Deinonychus

Chapter • Meet the dinosaur

Overview

Deinonychus was a lightly built predator about three to three and a half metres long, much of that length taken up by a stiffened, tendon-braced tail. It weighed somewhere between 60 and 100 kilograms and stood just under a metre at the hip – roughly wolf-sized, but shaped nothing like one. The skull was fairly long, armed with recurved, serrated teeth; the eyes faced partly forward, giving good overlapping vision; and the arms were long, ending in three strongly clawed fingers. Its trademark feature was the enormously enlarged, sickle-shaped claw on the second toe, around 12 centimetres along the outer curve, which was held retracted clear of the ground while walking. The wrist carried a half-moon-shaped carpal bone that let the hand fold sideways in exactly the way a bird folds its wing, and the body was almost certainly feathered – close relatives such as Velociraptor and Microraptor preserve feathers and quill knobs on the forearm. This was an agile, fast-moving animal. The rigid tail worked as a dynamic balancing rod during sharp turns, and the limb proportions suggest short bursts of perhaps 30–40 kilometres per hour. How the great toe claw was used has been debated for decades. The old image of a slashing disembowelment has largely given way to the "raptor prey restraint" model: the predator leapt onto smaller prey, hooked the claws in to pin it down, and flapped its feathered arms for stability while it began to feed. In that picture the claw is a grappling hook rather than a knife. Deinonychus ate other vertebrates. Several quarries preserve shed Deinonychus teeth alongside skeletons of the much larger plant-eater Tenontosaurus, which was long read as evidence of cooperative pack hunting. More recent work on tooth chemistry and on the teeth of juveniles suggests instead that young and adults ate different food and that individuals gathered at carcasses without coordinated hunting, rather like modern Komodo dragons. Most of its diet probably consisted of lizards, early mammals, juvenile plant-eaters and perhaps eggs. The first bones were collected by Barnum Brown in Montana in 1931 but never properly described. In 1964 John Ostrom found new material in the Cloverly Formation, and in 1969 he named the species Deinonychus antirrhopus – "terrible claw" and "counterbalancing", a reference to the way the tail balanced the body. Ostrom's realisation that this was a fast, warm-blooded, bird-like hunter triggered the scientific upheaval known as the Dinosaur Renaissance and underpins today's understanding that birds are living dinosaurs.

Chapter • Where it lived

Habitat

Deinonychus lived in the Early Cretaceous, roughly 115–108 million years ago (Aptian–Albian), in what is now western and central North America. Fossils come from the Cloverly Formation of Montana and Wyoming, the Antlers Formation of Oklahoma and Texas, and the Arundel Formation of Maryland. The setting was a warm, humid lowland of meandering rivers, seasonally flooded plains, wetlands and forests of conifers, ferns and cycads, with the first flowering plants just beginning to spread. Deinonychus shared this landscape with the plant-eater Tenontosaurus, the armoured Sauropelta, the sauropod Sauroposeidon and the giant predator Acrocanthosaurus.

Chapter • Family life

Breeding

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy