13] Von Huene[29] 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).[3] 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.[5] Systematic research by Galton drastically reduced the number of genera and species. Galton synonymised all cranial material,[30][31][32] and described differences between the syntypes of P. engelhardti and the Trossingen material, which he referred to P. longiceps.[33] Galton recognised P. trossingensis (P. fraasianus and P. integer are junior objective synonyms) to be identical to P. longiceps.[34] Markus Moser, however, showed that P. longiceps is itself a junior synonym of P. engelhardti.[1] 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.[V] 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.[28] 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.[W] 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.[28]

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.[35][X] Some of this material is not diagnostic; other material has been recognised to be different, but was never sufficiently described.[Y]

Description

[edit]
Restoration of P. trossingensis

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.[36][6][1] The arms of Plateosaurus were very short, even compared to most other "prosauropods". However, they were strongly built, with hands adapted for powerful grasping.[6][37] The shoulder girdle was narrow (often misaligned in skeletal mounts and drawings),[37] with the clavicles (collar bones) touching at the body's midline,[6] as in other basal sauropodomorphs.[38] 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.[6][39][40] The proportionally long lower leg and metatarsus show that Plateosaurus could run quickly on its hind limbs.[6][37][39][40] The tail of Plateosaurus was typically dinosaurian, muscular and with high mobility.[37]

Side view of a skull and the anterior part of the neck. The skull is rectangular, nearly three times as long as it was high, with an almost rectangular lateral temporal foramen at the back. The large, round orbit (eye socket), the sub-triangular antorbital fenestra and the oval naris are of almost equal size. The lower jaw is shallow, and has a large process extending far behind the jaw joint. The teeth are small and form long rows.
P. trossingensis skull cast, Royal Ontario Museum

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.[36][6][30] 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).[36][6][30] The thick, leaf-shaped, bluntly serrated tooth crowns were suitable for crushing plant material.[36][6][30] The low position of the jaw joint gave the chewing muscles great leverage, so that Plateosaurus could deliver a powerful bite.[30] These features suggest that it fed primarily to exclusively on plants.[30] Its eyes were directed to the sides, rather than the front, providing all-round vision to watch for predators.[36][6][30] Some fossil skeletons have preserved sclerotic rings (rings of bone plates that protect the eye).[36][6][30]

Size comparison of four Plateosaurus specimens representing two species

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.[37] This is a typical value for birds, but not for mammals,[41] and indicates that Plateosaurus probably had an avian-style flow-through lung,[37] 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.[42][43] Combined with evidence from bone histology[3][44] this indicates that Plateosaurus was endothermic.[44][45]

The type species of Plateosaurus is P. trossingensis.[2] Adults of this species reached 4.8 to 10 metres (16 to 33 ft) in length,[44] and ranged in mass from 600 to 4,000 kilograms (1,300 to 8,800 lb).[40] 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).[13]

Classification

[edit]

Plateosaurus is a member of a group of early herbivores known as "prosauropods".[29] The group is not a monophyletic group (thus given in quotation marks), and most researchers prefer the term basal sauropodomorph.[46][47] Plateosaurus was the first "prosauropod" to be described,[29] and gives its name to the family Plateosauridae as the type genus.[34] 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.[2] In 1845, von Meyer created the group Pachypodes (a defunct junior synonym of Dinosauria) to include Plateosaurus, Iguanodon, Megalosaurus and Hylaeosaurus.[48] Plateosauridae was proposed by Othniel Charles Marsh in 1895 within Theropoda.[49] Later it was moved to "Prosauropoda" by von Huene,[50] a placement that was accepted by most authors.[1][13][51][52] 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".[53] 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[54] and possibly Unaysaurus.[55] Of these, Sellosaurus is probably another junior synonym of Plateosaurus.[13]

Mounted P. trossingensis skeleton in Sauriermuseum, Frick
Lateral view drawing of the animal; it is depicted as a biped with grasping hands with palms facing medially. The tail is held high, as is the neck.
Life restoration of P. gracilis, formerly known as Sellosaurus gracilis

Basal sauropodomorph phylogeny simplified after Yates, 2007.[56] This is only one of many proposed cladograms for basal sauropodomorphs. Some researchers do not agree that plateosaurs were the direct ancestors of sauropods.

Plateosauria

Palaeobiology

[edit]

Posture and gait

[edit]
Photograph of the lower arm and hand, seen from the side. The arm is hanging straight down, the fingers are slightly spread, the palm is directed medially.
Dorsal view of left lower arm and hand of P. trossingensis ("Skelett 2") at the museum of the Institute for Geosciences of the Eberhard-Karls-University Tübingen, Germany. The shape of the radius dictates that the hand could not be pronated (turned palm down), and thus not play a role in locomotion.

