Masiakasaurus is an oddity, all right, its mouth bristling with those slightly hooked, forward-poking teeth; but, then, odd too are an elephant's trunk and tusks, and an elk's antler rack, and a peacock's tail. A difficulty with dinosaurs is that we can't see them in action and tame them, as it were, with visual (and auditory and olfactory) witness. How weird might a human body look to them? That thin and featherless skin, that dish-flat face, that flaccid erectitude, those feeble, clawless five digits at the end of each limb, that ghastly utter lack of a tail—ugh. Whatever did this creature do to earn its place in the sun, a well-armored, nicely specialized dino might ask.
Dinosaurs dominated the planet's land surface from some 200 million years ago until their abrupt disappearance, 135 million years later. The vast span of time boggles the human mind, which took its present, Homo sapiens form less than 200,000 years ago and began to leave written records and organize cities less than 10,000 years in the past. When the first dinosaurs—small, lightweight, bipedal, and carnivorous—appeared in the Triassic, the first of three periods in the Mesozoic geologic era, the Earth held one giant continent, Pangaea; during their Jurassic heyday Pangaea split into two parts, Laurasia and Gondwana; and by the late Cretaceous the continents had something like their present shapes, though all were reduced in size by the higher seas, and India was still an island heading for a Himalaya-producing crash with Asia. The world was becoming the one we know: The Andes and the Rockies were rising; flowering plants had appeared, and with them, bees. The Mesozoic climate, generally, was warmer than today's, and wetter, generating lush growths of ferns and cycads and forests of evergreens, ginkgoes, and tree ferns close to the Poles; plant-eating dinosaurs grew huge, and carnivorous predators kept pace. It was a planetary summertime, and the living was easy.
Not that easy: Throughout their long day on Earth, there was an intensification of boniness and spikiness, as if the struggle for survival became grimmer. And yet the defensive or attacking advantage of skull frills and back plates is not self-evident. The solid-domed skull of Pachycephalosaurus, the largest of the bone-headed dinosaurs, seems made for butting—but for butting what? The skull would do little good against a big predator like Tyrannosaurus rex, which had the whole rest of Pachycephalosaurus's unprotected body to bite down on. Butting matches amid males of the same species were unlikely, since the bone, though ten inches (25.4 centimeters) thick, was not shock-absorbent. The skulls of some pachycephalosaurs, moreover, were flat and thin, and some tall and ridged—bad designs for contact sport. Maybe they were just used for discreet pushing. Or to make a daunting impression.