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Styracosaurus

Styracosaurus, meaning “spiked lizard” from the Ancient Greek styrax “spike at the butt-end of a spear-shaft” and sauros “lizard” was a genus of herbivorous ceratopsian dinosaur from the Cretaceous Period, about 76.5 to 75 million years ago. It had four to six long horns, stretching from its neck frill, a smaller horn on each cheek, and a single horn jutting out from its nose, which may have been up to 2 feet long and 6 inches wide. The function/functions of these horns and frills have been debated for years.

Styracosaurus was a fairly large dinosaur, reaching lengths of 18 ft long and weighing nearly 3 tons. It stood approximately 6 ft tall. It possessed four short legs and a bulky body. Its tail was quite short. The skull had a beak and shearing cheek teeth positioned in continuous dental batteries, suggesting that the animal sliced up plants. Like other ceratopsians, the dinosaur might have been a herd animal, traveling in large groups, as suggested by bonebeds.

It was named by Lawrence Lambe in the year 1913; Styracosaurus is a member of the Centrosaurinae. One species, S. albertensis, is currently assigned to Styracosaurus. Other species assigned to the genus have since been reassigned in a different place.

Individuals of the Styracosaurus genus were approximately 18 feet in length as adults and weight around 2.7 tons. The skull was enormous, with a large nostril, a tall straight nose horn, and a parietosquamosal frill crowned with at least four large spikes. Each of the four longest frill spines was comparable in length to the nose horn, at 19.7 to 21.7 inches long. The nasal horn is estimated at 19.7 inches long in the type specimen, but the horn is only partly complete. Based on other nasal horn cores from Styracosaurus and Centrosaurus, this horn might 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 changeable. Some individuals has small hood-like projections and knobs at the posterior margin of the frill, much like those in Centrosaurus, but smaller. Others had less outstanding tabs. Some, like the type individual, possessed 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 sub adults, but were replaced by pits in the adults. Like most ceratopsids, Styracosaurus had sizable fenestrae, which are skull openings, in its frill. The front of the mouth had a toothless beak.

The bulky body of Styracosaurus bears a resemblance to that of a rhinoceros. It had powerful shoulders which might have been useful in interspecies combat. On the fairly short tail, each toe bore a hoof-like ungual which was sheathed in horn.

Various limb positions have been proposed for Styracosaurus and ceratopsids in general, including forelegs which were held under the body, or alternatively, held in a sprawling position. The most recent work has put forward an intermediate crouched position has most probable.

Styracosaurus to the subfamily 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 and deep face relative to the chasmosaurines, and a projection into the rear of the nasal fenestra”. Other members of the clade include Centrosaurus, Pachyrhinosaurus, Avaceratops, Einiosaurus, Albertaceratops, Achelousaurus, Brachyceratops, and Monoclonius, although these last two listed are doubtful. Because of the variation between species and even individual specimens of centrosaurines, there has been much discussion over which genera and species are valid, especially whether Centrosaurus and/or Monoclonius are valid genera, undiagnosable, or possibly members of the opposite sex. In the year 1996, Peter Dodson found enough variation between Centrosaurus, Styracosaurus, and Monoclonius to call for 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. However, most other researchers have not accepted Monoclonius nasicornis as a female Styracosaurus, instead, regarding it as a synonym of Centrosaurus apertus. While sexual dimorphism has been anticipated for an earlier ceratopsian, Protoceratops, there isn’t firm evidence for sexual dimorphism in any coreopsis.

Goodwin and colleagues suggested in 1992 that Styracosaurus was part of the lineage leading to Einiosaurus, Achelousaurus and Pachyrhinosaurus. This suggestion was based on a series of fossil skulls from the Two Medicine Formation of Montana. The position of Styracosaurus in this lineage is now equivocal, as the remains that were though to represent Styracosaurus have been relocated to the genus Rubeosaurus.

The evolutionary origins of this dinosaur were not understood for many years due to the lack of fossil evidence for early ceratopsians. The discovery of Protoceratops, in 1992, 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 the Zuniceratops, the earliest known ceratopsian with brown horns, and Yinlong, the first known Jurassic ceratopsian, designate what the ancestors of Styracosaurus might have looked like. These new discoveries have been vital 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 start of the late Cretaceous in North America.

The first fossil remains of Styracosaurus were collected in Alberta, Canada by C.M. Sternberg and named by Lawrence Lamb in the year 1913. This quarry was revisited in 1935 by a Royal Ontario Museum crew who had found the lower missing jaws and most of the skeleton. These fossils illustrate that S. albertensis was around 5.5 to 5.8 meters in length and stood about 1.65 meters in height from the hips. An unusual feature of this first skull is that the smallest frill spike on the left side is partly overlapped at its base by the next spike. It appears that the frill suffered a break at this point in its life, and was shortened by about 2 inches. The normal shape of this area is not known because the corresponding area of the ride side of the frill was not recovered.

Barnum Brown and crew, working for the American Museum of Natural History in New York, collected an almost complete articulated skeleton with an incomplete skull in the year 1915. These fossils were also found in the Dinosaur Park Formation, close to Steveville, Alberta. Brown and Erich Maren Schlaikjer compared the finds, and, though they allowed that both of the specimens were from the same general location and geological formation, they considered the specimen sufficiently distinct from the holotype to merit erecting a new species, and described the fossils as Styracosaurus parksi, the name honoring William Parks. Among the differences between the specimens mentioned by Brown and Schlaikjer were a cheekbone fairly different from that of S. albertensis, and smaller tail vertebrae. S. parksi also had a more forceful 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 original 1937 paper didn’t illustrate the actual bones of the skull. It’s now accepted as a specimen of S. albertensis.