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).[6][57] 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.[58] Only a year later, Jaekel instead favoured a clumsy, kangaroo-like hopping,[36] a change of heart for which he was mocked by German zoologist Gustav Tornier,[59] 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.[60][61] 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.[62] However, most of these adaptations are actually present in Plateosaurus.[37][40]

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,[39][63] led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back.[Z][64][65][66][AA][68] Many researchers were of the opinion that Plateosaurus could use both quadrupedal gaits (for slow speeds) and bipedal gaits (for rapid locomotion),[39][63][66][67] and Wellnhofer insisted that the tail curved strongly downward, making a bipedal posture impossible.[68] However, Moser showed that the tail was in fact straight.[AB]

Photograph of a mounted cast in left lateral view, with tail dragging on the ground.
Mounted cast of SMNS 13200, holotype of P. trossingensis. An example of the out-dated skeleton mounts in the State Museum of Natural History Stuttgart in quadrupedal posture. The shoulder girdle is in an anatomically infeasible position, the elbow is disarticulated, and the ribcage has the wrong shape, wide instead of high oval.

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.[69] 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.[37][40][70] 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.[71]

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.[40] 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.[6] 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.[72]

Feeding and diet

[edit]

Important cranial characteristics (such as jaw articulation) of most "prosauropods" are closer to those of herbivorous reptiles than those of carnivorous ones, and the shape of the tooth crown is similar to that of modern herbivorous or omnivorous iguanas. The maximum width of the crown was greater than that of the root for the teeth of most "prosauropods", including Plateosaurus; this results in a cutting edge similar to those of extant herbivorous or omnivorous reptiles.[65] Paul Barrett proposed that prosauropods supplemented their mostly herbivorous diets with small prey or carrion, thus making them omnivores.[73]

So far, no fossil of Plateosaurus has been found with gastroliths (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.[74][75] The use of gastroliths for digestion seems to have developed on the line from basal theropods to birds, with a parallel development in Psittacosaurus.[75]

Life history and metabolism

[edit]
Photograph of the mounted skeleton, seen from the front left. The animal stands on the hind limbs, with the body and tail horizontal. The neck curves down so that the snout is near the ground, as if the animal was feeding. The arms are flexed, with the hands well clear of the ground, and the palm directed medially.
Mount of P. trossingensis GPIT/RE/7288, a nearly complete individual from Trossingen at the museum of the Institute for Geosciences of the Eberhard-Karls-University Tübingen, Germany. Anatomically, this mount created under the direction of Friedrich von Huene is one of the best in the world, epitomising the agile, bipedal and digitigrade view of Plateosaurus confirmed by recent research.

Similar to all non-avian dinosaurs studied to date, Plateosaurus grew in a pattern that is unlike that of both extant mammals and birds. In the closely related sauropods with their typical dinosaurian physiology, growth was initially rapid, continuing somewhat more slowly well beyond sexual maturity, but was determinate, i.e. the animals stopped growing at a maximum size.[76] Mammals grow rapidly, but sexual maturity falls typically at the end of the rapid growth phase. In both groups, the final size is relatively constant, with humans atypically variable. Extant reptiles show a sauropod-like growth pattern, initially rapid, then slowing after sexual maturity, and almost, but not fully, stopping in old age. However, their initial growth rate is much lower than in mammals, birds and dinosaurs. The reptilian growth rate is also very variable, so that individuals of the same age may have very different sizes, and final size also varies significantly. In extant animals, this growth pattern is linked to behavioural thermoregulation and a low metabolic rate (i.e. ectothermy), and is called "developmental plasticity".[44] (Note that is not the same as neural developmental plasticity).

Muscle reconstructions and pathologies of the tail

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 10 metres (33 ft). However, the bone microstructure indicates rapid growth, as in sauropods and extant mammals, which suggests endothermy. 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.[44] A further indication for endothermy is the avian-style lung of Plateosaurus.[37]

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.[44] 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 4.8 metres (16 ft) long, it is not possible to deduce a complete ontogenetic series for Plateosaurus or determine the growth rate of animals less than 10 years of age.[44]

Comparisons between the scleral rings and estimated orbit size of Plateosaurus and modern birds and reptiles suggest that it may have been cathemeral, active throughout the day and night, possibly avoiding the midday heat.[77]

Palaeoecology

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Restoration of Plateosaurus trossingensis and contemporary animals from the Trossingen Formation

Plateosaurus gracilis, the older species, is found in the Löwenstein Formation (lower to middle Norian).[AC] P. trossingensis and P. longiceps stem from the Trossingen Formation (upper Norian) and equivalently aged rock units.[AD][78] Plateosaurus thus lived probably between approximately 227 and 208.5 million years ago.[79]

Taphonomy

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The taphonomy (burial and fossilisation process) of the three main Plateosaurus sites—Trossingen, Halberstadt and Frick—is unusual in several ways.[3] All three sites are nearly monospecific assemblages, meaning that they contain practically only one species, which requires very special circumstances.[3] However, shed teeth of theropods have been found at all three sites, as well as remains of the early turtle Proganochelys.[3] Additionally, a partial "prosauropod" skeleton was found in Halberstadt that does not belong to Plateosaurus, but is preserved in a similar position.[5] All sites yielded almost complete and partial skeletons of Plateosaurus, as well as isolated bones.[3] The partial skeletons tend to include the hind limbs and hips, while parts of the anterior body and neck are rarely found in isolation.[3] The animals were all adults or subadults (nearly adult individuals); no juveniles or hatchlings are known.[3] Complete skeletons and large skeleton parts that include the hind limbs all rest dorsal (top) side up, as do the turtles.[3] Also, they are mostly well-articulated, and the hind limbs are three-dimensionally preserved in a zigzag posture, with the feet often much deeper in the sediment than the hips.[3]

