Euoplocephalus
Name:
Euoplocephalus
(Well armoured head).
Phonetic: Yu-oh-plo-seff-ah-lus.
Named By: Lawrence Lambe - 1910.
Synonyms: Anodontosaurus, Scolosaurus.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Thyreophoroidea, Ankylosauria, Ankylosauridae,
Ankylosaurinae.
Species: E. tutus (type).
Diet: Herbivore.
Size: 6 meters long.
Known locations: Canada, Alberta - Dinosaur
Park & Horseshoe Canyon Formation. USA, Montana -
Judith River Formation.
Time period: Campanian to Maastrichtian of the
Cretaceous.
Fossil representation: Multiple specimens.
Whereas
Ankylosaurus
is the most famous ankylosaurid dinosaur, Euoplocephalus
is one of the most important because of the huge number of remains that
have been attributed to the genus. These include remains of over
forty individual Euoplocephalus, comprising
fifteen known skulls and
some post cranial skeletons that are almost complete. This wealth of
material has not only helped to increase our understanding of
Euoplocephalus and the Ankylosauridae as a group,
but has also
revealed avenues of research that were not previously considered by
palaeontologists.
The
skull is probably the
single most studied area of Euoplocephalus, and
is wider than it
is long in form. This gives Euoplocephalus a
very broad cropping
mouth similar to other ankylosaurids, but different to the
nodasaurids like Edmontonia
and Nodosaurus
which had narrow mouths.
This meant that Euoplocephalus was a more
generalist browser of low
vegetation, and possibly had a more advanced or larger digestive
system to cope with digesting a greater variety of plants. The teeth
inside the mouth of Euoplocephalus are small, and
like other
ankylosaurids are more suitable for chopping Along with a presence of a
hard palate that would allow Euoplocephalus to
breathe while it had
food in its mouth, it probably spent some time processing food with
up and down movements of its mouth before swallowing. This processing
in itself would allow ankylosaurids like Euoplocephalus
to obtain
more nutrition from their food regardless of if they had a more
developed digestive system.
An
additional area of study
is the complex series of nasal passages that are in the snout. These
have also been seen in other ankylosaurid genera such as Saichania,
and reveal an interesting adaptation that seems to be independently
evolved by the ankylosaurids, as usually it is only seen in mammals.
Initial explanations for these nasal passages was that they would
allow for a greater sampling of air so that Euoplocephalus
could smell
things, but endocasts of the brain do not support this as the
olfactory region is not especially well developed to take advantage of
this extra area. Instead it seems more likely that the purpose of
these passages was to actually moisten air that was being breathed in.
Ankylosaurids like Euoplocephalus and the
aforementioned Saichania
seem to have been present in ecosystems that had dry climates
(either a semi-arid climate or a prolonged dry season), and that
moistening the dry air as it was breathed in would make these kinds of
climates far more tolerable for ankylosaurids to live in, as it would
relieve them of respiratory problems as well as reduce the amount of
moisture lost through respiration.
More
general study of
Euoplocephalus, as with other ankylosaurids, has
focused upon the
club like tail and body armour, the plates of which are probably the
most commonly preserved fossils because of their solid form. The back
and upper flanks of Euoplocephalus were covered in
bony plates that are
called osteoderms (also sometimes referred to as scutes). The
main osteoderms were arranged in bands that followed one another down
the length of the animal and formed armour that was rigid but flexible
so that the normal movement of Euoplocephalus was
not hindered.
In
addition to the plates,
large spikes rose up vertically from the body, particularly two
large spikes that rose up from above the shoulders. These spikes
would have made it more difficult for large predators to gain a grip on
the body with their mouths, reducing the chance of effectively biting
through the plates. However these spikes may have also been a form of
species recognition which allowed Euoplocephalus to
recognise others of
their own kind from amongst similarly built ankylosaurids.
The
head of Euoplocephalus
was also well armoured, in fact the armour of the head was the
inspiration for the name Euoplocephalus which
means ‘well armoured
head’. One trait that Euoplocephalus shared
with other
ankylosaurids was two short pyramidal horns that grew from the back of
the skull, features that may have made it difficult for large
theropod dinosaurs to close their mouths around the head.
Euoplocephalus also possessed armoured eyelids
where small bony plates
could slide over the eyeball. Together with the rear head spikes this
might suggest that the preferred method of attack by large predators
may have been to bite at the head, an area which may have been
perceived by them to be an easier target than the main body.
Like
with other
ankylosaurids, the lower portion of the tail of Euoplocephalus
was
rigid because of the support of ossified tendons in this region which
meant that the only flexibility was in the upper portion of the tail.
Combined with the bony club on the end, this would allow
Euoplocephalus to swing its tail at other dinosaurs
like it was a
hammer. When this tail was used depends upon the behaviour of
Euoplocephalus as while the classic image of
ankylosaurids has them
using their tails against predators like tyrannosaurs, they may have
also used them upon each other. This means inter specific combat
where two rival Euoplocephalus would face each
other side to side,
possibly in a head to tail orientation, and hit each other in their
flanks until one submitted to the stronger individual. Combat between
two Euoplocephalus is also supported by the
arrangement of the armour
plates located at areas such as the back of the forelimbs, areas that
would have been more vulnerable to attacks from the sides rather than
above.
The
reasons for such combat
can be very varied and range from two males competing for the right to
mate with a female, territory control, or possibly even for control
of a group, such as head animal in a herd, or access to a harem of
a small number of females. At this time it is impossible to say which
theory if any is the correct one, but even if they are correct it
does not rule out the possibility of predator defence as well. After
all an animal that had carried a specialised weapon that could be used
against others of its own kind would have absolutely no qualms about
using it against a different type of animal that was trying to kill it.
The
large number of
Euoplocephalus remains compared with the relatively
small number of
remains for other similar dinosaurs suggests that Euoplocephalus
was
one of the most common armoured dinosaurs in the late Cretaceous of
North America. However Euoplocephalus has in the
past been the
subject of a lot of debate regarding its validity as a genus, as well
as the remains attributed to it. First is that it may have been the
same dinosaur as Ankylosaurus that was named
earlier in 1908,
although today this idea is no longer considered as plausible. The
variation in the skulls of Euoplocephalus has also
been taken to
indicate either a number of individual species, or strong individual
variation between different specimens of a single species (W.
Coombs, 1971). As such it may be that the head spikes also
served a display purpose between individuals. A number of other
ankylosaurid genera have also been synonymised into the Euoplocephalus
genus, although one of these, Dyoplosaurus,
was resurrected as
its own genus in a 2009 review of the fossil material.