Plateosaurus
Name:
Plateosaurus
(Broad lizard).
Phonetic: Plat-e-o-sore-us.
Named By: Christian Erich Hermann von Meyer -
1837.
Synonyms: Dimodosaurus, Gresslyosaurus,
Pachysaurops, Pachysaurus, Pachysauriscus, Sellosaurus.
Former Plateosaurus species that are either invalid or referred to the
type species include P. erlenbergensis, P. integer,
P. longiceps, P. plieningeri, P. quenstedti and P.
reinigeri.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Sauropodomorpha, Plateosauridae.
Species: P. engelhardti
(type), P. gracilis.
Diet: Herbivore.
Size: Between 5 and 10 meters long, the
genus seems to be highly variable in terms of adult size.
Known locations: Across Europe. Also in Greenland
- Fleming Fjord Formation.
Time period: Norian to Rhaetian of the Triassic.
Fossil representation: Multiple individuals, some
very well preserved. Adults and subadults known.
Plateosaurus
is probably the best understood sauropodomorph
dinosaur currently known,
and also one of the oldest dinosaur genera. Named in 1837,
Plateosaurus actually predated the creation of the
Dinosauria by
Richard Owen in 1842, though the genus missed out on being one of
the defining dinosaur genera (instead Owen used Megalosaurus,
Iguanodon
and Hylaeosaurus).
Regardless of this, study of
Plateosaurus has revealed that in terms of
contribution to the science
of palaeontology, Plateosaurus is one of the most
important dinosaurs.
Plateosaurus
used to be known as a prosauropod, but modern terminology sees it
described as a sauropodomorph. Either way, what this means is that
the Plateosaurus genus represents a type of
dinosaur that was ancestral
to the later and larger sauropods of the Jurassic. The
sauropodomorphs also help to reveal how sauropods and theropods have a
shared ancestry despite being very different animals in terms of
ecological niche.
Plateosaurus
are most often associated with central Europe, especially Germany
where the bulk of known specimens come from. Remains are known from
Greenland however, with other remains speculated from South America.
Plateosaurus can also go down in history as being
the first dinosaur
genus to be found in Norway. The sheer number of Plateosaurus
fossils
compared with the somewhat limited remains of other dinosaurs suggest
that it may have been one of the most common dinosaurs in Europe during
the Triassic. However there is an alternative explanation to this.
Most
of the known Plateosaurus individuals are known
from the fossil sites
of Trossingen, Halberstadt and Frick, but they are unusual in that
the only dinosaur skeletons known from them are Plateosaurus.
The
only other remains are indeterminate theropod dinosaur teeth and an
individual of the turtle Proganochelys. Study of
the locations
reveals that in the Triassic the area was covered by large expanses of
mud which acted as a mire. Plateosaurus probably
came to these areas
to feed upon the plants growing in these bog-like conditions, and the
most popular consensus is that the larger Plateosaurus
occasionally
became stuck in the mud. The more they would struggle to free
themselves, the more they would get stuck, and eventually
exhaustion would cause them to collapse. Theropod dinosaurs of the
time were not only lighter but had bigger feet than Plateosaurus
which
meant that they had a lower ground pressure. This means that they
could walk on areas of a bog without sinking in like a large
Plateosaurus. Because they were more susceptible
to getting stuck,
more Plateosaurus got preserved than anything
else, but this also
explains the current lack of juvenile specimens of Plateosaurus
since
their lighter builds meant that they could navigate the bogs without
getting stuck.
Plateosaurus
has been reconstructed in many ways over the years, sometimes as a
primarily quadrupedal dinosaur, others times only bipedal. For the
last few decades now though, Plateosaurus has
almost always been
depicted as a primarily bipedal dinosaur that walked around on just its
hind legs. It was already more heavily built than theropod dinosaurs
of the time, and it is not out of the question that it may have
rested on all fours when browsing on low vegetation. Later as
sauropodomorphs grew bigger and had to accommodate a larger digestive
system, they would be forced to walk around on all fours.
The
centre of gravity in Plateosaurus would have been
roughly where the
hips were, which meant that the body weight went straight down the
hind legs. Further support for a bipedal stance in Plateosaurus
comes
from the simple observation that when the forearms are correctly set up
the hands are incapable of pronating, which means that they just
could not support the body weight properly.
The
fingers of Plateosaurus had long claws on them
which could have been
used for hooking around branches and fronds of vegetation so that they
were held steady while an individual fed. Alternatively they may have
also been used to defend against predators with an individual swiping
them at an attacking predator to try and slash them.