Earlier interpretations

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Photograph of the dinosaur skeleton in dorsal view. It is partly embedded in rock, so that all bones are in the position they were found in. The animal rests on its belly, neck and tail curving so that the overall shape is almost a U, with the limbs folded and spread widely, while its right arm is buried under the trunk, and the left upper arm extends outwards. The left lower arm cannot be seen, because it points down into the sediment. The ribcage is partly torn, and the ribs and gastral ribs are scattered, but the backbone is intact. The tail shows a gap where bones were destroyed during discovery.
P. engelhardti, collection number MSF 23 of the Sauriermuseum Frick, Switzerland, in dorsal view. This is the most complete Plateosaurus skeleton from Frick.

In the first published discussion of the Trossingen Plateosaurus finds, Fraas suggested that only miring in mud allowed the preservation of the single complete skeleton then known.[60] Similarly, Jaekel interpreted the Halberstadt finds as animals that waded too deep into swamps, became mired and drowned.[5] He interpreted partial remains as having been transported into the deposit by water, and strongly refuted a catastrophic accumulation.[5] In contrast, von Huene interpreted the sediment as aeolian deposits, with the weakest animals, mostly subadults, succumbing to the harsh conditions in the desert and sinking into the mud of ephemeral water holes.[7] He argued that the completeness of many finds indicated that transport did not happen, and saw partial individuals and isolated bones as results of weathering and trampling.[7] Seemann developed a different scenario, in which Plateosaurus herds congregated on large water holes, and some herd members got pushed in.[80] Light animals managed to get free, while heavy individuals got stuck and died.[80]

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.[4] Weishampel explained the curious monospecific assemblage by theorising that Plateosaurus were common during this period.[4] 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,[64] and has since become the standard explanation on most internet sites and in popular books on dinosaurs.[1] Rieber proposed a more elaborate scenario, which included the animals dying of thirst or starvation, and being concentrated by mudflows.[81]

Mud-miring trap

[edit]

A detailed re-assessment of the taphonomy by palaeontologist Martin Sander of the University of Bonn, Germany, found that the mud-miring hypothesis first suggested by Fraas[60] is true:[3] animals above a certain body weight sank into the mud, which was further liquefied by their attempts to free themselves. Sander's scenario, similar to that proposed for the famous Rancho La Brea Tar Pits, is the only one explaining all taphonomic data. The degree of completeness of the carcasses was not influenced by transport, which is obvious from the lack of indications for transport before burial, but rather by how much the dead animals were scavenged. Juveniles of Plateosaurus and other taxa of herbivores were too light to sink into the mud or managed to extract themselves, and were thus not preserved. Similarly, scavenging theropods were not trapped due to their lower body weights, combined with proportionally larger feet. There is no indication of herding, or of catastrophic burial of such a herd, or catastrophic accumulation of animals that previously died isolated elsewhere.[3]

Pathologies affecting the chevrons of specimen SMNS 13200 have been hypothesized to be the result of capture myopathy, induced by a mud-miring trap.[82]

Notes

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References

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Plateosaurus

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Plateosaurus is a of basal sauropodomorph that lived during the period, specifically the Norian stage approximately 214 to 204 million years ago, in what is now Central and as well as . The includes at least two valid , though remains under study. It represents one of the earliest large-bodied dinosaurs, characterized by a bipedal posture with powerful hind limbs for locomotion, a long flexible neck supporting a small , and spoon-shaped teeth suited for processing material. Adults typically measured 4.8 to 10 meters in length and weighed between 600 and 1,000 kilograms, making it a dominant in its . The first fossils of Plateosaurus were discovered in 1834 near Heroldsberg, , by Johann Friedrich Engelhardt, and formally described in 1837 by Hermann von Meyer, who named it after the broad plates (Greek plateia) on its vertebrae. Since then, over 100 skeletons—ranging from juveniles to adults—have been unearthed from more than 40 localities, including notable bonebeds at Trossingen and Frick, which suggest gregarious behavior or mass mortality events due to miring in muds. These abundant remains have made Plateosaurus one of the best-understood early dinosaurs, providing insights into sauropodomorph and growth patterns through histological analysis of bones. Anatomically, Plateosaurus featured a subhorizontal backbone, a narrow ribcage, and grasping hands with a large potentially used for or defense, though its short forelimbs limited their role in . Its diet was primarily herbivorous, inferred from and dental wear patterns indicating leaf-stripping and grinding of plant material such as ferns, cycads, and , though dental studies suggest possible opportunistic omnivory with small prey or carrion. Recent discoveries, such as a nearly complete from 2025, highlight adaptations like a flexible, whip-like distal that may have served as a against predators. Paleoenvironmentally, Plateosaurus inhabited semi-arid floodplains and river valleys with seasonal vegetation, coexisting with early theropods like Liliensternus and other sauropodomorphs. Its rapid growth, evidenced by bone microstructure, allowed it to reach large size quickly, potentially reducing predation risk and contributing to the diversification of herbivorous dinosaurs leading to true sauropods in the . Ongoing continues to refine its locomotor capabilities, with evidence supporting primarily bipedal but facultatively quadrupedal locomotion in some individuals.

