Pinacosaurus
Name:
Pinacosaurus
(Plank lizard).
Phonetic: Pin-ah-coe-sore-us.
Named By: Charles W. Gilmore - 1933.
Synonyms: Ninghsiasaurus, Pinacosaurus
ninghsiensis, Syrmosaurus.
Classification: Chordata, Reptilia,
Dinosauria, Onithischia, Thyreophora, Ankylosauria,
Ankylosauridae, Ankylosaurinae.
Species: P. grangeri
(type), P. mephistocephalus.
Diet: Herbivore.
Size: About 5 meters long.
Known locations: China, Ningxia Hui Autonomous
Region. Mongolia - Bayan Mandahu Formation, Djadokhta
Formation. Possibly in other areas of Asia, particularly in areas
associated with known regions.
Time period: Late Santonian to Campanian of the
Cretaceous.
Fossil representation: Multiple individuals,
including some juveniles. Completeness of individuals ranges from
almost complete, to partial post cranial remains and isolated skulls.
So
far Pinacosaurus appears to have been one of the
most numerous of the
Asian ankylosaurs given the large numbers of fossil remains that have
been found for this genus. This large number combined with the high
level of preservation in many of the specimens mean that the validity
of the genus is without question. However at the time of its initial
description by Gilmore, Pinacosaurus was actually
considered to have
been a nodosaur, a member of a group of armoured dinosaurs that are
considered to be both related and ancestral to ankylosaurs, though
they continued to live alongside ankylosaurs after they appeared. For
clarity, Pinacosaurus is today regarded as an
ankylosaurine
ankylosaur, which means that it is related to more advanced
ankylosaur forms. Out of these genera Pinacosaurus
has been
considered to be more closely related to Minotaurasaurus
(Thompson et
al 2011, below).
Pinacosaurus
was your atypical ankylosaur, wide stocky body, armoured scutes
down the back, club tail, all mounted on four short stocky legs.
The defining characteristic that makes Pinacosaurus
stand out from
other ankylosaur genera more than anything else are the egg shaped
holes in the skull that appear where the nostrils are normally
located. Sometimes these holes are arranged in two pairs, but in
a juvenile specimen they numbered five pairs. Why the number of pairs
varies is uncertain, perhaps juveniles had more than adults,
perhaps they represent another new species of Pinacosaurus.
Why they
were there is also a mystery, though ankylosaurs are noted for having
more complex nasal passages than other types of dinosaur, adaptations
that reduced moisture loss through respiration in arid environments.
This does not sufficiently explain why Pinacosaurus
had extra holes
when other genera did not need them however. It may be that the holes
were a sexually selected characteristic that allowed Pinacosaurus
to
identify one another from amongst the other ankylosaur genera of late
Cretaceous Asia such as Talarurus.
An
exciting find associated with Pinacosaurus is the
discovery of several
juveniles that died while nestled together. It is believed that these
individuals were suffocated by being buried in a sand storm, but it
is not so much the circumstances of the death that matter, but the
fact that they all died together. Finds like this prove that at the
very least juveniles would live in groups, presumably for the greater
protection afforded from predators since several individuals have a
much better chance at spotting potential predators than just one. We
still don’t know for certain if ankylosaurs like Pinacosaurus
lived in
groups when they were adults, but plant eating animals often do
cluster and travel together to make it harder from them to be singled
out by predators.
The
only way that this could be speculated with greater confidence for
ankylosaurs is if many adults were found buried together at what would
have been about the same time, such as a bonebed deposit of mostly if
not exclusively a single species, however the circumstance for this
to happen would be rare events, and made even rarer when you add to
the mix that those remains need to fossilise. Finding single
individuals may also be misleading when at other times in a group only
one individual was likely to die at a time through old
age/disease/predator attack, and by the time the next group member
died the group could be many miles away. The distance between
expected remains would also increase when you remember that not all
remains would fossilise, furthering the idea that such animals were
solitary. As already mentioned however, the only current proof of
group living in Pinacosaurus living together is
in the collections of
juveniles.
The
heavy armour of the body and club tail of ankylosaurs served one
purpose above all others; to make them too tough for predators to
kill. Small predators such as Linheraptor,
Byronosaurus
and
Velociraptor
would have been of little to no threat to a fully grown
adult Pinacosaurus, and even developed juveniles
would have been
tough targets for them. A more serious threat is however hinted at by
the presence of indeterminate tyrannosaur remains from the same
formations that Pinacosaurus individuals are known
from. Some of
these remains might belong to Alectrosurus,
while others are too
incomplete to reveal which genus they belong too, but we do know that
even medium sized tyrannosaurs would have been big and powerful enough
to have a serious chance of killing a juvenile Pinacosaurus,
with
larger genera having a shot at even adult Pinacosaurus.
This would
especially be the case if they were capable of flipping them over onto
their backs to strike at the unarmoured belly.
Further reading
- Two new dinosaurian reptiles from Mongolia with notes on some
fragmentary specimens, Charles W. Gilmore - 1933.
- A new species of the ankylosaurid dinosaur Pinacosaurus
from the
Late Cretaceous of Inner Mongolia (P.R. China), P.
Godefroit, X. Pereda-Suberbiola, H. Li and Z. Dong -
1999.
- A New Specimen of Pinacosaurus grangeri
(Dinosauria:
Ornithischia) from the Late Cretaceous of Mongolia: Ontogeny and
Phylogeny of Ankylosaurs, R. V. Hill, L. W. Witmer, M.
A. Norell - 2003.
- Juvenile specimens of Pinacosaurus grangeri
Gilmore, 1933
(Ornithischia: Ankylosauria) from the Late Cretaceous of China,
with comments on the specific taxonomy of Pinacosaurus,
M. B.
Burns, P. J. Currie, R. L. Sissons, V. M. Arbour
- 2011.
- Phylogeny of the ankylosaurian dinosaurs (Ornithischia:
Thyreophora), Richard S. Thompson, Jolyon C. Parish,
Susannah C. R. Maidment & Paul M. Barrett - 2011.
- Postcrania of juvenile Pinacosaurus grangeri
(Ornithischia:
Ankylosauria) from the Upper Cretaceous Alagteeg Formation, Alag Teeg,
Mongolia: implications for ontogenetic allometry in ankylosaurs. -
Journal of Paleontology. 89 (1): 168–182. - Michael Burns, Tatiana
Tumanova & Philip Currie - 2015.
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