Stegoceras

Chapter • Meet the dinosaur

Overview

Stegoceras validum was a small, two-legged plant-eater with one of the most distinctive skulls in the dinosaur world. In adults the roof of the head was rebuilt into a solid bony dome up to about 7–8 centimetres thick, framed at the back by a shelf of small bony knobs and spikes. The rest of the animal was comparatively plain: a compact body, short arms, powerful hind legs and a stiffened tail held straight out behind to balance the horizontal body. At roughly 2 to 2.5 metres long and somewhere between ten and forty-odd kilograms, Stegoceras was about the size of a large sheep, but far nimbler. Whether its skin carried simple filament-like structures, as in some other ornithischians, is unknown — no skin impressions of Stegoceras have been found. The purpose of the dome has been argued about for more than a century. CT scans show that the interior is built from densely packed, radially arranged bone struts, an architecture well suited to spreading out impact forces. Finite element simulations suggest the skull could survive substantial collisions, and several domes preserve healed injuries and bone infection consistent with blows to the head or flanks. Together this evidence supports genuine combat, probably rival contests over mates or territory, rather than the dome being purely a display flag. Even so, many researchers stress that the dome was highly visible and may also have served as a species recognition signal. The teeth show that Stegoceras was a herbivore, though probably not a strict one. The front teeth of the upper jaw were small and pointed while the cheek teeth were leaf-shaped with coarse serrations — a set-up suited to shredding soft leaves, fruit and shoots close to the ground, and quite possibly supplemented with insects or other small prey. The narrow snout is usually read as a sign of selective browsing, picking out the most nutritious parts of plants rather than mowing down everything in reach. Stegoceras was the first pachycephalosaur ever named. Lawrence Lambe described the species in 1902 from dome fragments collected along the Red Deer River in Alberta, Canada; the name means roughly "roof horn". For years the isolated domes were confused with teeth that had been named Troodon, and in 1924 Charles W. Gilmore treated Stegoceras as a synonym of Troodon while describing a nearly complete skull (UALVP 2). Only in 1945 did Charles M. Sternberg untangle the mess and restore Stegoceras as its own genus. Today the species is known from several skulls and partial skeletons from the Dinosaur Park, Oldman and Foremost formations of Alberta, making it one of the best-understood pachycephalosaurs.

Chapter • Where it lived

Habitat

Stegoceras validum lived about 77.5 to 74 million years ago, during the Campanian age of the Late Cretaceous, in what is now southern Alberta, Canada. Its fossils come mainly from the Dinosaur Park, Oldman and Foremost formations, deposited on a lush coastal plain along the western shore of the Western Interior Seaway. The landscape was a mosaic of meandering rivers, floodplains, swamps and patches of woodland with conifers, ferns and early flowering plants. Sites such as Dinosaur Provincial Park have yielded thousands of dinosaur bones, and Stegoceras shared its world with hadrosaurs like Corythosaurus, horned dinosaurs such as Centrosaurus and Chasmosaurus, and predators including Gorgosaurus. Some fragmentary material from New Mexico has been proposed to belong to the genus, but that referral remains debated.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy