Name:
Styracosaurus
(Spiked lizard).
Phonetic: Sty-rak-oh-sore-us.
Named By: Lawrence Lambe - 1913.
Synonyms: Styracosaurus parksi, S.
sphenocerus, ‘S. borealis’.
Classification: Chordata, Reptilia, Dinosauria,
Ornithischia, Cerapoda, Ceratopsia, Ceratopsidae,
Centrosaurinae.
Species: S. albertensis
(type). Other species have existed but after additional study of
these only the type species is now recognised as valid, see main text
for details.
Diet: Herbivore.
Size: Around 5.5 meters long, but some
specimens show that it could have grown slightly
larger.
Known locations: Canada, Alberta - Dinosaur
Park Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Many remains, some of
almost complete skeleton, and bone beds are many individuals that
died together.
With the exception of Triceratops, Styracosaurus is the ceratopsian dinosaur that most people are familiar with. In fact it could even be argued that Styracosaurus has had even greater exposure in popular media such as films, books and games. This popularity is all down to the very distinctive arrangement of horns that extend from the back of the neck frill coupled with a large nasal horn that gave Styracosaurus a fierce looking appearance even though it was a plant eater.
Classification and species
Styracosaurus
was first described from an almost complete skull that was recovered by
Charles M. Sternberg from what is today known as the Dinosaur Park
Formation. It was not until 1935 however that a subsequent visit
to the site recovered the dentaries (lower jaws) and most of the
post cranial skeleton as well. However even with just the skull it
was clear to the describers that this specimen belonged to the
Centrosaurinae group of ceratopsian dinosaurs. These are the
ceratopsians typified by Centrosaurus
which have reduced frills but
increased horn growth which makes them markedly different to the
chasmosaurine ceratopsians that are typified by Chasmosaurus
which
overall have reduced horns but increased frills.
Over
the remaining course of the twentieth century further remains continued
to be discovered by other palaeontologists, but many of these were
slightly different to the type specimen that characterised the type
species of Styracosaurus albertensis (which
translates to English as
‘spiked lizard from Alberta’). This led to the establishment of
new species for the type species, but as the number of species
increased so did the controversy regarding their validity. This has
led to more in depth study of fossils attributed to the genus which has
subsequently resulted in only the type species being considered
valid. S. parksi and S. sphenocerus
are regarded the same as S.
albertensis, and by extension the informally named ‘S.
borealis’ which is an earlier name for S.
parksi. Another
informally named species ‘S. makeli’ is now
attributed to
Einiosaurus,
while the species S. ovatus has
been established as
representing its own genus of Rubeosaurus.
Why the horns and frill?
Most
of the time different species and genera of ceratopsian dinosaurs are
established by the arrangement, shape and signs of the horns and
frill, but in Styracosaurus there does appear to
be some confusion as
there is a degree of individualism between specimens. Usually however
Styracosaurus is depicted as having six large horns
emerging from the
upper portion of the neck frill. The upper pair point upwards and
gently curve out to the sides, the lower two pairs point directly out
to the sides. Other smaller horns are lower down as well as two large
pointed jugals (cheek bones) that are commonly seen in other
ceratopsians. A single large nasal horn rose upwards from the tip of
the snout and was around sixty centimetres long, slightly larger than
the largest frill horns. The frill itself was well developed to
support the growth of the horns, but reduced in size overall,
especially when compared to the large frills of the chasmosaurine
ceratopsians.
The
purpose and functions of the frill and horns is one of the longest
running debates in palaeontology and has existed ever since the first
ceratopsian dinosaurs were discovered. The idea that most people are
familiar with is that Styracosaurus used its horns
as weapons to
protect itself from predators, but this idea is actually considered
the least likely reason for them. One reason against is that the
horns and frill only cover the head and neck, living the body with
relatively little in the way of protection. Another is that horn and
frill shapes were constantly changing and adapting amongst genera,
sometimes even to the point where adaptions that were supposed to
protect them became smaller or even disappeared, and this in the face
of the development of even bigger and more powerful predators like
tyrannosaurs.
Logic would at least dictate that a successful
anti-predator design would become stabilised and even enhanced like can
be seen in the ankylosaurs.
Another
theory is that the horns were actually anchor points for well-developed
jaw muscles that would offer tremendous bite force for the shearing
beak. Again however the problem of variation in ceratopsian forms
exists, as different arrangements and shapes would result in
different muscles and attachments between genera. Further to this is
the observation that clear muscle attachments points are lacking.
Another theory concerns thermoregulation where the frill allows for
more rapid warming when faced into the early morning sun, and cooling
during the heat of the day by offering a larger surface area for heat
loss. This could in part explain the development of chasmosaurine
ceratopsian that are better known from later in the Cretaceous which
could have been warmer.
So
far there is only one explanation which explains why Styracosaurus
was
different from other ceratopsians like Centrosaurus
and
Pachyrhinosaurus
is display. When they first hatch,
ceratopsians have underdeveloped horns which continually grow until
the individual reaches maturity, which signals to others that they
are old enough to reproduce. The problem then arises that there was
not just one species of ceratopsian active at the time but possibly
several together. In order to continue their species a ceratopsian
like Styracosaurus needs to identify others of its
kind, and this is
where the distinctive head ornamentation comes in. For example; If
a Styracosaurus ever met an Einiosaurus,
it would know straight away
that it was not the dinosaur it was looking for because Einiosaurus
has
just two large horns that rise from the back of the frill and a short
nasal horn that curves round to point forwards. This would also work
for the Einiosaurus, and by recognising each
other in this way they
would not waste time and energy trying to attract and court one another.
Whereas
the horns allowed for quick identification of other species, the
frill may have been the main signalling device for communicating with
others of its species. The large fenestra (holes in the frill)
would have supported a growth of skin and tissue, and its plausible
that ceratopsian like Styracosaurus may have
flushed blood into it to
produce vivid colour displays that signalled their virility to others
of their species. Some Styracosaurus skulls
however do have damage
that has been interpreted by some as being caused by the horns of rival
Styracosaurus in dominance combat. However this
damage has also been
interpreted to being caused by parasites in a similar manner to how
supposed tooth marks on tyrannosaur skulls have been caused.
Supporters of the horns being used in combat with rival individuals
however have suggested that the horns may have been used to try and
score a hit on the side of the body rather than the head, with the
more mature individuals with larger horns having a better chance of
success.
Styracosaurus
the dinosaur
Like
with other ceratopsians, Styracosaurus is
interpreted as a low
browsing herbivore that could eat anything from cycads to palms.
Ceratopsians have in the past been seen as being large and heavy
enough to knock down trees to get at the softer vegetation that grows
in the tree canopy, although this view is not accepted by all
palaeontologists. Also as in others, Styracosaurus
cropped
mouthfuls of food with its beak, although some speculate that it used
its beak to grip and pull food rather than shear through it. The main
processing took place at the back of the mouth where batteries of
shearing teeth cut up plant matter into smaller pieces so that they
could be more easily digested.
Styracosaurus
also had the typical ceratopsian dinosaur shape with a stout body
supported by all four legs. The rear legs were longer than the front
legs which resulted in the hips being higher than the shoulder. There
is still debate as to whether Styracosaurus like
other ceratopsians
supported its weight by keeping its legs directly beneath its body,
or if the front legs sprawled out to the sides like in Computer
modelling has suggested however that an intermediate position of the
fore legs between sprawling and direct support was the most likely as
it offered efficient locomotion with agility while browsing.
It
has been commonly suggested that Styracosaurus
lived in herds due to
the presence of bonebeds that have numerous Styracosaurus
individuals
within them. Usually these bonebeds have been explained as a large
number of individuals travelling and trying to cross a river swollen
with flood water together, with many individuals drowning in the
process. Some palaeontologists however have offered an alternative
explanation of these collections by saying the remains of what were
solitary individuals that clustered together around a watering hole in
the dry season. When the last of the water disappeared the
Styracosaurus had nowhere to go and so died of
thirst en masse. Some
deposits also suggest the presence of other dinosaurs amongst the
Styracosaurus, but these remains could support
either theory.
While
the idea of Styracosaurus travelling in herds is
all down to ones
interpretation of the fossil deposits, it would be a worthwhile
strategy for ceratopsian dinosaurs like Styracosaurus
to stick together
since large and powerful tyrannosaurs like Daspletosaurus
were roaming
the North American landscape at this time. Even with its horns one
Styracosaurus would have a hard time defending
itself from a predator
like this, but several Styracosaurus clustered
together in a form of
phalanx would have been an incredibly difficult target for even a
tyrannosaur to attack. The numbers involved would not have to be
particularly high, just enough to cover one another.
The
bonebed deposits of Styracosaurus have helped to
establish at least one
fact. The related Centrosaurus is also known from
bonebed deposits
that are similar in form to Styracosaurus, but
always in older
deposits. This means that Styracosaurus had the
same ecological niche
as Centrosaurus, but lived at a slightly later
time, perhaps even
being the dinosaur that replaced Centrosaurus.
Further reading
- A new genus and species from the Belly River Formation of Alberta -
Ottawa Naturalist 27: 109–116 - L. M. Lambe - 1913.
- On dinosaurian reptiles from the Two Medicine Formation of Montana -
Proceedings of the United States National Museum 77 (16): 1–39 -
Charles W. Gilmore - 1930.
- The skeleton of Styracosaurus with the
description of a new species -
American Museum novitates (New York City : The American Museum of
Natural History). no. 955: 12 - Barnum Brown & Erich Maren
Schlaikjer - 1937.
- The behavioral significance of frill and horn morphology in
ceratopsian dinosaurs - Evolution 29 (2): 353–361 - J. O. Farlow
& P, Dodson - 1975.
- Craniofacial ontogeny in centrosaurine dinosaurs (Ornithischia:
Ceratopsidae): taphonomic and behavioral phylogenetic implications -
Zoological Journal of the Linnean Society 121 (3): 293–337 - S. D.
Sampson, M. J. Ryan & D. H. Tanke - 1997.
- New centrosaurine ceratopsids from the late Campanian of Alberta and
Montana and a review of contemporaneous and regional patterns of
centrosaurine evolution - Journal of Vertebrate Paleontology 23 (3) -
M. J. Ryan & A. P. Russel - 2003.
- A revision of the late Campanian centrosaurine ceratopsid genus
Styracosaurus from the Western Interior of North
America - Journal of
Vertebrate Paleontology 27 (4): 944–962 - Michael J. Ryan, Robert
Holmes & A. P. Russel - 2007.
- New Material of "Styracosaurus" ovatus
from the Two Medicine
Formation of Montana - In: Michael J. Ryan, Brenda J.
Chinnery-Allgeier, and David A. Eberth (eds), New Perspectives on
Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium,
Indiana University Press - Andrew T. McDonald & John R. Horner
- 2010.
- The postcranial skeleton of Styracosaurus albertensis
- Kirtlandia
58:5-37 - R. B. Homes & M. J. Ryan - 2013.
- Morphological variation and asymmetrical development in the skull of
Styracosaurus albertensis. - Cretaceous Research. -
R. B. Holmes, W. S.
Persons, B. Singh Rupal, A. Jawad Qureshi & P. J. Currie -
2019.