In the summer of 2006, Darren Tanke of the Royal Tyrrell Museum of Paleontology in Drumheller, Alberta relocated the long lost S. parksi location. Pieces of the skull, which had evidently been abandoned by the 1915 crew, were found in the quarry. These were collected and it’s hoped more pieces will be found, perhaps enough to call for a redescription of the skull and test whether S. albertensis and S. parksi are the same. The Tyrrell Museum has also collected several incomplete Styracosaurus skulls. At least one confirmed bonebed in Dinosaur Provincial Park has also been investigated. Bonebed 42 is known to contain numerous pieces of skulls such as horn cores, frill pieces and jaws.

A third species, S. ovatus, from the Two Medicine Formation of Montana, was described by Gilmore in the year 1030. The fossil material is limited, with the best being a portion of the parietal bone of the frill, but one strange 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 rather than three. The spikes are much shorter than in S. albertensis, with the longest one being only 11.6 inches long. A 2012 review of Styracosaurus skull remains by Ryan, Homes, and Russell found it to be distinct, and in 2010, McDonald and Horner placed it in its own genus, Rubeosaurus.

Several other species which were assigned to Styracosaurus have since been designated to other genera. S. sphenocerus, described by Edward Drinker Cope in 1890 as a species of Monoclonius and based on a nasal bone with a broken Styracosaurus-like straight nose horn, was attributed to Styracosaurus in the year 1915. “S. makeli”, mentioned unceremoniously by amateur paleontologists Stephen and Sylvia Czerkas in 1990 in a caption to an illustration, is an early name for Einiosaurus. “S. borealis” is an early and informal name for S. parksi.

Styracosaurus and other horned dinosaurs are frequently depicted in popular culture as herd animals. A bonebed composed of Styracosaurus remains is known from the Dinosaur Park Formation of Alberta, about a half of the way up the formation. This bonebed is linked with different types of river deposits. The mass deaths may have been a result of otherwise non-herding animals coming together around a waterhole in a period of drought, with evidence suggesting the environment may have been semiarid and seasonal. Styracosaurus is known from a higher position in the formation than the closely related Centrosaurus, suggesting that Styracosaurus displaced Centrosaurus as the environment changed over dimension and/or time.

They were herbivorous dinosaurs; they most likely fed mainly on low growth because of the position of the head. They may, however, have been able to knock down taller plants utilizing their horns, bulk and beak. The jaws were tipped with a deep, narrow beak, believed to have been better at plucking and grasping than biting.

Ceratopsid teeth, including those of Styracosaurus, were positioned in groups called batteries. Older teeth on the top were continually replaced by the teeth that were underneath them. Unlike hadrosaurids, which also had dental batteries, ceratopsid teeth sliced, but didn’t grind. Some scientists have suggested that ceratopsids like Styracosaurus at cycads and palms, while others have suggested ferns. Dodson has proposed that Late Cretaceous ceratopsians might have knocked down angiosperm trees and then sheared off the twigs and leaves.

The sizable nasal horns and frills of the Styracosaurus are among the most distinctive facial decoration of all dinosaurs. Their function has been the subject of arguments since the first horned dinosaurs were discovered.

In the early 20th century, paleontologist R. S. Lull proposed that the frills of ceratopsian dinosaurs acted as anchor points for the muscles in their jaw. He later noted that for Styracosaurus, the spikes would have given it a frightening appearance. In 1996, Dodson supported the idea of muscle attachments in part and constructed detailed diagrams of possible muscle attachments in the frills of Styracosaurus and Chasmosaurus, but didn’t subscribe to the idea that they completely filled in the fenestrae. C.A Forster, however, found no evidentiary support of large muscle attachments on the frill bones.

It was long believed that ceratopsians like the Styracosaurus utilized their frills and horns in defense against the large predatory dinosaurs of that time. Although pitting, lesions, holes, and other damage on ceratopsid skulls are frequently attributed to horn damage in combat, a 2006 study found no evidence for horn thrust injuries causing these types of damage. Instead, non-pathological bone resorption, or unknown bone diseases, are proposed as causes.

However, a new study compared incidence rates of skull lesions in Triceratops and Centrosaurus and showed that these were consistent with Triceratops utilizing its horns in combat and the frill being adapted as a protective structure, while lower pathology rates in Centrosaurus might 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 the Styracosaurus and both genera had long nasal horns, the outcome for this genus would be ore applicable for Styracosaurus. The researchers also came to a conclusion that the damage found on the specimens in the study was often too localized to be caused by bone disease.

The large frill on the Styracosaurus and related genera also might have helped to increase bone area to regulate their body temperature, like the ears of the modern elephant. A similar theory has been proposed in regards to the plates of Stegosaurus, although this use alone would not account for the strange 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 initially suggested in 1961 by Davitashvili. This theory has gained increasing approval. Evidence that visual display was significant, either in social behavior or courtship, can be seen in the fact that horned dinosaurs differ noticeably in the adornments, making each species unique. Also, modern living creatures with such displays of horns and adornments utilize them in similar behavior.

Due to the unique frill and horns of the Styracosaurus, depictions of these animals are easily recognizable. The hooks, spines, and horns that are 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 different films ever since. Notable among them are The Son of Kong, The Valley of Gwangi, and The Land That Time Forgot.

Image Caption: Styracosaurus skeleton at Canadian Museum of Nature, Ottawa, Ontario. The Vagaceratops irvinensis type specimen can be seen in the lower left corner. Credit: D. Gordon E. Robertson/Wikipedia (CC BY-SA 3.0)

Styracosaurus


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