Discovery and research history

Initial discoveries

The first fossils attributed to Plateosaurus were unearthed in 1834 at Heroldsberg, near in , by the physician and amateur naturalist Johann Friedrich Philipp Engelhardt. These initial remains consisted of vertebrae and leg bones from the Upper Knollenmergel Formation. Three years later, in 1837, the German paleontologist Christian Erich Hermann von Meyer formally described the material, establishing the genus Plateosaurus and the species P. engelhardti based on these specimens. Major subsequent discoveries occurred at several key quarries in during the late 19th and early 20th centuries. The Trossingen site in the Black Forest, worked intermittently from 1911 to 1932 by paleontologists including Eberhard Fraas, Friedrich von Huene, and Reinhold Seemann, produced remains of over 80 individuals, including numerous partial skeletons from bonebeds in the Trossingen Formation. Other significant German localities included the quarry in , which yielded dozens of specimens between 1910 and the 1920s, and additional finds at Heroldsberg. Fossils from these sites provided the bulk of early Plateosaurus material, revealing its abundance in Norian-age deposits. Beyond Germany, Plateosaurus remains have been recovered from at the Frick clay pits, where excavations since the have uncovered multiple bonefields, and from several sites in , including and Saint-Nicolas-de-Port. More recent excavations at Frick, , have continued to yield significant material, including a nearly complete tail skeleton described in 2025. Many specimens from and Trossingen were transferred to the Museum für Naturkunde in after , where a significant portion—estimated at over 40 from Trossingen alone—was destroyed in Allied bombings during ; however, pre-war casts, photographs, and excavation reports have allowed much of the anatomical data to be preserved and studied. In total, nearly 200 individuals are represented by complete or partial skeletons and isolated elements across more than 40 localities in , establishing Plateosaurus as one of the most abundantly known early dinosaurs.

Etymology and naming

The genus name Plateosaurus is derived from the Ancient Greek words platys (πλατύς), meaning "flat" or "broad," and sauros (σαῦρος), meaning "lizard" or "reptile," thus translating to "flat lizard" or "broad lizard." This name refers to the broad, plate-like neural spines observed in the initial specimens, which contributed to the perception of a flattened or expansive vertebral structure. The genus was formally established in 1837 by German palaeontologist Hermann von Meyer, who named the Plateosaurus engelhardti based on fragmentary fossils discovered at Heroldsberg near , . The specific epithet "engelhardti" honors Johann Friedrich Engelhardt, the amateur geologist and pastor who unearthed the initial bones in 1834 while quarrying . Von Meyer's brief description in Museum Senckenbergianum marked Plateosaurus as one of the earliest named non-avian dinosaurs, highlighting its significance in early palaeontology. In 2019, the (ICZN) issued Opinion 2435, designating Plateosaurus trossingensis Fraas, 1913, as the of the genus to ensure nomenclatural stability. This ruling replaced P. engelhardti because its , consisting of a series of approximately 45 fragmentary bones (of which nearly half are lost), preserved at the Institute of Paleontology, University of Bonn, proved undiagnostic for distinguishing the genus. The decision conserved prevailing usage by designating the well-preserved specimen (SMNS 13200) of P. trossingensis from Trossingen as the name-bearing type, aligning with Article 75 of the .

Species and taxonomy

The genus Plateosaurus is currently recognized as comprising three valid , reflecting a post-2010 consensus derived from morphometric analyses of skeletal material that distinguishes discrete morphotypes while accounting for potential intraspecific variation. The , P. trossingensis (Fraas, 1913), is known primarily from robust specimens recovered from the Trossingen locality in southwestern , characterized by proportionally broader postcranial elements. P. longiceps (Huene, 1907) derives from the Tübingen collection and features an elongated relative to body size, though its distinction from P. trossingensis remains debated. P. gracilis (Jaekel, 1913), originally classified under Sellosaurus, represents a more slender form documented from sites including Frick in , often treated as a metataxon encompassing less robust variants. Several historically named species have been invalidated or synonymized through revisions in the 2000s, reducing taxonomic complexity. P. engelhardti (Meyer, 1837), the original type species, is now considered a nomen dubium due to undiagnostic holotype material lacking distinguishing features. Other taxa, such as P. fraasi (Fraas, 1913) and P. plumai (Jaekel, 1913–1914), along with junior synonyms like Gresslyosaurus plieningeri and Pachysaurus ajax, have been referred to either P. trossingensis (for more robust forms) or P. gracilis (for slender ones) based on cladistic and morphometric reassessments of German Löwenstein Formation specimens. Taxonomic debates center on whether observed morphological differences among Plateosaurus specimens reflect true interspecific variation or artifacts of , , or preservation bias. The absence of confirmed juvenile material hinders differentiation, as growth-related changes could mimic species-level distinctions; for instance, slender builds in P. gracilis might represent immature stages of P. trossingensis. Recent studies, including finite element and geometric morphometric approaches on postcranial and cranial elements from and Frick assemblages, support retaining three species but emphasize ongoing uncertainty, particularly regarding P. longiceps as a potential of P. trossingensis.

