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Discovered in 1834 by Johann Friedrich Engelhardt and described three years later by [[Christian Erich Hermann von Meyer|Hermann von Meyer]], ''Plateosaurus'' was the fifth named dinosaur genus that is still considered valid today. However, it was not one of the three genera originally used by [[Richard Owen]] in 1842 to define Dinosauria, 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, with over 100 skeletons found, some of them nearly complete. It was nicknamed the ''Schwäbischer Lindwurm'' (Swabian dragon) because it was so common a fossil in south-western Germany. |
Discovered in 1834 by Johann Friedrich Engelhardt and described three years later by [[Christian Erich Hermann von Meyer|Hermann von Meyer]], ''Plateosaurus'' was the fifth named dinosaur genus that is still considered valid today. However, it was not one of the three genera originally used by [[Richard Owen]] in 1842 to define Dinosauria, 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, with over 100 skeletons found, some of them nearly complete. It was nicknamed the ''Schwäbischer Lindwurm'' (Swabian dragon) because it was so common a fossil in south-western Germany. |
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''Plateosaurus'' was a [[bipedalism|bipedal]] [[herbivore]] with a small skull on a long, mobile 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 {{convert|4.8|and|10|m|ft}} long and weighed between {{convert|600|and|4000|kg|lb}}. Commonly, the animals lived for at least 12 to 20 years, but the maximum life span is not known. |
''Plateosaurus'' was a [[bipedalism|bipedal]] [[herbivore]] with a small skull on a long, mobile 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 {{convert|4.8|and|10|m|ft}} long and weighed between {{convert|600|and|4000|kg|lb}}. Commonly, the animals lived for at least 12 to 20 years, but the maximum life span is not known. |
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Despite the great quantity and excellent quality of the fossil material, ''Plateosaurus'' was for a long time one of the most misunderstood dinosaurs. Some researchers proposed theories that were later shown to conflict with [[Geology|geological]] and [[paleontology|palaeontological]] evidence, but have become the paradigm of public opinion. Since 1980 the [[taxonomy]] (relationships), [[taphonomy]] (how the animals became embedded and fossilized), 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. |
Despite the great quantity and excellent quality of the fossil material, ''Plateosaurus'' was for a long time one of the most misunderstood dinosaurs. Some researchers proposed theories that were later shown to conflict with [[Geology|geological]] and [[paleontology|palaeontological]] evidence, but have become the paradigm of public opinion. Since 1980 the [[taxonomy]] (relationships), [[taphonomy]] (how the animals became embedded and fossilized), 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. |
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The second major German locality with ''P. engelhardti'' finds, a quarry in [[Trossingen]] in the [[Black Forest]], was worked repeatedly in the 20th century.<ref name=Weis1984/> Between 1911 and 1932, excavations during six field seasons led by German |
The second major German locality with ''P. engelhardti'' finds, a quarry in [[Trossingen]] in the [[Black Forest]], was worked repeatedly in the 20th century.<ref name=Weis1984/> Between 1911 and 1932, excavations during six field seasons led by German palaeontologists Eberhard Fraas (1911–1912), [[Friedrich von Huene]] (1921–23),<ref name=Huene1926/><ref name=Huene1928/> 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.<ref name=Weis1984/> The large number of specimens from that area caused German palaeontologist Friedrich August von Quenstedt to nickname the animal ''Schwäbischer Lindwurm'' (Swabian lindworm or Swabian dragon).{{#tag:ref|Quenstedt (1858)<ref name=Quenstedt1858/>, cited on p. 255 in Sander (1992)<ref name=Sander1992/>|group="upper-alpha"}} |
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The ''Plateosaurus'' skeletons in a clay pit of the Tonwerke Keller AG in [[Frick, Switzerland|Frick]], Switzerland, were first noticed in 1976.<ref name=Sander1992/> While the bones are often significantly deformed by [[taphonomy|taphonomic]] processes, Frick yields skeletons of ''P. engelhardti'' comparable in completeness and position to those of Trossingen and Halberstadt.<ref name=Sander1992/> |
The ''Plateosaurus'' skeletons in a clay pit of the Tonwerke Keller AG in [[Frick, Switzerland|Frick]], Switzerland, were first noticed in 1976.<ref name=Sander1992/> While the bones are often significantly deformed by [[taphonomy|taphonomic]] processes, Frick yields skeletons of ''P. engelhardti'' comparable in completeness and position to those of Trossingen and Halberstadt.<ref name=Sander1992/> |
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''Plateosaurus'' was the first "prosauropod" to be described,<ref name=Huene1932/> and gives its name to the family [[Plateosauridae]] as [[type genus]]. Initially, when the genus was poorly known, it was only included in [[Sauria]], being some kind of reptile, but not in any more narrowly defined taxon.<ref name=vonmeyer1837/> In 1845, von Meyer created the group [[Dinosaur|Pachypodes]] (a defunct junior [[Synonym (taxonomy)|synonym]] of Dinosauria) to include ''Plateosaurus'', ''[[Iguanodon]]'', ''[[Megalosaurus]]'' and ''[[Hylaeosaurus]]''.<ref name=vonmeyer1845/> Plateosauridae was proposed by [[Othniel Charles Marsh]] in 1895 within [[Theropoda]].<ref name=Marsh1895/> Later it was moved to "[[Prosauropoda]]" by von Huene,<ref name=Huene1926b/> a placement that was accepted by most authors.<ref name=Young1941/><ref name=Bonaparte1971/><ref name=Moser2003/><ref name=Yates2003/> For many years the clade only included ''Plateosaurus'' and various junior synonyms, but later two more genera were considered to belong to it: ''Sellosaurus''<ref name=Huene1905/> and possibly ''[[Unaysaurus]]''.<ref name=Lealetal2004/> Of these, ''Sellosaurus'' is probably another junior synonym of ''Plateosaurus''.<ref name=Yates2003/> |
