FLORIDA STATE UNIVERSITY DR. PARKER IFS 2087 STEGOCERAS FORM OF DEFENSE: HEAD-BUTTING OR FLANK-BUTTING? By Angela Ging Draft 2 November 23rd 2015 Word Count: 2184 ABSTRACT Stegoceras was discovered by Lawrence M. Lambe in 1902. Their skeletons have been uncovered across the North American continent. After numerous years of researching the dinosaur, there have been speculations about how they defended themselves and their bone structure. Stegoceras is one of few dinosaurs that had full skeleton sets discovered from one dig. The main controversy regarding Stegoceras concerns head-butting as a form of defense. The uncertainty of the shape of their necks and the air pathway in their skull are the two key forms of evidence regarding this controversy. They also had increasingly thick skulls, which would lead paleontologists to believe that they would withstand a head-butt attack. Researchers propose the idea that instead of head-butting, Stegoceras may have been better at flank-butting. This paper considers if Stegoceras’ skull could withstand a lifetime of head-butting and I conclude that Stegoceras were able to defend themselves through the use of head-butting due to the strength of their skulls and the shape of their neck. INTRODUCTION Stegoceras roamed the earth during the Cretaceous period, during the Mesozoic Era (The Age of Reptiles), approximately 70 million years ago. They were discovered by Lawrence M. Lambe, a paleontologist from Canada, in 1902. (All About Dinosaurs 2015) Lambe was born in 1849 and died in 1934. He not only discovered and named Stegoceras, but also named multiple other dinosaurs including Chasmosaurus, Edmontosaurus, Euoplocephalus and Styracosaurus. Lambe worked for the Geological Survey of Canada and was held accountable for discovering fossils in fossil beds in Alberta, Canada. (Strauss 2015) He is commonly known for his discoveries Stegoceras (Google Images 2015) in paleontology. However, he made even more influential accomplishments during his lifetime. He was appointed a specialist in prehistoric fishes of the Devonian period and named the Canadian fossil crocodile Leidysuchus after an American paleontologist, Joseph Leidy. (Strauss 2015) “Stegoceras” means roof horn, and was inspired by the shape of its skull and is classified as Chordata, Reptilia, Dinosauria, Ornithischia, Pachycephalosauria. Stegoceras evolved from a Hypsilophodon and were approximately 2 meters long and 1.3 meters tall. Their weight is estimated to be around 78 kilograms (170 lbs.). (All About Dinosaurs 2015) More recently, different versions of Stegoceras skeletons with variations in size, have been found “from southwest/central Canada to the southwestern states of the USA.” (Prehistoric Wildlife 2011) Three specific regions where partial skeletons have been found are in Alberta, Canada, and in New Mexico and Montana in the United States. “The Stegoceras was first discovered on the Judith River Wedge, on the east side of the Red Deer River, in Alberta, Canada.” (Hamilton 2010) Stegoceras were bipedal herbivorous dinosaurs, but were not always thought to be this way. In earlier years, the Stegoceras were commonly mistaken for Troodon due to its similar tooth structure. (Holtz 1998) Stegoceras had small, sharp curved teeth. “The similarity of troodontid teeth to those of herbivorous dinosaurs continues to lead many paleontologists to believe that these animals were omnivores.” (Sternberg 1945) However, Stegoceras were classified as different dinosaurs because the Troodon was proved to have more omnivorous traits and sharper teeth. Stegoceras had numerous different characteristics that have been found in fossils. Their back legs were three times the size of their forearms. They had large eyes, equally spaced and both facing forward in the front of its head, meaning it had depth perception. Stegoceras also had a large head, suggesting that it had a large brain and a thick skull (around 8 centimeters thick). Males had thicker skulls than females, along with older Stegoceras having thicker skulls than younger generations. (Hamilton 2010) They also breathed heavier than traditional dinosaurs due to its nasal passages through openings in the skull structure. (Mancini 2015) The most controversial topic concerning Stegoceras has been about their skull structure and how they defended themselves on a daily basis. At the time of discovery, they were believed to defend themselves by using the technique of head-butting. Researchers have further investigated the topic by conducting more studies and analysis concerning their skull structure to see if they were actually able to withstand the impact of a head-butt attack. (Mancini 2015) On the contrary, researchers have proposed the idea that Stegoceras used the technique of flank-butting rather than head-butting. (Carpenter 1997) The difference between the two is that head-butting is when the predator uses force in the front of it’s head in order to ram into its opponent and flank- butting is when the predator faces its opponent directly parallel and aims the peak of its skull towards its opponent. Along with the skull