Styracosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Ceratopsidae

Genus:Styracosaurus

Species:Styracosaurus albertensis

Introduction

Known for their great horns and elaborate neck frills, ceratopsids such as Styracosaurus flourished in the Late Cretaceous period. The ceratopsids are believed to have been one of the more populous dinosaur families. Though fewer fossils have been found for Styracosaurus than for some of its relatives, adequate finds have given a good account of the skeletal anatomy of the dinosaur. Also, the presence of Styracosaurus remains in a large bone bed supports conclusions that the ceratops species were gregarious and indicates that some disastrous event resulted in the mass death of many dinosaurs, including members of Styracosaurus.

Styracosaurus, like its fellow ceratopsids, is notable for its elaborate neck frills and large horns. It is this visual display that most distinguishes Styracosaurus. The dinosaur possessed a short neck frill, but it was arrayed in large and short horns. It also displayed a remarkably long nose horn. Both of these features likely served multiple purposes.

Classification

Paleontologists generally use the hierarchical Linnaean classification system, developed by Carl Linnaeus in 1735, for dinosaur taxonomy. This system comprises different tiers of classification (class, order, family, genus, and species) based on shared characteristics within each grouping. Species, the lowest tier, is based on the most specific shared traits. Additional sub-categories were added later.

Under the Linnaean system, Styracosaurus belongs to the Ornithischia order of dinosaurs. One of two orders, the ornithischians were known for their bird-like hip structure, with its pelvic bone pointed down and back towards the tail. Dinosaurs in this order also tended to be herbivores and to have hoof-like claws on their feet. The ornithischian order further breaks down into suborders and infraorders. Styracosaurus has been classified as a member of the Cerapoda suborder and the Ceratopsia infraorder. These ceratopsians were distinguished by their beak-like mouths and the triangular shape of their skulls.

Within the ceratopsian infraorder, Styracosaurus is further classified as a member of the Ceratopsidae family. Members of this family group comprised herbivorous quadrupeds notable for their elaborate neck frills and prominent horns, often situated over the snout if not elsewhere. Ceratopsid dinosaurs such as Styracosaurus had large skulls and torsos, with short, sturdy legs, and tails. The Styracosaurus genus is noted for its short neck frill framed in short and long horns and the exceptionally long horn on its nose. These horns earned Styracosaurus its genus name, which means “spiked lizard.” The species taxon, albertensis, refers to the first fossil's discovery in Alberta, Canada. In 1930, another species of Stryracosaurus was described, Stryracosaurus ovatus, based on slight differences in a few skull elements found on a new specimen. A third species of Stryracosaurus, Stryracosaurus parksi, was described in 1937. In 2007, however, paleontologists Michael Ryan, Robert Holmes, and A.P. Russell reviewed the classifications of the three species, finding that the variation of the ornaments on the frill of the Stryracosaurus parksi fell within the variation documented for Stryracosaurus albertensis, thus eliminating the Stryracosaurus parksi species. In 2010, paleontologists Andrew McDonald and Jack Horner suggested that the single specimen of Stryracosaurus ovatus actually belonged to a different genus, thus leaving Stryracosaurus albertensis the only confirmed Stryracosaurus species.

Scientists may also use another classification system, called phylogenetic or cladistic classification. This system classifies animals in family trees, called cladograms, grouped by common ancestry. Each split in the tree creates a new group based on shared evolutionary novelties. Within cladistics, Styracosaurus falls under the ceratsopsian branch, or clade, of the dinosaur family tree. The ceratopsian clade breaks down into further branches, including the Neoceratopsia and the Ceratopsidae. Styracosaurus falls along the Ceratopsidae branch and further aligns with the Centrosaurinae clade, one of two clades under Ceratopsidae. The Centrosaurinae are distinguished by their short neck frills. Under Centrosaurinae, Styracosaurus belongs to one smaller subclade, which comprises Styracosaurus and Centrosaurus.

Anatomy

Styracosaurus, a medium-sized member of the Ceratopsidae, displays the characteristic neck frill and horns that distinguish the family, as well as other common features. True to its relations, the dinosaur has a heavy, thick body situated on four stout legs. Its hind legs are longer than its forelimbs, and scientists have avidly debated whether the forelegs stood straight or bent and jutted out as modern crocodile limbs do. Current consensus favors the bent leg hypothesis, which would widen and lower the stance of Styracosaurus, but evidence is not yet conclusive. Each leg ended in a broad foot with five hoof-capped toes. Sturdy ornithischian hips gave way to a short but thick tail.

The skull of Styracosaurus has a triangular shape when viewed from above but is most remarkable for its neck frill and prominent horns. Though the neck frill is short, it is studded in six long horns at its top and several smaller horns around its sides. This frill was largely hollow. Two fenestrae, or large openings, lightened the skeletal frame, making it likely that the frill was more for ornamentation or intimidation than for fighting or defense. Two very small horns protruded above the dinosaur's eyes and one long (up to 0.6 meters [or two ft]) horn extended from the dinosaur's deep snout. The snout itself tapered to a beak-like mouth within which were arrayed numerous teeth. These teeth differed from those of other herbivores in that they were designed to slice and shear plant material rather than simply chew and grind it.

Scientists have long considered dinosaurs to be cold-blooded animals, like modern lizards. However, the term “cold blooded” itself is deceptive. Modern lizards are ectothermic, meaning that they rely on the sun and other environmental factors to warm their bodies. Though science has traditionally held dinosaurs, specifically non-avian dinosaurs, to be ectothermic, evidence suggests that some might have been endothermic, meaning that they could heat their bodies from within by consuming food. Scientists continue to debate whether ceratopsians such as Styracosaurus might have been ectotherms, endotherms or something in between.