Physical description

Size and general build

Plateosaurus individuals varied considerably in body size, with total lengths ranging from 4.8 to 10 meters in adults, reflecting ontogenetic growth and possibly intraspecific variation. Hip height, measured from the ground to the in bipedal posture, scaled accordingly from approximately 1.7 meters in smaller specimens to 4 meters in the largest. estimates, derived from volumetric reconstructions of complete or near-complete skeletons, range from about 270 kg in juveniles to 4,000 kg or more in the largest adults, though typical mature individuals weighed 600–1,000 kg; for instance, a "slim" reconstruction of a 5–6 meter specimen yielded 630 kg, while a "robust" version reached 912 kg. The overall build was slender and adapted for bipedal locomotion, featuring a lightweight frame with a long, flexible composed of 10 (plus a rudimentary proatlas), which accounted for a substantial portion of the presacral length. The torso was barrel-shaped, supported by 15 dorsal vertebrae and three sacrals, providing a stable core for the elongated structure. A long tail, consisting of approximately 45 caudal vertebrae and comprising about 45% of total body length, served as a counterbalance to the anterior mass. Specimens exhibit notable morphological variations, including more gracile forms with lighter builds and robust ones with heavier limb bones and broader torsos, likely attributable to growth stages or individual differences rather than separate . For example, the rarer Plateosaurus gracilis displays a lighter, more slender morphology, with estimates around 600 kg for adults under 5 long. This variability underscores the high developmental plasticity in Plateosaurus, akin to the proportional elongation seen in modern giraffes relative to their body size, facilitating access to higher vegetation.

Skull, neck, and dentition

The of Plateosaurus is relatively small, with total lengths reaching up to 36.3 cm in adult specimens, though the exposed lateral surface of the typically measures 12.5–20.3 cm. It possesses an elongated, boxy formed by a with a straight to slightly concave ventral margin, contributing to a robust anterior profile suited for browsing . A prominent feature is the large , which spans 1.08–1.3 times the length of the and occupies a significant portion of the lateral surface, reducing weight while accommodating soft tissues such as the antorbital sinus. The is subcircular and positioned laterally with a slight dorsal tilt, measuring slightly longer than high, which likely positioned the eyes to provide a broad during . The exhibits flexibility due to the curved shaft of the quadrate, oriented posteriorly at approximately 55°, allowing limited kinesis for processing tough plant matter. The braincase is compact, with a high interbasipterygoid featuring a variable median process that supports the , indicative of a streamlined cranial architecture. While direct endocranial data for Plateosaurus are limited, the overall small size of the braincase suggests a modest cerebral volume relative to body mass, consistent with early sauropodomorphs. The neck comprises 10 elongated , characterized by low, transversely thin neural spines that decrease in anteroposterior length anteriorly and increase in height posteriorly, facilitating a flexible, S-shaped posture for reaching high . These vertebrae are relatively low in overall height and hourglass-shaped in transverse section, enhancing lateral mobility. The presacral column includes 15 dorsal vertebrae, followed by 3 sacral vertebrae that form a rigid for the pelvic . Dentition in Plateosaurus consists of heterodont teeth adapted for herbivory, with 5–6 premaxillary teeth, 22–28 maxillary teeth, and 20–23 dentary teeth, yielding approximately 27–34 teeth in the and 20–23 in the lower. The crowns are leaf-shaped, spatulate to lanceolate, with fine serrations along the mesial and distal margins, and pronounced longitudinal striations on the lingual surface, particularly in premaxillary teeth. Teeth are spaced evenly, with anterior tilting in the and vertical to posterior orientation in the dentary, promoting efficient leaf-stripping from branches. patterns vary by position, featuring polished facets and oblique striations on lingual and buccal surfaces that indicate intraoral grinding and processing of fibrous material, with crown height decreasing posteriorly in the upper .

Limbs and tail

The forelimbs of Plateosaurus measure approximately 60–70% of hindlimb length, reflecting a reduced but robust build adapted for manipulation rather than primary locomotion. The humerus exhibits a sigmoidal profile in lateral view, with the proximal end mediolaterally expanded to about 40% of shaft length and a prominent deltopectoral crest extending along 57% of the shaft; the distal condyles are asymmetrical, comprising 35% of total length. The radius reaches 62% of humerus length, featuring a saddle-shaped proximal articular surface and an ellipsoid distal end, while the ulna has a D-shaped shaft and proximally expanded olecranon process measuring 36% anteroposteriorly and 25% mediolaterally. The manus bears five digits following the phalangeal formula 2-3-4-3-3, with metacarpals II and III being the longest; the inner three digits terminate in large, curved unguals, the thumb claw attaining up to 10 cm in length to facilitate grasping of vegetation or objects. The hindlimbs are robust and pillar-like, with the straight along its posterior margin and sigmoidally curved laterally; the projects anteromedially at roughly 45°, offset by a distinct . The constitutes 86% of length, with the proximal end expanded anteroposteriorly to 31% and mediolaterally to 25% of its length, and the distal end broadened mediolaterally to 24%; the measures 94% of length (80% of ), showing similar proximal expansions of 23% anteroposteriorly. The pes is tridactyl, with digits I–IV supporting weight via phalanges that allow flexion, and the three main toes bearing recurved claws; metatarsals II–IV are elongate and subequal, while metatarsal V is reduced. The forms a broad saurischian structure, with the ilium featuring a narrow preacetabular process and a larger postacetabular process, both sub-triangular in outline; the pubic peduncle projects anteroventrally at 60°. The pubis attains 82% of length, with a robust proximal and a plate-like pubic spanning 70% of its total length and 34% mediolaterally; the distal expands dorsoventrally to 16% of length. The has a dorsoventrally expanded proximal plate, a sub-triangular shaft, and a rugose distal end, collectively contributing to a U-shaped that anchors the musculature. The is elongated, comprising approximately 45 caudal vertebrae that taper progressively toward the distal end, enhancing balance and flexibility. Anterior caudal are amphicoelous and dorsoventrally taller than long (length/ ratio 0.75–0.94), with ratios increasing to 2.5 posteriorly; neural spines are low and elongate anteroposteriorly (>40% of in proximal vertebrae), while transverse processes diminish caudally. Haemal arches (chevrons) articulate along much of the length, providing ventral support and enclosing the caudal blood vessels; some specimens preserve an articulated, whip-like distal portion with slender . Ossified tendons are evident in select individuals, contributing to localized stiffening along the .