The
hind limbs were well adapted for bearing the body weight, but lacked
muscles that were capable of providing a ‘spring’. What this
means is that when Plateosaurus walked, one of
the hind feet had to
be touching the ground at all times, and that speed was controlled by
altering the stride and changing the speed of leg movement. This
would be as close as to running as what Plateosaurus
could get, but
true running however is defined by an ‘airborne’ phase where the
rear foot pushing leaves contact with the ground before the landing
foot touches it. However this does not mean to say that Plateosaurus
were slow, they would only need to be able to outpace predators to
stay safe.
There
has been much debate over exactly what sauropodomorph dinosaurs ate
since they immediately evolved from meat eating ancestors, and would
eventually have exclusively plant eating descendants. Plateosaurus
however were almost certainly herbivorous, this can be seen just from
looking at the teeth and skull. The teeth of Plateosaurus
are broad
and leaf shaped, not the pointed triangular teeth of a predatory
theropod. The skull is also adapted for a strong bite which means
that in all probability the jaw muscles combined with the teeth for
processing plants by slicing and mashing. This could also denote a
preference for tougher plants or processing them in the mouth because
they lacked a large enough digestive system to break down the plants by
processes such as fermentation. Later sauropods with larger digestive
systems would basically just gulp down mouthfuls of plants with little
to no processing taking place in the mouth. Gastroliths (stones)
are known to have been swallowed by some dinosaurs, and some that
you might not expect such as the theropod Lourinhanosaurus.
No
gastroliths have ever been found in association with Plateosaurus
however, and given that members of the genus could process food in
their mouths, it is very unlikely that they made use of them.
One
of the most startling revelations about Plateosaurus
is that it seems
to have had an avian-like (bird-like) respiratory system. This
was originally indicated by analysis of the growth patterns in the
bones, but new studies of the anterior portion of the post cranial
skeleton now reveal that in life Plateosaurus would
have had a system
of air sacs similar to how birds do today. The presence of such a
respiratory system has long been suspected for later sauropod dinosaurs
and is part of the explanation for how they could lift their necks,
because if they were filled with a network of air sacs they would have
been far lighter than if they were just solid tissue.
To
fully appreciate how the presence of an avian-like respiration system
present in Plateosaurus can affect our wider
understanding of
dinosaurs and evolutionary theory, you need to bear in mind that
birds evolved from the theropod line of dinosaurs, not the
sauropods. This leaves us two possibilities, the mundane of which
is that an avian-like respiratory system evolved twice, once in the
sauropodomorphs, and again in the theropods. An alternative and
much more exciting possibility however is that the avian system goes
back further than Plateosaurus, all the way to
the very first
dinosaurs before they had split into the theropod and sauropodomorph
groups.
The
presence of an avian-like respiratory system also yields a further
possibility for dinosaur biology; that all dinosaurs were indeed
endothermic. This means that much of their body heat was produced by
internal body processes and that they were not reliant upon heat from
the surrounding environment to survive like more primitive reptiles
like lizards were. In simpler terms, dinosaurs were more like
warm-blooded animals than cold-blooded ones.
Further
support for an endothermic metabolism comes from study of the growth
patterns of the bones. Like with all other known dinosaurs,
Plateosaurus experienced the fastest rate of growth
when juvenile,
before slowing down in later life. The scleral rings of Plateosaurus
also indicate that individuals would be active for short periods both
during the day and night times. Such variation also suggests an
endothermic metabolism since they would not be restricted to feeding
only during certain parts of the day.
Because
so many individuals are known, and study of the growth stages of
individuals is possible, palaeontologists can even determine the age
range for Plateosaurus. Most known individuals
are between 12
and 20 years old, and further to this, Plateosaurus
seemed to
have reached adult size by 12 years of age. Plateosaurus
however
did not stop growing here, they just continued at a slower rate.
While the average age of Plateosaurus seems to
have been 12 to
20 years, remains of one individual known to have reached 27
have been studied. It also needs to be appreciated that the average
age of 12-20 years may be skewed because it is based upon
individuals that died after getting stuck in mud rather than dying from
old age. At the time of writing the youngest Plateosaurus
individual
known was 10 years old when it died.
One
thing that is unusual for Plateosaurus and is not
commonly seen in
dinosaurs is that adult size between individuals can vary greatly.
Termed developmental plasticity, some individuals of Plateosaurus
were only 4.8 meters long when then reached adulthood, while
others comfortably reached 10 meters long. The reasons for this
great variation are not fully known, but it could be that times of
food shortages meant that there was less available energy to devote
towards growth, therefore individuals living in these times became
stunted. By contrast, individual Plateosaurus
living in times of
plenty had more energy for growth and so became bigger. This may be
an inherent survival mechanism where rather than starving and becoming
extinct, the genus simply adapted to changing food availability so
that they did not grow beyond a point where they could not support
themselves. Such dwarfism is often seen in animal populations that
find themselves on islands cut off from the mainland and then grow
physically smaller to adapt to the reduced food resources.
