| Plateosaurus | |
|---|---|
 | |
| Mounted skeleton ofP. trossingensis (GPIT "Skelett 2"), consisting of two individual specimens from theTrossingen Formation, museum of the Institute for Geosciences (GPIT) of theEberhard-Karls-UniversityTübingen, Germany | |
Scientific 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 | |
| Synonyms | |
| |
Plateosaurus (probably meaning "broadlizard", often mistranslated as "flat lizard") is agenus ofplateosauriddinosaur that lived during theLate Triassic epoch of theTriassicperiod, around 214 to 204million years ago, in what is nowCentral andNorthern Europe.Plateosaurus is abasal (early)sauropodomorph dinosaur, a so-called"prosauropod". Thetype species isPlateosaurus trossingensis; before 2019, that honor was given toPlateosaurus engelhardti, but it was ruled as undiagnostic (i.e. indistinguishable from other dinosaurs) by theICZN. Currently, there are three validspecies; in addition toP. trossingensis,P. longiceps andP. gracilis are also known. However, others have been assigned in the past, and there is no broad consensus on the speciestaxonomy of plateosaurid dinosaurs. Similarly, there are a plethora ofsynonyms (invalid duplicate names) at the genus level.
Discovered in 1834 by Johann Friedrich Engelhardt and described three years later byHermann von Meyer,Plateosaurus was the fifth named dinosaur genus that is still considered valid. Although it had been described beforeRichard 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 inSwabia, Germany, has led to the nicknameSchwäbischer Lindwurm (Swabianlindworm).
Plateosaurus was abipedalherbivore with a smallskull on a long, flexible neck, sharp but plump plant-crushingteeth, 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 withgeological andpalaeontological 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) ofPlateosaurus have been re-studied in detail, altering the interpretation of the animal's biology, posture and behaviour.
In 1834, physician Johann Friedrich Engelhardt discovered some vertebrae and leg bones atHeroldsberg nearNuremberg, Germany.[2] Three years later GermanpalaeontologistHermann von Meyer designated them as thetype specimen of a new genus,Plateosaurus.[2] Since then, remains of well over 100 individuals ofPlateosaurus have been discovered at various locations throughout Europe.[3]
Material assigned toPlateosaurus has been found at over 50 localities in Germany (mainly along theNeckar andPegnitz 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: nearHalberstadt inSaxony-Anhalt, Germany;Trossingen inBaden-Württemberg, Germany; and Frick.[3] Between the 1910s and 1930s, excavations in aclay pit in Saxony-Anhalt revealed between 39 and 50 skeletons that belonged toPlateosaurus, along with teeth and a small number of bones of thetheropodLiliensternus, and two skeletons and some fragments of the turtleProganochelys.[3] Some of the plateosaur material was assigned toP. longiceps, a species described by palaeontologistOtto Jaekel in 1914.[5] Most of the material found its way to theMuseum 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]
The second major German locality withPlateosaurus finds, a quarry in Trossingen in theBlack 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 ofPlateosaurus, as well as fragmentary remains of approximately 70 more individuals.[4] The large number of specimens fromSwabia had already caused German palaeontologist Friedrich August von Quenstedt to nickname the animalSchwäbischer Lindwurm (Swabianlindworm or Swabiandragon).[B] Much of the Trossingen material was destroyed in 1944, when the Naturaliensammlung in Stuttgart (predecessor to theState 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]
ThePlateosaurus 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 bytaphonomic processes, Frick yields skeletons ofP. trossingensis comparable in completeness and position to those of Trossingen.[3]
In 1997, workers of anoil platform of theSnorre oil field, located at the northern end of theNorth Sea within theLunde Formation, were drilling throughsandstone 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 theUniversity of Bonn, analysed the bone microstructure and concluded that the rock preserved fibrous bone tissue from a fragment of a limb bone belonging toPlateosaurus,[10] making it the first dinosaur found in Norway. Material referred toPlateosaurus has also been found in theFleming Fjord Formation of East Greenland,[11] but they were given the new genus nameIssi in 2021.
The type series ofPlateosaurus 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 theUniversity of Erlangen-Nuremberg, Germany.[F] From these bones, German palaeontologist Markus Moser in 2003 selected a partialsacrum (series of fused hip vertebrae) as alectotype.[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 ofPlateosaurus gracilis, an incompletepostcranium, is kept at theStaatliches Museum für Naturkunde Stuttgart, Germany, and the type locality is Heslach, a suburb of the same city.[I]
The type specimen ofPlateosaurus trossingensis is SMNS 132000, stored in the same museum asP. gracilis. Its type locality is Trossingen, within theTrossingen Formation.