Classification

Historical classifications

When first described by Christian Erich Hermann von Meyer in 1837 based on fragmentary limb bones from , , Plateosaurus was interpreted as a large, lizard-like akin to a giant or crocodilian, reflecting the limited understanding of reptiles at the time. This initial classification persisted into the 1850s as additional material was recovered, with early paleontologists viewing it as a member of the reptilian order Lacertilia or a related saurian group due to its robust skeletal elements. In 1842, reassigned Plateosaurus to his newly established order Dinosauria, recognizing shared traits like columnar limbs among early giants such as Megalosaurus and Iguanodon, marking its formal entry into the dinosaurian framework. By 1878, included it within , a suborder he defined for massive, herbivorous dinosaurs with pillar-like limbs, based on Plateosaurus's considerable size estimates exceeding 5 meters in length. This placement emphasized its role as an early representative of long-necked giants, though Marsh's focus was primarily on forms. During the early 20th century, classifications shifted amid growing fossil evidence; Friedrich von Huene in the 1920s tentatively allied some Plateosaurus material with , interpreting certain limb and pelvic features as indicative of carnivorous, bipedal predators within , before refining this view. Huene later formalized Prosauropoda in 1920 as a distinct group of basal saurischians closer to Plateosaurus engelhardti (now superseded as by P. trossingensis per ICZN Opinion 2435, 2019) than to advanced sauropods, highlighting their transitional morphology between small theropods and larger herbivores. had earlier named the family in 1895 with Plateosaurus as the , but it was Peter Galton's 1973 monograph that solidified the group's , detailing cranial and postcranial synapomorphies and establishing Plateosauridae as a core prosauropod . Mid-20th-century debates centered on whether prosauropods like Plateosaurus represented primitive early sauropods or a separate lineage ancestral to them, with figures such as Galton advocating for their distinction based on dental and locomotor adaptations. Prior to the 1990s, Plateosaurus was commonly grouped with other "prosauropods" as facultatively quadrupedal herbivores, a reconstruction emphasizing their long necks and forelimbs for browsing low vegetation, though this view arose from incomplete skeletons and preconceptions about dinosaur posture.

Phylogenetic position

Plateosaurus is recognized as a basal sauropodomorph , positioned outside the and within the non-sauropodan grade of early sauropodomorphs. It is the of the family , which encompasses other and is occasionally synonymized with the broader Massospondylidae in some taxonomic schemes, though recent analyses maintain them as distinct. Phylogenetic matrices from the 2020s consistently recover Plateosaurus trossingensis within , as the to Sellosaurus gracilis (though sometimes considered a junior synonym of Plateosaurus), with this pairing forming the to Unaysaurus tolentinoi; together, they comprise a sometimes termed Unaysauria or a basal assemblage leading toward more derived sauropodomorphs like those in Massopoda. This placement is supported by characters such as the presence of six premaxillary teeth, a nasal longer than half the skull roof length, and a incorporating two primordial vertebrae plus an unfused caudosacral. Earlier analyses, including McPhee et al. (2014), positioned Plateosaurus more basally as sister to a including and other plateosaurian forms, highlighting ongoing refinements in character scoring and sampling. Plateosaurus shares diagnostic traits with fellow basal sauropodomorphs, including an elongated cervical series enabling elevated feeding and manus with long, curved phalanges adapted for grasping, which distinguish it from contemporaneous theropods. It further diverges from theropods in pelvic morphology, featuring a retroverted pubis and a perforate that accommodated quadrupedal tendencies in some individuals. These features underscore its role in the evolutionary transition toward the long-necked, herbivorous giants of . The of the informal group "Prosauropoda"—encompassing Plateosaurus and similar taxa—remains debated, with most cladistic studies rejecting it in favor of a paraphyletic grade of basal sauropodomorphs that sequentially branches toward , excluding the most primitive forms like Saturnalia. Plateosaurus typically anchors the more derived portion of this grade, often within Unaysauria, reflecting its intermediate position in the diversification of herbivorous dinosaurs during the .