''Plateosaurus'' was the first "prosauropod" to be described,<ref name=Huene1932/> and gives its name to the family [[Plateosauridae]] as [[type genus]]. Initially, when the genus was poorly known, it was only included in [[Sauria]], being some kind of reptile, but not in any more narrowly defined taxon.<ref name=vonmeyer1837/> In 1845, von Meyer created the group [[Dinosaur|Pachypodes]] (a defunct junior [[Synonym (taxonomy)|synonym]] of Dinosauria) to include ''Plateosaurus'', ''[[Iguanodon]]'', ''[[Megalosaurus]]'' and ''[[Hylaeosaurus]]''.<ref name=vonmeyer1845/> Plateosauridae was proposed by [[Othniel Charles Marsh]] in 1895 within [[Theropoda]].<ref name=Marsh1895/> Later it was moved to "[[Prosauropoda]]" by von Huene,<ref name=Huene1926b/> a placement that was accepted by most authors.<ref name=Young1941/><ref name=Bonaparte1971/><ref name=Moser2003/><ref name=Yates2003/> For many years the clade only included ''Plateosaurus'' and various junior synonyms, but later two more genera were considered to belong to it: ''Sellosaurus''<ref name=Huene1905/> and possibly ''[[Unaysaurus]]''.<ref name=Lealetal2004/> Of these, ''Sellosaurus'' is probably another junior synonym of ''Plateosaurus''.<ref name=Yates2003/> |
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The type series of ''Plateosaurus engelhardti'' included "roughly 45 bones",{{#tag:ref|p. 74 in Blankenhorn (1898)<ref name=blankenhorn1898/>|group="upper-alpha"}} of which nearly half are lost.{{#tag:ref|p. 12 in Moser (2003) (English summary on p. 170)<ref name=Moser2003/>|group="upper-alpha"}} The remaining material is kept in the Institute for Palaeontology of the [[University of Erlangen-Nuremberg]], Germany.{{#tag:ref|p. 13 in Moser (2003) (English summary on p. 161)<ref name=Moser2003/>|group="upper-alpha"}} From it, German palaeontologist Markus Moser in 2003 selected a partial [[sacrum]] (series of fused hip vertebrae) as a [[syntype|lectotype]].{{#tag:ref|p.13 in Moser (2003), see also pp. 17 and pp. |
The type series of ''Plateosaurus engelhardti'' included "roughly 45 bones",{{#tag:ref|p. 74 in Blankenhorn (1898)<ref name=blankenhorn1898/>|group="upper-alpha"}} of which nearly half are lost.{{#tag:ref|p. 12 in Moser (2003) (English summary on p. 170)<ref name=Moser2003/>|group="upper-alpha"}} The remaining material is kept in the Institute for Palaeontology of the [[University of Erlangen-Nuremberg]], Germany.{{#tag:ref|p. 13 in Moser (2003) (English summary on p. 161)<ref name=Moser2003/>|group="upper-alpha"}} From it, German palaeontologist Markus Moser in 2003 selected a partial [[sacrum]] (series of fused hip vertebrae) as a [[syntype|lectotype]].{{#tag:ref|p. 13 in Moser (2003), see also pp. 17 and pp. 36–40, English summary on pp. 160–161 and 163–164<ref name=Moser2003/>|group="upper-alpha"}} 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, concluding that the material probably stems from the "Buchenbühl", roughly {{convert|2|km|mi}} south of Heroldsberg near [[Nuremberg]], Bavaria, Germany.{{#tag:ref|pp. 14–15 in Moser (2003) (English summary on p. 160)<ref name=Moser2003/>|group="upper-alpha"}} |
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The type specimen of ''Plateosaurus gracilis'', an incomplete [[postcranium]], is kept at the [[State Museum of Natural History Stuttgart|Staatliches Museum für Naturkunde Stuttgart]], Germany.{{#tag:ref|pp. |
The type specimen of ''Plateosaurus gracilis'', an incomplete [[postcranium]], is kept at the [[State Museum of Natural History Stuttgart|Staatliches Museum für Naturkunde Stuttgart]], Germany.{{#tag:ref|pp. 331–332 in Yates (2003)<ref name=Yates2003/>|group="upper-alpha"}} The type locality is Heslach, a suburb of [[Stuttgart]], Germany.{{#tag:ref|pp. 331–332 in Yates (2003)<ref name=Yates2003/>|group="upper-alpha"}}<!-- I'll try to get a picture of the "Sellosaurus" remains, and add some text in the appropriate sections on it. However, that's gonna be bony&dry--> |
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===Etymology=== |
===Etymology=== |
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[[File:Plateosaurus quenstedti.jpg|thumb|''Plateosaurus engelhardti'' (previously ''P. quenstedti'') skull and neck at the Museum für Naturkunde, Berlin |alt=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''.]] |
[[File:Plateosaurus quenstedti.jpg|thumb|''Plateosaurus engelhardti'' (previously ''P. quenstedti'') skull and neck at the Museum für Naturkunde, Berlin |alt=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''.]] |
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All named species of ''Plateosaurus'' except ''P. gracilis'' have turned out to be junior synonyms of the type species or invalid names.<ref name=Moser2003/><ref name=Yates2003/> Huene<ref name=Huene1932/> 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'').<ref name=Sander1992/> Later, he collapsed 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.<ref name=Jaekel1913/> Systematic research by Galton drastically reduced the number of genera and species. Galton synonymised all cranial material,<ref name=Galton1984/><ref name=Galton1985/><ref name=Galton1986/> and described differences between the [[syntype]]s of ''P. engelhardti'' and the Trossingen material, which he referred to ''P. longiceps''.<ref name=Galton2000/> Galton recognized ''P. trossingensis'', ''P. fraasianus'' and ''P. integer'' to be identical to ''P. longiceps''.<ref name="Galton2001"/> Markus Moser, however, showed clearly that ''P. longiceps'' is itself a junior synonym of ''P. engelhardti''.<ref name=Moser2003/> 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''.{{#tag:ref|Moser (2003), summarized on p. 152 (English summary on p. 179)<ref name=Moser2003/>|group="upper-alpha"}} |
All named species of ''Plateosaurus'' except ''P. gracilis'' have turned out to be junior synonyms of the type species or invalid names.<ref name=Moser2003/><ref name=Yates2003/> Huene<ref name=Huene1932/> 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'').<ref name=Sander1992/> Later, he collapsed 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.<ref name=Jaekel1913/> Systematic research by Galton drastically reduced the number of genera and species. Galton synonymised all cranial material,<ref name=Galton1984/><ref name=Galton1985/><ref name=Galton1986/> and described differences between the [[syntype]]s of ''P. engelhardti'' and the Trossingen material, which he referred to ''P. longiceps''.<ref name=Galton2000/> Galton recognized ''P. trossingensis'', ''P. fraasianus'' and ''P. integer'' to be identical to ''P. longiceps''.<ref name="Galton2001"/> Markus Moser, however, showed clearly that ''P. longiceps'' is itself a junior synonym of ''P. engelhardti''.<ref name=Moser2003/> 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''.{{#tag:ref|Moser (2003), summarized on p. 152 (English summary on p. 179)<ref name=Moser2003/>|group="upper-alpha"}} |
