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Description
The skull was massive, with a large nostril, a tall
straight nose horn, and a parietosquasomal frill (a
neck frill) crowned
with at least four large spikes. Each of the four longest frill spines was
comparable in length to the nose horn, at 50 to 55 centimetres long (19.7 to
21.7 in). The nasal horn is estimated at 57 centimeters long (19.7 in) in
the type specimen, but the
horn is only partially complete. Based on other nasal horn cores from
Styracosaurus and
Centrosaurus, this
horn may have come to a rounded point at around half of that length.
Aside from the large nasal horn and
four long frill spikes, the cranial ornamentation was variable. Some
individuals had small hook-like projections and knobs at the
posterior margin of the
frill, similar to but smaller than those in
Centrosaurus. Others had less prominent tabs.
Some, like the type individual, had a third pair of long frill spikes.
Others had much smaller projections, and small points are found on the side
margins of some but not all specimens. Modest pyramid-shaped brow horns were
present in subadults, but were replaced by pits in adults. Like most
ceratopsids, Styracosaurus
had large fenestrae (skull
openings) in its frill. The front of the mouth had a toothless beak.
The bulky body of
Styracosaurus resembled
that of a rhinoceros. It had
powerful shoulders which may have been useful in intraspecies combat.
Styracosaurus had a
relatively short tail. Each toe bore a hooflike
ungual which was
sheathed in horn.
Various limb positions have been
proposed for Styracosaurus
and ceratopsids in general, including forelegs which were held underneath
the body, or, alternatively, held in a sprawling position. The most recent
work has put forward an intermediate crouched position as most likely.
Paleontologists
Gregory Paul and Per
Christiansen of the Zoological Museum of the University of Copenhagen
in Denmark proposed that large ceratopsians such as
Styracosaurus were able to
run faster than an elephant, based on
possible ceratopsian trackways which did not
exhibit signs of sprawling forelimbs.
Classification
Styracosaurus
is a member of the
Centrosaurinae, a
subfamily of large North American horned dinosaurs
characterized by their "prominent nasal horns, subordinate brow horns, short
squamosals in a short
frill, a tall, deep face relative to the ceratopines, and a projection into
the rear of the nasal fenestra." Other members of the
clade include
Centrosaurus (from
which the group takes its name),
Pachyrhinosaurus,
Avaceratops,
Einiosaurus,
Albertaceratops,
Achelousaurus,
Brachyceratops, and
Monoclonius, although
these last two are
dubious. Because of the
variation between species and even individual specimens of centrosaurines,
there has been much debate over which genera and species are valid,
particularly whether Centrosaurus
and/or Monoclonius
are valid genera, undiagnosable, or possibly members of the opposite sex. In
1996, Peter Dodson found
enough variation between
Centrosaurus,
Styracosaurus, and
Monoclonius to
warrant separate genera, and that Styracosaurus
resembled Centrosaurus
more closely than either resembled Monoclonius.
Dodson also believed one species of Monoclonius,
M. nasicornis, may
actually have been a female Styracosaurus.
His assessments have been partially followed, with other researchers not
accepting Monoclonius nasicornis
as a female Styracosaurus,
or Monoclonius as a
valid genus. While
sexual dimorphism has
been proposed for an earlier ceratopsian,
Protoceratops, there
is no firm evidence for sexual dimorphism in any ceratopsid.
Origins
The evolutionary origins of
Styracosaurus were not
understood for many years because fossil evidence for early ceratopsians was
sparse. The discovery of
Protoceratops, in
1922, shed light on early ceratopsid relationships, but several decades
passed before additional finds filled in more of the blanks. Fresh
discoveries in the late 1990s and 2000s, including
Zuniceratops, the
earliest known ceratopsian with brow horns, and
Yinlong, the first
known Jurassic ceratopsian,
indicate what the ancestors of
Styracosaurus
may have looked like. These new discoveries have been important in
illuminating the origins of horned dinosaurs in general, and suggest that
the group originated during the Jurassic in Asia, with the appearance of
true horned ceratopsians occurring by the beginning of the late Cretaceous
in North America.