Palaeobiology

Locomotion and posture

Plateosaurus exhibited an obligate bipedal posture, as evidenced by digital skeletal reconstructions that position the center of mass over the , supporting stability without involvement. Limb ratios further corroborate this, with significantly shorter than ( length approximately 40-50% of length), indicating for bipedal rather than . The featured a horizontal sacral orientation, aligning the for erect posture with the protracted at about 20° from vertical, enabling efficient ground reaction forces during movement. Hindlimb mechanics emphasized a straight-legged stance, where powerful was generated primarily through femoral retraction (up to 65° range) powered by the caudofemoralis musculature, rather than extensive extension. This configuration allowed for stride lengths of around 1.34 m in adults, facilitating bipedal locomotion at various speeds. Estimated average walking speeds are approximately 3.7 km/h. Trackway evidence from deposits in , such as narrow-gauge ichnofossils attributed to prosauropods, confirms a bipedal with minimal lateral sway and no manus impressions, ruling out quadrupedal progression. The forelimbs, while robust, were specialized for manipulation rather than locomotion, lacking the pronation capability needed for sustained weight support. Motion analyses show limited and flexion suitable for grasping but insufficient for quadrupedal stances, even in more gracile specimens. No skeletal or evidence supports habitual quadrupedality, reinforcing that Plateosaurus relied exclusively on bipedal mechanics for terrestrial travel.

Diet and feeding mechanisms

Plateosaurus was a primarily herbivorous , subsisting on such as ferns, cycads, and through a strategy enabled by its long neck and bipedal or tripodal posture. Its , featuring leaf-shaped teeth with serrated margins in the posterior jaw, was adapted for shearing and puncturing plant tissues rather than grinding, supporting this . Tooth microwear patterns further indicate exposure to abrasive materials like phytoliths (silica bodies in ), consistent with regular consumption of tough, fibrous . The feeding apparatus of Plateosaurus exhibited relatively weak jaw mechanics, with estimated bite forces ranging from approximately 70 to 190 N (averaging around 160 N), limiting its ability to process highly resistant foods through mastication. This low bite was compensated by rapid jaw closure speeds, particularly in the anterior portion of the for cropping foliage, and reliance on precise nipping actions using the beak-like predentary and recurved . The elongated neck allowed access to elevated browse, while postcranial adaptations, such as a flexible for balance, facilitated stable positioning during feeding. Gastroliths, or stomach stones, have been proposed as an aid to mechanical digestion of fibrous in the gut, similar to modern herbivorous birds, though none have been definitively associated with Plateosaurus specimens; over 170 such stones occur in some later sauropodomorph individuals, suggesting a potential shared strategy among early herbivores. Juvenile Plateosaurus individuals may have exhibited omnivorous tendencies, inferred from ontogenetic variation in tooth morphology where smaller, more conical resemble those of small carnivores or omnivores capable of capturing or small vertebrates. However, there is no of predation or consumption in adults or juveniles, and the sharp hand claws likely served defensive or locomotor functions rather than foraging tools.

Growth, reproduction, and physiology

Bone histological studies of Plateosaurus long bones reveal a cortex dominated by fibrolamellar tissue, indicative of rapid, continuous growth typical of dinosaurs, with vascular canals oriented parallel to the bone surface in a laminar pattern. This tissue type, interrupted by lines of arrested growth (LAGs) averaging 16–17 per individual (ranging from 12 to 24), records annual pauses and supports a maximum lifespan of approximately 20–25 years, with some individuals surviving several years after somatic growth ceased; a 2025 histological analysis of a mature specimen identified 22 LAGs, estimating its age at 23–25 years and highlighting developmental plasticity in maturity timing. Growth modeling from histological data estimates sexual maturity at 10–13 years and full adult size at 16–19 years, with peak growth rates reaching 680–820 g/day during early ontogeny. Juvenile specimens are rare in the fossil record, with only a few early-stage individuals preserved from sites like Frick, Switzerland, likely due to differing taphonomic biases that favored larger subadults and adults in mudflat bonebeds. Morphometric analyses of adult femora from Trossingen suggest possible , with "robust" and "gracile" morphs differing in overall build and limb proportions, potentially reflecting sex-based variation rather than ontogenetic or pathologic differences. in Plateosaurus was likely oviparous, consistent with the reproductive mode of all known non-avian dinosaurs, involving the laying of hard-shelled eggs in terrestrial nests. Clutch sizes are inferred from nesting analogs in related early sauropodomorphs like , which laid at least 20–34 eggs per clutch in shallow, flask-shaped burrows, suggesting similar strategies for Plateosaurus despite the absence of direct . Physiological inferences from Plateosaurus indicate a metabolism elevated above that of modern reptiles, approaching endothermy, as supported by the fibrolamellar bone microstructure enabling sustained high growth rates and the presence of growth curves without prolonged stasis. Sporadic pneumatic foramina in vertebrae and ribs hint at a rudimentary air sac system, potentially aiding respiratory efficiency and lightweight construction in this basal sauropodomorph, though less extensive than in later sauropods. This combination of traits underscores an active lifestyle with elevated metabolic demands, facilitating the evolutionary transition toward sauropod gigantism.