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However, there is much prosauropod material from the German [[Knollenmergel]] in museum collections, most of it labelled as ''Plateosaurus'', that does not belong to the type species, and possibly not to ''Plateosaurus'' at all.<ref name=Weishampeletal2004Dinosauria/>{{#tag:ref|p. 152 in Moser (2003) (English summary on p. 179)<ref name=Moser2003/>|group="upper-alpha"}} Some of this material is not diagnostic; other material has been recognized to be different, but was never sufficiently described.{{#tag:ref|pp. |
However, there is much prosauropod material from the German [[Knollenmergel]] in museum collections, most of it labelled as ''Plateosaurus'', that does not belong to the type species, and possibly not to ''Plateosaurus'' at all.<ref name=Weishampeletal2004Dinosauria/>{{#tag:ref|p. 152 in Moser (2003) (English summary on p. 179)<ref name=Moser2003/>|group="upper-alpha"}} Some of this material is not diagnostic; other material has been recognized to be different, but was never sufficiently described.{{#tag:ref|pp. 193–194 in Jaekel (1913-1914)<ref name=Jaekel1913/>|group="upper-alpha"}} |
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==Taphonomy== |
==Taphonomy== |
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The [[taphonomy]] (burial and fossilization process) of the three main ''Plateosaurus'' sites—Trossingen, Halberstadt (both in Germany) and Frick (Switzerland)—is unusual in several ways.<ref name=Sander1992/> All three sites are nearly monospecific assemblages, meaning that they contain practically only one species, which requires very special circumstances.<ref name=Sander1992/> However, shed teeth of [[theropoda|theropod]]s have been found at all three sites, as well as remains of ''Proganochelys'', an early turtle.<ref name=Sander1992/> Additionally, a partial "prosauropod" skeleton was found in Halberstadt that does not belong to ''Plateosaurus'', but is preserved in a similar position.<ref name=Jaekel1913/> All sites yielded almost complete and partial skeletons of ''Plateosaurus'', as well as isolated bones.<ref name=Sander1992/> The partial skeletons tend to include the hind limbs and hips, while parts of the anterior body and neck are rarely found in isolation.<ref name=Sander1992/> The animals were all |
The [[taphonomy]] (burial and fossilization process) of the three main ''Plateosaurus'' sites—Trossingen, Halberstadt (both in Germany) and Frick (Switzerland)—is unusual in several ways.<ref name=Sander1992/> All three sites are nearly monospecific assemblages, meaning that they contain practically only one species, which requires very special circumstances.<ref name=Sander1992/> However, shed teeth of [[theropoda|theropod]]s have been found at all three sites, as well as remains of ''Proganochelys'', an early turtle.<ref name=Sander1992/> Additionally, a partial "prosauropod" skeleton was found in Halberstadt that does not belong to ''Plateosaurus'', but is preserved in a similar position.<ref name=Jaekel1913/> All sites yielded almost complete and partial skeletons of ''Plateosaurus'', as well as isolated bones.<ref name=Sander1992/> The partial skeletons tend to include the hind limbs and hips, while parts of the anterior body and neck are rarely found in isolation.<ref name=Sander1992/> The animals were all adults or subadults (nearly adult individuals); no juveniles or hatchlings are known.<ref name=Sander1992/> Complete skeletons and large skeleton parts that include the hind limbs all rest right side up, as do the turtles.<ref name=Sander1992/> 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.<ref name=Sander1992/> |
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===Earlier interpretations=== |
===Earlier interpretations=== |
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[[File:Plateosaurus SMNS F33.jpg|thumb|left|''P. engelhardti'', collection number F 33 of the Staatliches Museum für Naturkunde Stuttgart, Germany, in dorsal view. The skeleton was kept in articulation as found at Trossingen (Germany) 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.<ref name=Sander1992/>| alt=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.]] |
[[File:Plateosaurus SMNS F33.jpg|thumb|left|''P. engelhardti'', collection number F 33 of the Staatliches Museum für Naturkunde Stuttgart, Germany, in dorsal view. The skeleton was kept in articulation as found at Trossingen (Germany) 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.<ref name=Sander1992/>| alt=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.]] |
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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.<ref name=Fraas1913/> Similarly, Jaekel interpreted the Halberstadt finds as animals that waded too deep into swamps, became mired and drowned.<ref name=Jaekel1913/> He interpreted partial remains as having been transported into the deposit by water, and strongly refuted a catastrophic accumulation.<ref name=Jaekel1913/> In contrast, von Huene interpreted the sediment as [[Aeolian processes#Deposition|aeolian deposits]], with the weakest animals, mostly subadults |
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.<ref name=Fraas1913/> Similarly, Jaekel interpreted the Halberstadt finds as animals that waded too deep into swamps, became mired and drowned.<ref name=Jaekel1913/> He interpreted partial remains as having been transported into the deposit by water, and strongly refuted a catastrophic accumulation.<ref name=Jaekel1913/> In contrast, von Huene interpreted the sediment as [[Aeolian processes#Deposition|aeolian deposits]], with the weakest animals, mostly subadults, succumbing to the harsh conditions in the desert and sinking into the mud of [[Ephemeral#Geographical_examples|ephemeral]] water holes.<ref name=Huene1928/> 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.<ref name=Huene1928/> Seemann developed a different scenario, in which ''Plateosaurus'' herds congregated on large water holes, and some herd members got pushed in.<ref name=Seemann1933/> Light animals managed to get free, heavy ones got stuck and died.<ref name=Seemann1933/> |