Discoveries
and species
The first fossil remains of
Styracosaurus were
collected in Alberta, Canada by
C.M. Sternberg (from an
area now known as
Dinosaur Provincial Park,
in a formation now called
the
Dinosaur Park Formation)
and named by
Lawrence Lambe in 1913.
This quarry was revisited in 1935 by a Royal Ontario Museum
crew who found the missing lower jaws and most of the skeleton. These
fossils indicate that
S. albertensis
was around 5.5 to 5.8 meters in length and stood about 1.65 meters high at
the hips. An unusual feature of this first skull is that the smallest frill
spike on the left side is partially overlapped at its base by the next
spike. It appears that the frill suffered a break at this point in life and
was shortened by about 6 centimeters (2 in). The normal shape of this area
is unknown because the corresponding area of the right side of the frill was
not recovered.
Barnum Brown and crew,
working for the
American Museum of Natural History
in New York, collected a nearly complete articulated skeleton with a partial
skull in 1915. These fossils were also found in the Dinosaur Park Formation,
near Steveville, Alberta.
Brown and
Erich Maren Schlaikjer
compared the finds, and, though they allowed that both specimens were from
the same general locality and geological formation, they considered the
specimen sufficiently distinct from the holotype to warrant
a new species, and
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| S. parksi |
described the fossils as
Styracosaurus parksi,
named in honor of
William Parks. Among
the differences between the specimens cited by Brown and Schlaikjer were a
cheekbone quite
different from that of
S. albertensis,
and smaller tail
vertebrae.
S. parksi also had a more
robust jaw, a shorter dentary, and the frill
differed in shape from that of the type species. However, much of the skull
consisted of plaster reconstruction, and the original 1937 paper did not
illustrate the actual skull bones. It is now accepted as a specimen of
S. albertensis.
In the summer of 2006, Darren Tanke of the
Royal Tyrrell Museum of Palaeontology
in Drumheller, Alberta
relocated the long lost
S. parksi
site. Pieces of the skull, evidently abandoned by the 1915 crew, were found
in the quarry. These were collected and it is hoped more pieces will be
found, perhaps enough to warrant a redescription of the skull and test
whether S. albertensis
and S. parksi are
the same. The Tyrrell Museum has also collected several partial
Styracosaurus skulls. At
least one confirmed bonebed (bonebed 42) in Dinosaur Provincial Park has
also been explored (other proposed
Styracosaurus bonebeds instead have fossils from
a mix of animals, and nondiagnostic ceratopsian remains). Bonebed 42 is
known to contain numerous pieces of skulls such as horncores, jaws and frill
pieces.
A third species,
S. ovatus, from the
Two Medicine Formation
of Montana, was described
by Gilmore in 1930. The
fossil material is limited, with the best being a portion of the
parietal bone of the
frill, but one unusual feature is that the pair of spikes closest to the
midline converge towards the midline, rather than away from it as in
S. albertensis. There also
may only have been two sets of spikes on each side of the frill, instead of
three. The spikes are much shorter than in S.
albertensis, with the longest only 295
millimeters (11.6 in) long. A 2010 review of styracosaur skull remains by
Ryan, Holmes, and Russell found it to be a distinct species, and in 2010
McDonald and Horner placed it in its own genus,
Rubeosaurus.
Paleobiology
Styracosaurus
and other horned dinosaurs are often depicted in popular culture as herd animals. A bonebed
composed of
Styracosaurus
remains is known from the
Dinosaur Park Formation
of Alberta, about halfway up the formation. This bonebed is associated with
different types of river deposits. The
mass deaths may have been a result of otherwise non-herding animals
congregating around a waterhole in a period of drought, with evidence
suggesting the environment may have been seasonal and semiarid.
Styracosaurus is known
from a higher position in the formation (relating specifically to its own
genus) than the closely related Centrosaurus,
suggesting that Styracosaurus
displaced Centrosaurus
as the environment changed over time and/or dimension.
Dentition
and diet
Styracosaurs were herbivorous dinosaurs;
they probably fed mostly on low growth because of the position of the head.
They may, however, have been able to knock down taller plants with their
horns, beak, and bulk. The
jaws were tipped with a
deep, narrow beak, believed to have been better at grasping and plucking
than biting.
