Posture and gait 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.|alt=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. Practically every imaginable posture has been suggested for
Plateosaurus in the scientific literature at some point. Von Huene assumed
digitigrade bipedality with erect hind limbs for the animals he excavated at Trossingen, with the backbone held at a steep angle (at least during rapid locomotion). In contrast, Jaekel, the main investigator of the Halberstadt material, initially concluded that the animals walked
quadrupedally, like lizards, with a sprawling limb position,
plantigrade feet, and
laterally undulating the body. Only a year later, Jaekel instead favoured a clumsy,
kangaroo-like hopping, a change of heart for which he was mocked by German
zoologist Gustav Tornier, who interpreted the shape of the articulation surfaces in the hip and shoulder as typically reptilian. Fraas, the first excavator of the Trossingen
lagerstätte, also favoured a reptilian posture. Müller-Stoll listed a number of characters required for an erect limb posture that
Plateosaurus supposedly lacked, concluding that the lizard-like reconstructions were correct. However, most of these adaptations are actually present in
Plateosaurus. From 1980 on, a better understanding of dinosaur biomechanics, and studies by palaeontologists Andreas Christian and Holger Preuschoft on the resistance to bending of the back of
Plateosaurus, led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back. Many researchers were of the opinion that
Plateosaurus could use both quadrupedal gaits (for slow speeds) and bipedal gaits (for rapid locomotion), and
Wellnhofer insisted that the tail curved strongly downward, making a bipedal posture impossible. However, Moser showed that the tail was in fact straight. 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.|alt=Photograph of a mounted cast in left lateral view, with tail dragging on the ground. The bipedal-quadrupedal consensus was changed by a detailed study of the forelimbs of
Plateosaurus by
Bonnan and Senter (2007), which clearly showed that
Plateosaurus was incapable of
pronating its hands. The pronated position in some museum mounts had been achieved by exchanging the position of
radius and
ulna in the elbow. The lack of forelimb pronation meant that
Plateosaurus was an obligate (i.e. unable to walk in any other way) biped. Further indicators for a purely bipedal mode of locomotion are the great difference in limb length (the hind limb is roughly twice as long as the forelimb), the very limited motion range of the forelimb, and the fact that the
centre of mass rests squarely over the hind limbs. 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
metatarsus and a digitigrade foot posture. However, in contrast to
mammalian cursors, the
moment arms of the limb
extending muscles are short, especially in the ankle, where a distinct, moment arm-increasing tuber on the
calcaneum is missing. This means that in contrast to running mammals,
Plateosaurus probably did not use gaits with aerial, unsupported phases. Instead,
Plateosaurus must have increased speed by using higher stride frequencies, created by rapid and powerful limb retraction. Reliance on
limb retraction instead of extension is typical for non-avian dinosaurs.
Palaeoecology 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. Paul Barrett proposed that prosauropods supplemented their mostly herbivorous diets with small prey or
carrion, thus making them omnivores. 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. The use of gastroliths for digestion seems to have developed on the line from basal theropods to birds, with a parallel development in
Psittacosaurus.
Palaeopathology Pathologies affecting the
chevrons of specimen SMNS 13200 have been hypothesized to be the result of
capture myopathy, induced by a mud-miring trap. Another specimen, SMNS 91296, bears lesions that were most likely caused by a fall or a similar form of trauma. Both of these specimens'
palaeopathologies could possibly also be explained as the result of an attack by a predator in which the predator did not penetrate the muscle of the tail far enough to leave any bite traces on the bone.
Life history and metabolism 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.| alt=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. 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. 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". (Note that is not the same as neural
developmental plasticity).
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
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. 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
ontogenetic series for
Plateosaurus or determine the growth rate of animals less than 10 years of age. 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.
Taphonomy The
taphonomy (burial and fossilisation process) of the three main
Plateosaurus sites—Trossingen, Halberstadt and Frick—is unusual in several ways. All three sites are nearly monospecific assemblages, meaning that they contain practically only one species, which requires very special circumstances. However, shed teeth of
theropods have been found at all three sites, as well as remains of the early turtle
Proganochelys. Additionally, a partial "prosauropod" skeleton was found in Halberstadt that does not belong to
Plateosaurus, but is preserved in a similar position. All sites yielded almost complete and partial skeletons of
Plateosaurus, as well as isolated bones. The partial skeletons tend to include the hind limbs and hips, while parts of the anterior body and neck are rarely found in isolation. The animals were all adults or subadults (nearly adult individuals); no juveniles or hatchlings are known. Complete skeletons and large skeleton parts that include the hind limbs all rest dorsal (top) side up, as do the turtles. 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.
Earlier interpretations .| alt=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. 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. Similarly, Jaekel interpreted the Halberstadt finds as animals that waded too deep into swamps, became mired and drowned. He interpreted partial remains as having been transported into the deposit by water, and strongly refuted a catastrophic accumulation. 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. 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. Seemann developed a different scenario, in which
Plateosaurus herds congregated on large water holes, and some herd members got pushed in. Light animals managed to get free, while heavy individuals got stuck and died. 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.
Mud-miring trap 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 is true: 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. The palaeopathologies on one specimen of
P. trossingenensis are consistent with being caused by the animal being mired in mud and support this hypothesis. ==Notes==