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A different school of thought developed almost half a century later, with palaeontologist [[David B. Weishampel|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.<ref name=Weis1984/> Weishampel explained the curious monospecific assemblage by theorizing that ''Plateosaurus'' were common during this period.<ref name=Weis1984/> 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]],<ref name=WeisWest1984/> and has since become the standard explanation on most internet sites and in popular books on dinosaurs.<ref name=Moser2003/> Rieber proposed a more elaborate scenario, which included the animals dying of thirst or starvation, and being concentrated by mudflows.<ref name=Rieber1985a/> |
A different school of thought developed almost half a century later, with palaeontologist [[David B. Weishampel|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.<ref name=Weis1984/> Weishampel explained the curious monospecific assemblage by theorizing that ''Plateosaurus'' were common during this period.<ref name=Weis1984/> 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]],<ref name=WeisWest1984/> and has since become the standard explanation on most internet sites and in popular books on dinosaurs.<ref name=Moser2003/> Rieber proposed a more elaborate scenario, which included the animals dying of thirst or starvation, and being concentrated by mudflows.<ref name=Rieber1985a/> |
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[[Image:Plateosaurus engelhardti - Trias.jpg|thumb|Mounted cast of SMNS 13200. 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.|alt=Photograph of a mounted cast in left lateral view, with tail dragging on the ground.]] |
[[Image:Plateosaurus engelhardti - Trias.jpg|thumb|Mounted cast of SMNS 13200. 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.|alt=Photograph of a mounted cast in left lateral view, with tail dragging on the ground.]] |
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Practically any imaginable posture has been suggested for ''Plateosaurus'' in the scientific literature at some point. [[Friedrich von Huene|Von Huene]] assumed [[digitigrade]] [[bipedalism|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.<ref name=Huene1926/><ref name=Huene1908/> In contrast, the main investigator of the [[Halberstadt]] material, Jaekel, initially concluded that the animals walked [[quadrupedalism|quadruped]]ally, like lizards, with a sprawling limb position, [[plantigrade]], and [[Undulatory locomotion|laterally undulating]] the body.<ref name=Jaekel1910/> Only a year later, Jaekel instead favoured a clumsy, kangaroo-like hopping,<ref name=Jaekel1911/> a change of heart for which he was mocked by [[Germans|German]] [[zoology|zoologist]] Gustav Tornier,<ref name=Tornier1912/> 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.<ref name=Fraas1913/><ref name=Fraas1912/> 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.<ref name=MullStoll1935/> However, most of these adaptations are actually present in ''Plateosaurus''.<ref name=MallisonTDPII/><ref name=MallisonTDPI/> |
Practically any imaginable posture has been suggested for ''Plateosaurus'' in the scientific literature at some point. [[Friedrich von Huene|Von Huene]] assumed [[digitigrade]] [[bipedalism|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.<ref name=Huene1926/><ref name=Huene1908/> In contrast, the main investigator of the [[Halberstadt]] material, Jaekel, initially concluded that the animals walked [[quadrupedalism|quadruped]]ally, like lizards, with a sprawling limb position, [[plantigrade]], and [[Undulatory locomotion|laterally undulating]] the body.<ref name=Jaekel1910/> Only a year later, Jaekel instead favoured a clumsy, kangaroo-like hopping,<ref name=Jaekel1911/> a change of heart for which he was mocked by [[Germans|German]] [[zoology|zoologist]] Gustav Tornier,<ref name=Tornier1912/> 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.<ref name=Fraas1913/><ref name=Fraas1912/> 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.<ref name=MullStoll1935/> However, most of these adaptations are actually present in ''Plateosaurus''.<ref name=MallisonTDPII/><ref name=MallisonTDPI/> |
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[[File:Plateosaurus arm and hand.jpg|thumb|upright|left|[[Anatomical terms of location#Arms|Dorsal]] view of left lower arm and hand of ''P. engelhardti'' ("Skelett 2") at the museum of the Institute for Geosciences of the Eberhard-Karls-University Tübingen, Germany. The shape of the [[Radius (bone)|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.]]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'',<ref name=Christetal1996/><ref name=ChristPreu1996/> led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back.{{#tag:ref|pp. |
[[File:Plateosaurus arm and hand.jpg|thumb|upright|left|[[Anatomical terms of location#Arms|Dorsal]] view of left lower arm and hand of ''P. engelhardti'' ("Skelett 2") at the museum of the Institute for Geosciences of the Eberhard-Karls-University Tübingen, Germany. The shape of the [[Radius (bone)|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.]]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'',<ref name=Christetal1996/><ref name=ChristPreu1996/> led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back.{{#tag:ref|pp. 138–142 in Moser (2003) (English summary on p. 176)<ref name=Moser2003/>|group="upper-alpha"}}<ref name=WeisWest1984/><ref name=GaltonUpchurch2004Dinosauria/><ref name=Galton1990Dinosauria/>{{#tag:ref|p. 145 in Paul (1997)<ref name=Paul1997/>|group="upper-alpha"}}<ref name=Welln1994/> Many researchers were of the opinion that ''Plateosaurus'' could use both quadrupedal gaits (for slow speeds) and bipedal gaits (for rapid locomotion),<ref name=Christetal1996/><ref name=ChristPreu1996/><ref name=Galton1990Dinosauria/><ref name=Paul1997/> while [[Peter Wellnhofer|Wellnhofer]] insisted that the tail curved strongly downward, making a bipedal posture impossible.<ref name=Welln1994/> However, Moser showed that the tail was in fact straight.{{#tag:ref|pp. 142–144 in Moser (2003) (English summary on pp. 176–177)<ref name=Moser2003/>|group="upper-alpha"}} |