Ceratopsid teeth, including those of
Styracosaurus, were
arranged in groups called batteries. Older teeth on top were continually
replaced by the teeth underneath them. Unlike hadrosaurids, which
also had dental batteries, ceratopsid teeth sliced but did not grind. Some
scientists have suggested that ceratopsids like
Styracosaurus ate palms and cycads, while others
have suggested ferns. Dodson has
proposed that Late Cretaceous ceratopsians may have knocked down angiosperm trees and
then sheared off leaves and twigs.
Horns and
frill
The large nasal horns and frills of
Styracosaurus are
among the most distinctive facial adornments of all dinosaurs. Their
function has been the subject of debate since the first horned dinosaurs
were discovered.
Early in the 20th century,
paleontologist
R. S. Lull proposed
that the frills of ceratopsian dinosaurs acted as anchor points for their
jaw muscles. He later noted that for
Styracosaurus, the spikes would have given it a
formidable appearance. In 1996, Dodson supported the idea of muscle
attachments in part and created detailed diagrams of possible muscle
attachments in the frills of Styracosaurus
and Chasmosaurus,
but did not subscribe to the idea that they completely filled in the
fenestrae. C.A. Forster, however, found no evidence of large muscle
attachments on the frill bones.
It was long believed that
ceratopsians like Styracosaurus
used their frills and horns in defense against the large predatory dinosaurs
of the time. Although pitting, holes, lesions, and other damage on
ceratopsid skulls are often attributed to horn damage in combat, a 2006
study found no evidence for horn thrust injuries causing these forms of
damage (for example, there is no evidence of infection or healing). Instead,
non-pathological bone
resorption, or unknown
bone diseases, are suggested as causes.
However, a newer study compared
incidence rates of skull lesions in
Triceratops and
Centrosaurus and
showed that these were consistent with
Triceratops using its horns in combat and the
frill being adapted as a protective structure, while lower pathology rates
in Centrosaurus may
indicate visual rather than physical use of cranial ornamentation, or a form
of combat focused on the body rather than the head; as
Centrosaurus was more
closely related to Styracosaurus
and both genera had long nasal horns, the results for this genus would be
more applicable for Styracosaurus.
The researchers also concluded that the damage found on the specimens in the
study was often too localized to be caused by bone disease.
The large frill on
Styracosaurus and related
genera also may have helped to increase body area to
regulate body temperature,
like the ears of the modern elephant. A similar
theory has been proposed regarding the plates of
Stegosaurus, although
this use alone would not account for the bizarre and extravagant variation
seen in different members of the Ceratopsidae. This
observation is highly suggestive of what is now believed to be the primary
function, display.
The theory of frill use in sexual display was first
proposed in 1961 by Davitashvili. This theory has gained increasing
acceptance. Evidence that visual display was important, either in courtship
or in other social behavior, can be seen in the fact that horned dinosaurs
differ markedly in their adornments, making each species highly distinctive.
Also, modern living creatures with such displays of horns and adornments use
them in similar behavior.
In popular
culture
Because of the distinctive frill and
horns of Styracosaurus,
depictions of these animals are easily recognizable. The spines, hooks, and
horns attached to the head of this dinosaur sparked the imagination of
filmmakers during the earliest days of motion pictures, and this has led to
its appearance in films ever since. Notable among them are:
The Son of Kong
(1933), where a Styracosaurus
battles the movie's heroes;
The Valley of Gwangi
(1969), where Styracosaurus
is pitted against a carnivorous dinosaur;
The Land That Time Forgot
(1975) where two animals are shelled by a German U-boat; and Disney's
CGI film
Dinosaur (2000), where
an
anthropomorphic
Styracosaurus named Eema has a pet
Ankylosaurus. The
genus also appeared in the novel of
Jurassic Park, in the
list of dinosaurs present in the park, but was not seen in the film
adaptation.
On the
small screen,
Styracosaurus has appeared
in many cartoons and anime, including
Power Rangers: Dino Thunder
(Bakuryuu
Sentai Abaranger),
Dinosaur King,
Dinozaurs, "Dinosquad"Dino-Riders,
Dinosaucers, and
Zoids.
Styracosaurus has also
been featured in various video games, including the popular
Jurassic Park,
Turok,
Zoo Tycoon, and
Banjo-Kazooie game
franchises.
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