The type specimen ofPlateosaurus longiceps is MB.R.1937, which is stored in theMuseum für Naturkunde in Berlin. Its type locality is Halberstadt, located in Saxony-Anhalt and theTrossingen Formation.[14]
_(14764329552).jpg)
Theetymology of the namePlateosaurus is not entirely clear, as the original description contains no information and various authors have offered differing interpretations.[J] German geologistHanns Bruno Geinitz in 1846 gave "(πλᾰτῠ́ς, breit)" [English: broad][K] as the origin of the name, with von Meyer's Latin spellingPlateosaurus evidently derived from the stem of πλᾰτέος (plateos), the genitive case of the masculine adjectiveplatys in Ancient Greek. In the same year, Agassiz proposed that the name derives from theAncient Greekπλατη (platê – "paddle", "rudder"; Agassiz translates this asLatinpala = "spade") andσαυρος (sauros – "lizard").[L] Agassiz consequently renamed the genusPlatysaurus,[M] probably from Greekπλατυς (platys – "broad, flat, broad-shouldered"), creating an invalid junior synonym. Later authors often referred to this derivation, and the secondary meaning "flat" ofπλατυς, so thatPlateosaurus is often translated as "flat lizard". Often, claims were made thatπλατυς is supposed to have been intended as a reference to flat bones, for example the laterally flattened teeth ofPlateosaurus,[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 forPlateosaurus, but noted (as translated into English by British biologistThomas 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 toIguanodon and toMegalosaurus, 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 ofPlateosaurus with illustrations, but again gave no details on the etymology. He repeatedly referred to its gigantic size ("Riesensaurus" = giant lizard) and massive limbs ("schwerfüssig"), comparingPlateosaurus 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 1852Ueber 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 describedPlateosaurus, 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 ofGoethite iron ore, as well as toe phalanges, which were also broad and hollow...; it would be the oldest pachypode [dinosaur] yet found.][25]
.jpg)
The taxonomic history ofPlateosaurus 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 speciesP. trossingensis, P. longiceps, andP. gracilis, previously assigned to its own genusSellosaurus. Moser performed the most extensive and detailed investigation of all plateosaurid material from Germany and Switzerland, concluding that allPlateosaurus and most other prosauropod material from theKeuper stems from the same species as the type material ofPlateosaurus engelhardti.[1] However, this is problematic due to the undiagnostic state of the lectotype.[27] Moser consideredSellosaurus to be the same genus asPlateosaurus, but did not discuss whetherS. gracilis andP. engelhardti belong to the same species.[R] Palaeontologist Adam Yates of theUniversity of the Witwatersrand cast further doubt on the generic separation. He included the type material ofSellosaurus gracilis inPlateosaurus asP. gracilis and reintroduced the old nameEfraasia for some material that had been assigned toSellosaurus.[13] In 1926, von Huene had already concluded the two genera were the same.[S]
Yates has cautioned thatP. 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 isparaphyletic (belongs to several species).[T] This is the case because the holotype ofP. (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 toPlateosaurus.[U]
Some scientists regard other species as valid as well, for exampleP. erlenbergensis andP. engelhardti.[28] These claims are problematic since bothP. erlenbergensis andP. engelhardti have undiagnostic type specimens.[27]
All named species ofPlateosaurus except the type species,P. gracilis, orP. 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 ofPachysaurus and seven ofPlateosaurus) and Halberstadt (one species ofGresslyosaurus and eight ofPlateosaurus).[3] Later, he merged several of these species, but remained convinced that more than one genus and more than one species ofPlateosaurus 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 thesyntypes ofP. engelhardti and the Trossingen material, which he referred toP. longiceps.[33] Galton recognisedP. trossingensis (P. fraasianus andP. integer are junior objective synonyms) to be identical toP. longiceps.[34] Markus Moser, however, showed thatP. longiceps is itself a junior synonym ofP. engelhardti.[1] Furthermore, a variety of species in other genera were created for material belonging toP. engelhardti, includingDimodosaurus poligniensis,Gresslyosaurus robustus,Gresslyosaurus torgeri,Pachysaurus ajax,Pachysaurus giganteus,Pachysaurus magnus andPachysaurus wetzelianus.[V]G. ingens has been considered separate fromPlateosaurus, pending a revision of the material.
The skull of AMNH FARB 6810, the best-preserved skull ofPlateosaurus 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 toP. erlenbergensis, a species erected in 1905 by Friedrich von Huene and regarded as a synonym ofP. engelhardti by Markus Moser.[W] If theP. erlenbergensis holotype is diagnostic (i.e., has enough characters to be distinct from other material), it is the correct name for the material assigned toP. longiceps Jaekel, 1913.[28]
Aside from fossils clearly belonging toPlateosaurus, there is much prosauropod material from the GermanKnollenmergel in museum collections, most of it labeled asPlateosaurus, that does not belong to the type species and possibly not toPlateosaurus 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]
Plateosaurus had the typical body shape of a herbivorous bipedal dinosaur: a small skull, a long and flexible neck composed of 10cervical vertebrae, a stocky body, and a long, mobile tail composed of at least 40caudal vertebrae.[36][6][1] The arms ofPlateosaurus were very short, even compared to most other "prosauropods". However, they were strongly built, with hands adapted for powerful grasping.[6][37] Theshoulder girdle was narrow (often misaligned in skeletal mounts and drawings),[37] with theclavicles (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 wasdigitigrade, meaning the animal walked on its toes.[6][39][40] The proportionally long lower leg andmetatarsus show thatPlateosaurus could run quickly on its hind limbs.[6][37][39][40] The tail ofPlateosaurus was typically dinosaurian, muscular and with high mobility.[37]
.jpg)
The skull ofPlateosaurus is small and narrow, rectangular in side view, and nearly three times as long as it is high. There is an almost rectangular lateraltemporal foramen at the back. The large, roundorbit (eye socket), the sub-triangularantorbital fenestra and the ovalnaris (nostril) are of almost equal size.[36][6][30] The jaws carried many small, leaf-shaped, socketed teeth: 5 to 6 perpremaxilla, 24 to 30 permaxilla, and 21 to 28 perdentary (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 thatPlateosaurus 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 forpredators.[36][6][30] Some fossil skeletons have preservedsclerotic rings (rings of bone plates that protect the eye).[36][6][30]
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 aP. 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 thatPlateosaurus probably had anavian-style flow-through lung,[37] although indicators forpostcranial 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 bonehistology[3][44] this indicates thatPlateosaurus wasendothermic.[44][45]
Thetype species ofPlateosaurus isP. 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 namedSellosaurus gracilis), was somewhat smaller, with a total length of 4 to 5 metres (13 to 16 ft).[13]
Plateosaurus is a member of a group of earlyherbivores known as "prosauropods".[29] The group is not amonophyletic group (thus given in quotation marks), and most researchers prefer the termbasalsauropodomorph.[46][47]Plateosaurus was the first "prosauropod" to be described,[29] and gives its name to the familyPlateosauridae as thetype genus.[34] Initially, when the genus was poorly known, it was only included inSauria, being some kind of reptile, but not in any more narrowly defined taxon.[2] In 1845, von Meyer created the groupPachypodes (a defunct juniorsynonym of Dinosauria) to includePlateosaurus,Iguanodon,Megalosaurus andHylaeosaurus.[48] Plateosauridae was proposed byOthniel Charles Marsh in 1895 withinTheropoda.[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 ofcladistics in paleontology during the 1980s, with its emphasis onmonophyletic 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 includedPlateosaurus and various junior synonyms, but later two more genera were considered to belong to it:Sellosaurus[54] and possiblyUnaysaurus.[55] Of these,Sellosaurus is probably another junior synonym ofPlateosaurus.[13]
Basal sauropodomorphphylogeny simplified after Yates, 2007.[56] This is only one of many proposedcladograms for basal sauropodomorphs. Some researchers do not agree that plateosaurs were the direct ancestors of sauropods.
Plateosaurus gracilis, the older species, is found in theLöwenstein Formation (lower to middle Norian).[Z]P. trossingensis andP. longiceps stem from theTrossingen Formation (upper Norian) and equivalently aged rock units.[AA][57]Plateosaurus thus lived probably between approximately 227 and 208.5 million years ago.[58]
Practically every imaginable posture has been suggested forPlateosaurus in the scientific literature at some point. Von Huene assumeddigitigradebipedality 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][59] In contrast, Jaekel, the main investigator of the Halberstadt material, initially concluded that the animals walkedquadrupedally, like lizards, with a sprawling limb position,plantigrade feet, andlaterally undulating the body.[60] Only a year later, Jaekel instead favoured a clumsy,kangaroo-like hopping,[36] a change of heart for which he was mocked by GermanzoologistGustav Tornier,[61] who interpreted the shape of the articulation surfaces in the hip and shoulder as typically reptilian. Fraas, the first excavator of the Trossingenlagerstätte, also favoured a reptilian posture.[62][63] Müller-Stoll listed a number of characters required for an erect limb posture thatPlateosaurus supposedly lacked, concluding that the lizard-like reconstructions were correct.[64] However, most of these adaptations are actually present inPlateosaurus.[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 ofPlateosaurus,[39][65] led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back.[AB][66][67][68][AC][70] Many researchers were of the opinion thatPlateosaurus could use both quadrupedal gaits (for slow speeds) and bipedal gaits (for rapid locomotion),[39][65][68][69] andWellnhofer insisted that the tail curved strongly downward, making a bipedal posture impossible.[70] However, Moser showed that the tail was in fact straight.[AD]