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This consensus was changed by a detailed study of the forelimbs of ''Plateosaurus'' by [[Matthew Bonnan|Bonnan]] and Senter (2007), which clearly showed that ''Plateosaurus'' was incapable of [[Pronation|pronating]] its hands.<ref name=BonnSent2007/> The pronated position in some museum mounts had been achieved by exchanging the position of [[radius]] and [[ulna]] in the elbow. This meant that ''Plateosaurus'' was an obligate digitigrade 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 [[center of mass]] rests squarely over the hind limbs.<ref name=MallisonTDPII/><ref name=MallisonTDPI/><ref name=MallisonBook1/> |
This consensus was changed by a detailed study of the forelimbs of ''Plateosaurus'' by [[Matthew Bonnan|Bonnan]] and Senter (2007), which clearly showed that ''Plateosaurus'' was incapable of [[Pronation|pronating]] its hands.<ref name=BonnSent2007/> The pronated position in some museum mounts had been achieved by exchanging the position of [[radius]] and [[ulna]] in the elbow. This meant that ''Plateosaurus'' was an obligate digitigrade 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 [[center of mass]] rests squarely over the hind limbs.<ref name=MallisonTDPII/><ref name=MallisonTDPI/><ref name=MallisonBook1/> |
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===Growth, metabolism and life span=== |
===Growth, metabolism and life span=== |
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[[File:Human-plateosaurus size comparison(V2).png|thumb|Size comparison between a maximum size individual of ''P. engelhardti'' and a human.| alt=A silhouette drawing of ''Plateosaurus'' in lateral view, and a human male. The dinosaur is depicted as a biped. The 1.8 m tall (6 ft) human does not reach hip height of ''Plateosaurus''.]] |
[[File:Human-plateosaurus size comparison(V2).png|thumb|Size comparison between a maximum size individual of ''P. engelhardti'' and a human.| alt=A silhouette drawing of ''Plateosaurus'' in lateral view, and a human male. The dinosaur is depicted as a biped. The 1.8 m tall (6 ft) human does not reach hip height of ''Plateosaurus''.]] |
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Similar to all non-avian dinosaurs studied to date, ''Plateosaurus'' grew in a pattern that is dissimilar to both extant mammals and avian dinosaurs. In the closely related sauropods with their typical [[physiology of dinosaurs|dinosaurian physiology]], growth was initially rapid, continued somewhat slower well beyond sexual maturity, but was determinate, i.e. the animals stopped growing at a maximum size.<ref name=Sander1999/> 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. |
Similar to all non-avian dinosaurs studied to date, ''Plateosaurus'' grew in a pattern that is dissimilar to both [[Extant taxon|extant]] mammals and avian dinosaurs. In the closely related sauropods with their typical [[physiology of dinosaurs|dinosaurian physiology]], growth was initially rapid, continued somewhat slower well beyond sexual maturity, but was determinate, i.e. the animals stopped growing at a maximum size.<ref name=Sander1999/> 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 [[Thermoregulation#Behavioural_temperature_regulation|behavioural thermoregulation]] and a low [[metabolism|metabolic]] rate (i.e. [[ectotherm]]y), and is called "developmental plasticity".<ref name=SK2005/> (Note that is not the same as neural [[developmental plasticity]].) |
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''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 {{convert|4.8|m|ft}} total length, while others reached {{convert|10|m|ft}}. However, the bone microstructure indicates rapid growth, as in sauropods and extant mammals, which suggests [[warm-blooded|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 [[University of Bonn|the University of Bonn]], Germany.<ref name=SK2005/> A further indication for endothermy is the avian-style lung of ''Plateosaurus''.<ref name=MallisonTDPII/> |
''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 {{convert|4.8|m|ft}} total length, while others reached {{convert|10|m|ft}}. However, the bone microstructure indicates rapid growth, as in sauropods and extant mammals, which suggests [[warm-blooded|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 [[University of Bonn|the University of Bonn]], Germany.<ref name=SK2005/> A further indication for endothermy is the avian-style lung of ''Plateosaurus''.<ref name=MallisonTDPII/> |
Revision as of 00:55, 13 November 2011
Plateosaurus Temporal range: Triassic,
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Mounted skeleton of P. engelhardti (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 | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Clade: | Dinosauria |
Clade: | Saurischia |
Clade: | †Sauropodomorpha |
Family: | †Plateosauridae |
Genus: | †Plateosaurus von Meyer, 1837 |
Type species | |
†Plateosaurus engelhardti von Meyer, 1837
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Species | |
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Synonyms | |
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Plateosaurus (meaning "broadway lizard", often mistranslated as "flat lizard" or "broad lizard") is a genus of plateosaurid dinosaur that lived during the Late Triassic period, around 216 to 199 million years ago, in what is now Central and Northern Europe. Plateosaurus is a basal (early) sauropodomorph dinosaur, a so-called "prosauropod". The latest research recognizes two species: the type species P. engelhardti from the late Norian and Rhaetian, and the slightly earlier P. gracilis from the lower Norian. 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 today. However, it was not one of the three genera originally used by Richard Owen in 1842 to define Dinosauria, 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, with over 100 skeletons found, some of them nearly complete. It was nicknamed the Schwäbischer Lindwurm (Swabian dragon) because it was so common a fossil in south-western Germany.
Plateosaurus was a bipedal herbivore with a small skull on a long, mobile 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 fossilized), 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.
