Tenontosaurus

Chapter • Meet the dinosaur

Overview

Tenontosaurus was a medium-sized plant-eating ornithopod that reached about 6.5–8 metres in length and weighed somewhere between half a tonne and a tonne. Its most striking feature was the tail, which made up almost half the animal's total length and was bound together by a lattice of ossified tendons — the very feature that gave the genus its name. The head was small and low, ending in a horny beak, with rows of grinding cheek teeth further back and fleshy cheeks that probably held food in place while chewing. The forelimbs were unusually robust for an ornithopod, with broad hands, while the long hind limbs carried most of the body weight. The skin was scaly; no feathers are known from this branch of the dinosaur family tree and nothing in the fossil record suggests them. Tenontosaurus almost certainly ran on two legs but dropped onto all fours to browse or to walk at an easy pace. Juveniles had proportionally longer hind limbs and shorter arms than adults, which suggests that young animals were more habitually bipedal and became increasingly quadrupedal as they grew. Bone histology — the study of growth rings inside the bones — shows that Tenontosaurus grew quickly, reached sexual maturity at around five years of age, well before it was full grown, and approached adult size at roughly eight to ten years. A few individuals in the sampled material lived considerably longer. As a herbivore, Tenontosaurus cropped low-growing vegetation: ferns, horsetails, conifer twigs, cycads and the early flowering plants that were spreading across the Cretaceous world. The beak sheared off plant material and the tooth rows ground it down, though the chewing apparatus was simpler than the elaborate dental batteries of later hadrosaurs. Its size let it reach both ground cover and branches a couple of metres up when it reared onto its hind legs. The first specimens were collected by Barnum Brown's expeditions to the Cloverly Formation of Montana in the 1930s, but the animal was not formally described and named until John Ostrom did so in 1970. The species name tilletti honours the Tillett family, Montana ranchers on whose land much of the material was found. Tenontosaurus is now one of the best-known dinosaurs of its time in North America, represented by well over a hundred individuals of every age class, from hatchlings to large adults. A second species, Tenontosaurus dossi, was described from Texas in 1998.

Chapter • Where it lived

Habitat

Tenontosaurus lived during the Early Cretaceous, roughly 115–108 million years ago, in what is now western and southern North America. Most fossils come from the Cloverly Formation of Montana and Wyoming, with further material from the Antlers Formation of Oklahoma and Texas and from the Arundel deposits of Maryland. The landscape was one of broad floodplains crossed by meandering rivers, with seasonal floods, boggy patches and stands of conifers, ferns and cycads. The climate was warm and humid with pronounced dry spells. Its neighbours included the sickle-clawed Deinonychus, the huge predator Acrocanthosaurus, the armoured Sauropelta and the sauropod Sauroposeidon.

Chapter • Wild behavior

Behavior & Ecology

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Chapter • Scientific place

Taxonomy