Palaeoecology

Geological setting

Fossils of Plateosaurus are primarily recovered from deposits of the late to possibly the earliest stages of the , spanning approximately 214 to 204 million years ago. The most significant assemblages occur in the Trossingen Formation (formerly the Knollenmergel) and the Formation, located in and northern . These units form part of the Upper Keuper subgroup within the Germanic Basin, where Plateosaurus bonebeds are concentrated in layers representing repeated depositional events. The paleoenvironment of these formations consisted of and riverine settings with episodic sheet floods and overbank in a well-drained playa-like basin. Siliciclastic mudstones dominate the succession, interspersed with pedogenic horizons and carbonate nodules indicative of during subaerial exposure. A subtropical prevailed, marked by seasonal and influenced by the Pangaean megamonsoon system, which drove alternating wet and dry periods leading to calcrete development and periodic fluvial activity. Stratigraphic correlations across the reveal consistent lithofacies and depositional patterns in the Trossingen and formations, linking sites in , , and adjacent areas. The age range is corroborated by of interbedded volcanics in marine equivalents and based on co-occurring palynomorphs, such as those in the Lunatisporites assemblage zones. Plateosaurus fossils are exclusively known from , with no verified occurrences beyond this region. Material from the Fleming Fjord Formation in , once referred to Plateosaurus, was reclassified in 2021 as the related genus Issi saaneq.

Associated biota

The Late Triassic environments where Plateosaurus is found, such as the floodplain deposits of the Trossingen and Klettgau Formations in Germany and Switzerland, hosted a diverse but sparsely preserved assemblage of co-occurring vertebrates, with Plateosaurus dominating the bonebeds and few large predators present.90100-J) Theropod dinosaurs like Liliensternus, a basal neotheropod reaching about 5 meters in length, are known from isolated teeth and skeletal elements in the same Norian strata, suggesting it acted as a mid-sized carnivore potentially preying on juvenile or subadult Plateosaurus.00005-8) Armored aetosaurs such as Aetosaurus, small omnivorous pseudosuchians up to 1.5 meters long with osteoderm-covered bodies, coexisted in these continental settings, likely inhabiting similar riverine habitats. Rauisuchians, represented by taxa like Teratosaurus—a quadrupedal predator exceeding 4 meters—occurred in the Norian Stubensandstein of southern Germany, though direct associations with Plateosaurus bonebeds are rare, indicating no single large predator dominated the ecosystem. Early crocodylomorphs, including the agile, bipedal Saltoposuchus (1–1.5 meters long), are documented from the same formations, filling niches as small, terrestrial carnivores or scavengers. The flora of these floodplains was dominated by gymnosperms, with comprising 80–90% of assemblages based on macrofossils and records, including genera like Voltzia and Aethophyllum. Ginkgoaleans such as Baiera and ferns like Clathropteris were common understory components, while palynological evidence from sediments associated with Plateosaurus sites reveals diverse riparian forests along rivers, featuring horsetails, seed ferns, and cycadophytes adapted to moist, seasonal conditions. As a mid-sized (4–10 meters long), Plateosaurus occupied a key niche in this , on low- to mid-level amid a mix of herbivores and smaller carnivores, with limited evidence of intense competition but potential overlap with closely related, smaller sauropodomorphs like Sellosaurus (up to 4 meters), which shared similar bipedal forms and diets in the region.90100-J) Recent discoveries from the have enriched the known biota at Plateosaurus sites, particularly in Frick, , where fish remains (including actinopterygians like Ceratodus and chondrichthyans like Hybodus) indicate nearby aquatic environments, and a 2022 find of the turtle Proganochelys quenstedtii—one of the earliest testudinates—suggests semiaquatic elements in the otherwise terrestrial assemblage.00005-8)

Taphonomy and preservation

Plateosaurus fossils are predominantly preserved in overbank deposits of the Norian Knollenmergel, where individuals became entrapped in sticky mud mires, leading to rapid burial primarily of adults and resulting in commonly disarticulated but associated skeletons. This miring mechanism is evidenced by upright or "life-like" postures, such as flexed hindlimbs and deep embedding of hindquarters, with minimal post-mortem transport indicated by the absence of hydraulic sorting. Scavenging by small theropods, marked by shed teeth marks on bones, occurred prior to full burial, contributing to the disarticulation observed in many specimens. Prior to the 1980s, these bonebeds were interpreted as mass death assemblages resulting from catastrophic events like droughts or flash floods, reflecting early paleontological views on accumulations. Modern analyses, however, favor individual entrapments in seasonally wet muds, where the mass created sufficient foot pressure to cause sinking, as supported by sedimentological and taphonomic studies from sites like Trossingen. Juvenile Plateosaurus remains are rare, likely because their lighter bodies generated lower foot pressure, allowing escape from mires that trapped heavier adults. weathering stages, including flaking and cracking, suggest subaerial exposure for 2–4 years before , particularly in upper bonebed horizons, biasing preservation toward more durable posterior skeletal elements. Significant fossil material from the Halberstadt quarries was lost during bombings that destroyed collections at the Museum für Naturkunde in . Modern non-destructive techniques, such as CT scans applied to specimens from Trossingen and Frick since the 2000s, have revealed hidden pathologies, including infections like affecting the limbs and trauma-related issues in approximately 10–15% of examined individuals.

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