Description
Plateosaurus is a member of a group of early herbivores known as "prosauropods".[1] The group name is obsolete, as "Prosauropoda" is not a monophyletic group (thus given in quotation marks), and most researchers prefer the term basal sauropodomorph.[2][3] Plateosaurus had the typical body shape of a herbivorous bipedal dinosaur: a small skull, a long and flexible neck composed of ten cervical (neck) vertebrae, a stocky body and a long, mobile tail composed of at least 40 caudal (tail) vertebrae.[4][5][6] The arms of Plateosaurus were very short, even compared to most other "prosauropods", but strongly built, with hands adapted to powerful grasping.[5][7] The shoulder girdle was narrow (often misaligned in skeletal mounts and drawings),[7] with the clavicles (collar bones) touching at the body midline,[5] as is the case in other basal sauropodomorphs.[8] The hind limbs were held under the body, with slightly flexed knees and ankles, and the foot digitigrade – the animal walked on its toes.[5][9][10] The proportionally long lower leg and metatarsus show that Plateosaurus was adapted to rapid bipedal locomotion.[5][7][9][10] The tail of Plateosaurus was typically dinosaurian, muscular and with high mobility.[7]
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, and a large, round orbit (eye socket), a sub-triangular antorbital fenestra and an egg-shaped naris (nostril) of almost equal size.[4][5][11] The snout carried many small, leaf-shaped, socketed teeth in both the upper and lower jaw, 5 to 6 on the premaxilla, 24 to 30 on the maxilla, and 21 to 28 on the dentary (lower jaw).[4][5][11] The teeth had bluntly serrated, thick, leaf-shaped crowns suitable for crushing plant material.[4][5][11] The low position of the jaw joint gave the chewing muscles great leverage, so that Plateosaurus could deliver a powerful bite.[11] These features suggest that it fed exclusively or mainly on plants.[11] Its eyes were directed to the sides, rather than the front, providing all-round vision to watch for predators.[4][5][11] Some fossil skeletons have preserved sclerotic rings (rings of bone plates that protect the eye).[4][5][11]
The ribs were connected to the dorsal (trunk) vertebrae with two joints, together acting as a simple hinge joint, which has allowed reconstructing the inhaled and exhaled positions of the ribcage. The difference in volume between both positions determines the air exchange volume (the amount of air moved with each breath), determined to be ~20 l for a P. engelhardti individual estimated to have weighed 690 kg, or 29 ml/kg bodyweight.[7] This is a typical value for birds, but not for mammals,[12] and indicates that Plateosaurus probably had an avian-style flow-through lung,[7] although indicators for postcranial pneumaticity (air sacs of the lung invading the bones to reduce weight) can be found on the bones of only few individuals, and were only recognized recently.[13][14] Combined with evidence from bone histology[15][16] this indicates that Plateosaurus was an endotherm.[16][17]
The type species of Plateosaurus is P. engelhardti.[18] Adult individuals of this species reached 4.8 to 10 metres (16 to 33 ft) in length.[16] Average individuals had a mass of around 600 to 4,000 kilograms (1,300 to 8,800 lb).[10] The older species, P. gracilis (formerly named Sellosaurus gracilis), was somewhat smaller, with a total length of 4 to 5 metres (13 to 16 ft).[19]
Discovery and history
In 1834, physician Johann Friedrich Engelhardt discovered some vertebrae and leg bones at Heroldsberg near Nuremberg, Germany.[18] Three years later German palaeontologist Hermann von Meyer designated them as the type specimen of a new genus, Plateosaurus.[18] Since then, remains of well over 100 individuals of Plateosaurus have been discovered at various locations throughout Europe.[15]
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.[20] Three localities are of special importance, because they yielded specimens in large numbers and unusually good quality.[15] Between the 1910s and 1930s, excavations in a clay pit in Saxony-Anhalt dug up 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.[15] Some of the plateosaur material was assigned to P. longiceps, a species now considered a junior synonym of P. engelhardti and described by palaeontologist Otto Jaekel in 1914.[21] Most of the material found its way to the Museum für Naturkunde in Berlin, where much of it was destroyed during World War II.[20] The Halberstadt quarry today is covered by a housing development.[20]
The second major German locality with P. engelhardti finds, a quarry in Trossingen in the Black Forest, was worked repeatedly in the 20th century.[20] Between 1911 and 1932, excavations during six field seasons led by German palaeontologists Eberhard Fraas (1911–1912), Friedrich von Huene (1921–23),[5][22] 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.[20] The large number of specimens from that area caused German palaeontologist Friedrich August von Quenstedt to nickname the animal Schwäbischer Lindwurm (Swabian lindworm or Swabian dragon).[B]
The Plateosaurus skeletons in a clay pit of the Tonwerke Keller AG in Frick, Switzerland, were first noticed in 1976.[15] While the bones are often significantly deformed by taphonomic processes, Frick yields skeletons of P. engelhardti comparable in completeness and position to those of Trossingen and Halberstadt.[15]
In 1997, workers of an oil platform of the Snorre oilfield located at the northern end of the North Sea were drilling through sandstone for oil exploration when in a drill core extracted from 2,256 meters below the seafloor they stumbled upon a fossil they believed to be plant material.[24] 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,[24] making it the first dinosaur found in Norway. Plateosaurus material has also been found in the Fleming Fjord Formation of East Greenland.[25]
Classification and type material
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Plateosaurus was the first "prosauropod" to be described,[1] and gives its name to the family Plateosauridae as type genus. Initially, when the genus was poorly known, it was only included in Sauria, being some kind of reptile, but not in any more narrowly defined taxon.[18] In 1845, von Meyer created the group Pachypodes (a defunct junior synonym of Dinosauria) to include Plateosaurus, Iguanodon, Megalosaurus and Hylaeosaurus.[27] Plateosauridae was proposed by Othniel Charles Marsh in 1895 within Theropoda.[28] Later it was moved to "Prosauropoda" by von Huene,[29] a placement that was accepted by most authors.[30][31][6][19] For many years the clade only included Plateosaurus and various junior synonyms, but later two more genera were considered to belong to it: Sellosaurus[32] and possibly Unaysaurus.[33] Of these, Sellosaurus is probably another junior synonym of Plateosaurus.[19]