Intelligence

Studies of ancient dinosaurs rely on fossil evidence, so the most reliable way to assess a dinosaur's intelligence is by measuring the encephalization quotient (EQ). To assess the EQ, scientists compare an animal's brain size, or weight, and body size, or weight. The resultant ratio provides a value, ranging from zero to as high as 8 on some scales. Dinosaurs assessed so far range between 0.1 and 5.8, with 0.1 being the lowest intelligence score.

Slower-moving herbivores tend to fall lower on the EQ scale than their faster, carnivorous, predatory counterparts. Ceratopsians such as Styracosaurus are believed to have ranked somewhere in the middle of dinosaur intelligence, between 0.6 and 0.9, smarter than most other herbivores but just below the fellow plant-eating hadrosaurs.

Reproduction and Population

Fossil evidence suggests that Ceratopsidae dinosaurs, including Styracosaurus, were among the most populous species of the Late Cretaceous. Scientists speculate that they were surpassed demographically only by their fellow herbivores, the hadrosaurs. One study proposes that ceratopsids made up between a quarter to more than half of the population in their communities during the final ages of the Late Cretaceous.

Styracosaurus and other ceratopsids featured distinctive head frills and horns that may have served some defensive function but just as likely served as ornamentation to attract mates. In addition to the horn and frill structures, distinctive skin patterns over the frills may have been used to signal potential mates. Styracosaurus might also have used its horns and bony frills to conduct physical contests in order to show off for females.

Existing evidence indicates that most dinosaurs, including Styracosaurus and ceratopsids, were oviparous. This means that they reproduced by laying eggs. In fact, the fossil remains of ceratopsids have contributed a great deal to the study of dinosaur reproduction and nesting. Fossil sites have revealed that many ceratopsids laid their eggs in communal nesting grounds. Females from one ceratopsian species, Protoceratops, are believed to have made nests from dirt and vegetation in which to embed their eggs. Fossilized egg evidence has not yet been uncovered for Styracosaurus; however, many scientists speculate that they, too, laid eggs in nests and likely remained with hatchlings for a time.

Diet

Styracosaurus, like the rest of its Ceratopsidae family, subsisted on plant life. Members of the genus likely spent much of their time searching for and consuming vegetation. The Late Cretaceous, particularly in North America, offered an abundance of diverse plant life, including the long-standing gymnosperms, such as conifers and cycads, and the newly evolved angiosperms, or flowering plants. Scientists speculate that Styracosaurus and other ceratopsids most likely fed on low-lying and high-fiber gymnosperms and ferns; they continue to debate whether gymnosperms or ferns comprised the bulk of the ceratopsid diet. The beaks and vertically sheared teeth indicate that Styracosaurus not only plucked and pulled but also sliced through tough vegetation.

Behavior

Fossil evidence for ceratopsian dinosaurs suggests that they were largely social animals. The collective bone beds of Styracosaurus and many of its relatives indicate that they were herd animals who traveled with others of their kind; however, some paleontologists have speculated that these congregations of fossils might have resulted from drought that attracted more isolated ceratopsids to a common watering hole.

The highly differentiated frills of ceratopsids such as Styracosaurus also supports the gregarious nature of the dinosaurs. Scientists believe that the skin patterns of these frills were unique and extravagant and that Styracosaurus used such decorative physiology to appeal to mates among numerous competitors and to identify members among large herds.

As with other social animals, the herd would have provided a degree of protection against predators. The size and horns of Styracosaurus equipped it for defense, and its skeletal structure reveals that it could move quickly when needed—such as to escape the pursuit of predators. In general, however, it likely had a slow quadrupedal gait designed for grazing.

Habitat and Other Life Forms

Fossils for Styracosaurus have only been found in western Canada, and place the genus in the Late Cretaceous, along with many of its relatives. The climate and landscape of this time period differed markedly from that of the same region today. The climate was far warmer, likely sub-tropical, and the land was more likely covered in thick forests and swamps. Among this habitat, the plant-eating Styracosaurus thrived.

By this time, the vast supercontinent of Pangaea had split into two smaller supercontinents, Gondwana and Laurasia. Throughout the Late Cretaceous, tectonic change continued, with the breaking apart of Laurasia into smaller continents. These tectonic shifts brought great changes to the climate and landscape. Species became more isolated even as new plants and animals emerged. The Late Cretaceous would prove to be the final period of dinosaur life on earth, and dinosaurs shared the land with a diverse variety of insects, birds, mammals, amphibians, and flora.

Among the dinosaurs that thrived during this period were also predators of Styracosaurus. Specifically, many large carnosaurs, including the famed Tyrannosaurus, stalked the land. It is likely that such predators either hunted ceratopsid herds or followed them in order to scavenge fallen members of the tribe. Styracosaurus also shared the land with numerous other ceratopsid species and a variety of herbivorous dinosaurs, including many hadrosaurs.

Research

In 1911, under the auspices of the Canadian Geological Survey, American paleontologist Charles H. Sternberg and his three sons excavated the first Styracosaurus fossil in the Dinosaur Park Formation in Alberta, Canada. Two years later, Lawrence Lambe identified the fossils as a new genus and species and named them Styracosaurus albertensis. Subsequent finds were made in 1917 and 1932. Altogether, the fossil evidence for Styracosaurus comprises two skulls and three skeletons as well as scattered remains in a well-populated bone bed.

Though additional Styracosaurus fossils have not been uncovered, the remains of numerous relatives have been unearthed in the same region as well as on several other continents. Among other localized finds were two species of Centrosaurus, the closest known relative of Styracosaurus. Contemporary to Styracosaurus, the fossils for Centrosaurus were discovered in the same Dinosaur Park Formation as well as in the nearby Oldman Formation. Other close relatives found in western Canada and the United States include Triceratops, Pentaceratops and Pachyrhinosaurus.

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