There
is no clear indication to suggest that Plateosaurus
lived in herds,
but then there is also no indication to suggest they didn’t. Large
numbers of Plateosaurus discovered in what were
muddy bogs have been
interpreted as whole herds that became trapped in a mudflow, while
alternative explanations propose that the large numbers of Plateosaurus
exist because they were more common. But as a herbivore, there is a
chance that Plateosaurus may have travelled around
in loose herds, or
at the very least congregated together because of food availability.
Herbivores sticking around together also have a higher chance of
survival because they are more likely to spot threats like roaming
predators.
Plateosaurus
would have been one of the main herbivorous dinosaurs present in Europe
at the end of the Cretaceous, and as such it was likely a commonly
targeted prey species. Early theropod dinosaurs would have been an
obvious threat, and discoveries of saurischian dinosaurs like the
South American Herrerasaurus
prove that these kinds of dinosaurs were
already growing to sizes that could threaten sauropodomorphs like
Plateosaurus. Other threats present also include
archosaurs like
Smok,
that while possibly slower than dinosaurs like Plateosaurus,
could have still hunted them by ambush tactics.
Further reading
- Die fossile Reptil-Ordnung Saurischia, ihre Entwicklung und
Geschichte" [The fossil order of reptiles Saurischia, their
development and history], F. von Huene - 1932.
- Cranial anatomy of the prosauropod dinosaur Plateosaurus
from the
Knollenmergel (Middle Keuper, Upper Triassic) of Germany. I.
Two complete skulls from Trossingen/W�rtt. With comments on the
diet, Peter M. Galton - 1984.
- Late Triassic continental vertebrates and depositional environments
of the Fleming Fjord Formation, Jameson Land, East Greenland, F.
A. Jenkins Jr., N. H. Shubin, W. W. Amaral, S. M.
Gatesy, C. R. Schaff, L. B. Clemmensen, W. R.
Downs, A. R. Davidson, N. Bonde, F. Osbaeck - 1994.
- Were the basal sauropodomorph dinosaurs Plateosaurus
and
Massospondylus habitual quadrupeds?", in
Barrett, P.M.;
Batten, D.J., Evolution and Palaeobiology of Early Sauropodomorph
Dinosaurs (Special Papers in Palaeontology 77), Matthew Bonnan
& Phil Senter - 2007.
- The Norian Plateosaurus bonebeds of central
Europe and their
taphonomy, P. M. Sander - 1992.
- Redescription of a nearly complete skull of Plateosaurus
(Dinosauria: Sauropodomorpha) from the Late Triassic of
Trossingen (Germany), A. Prieto-M�rquez & mark A.
Norell - 2011.
- Prosauropod dinosaurs from the Feuerletten (Middle Norian) of
Ellingen near Weissenburg in Bavaria. In "Second Georges Cuvier
Symposium, Montbeliard (France), P. Wellnhofer - 1994.
- Prosauropod dinosaurs and iguanas: Speculations on the diets of
extinct reptiles, paul M. Barrett - 2000.
- Prosauropod dinosaur Plateosaurus (=Gresslyosaurus)
(Saurischia: Sauropodomorpha) from the Upper Triassic of
Switzerland, Peter M. galton - 1986.
- The prosauropod dinosaur Plateosaurus Meyer,
1837 (Saurischia:
Sauropodomorpha; Upper Triassic). II. Notes on the referred
species, Peter M. Galton - 2001.
- The digital Plateosaurus II: an assessment of
the range of motion
of the limbs and vertebral column and of previous reconstructions using
a digital skeletal mount, H. Mallison - 2010.
- Nocturnality in dinosaurs inferred from scleral ring and orbit
morphology, L. Schmitz & R. Motani - 2011.
- What pneumaticity tells us about 'prosauropods', and vice
versa, M. J. Wedel - 2007.
- The early evolution of postcranial skeletal pneumaticity in
sauropodomorph dinosaurs, A. M. Yates, M. J. Wedel
& M. F. Bonnan - 2011.
- A revision of the problematic sauropodomorph dinosaurs from
Manchester, Connecticut and the status of Anchisaurus
Marsh, A.
M. Yates - 2010.
- Developmental plasticity in the life history of a prosauropod
dinosaur, M. Sander & N. Klein - 2005.
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