The type series of Plateosaurus engelhardti included "roughly 45 bones",[C] of which nearly half are lost.[D] The remaining material is kept in the Institute for Palaeontology of the University of Erlangen-Nuremberg, Germany.[E] From it, German palaeontologist Markus Moser in 2003 selected a partial sacrum (series of fused hip vertebrae) as a lectotype.[F] 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, concluding that the material probably stems from the "Buchenbühl", roughly 2 kilometres (1.2 mi) south of Heroldsberg near Nuremberg, Bavaria, Germany.[G]
The type specimen of Plateosaurus gracilis, an incomplete postcranium, is kept at the Staatliches Museum für Naturkunde Stuttgart, Germany.[H] The type locality is Heslach, a suburb of Stuttgart, Germany.[I]
Etymology
The etymology of the name Plateosaurus is not clear. Moser pointed out that the original description contains no information, and various authors have offered differing interpretations.[J] Agassiz offered the first explanation, listing Ancient Greek platê/πλατη ("paddle", "rudder"; Agassiz translates this as Latin pala = "spade") and sauros/σαυρος (lizard).[K] Agassiz consequently renamed the genus Platysaurus,[L] probably from Greek platys/πλατυς ("broad, flat, broad-shouldered"), creating an invalid junior synonym. This derivation was copied by later authors, so that Plateosaurus is often translated as "broad lizard" or "flat lizard". Often, claims were made that platys/πλατυς is supposed to have been intended as a reference to the laterally flattened teeth of Plateosaurus,[M] which is impossible because the teeth were unknown at the time of description. Palaeontologist Markus Moser suggests the Ancient Greek plateia/πλατεια (broadway) as an alternative, which corresponds better to the stem of Plateosaurus, which clearly is "plate-", and not "platy-". Thus, the name should be translated as "broadway lizard".[N]
Taxonomy
Valid species
The taxonomic history of Plateosaurus is complex and confusing.[6] As of 2009, only two species are accepted as valid,[6][19] the type species P. engelhardti and the older P. gracilis, previously referred to as its own genus Sellosaurus. British palaeontologist Peter Galton showed clearly that all cranial material from Trossingen, Halberstadt and Frick pertains to one species.[11] 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.[6] 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.[O] Palaeontologist Adam Yates of the University of the Witwatersrand casted further doubt on the generic separation, and included the type material, but not all assigned finds of Sellosaurus gracilis, in Plateosaurus as P. gracilis.[19] Previously, von Huene had already concluded this in 1926.[P]
However, Yates cautioned that P. gracilis may be a metataxon, meaning that there is neither evidence that material assigned to it is monophyletic (belongs to one species), nor that it is paraphyletic (belongs to several species).[Q] 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 certain that they belong to the same taxon. It is therefore possible that the known material contains more species belonging to Plateosaurus.[R]
Invalid species
All named species of Plateosaurus except P. gracilis have turned out to be junior synonyms of the type species or invalid names.[6][19] Huene[1] 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).[15] Later, he collapsed 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.[21] Systematic research by Galton drastically reduced the number of genera and species. Galton synonymised all cranial material,[11][38][39] and described differences between the syntypes of P. engelhardti and the Trossingen material, which he referred to P. longiceps.[40] Galton recognized P. trossingensis, P. fraasianus and P. integer to be identical to P. longiceps.[41] Markus Moser, however, showed clearly that P. longiceps is itself a junior synonym of P. engelhardti.[6] 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.[S] However, there is much prosauropod material from the German Knollenmergel in museum collections, most of it labelled as Plateosaurus, that does not belong to the type species, and possibly not to Plateosaurus at all.[42][T] Some of this material is not diagnostic; other material has been recognized to be different, but was never sufficiently described.[U]
Taphonomy
The taphonomy (burial and fossilization process) of the three main Plateosaurus sites—Trossingen, Halberstadt (both in Germany) and Frick (Switzerland)—is unusual in several ways.[15] All three sites are nearly monospecific assemblages, meaning that they contain practically only one species, which requires very special circumstances.[15] However, shed teeth of theropods have been found at all three sites, as well as remains of Proganochelys, an early turtle.[15] Additionally, a partial "prosauropod" skeleton was found in Halberstadt that does not belong to Plateosaurus, but is preserved in a similar position.[21] All sites yielded almost complete and partial skeletons of Plateosaurus, as well as isolated bones.[15] The partial skeletons tend to include the hind limbs and hips, while parts of the anterior body and neck are rarely found in isolation.[15] The animals were all adults or subadults (nearly adult individuals); no juveniles or hatchlings are known.[15] Complete skeletons and large skeleton parts that include the hind limbs all rest right side up, as do the turtles.[15] 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.[15]
Earlier interpretations
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.[43] Similarly, Jaekel interpreted the Halberstadt finds as animals that waded too deep into swamps, became mired and drowned.[21] He interpreted partial remains as having been transported into the deposit by water, and strongly refuted a catastrophic accumulation.[21] 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.[22] 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.[22] Seemann developed a different scenario, in which Plateosaurus herds congregated on large water holes, and some herd members got pushed in.[44] Light animals managed to get free, heavy ones got stuck and died.[44]
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.[20] Weishampel explained the curious monospecific assemblage by theorizing that Plateosaurus were common during this period.[20] 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,[45] and has since become the standard explanation on most internet sites and in popular books on dinosaurs.[6] Rieber proposed a more elaborate scenario, which included the animals dying of thirst or starvation, and being concentrated by mudflows.[46]