structure, researchers also evaluated the airflow of Stegoceras through the thickness of their skulls and the shape of their necks. DISCUSSION Head-butting and flank-butting are similar tactics in relation to form of defense but they use different parts of the skull. Head-butting is when the predator uses force in the front of it’s head in order to ram into its opponent. Flank-butting is when the predator faces its opponent directly parallel and aims the peak of its skull towards its opponent. There are two types of flank- butting due to dome shape of the skull. Stegoceras are classified in type one, “all of which have tall, rounded frontoparietal domes. Such Visual representation of Stegoceras air passageway (Google Images 2015) domes would maximize the mass of the head in flank-directed blows. Pain would be felt by the opponent without causing serious injury.” (Carpenter 1997) One trait that the Stegoceras has that leads researchers to believe that it was more likely to flank-butt rather than head-butt is the structure of it’s airways in the skull. Stegoceras are believed to be heavy breathers due to the bone structure of the skull. They breathed from the tip of their skull and up through an open airway in the skull towards the middle of their skull, similar to how humans breathe through their noses. “ ’The biggest difference between Stegoceras and [humans] (in terms of breathing) is that it would have breathed more like a bird or reptile in that it took longer, deeper breaths.’ says Ohio University doctoral student Jason Bourke. Bourke performed a CT scan of a Stegoceras skull in 2014 and discovered each breath likely helped keep its brain from overheating by cooling cranial blood vessels. Also, because reptiles lack nose hairs, Stegoceras must have relied heavily on mucous to avoid inhaling small, airborne objects.” (Mancini 2015) The Stegoceras air path is compatible in the idea that they would use flank- butting as a form of defense because their airways are towards the front of the skull. Numerous scientific texts and studies make claims regarding Stegoceras air passageways. According to The Science Book, “The Stegoceras specimens that were supposed to be from ‘the median line of head in advance of the nasals’ are to be interpreted rather as representing the frontal nasal elements of the skull.” (Brian 2011) If Stegoceras was to use head-butting instead, it could potentially crush it’s airways if the impact was too strong against the bone structure. If a Stegoceras were to have the front portion of their skull crushed from the impact of another dinosaur's skull, they would be unable to breathe and eventually suffocate. Flank- butting would be the Stegoceras preferred method of defense because it is equally as effective as using the peak of their heads to the front of their heads because they will still have the same amount of force exerted on their opponent. By using flank-butting over head-butting, their Stegoceras Skull (Google Images 2015) airways are more protected from damage than if they used head-butting. Stegoceras are also speculated to be unable to head-butt due to the shape of its neck and skull structure. Stegoceras is also categorized under pachycephalosaurus. “The angle between the skull and the neck of Stegoceras means that, when the head was down in the butting position, the neck would have been more or less in line with the force. The trunk vertebrae of pachycephalosaurus interlock in a way that seems likely to have made the spine rather rigid, and there were bony tendons or ligaments in the back as Neck structure of Stegoceras (Carpenter 1997) well as the tail. Scientists have interpreted these signs as showing that pachycephalosaurus had very stiff backs and have pictured them colliding with their backs ramrod straight.” (McNeill Alexander 1990) The fossil’s structure leads researchers to believe that the Stegoceras neck was a S or U shape curve, meaning it would be unable to withstand the pressure of a head-butt encounter. “This shape results from the nonparallel nature of the centrum articular face of the cervicals and anterior dorsals. The ventral margin of these centra may be longer or shorter than the dorsal margin at the left of the neural canal, producing a beveled, or wedge-shaped, centrum. Articulating these vertebrae so that the articular faces of sequential centra are parallel...produces a natural curve to the neck.” (Carpenter 1997) This bone structure provides researchers with evidence that Stegoceras were inclined to use flank-butting rather than head-butting due to their neck structure. The Stegoceras skull structure is believed to be another reason why they used flank-butting over head-butting as a form of defense. “Like with all pachycephalosaurus, the skull of Stegoceras is noted for having extreme thickening, which would have resulted in a dome-like structure on top of the skull.” (Prehistoric Wildlife 2011) Due to the thickness at the top of the skull, rather than the front, Stegoceras are believed to use flank-butting over head-butting because their skull can withstand more force at the dome than the front of the skull.