The bipedal-quadrupedal consensus was changed by a detailed study of the forelimbs ofPlateosaurus byBonnan and Senter (2007), which clearly showed thatPlateosaurus was incapable ofpronating its hands.[71] The pronated position in some museum mounts had been achieved by exchanging the position ofradius andulna in the elbow. The lack of forelimb pronation meant thatPlateosaurus 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 thecentre of mass rests squarely over the hind limbs.[37][40][72] 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 forPlateosaurus.[73]
Plateosaurus shows a number ofcursorial adaptations, including an erect hind limb posture, a relatively long lower leg, an elongatedmetatarsus and a digitigrade foot posture.[40] However, in contrast tomammalian cursors, themoment arms of the limbextending muscles are short, especially in the ankle, where a distinct, moment arm-increasing tuber on thecalcaneum 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 onlimbretraction instead of extension is typical for non-avian dinosaurs.[74]
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 toothcrown is similar to that of modern herbivorous or omnivorousiguanas. The maximum width of the crown was greater than that of the root for the teeth of most "prosauropods", includingPlateosaurus; this results in a cutting edge similar to those of extant herbivorous or omnivorous reptiles.[67] Paul Barrett proposed that prosauropods supplemented their mostly herbivorous diets with small prey orcarrion, thus making them omnivores.[75]
So far, no fossil ofPlateosaurus has been found withgastroliths (gizzard stones) in the stomach area. The old, widely cited idea that all large dinosaurs, implicitly alsoPlateosaurus, 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.[76][77] The use of gastroliths for digestion seems to have developed on the line from basal theropods to birds, with a parallel development inPsittacosaurus.[77]
Pathologies affecting thechevrons of specimen SMNS 13200 have been hypothesized to be the result ofcapture 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.[78]
Similar to all non-avian dinosaurs studied to date,Plateosaurus grew in a pattern that is unlike that of bothextant mammals and birds. In the closely related sauropods with their typicaldinosaurian 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.[79] 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 tobehavioural thermoregulation and a lowmetabolic rate (i.e.ectothermy), and is called "developmental plasticity".[44] (Note that is not the same as neuraldevelopmental 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 10 metres (33 ft). However, the bone microstructure indicates rapid growth, as in sauropods and extant mammals, which suggestsendothermy.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 ofPlateosaurus 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 ofPlateosaurus.[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 completeontogenetic series forPlateosaurus or determine the growth rate of animals less than 10 years of age.[44]
Comparisons between thescleral rings and estimated orbit size ofPlateosaurus and modern birds and reptiles suggest that it may have beencathemeral, active throughout the day and night, possibly avoiding the midday heat.[80]
Thetaphonomy (burial and fossilisation process) of the three mainPlateosaurus 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 oftheropods have been found at all three sites, as well as remains of the early turtleProganochelys.[3] Additionally, a partial "prosauropod" skeleton was found in Halberstadt that does not belong toPlateosaurus, but is preserved in a similar position.[5] All sites yielded almost complete and partial skeletons ofPlateosaurus, 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]
In the first published discussion of the TrossingenPlateosaurus finds, Fraas suggested that only miring in mud allowed the preservation of the single complete skeleton then known.[62] 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 asaeolian deposits, with the weakest animals, mostly subadults, succumbing to the harsh conditions in the desert and sinking into the mud ofephemeral 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 whichPlateosaurus herds congregated on large water holes, and some herd members got pushed in.[81] Light animals managed to get free, while heavy individuals got stuck and died.[81]
A different school of thought developed almost half a century later, with palaeontologistDavid 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 thatPlateosaurus 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,[66] 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.[82]
A detailed re-assessment of the taphonomy by palaeontologist Martin Sander of theUniversity of Bonn, Germany, found that the mud-miring hypothesis first suggested by Fraas[62] 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 RanchoLa Brea Tar Pits, is the only one explaining all taphonomic data. The degree of completeness of thecarcasses 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 ofPlateosaurus and other taxa of herbivores were too light to sink into the mud or managed to extract themselves, and were thus not preserved. Similarly, scavengingtheropods 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] The palaeopathologies on one specimen ofP. trossingenensis are consistent with being caused by the animal being mired in mud and support this hypothesis.[78]
Huxley, Thomas H. (1870). "On the Classification of the Dinosauria, with observations on the Dinosauria of the Trias".Quarterly Journal of the Geological Society of London. Vol. 26. pp. 32–51.doi:10.1144/gsl.jgs.1870.026.01-02.09 – viaWikisource.
Media related toPlateosaurus at Wikimedia Commons
Data related toPlateosaurus at Wikispecies