Current interpretation
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[43] is true:[15] 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, the scavenging theropods were not trapped due to their lower body weights, combined with a proportionally larger footprint. There is no indication of herding, or of catastrophic burial of such a herd, or catastrophic accumulation of animals that previously died isolated elsewhere.[15]
Palaeobiology
Posture and gait
Practically any 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.[5][47] In contrast, the main investigator of the Halberstadt material, Jaekel, initially concluded that the animals walked quadrupedally, like lizards, with a sprawling limb position, plantigrade, and laterally undulating the body.[48] Only a year later, Jaekel instead favoured a clumsy, kangaroo-like hopping,[4] a change of heart for which he was mocked by German zoologist Gustav Tornier,[49] 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.[43][50] 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.[51] However, most of these adaptations are actually present in Plateosaurus.[7][10]
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,[9][52] led to widespread acceptance of an erect, digitigrade limb posture and a roughly horizontal position of the back.[V][45][53][54][W][56] Many researchers were of the opinion that Plateosaurus could use both quadrupedal gaits (for slow speeds) and bipedal gaits (for rapid locomotion),[9][52][54][55] while Wellnhofer insisted that the tail curved strongly downward, making a bipedal posture impossible.[56] However, Moser showed that the tail was in fact straight.[X]
This 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.[57] The pronated position in some museum mounts had been achieved by exchanging the position of radius and ulna in the elbow. This meant that Plateosaurus was an obligate digitigrade 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 center of mass rests squarely over the hind limbs.[7][10][58]
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.[10] 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.[5] 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.[59]
Feeding and diet
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 those of modern herbivorous or omnivorous iguanas. The maximum width of the crown was greater than that of the root, resulting in a cutting edge similar to those of extant herbivorous or omnivorous reptiles. This is also true in Plateosaurus.[53] Paul Barrett proposed that prosauropods supplemented their herbivorous diets with small prey or carrion.[60]
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.[61][62] The use of gastroliths for digestion seems to have developed on the line from basal theropods to birds, with a parallel development in Psittacosaurus.[62]
Growth, metabolism and life span
Similar to all non-avian dinosaurs studied to date, Plateosaurus grew in a pattern that is dissimilar to both extant mammals and avian dinosaurs. In the closely related sauropods with their typical dinosaurian physiology, growth was initially rapid, continued somewhat slower well beyond sexual maturity, but was determinate, i.e. the animals stopped growing at a maximum size.[63] 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".[16] (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 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, Germany.[16] A further indication for endothermy is the avian-style lung of Plateosaurus.[7]
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 rapidly growing at 18 years. The oldest individual found was 27 years and still growing; most individuals were between 12 and 20 years old.[16] However, some individually 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.[16]
Daily activity patterns
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 mid-day heat.[64]
Notes
- ^ based on fig. 3 (p. 8) in Moser (2003)[6]
- ^ Quenstedt (1858)[23], cited on p. 255 in Sander (1992)[15]
- ^ p. 74 in Blankenhorn (1898)[34]
- ^ p. 12 in Moser (2003) (English summary on p. 170)[6]
- ^ p. 13 in Moser (2003) (English summary on p. 161)[6]
- ^ p. 13 in Moser (2003), see also pp. 17 and pp. 36–40, English summary on pp. 160–161 and 163–164[6]
- ^ pp. 14–15 in Moser (2003) (English summary on p. 160)[6]
- ^ pp. 331–332 in Yates (2003)[19]
- ^ pp. 331–332 in Yates (2003)[19]
- ^ p. 13 in Moser (2003)[6]
- ^ p. 34 in Agassiz (1844),[35] cited on p. 13 in Moser (2003)[6]
- ^ p. 296 in Agassiz (1846),[36] cited on p. 13 in Moser (2003)[6]
- ^ p. 57 in Vollrath (1959)[37]
- ^ p. 13 in Moser (2003)[6]
- ^ p. 152 in Moser (2003) (English summary on p. 179)[6]
- ^ p. 5 in Huene (1926)[5]
- ^ p. 331 in Yates (2003)[19]
- ^ p. 328 in Yates (2003)[19]
- ^ Moser (2003), summarized on p. 152 (English summary on p. 179)[6]
- ^ p. 152 in Moser (2003) (English summary on p. 179)[6]
- ^ pp. 193–194 in Jaekel (1913-1914)[21]
- ^ pp. 138–142 in Moser (2003) (English summary on p. 176)[6]
- ^ p. 145 in Paul (1997)[55]
- ^ pp. 142–144 in Moser (2003) (English summary on pp. 176–177)[6]
References
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- ^ Galton, Peter M. (2000). "The prosauropod dinosaur Plateosaurus Meyer, 1837 (Saurischia, Sauropodomorpha). I: The syntypes of P. engelhardti Meyer, 1837 (Upper Triassic, Germany), with notes on other European prosauropods with "distally straight" femora". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 216 (2): 233–275.
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- ^ Weishampel, D.B.; Barrett, P.M.; Coria, R.A.; Loeuff, J.L.; Xing, X.; Xijin, Z.; Sahni, A.; Gomani, E.M.P.; Noto, C. (2004). Weishampel, D.B.; Dodson, P.; Osmólska, H. (ed.). The Dinosauria (2 ed.). Berkeley: University of California Press. p. 524. ISBN 978-0-520-25408-4.
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ignored (help)CS1 maint: multiple names: editors list (link) - ^ a b Wellnhofer, P. (1994). "Prosauropod dinosaurs from the Feuerletten (Middle Norian) of Ellingen near Weissenburg in Bavaria. In "Second Georges Cuvier Symposium, Montbeliard (France)", 1992". Revue de Paléobiologie. Volume special 7: 263–271.
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has extra text (help) - ^ Bonnan, Matthew; Senter, Phil (2007). "Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?". In Barrett, P.M.; Batten, D.J. (ed.). Evolution and Palaeobiology of Early Sauropodomorph Dinosaurs (Special Papers in Palaeontology 77). Oxford: Blackwell Publishing. pp. 139–155. ISBN 978-1-4051-6933-2.
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External links
- Data related to Plateosaurus at Wikispecies