| Diet | Herbivore |
| Height | 2m |
| Length | 7m |
| Weight | 1 tonnes |
| Speed | 25 km/h |
| Environment | Land |
| Era | Cretaceous |
| Period | Early Cretaceous |
| Type | Ornithopod |
| Location | Western North America |
Tenontosaurus was a distinctive herbivorous ornithopod dinosaur that roamed the forests and plains of western North America during the Early Cretaceous period, between 121 and 106 million years ago. This remarkable dinosaur stood about 2 metres tall at the hip and measured approximately 7 metres in length, making it one of the larger ornithopods of its time.
What truly set Tenontosaurus apart from other ornithopods was its extraordinarily long, broad tail, which made up nearly half of its total body length. This massive tail, along with its back, was reinforced by a complex network of bony tendons that provided crucial support and stiffness. The dinosaur's body was built for both bipedal and quadrupedal movement, allowing it flexibility in how it moved and fed.
As a herbivore, Tenontosaurus possessed a typical ornithopod skull with a beak-like mouth perfect for cropping vegetation, and rows of grinding teeth for processing tough plant material. Its diet likely consisted of ferns, conifers, and other Early Cretaceous flora. The dinosaur's robust build and powerful limbs suggest it was well-adapted to its environment, though it faced constant threats from predators like Deinonychus.
Two species are currently recognised: Tenontosaurus tilletti, known from numerous specimens across several geological formations, and the rarer Tenontosaurus dossi, found only in Texas. The abundance of T. tilletti fossils has made this ornithopod one of the best-understood dinosaurs from the Early Cretaceous period.
Tenontosaurus was immediately recognisable by its exceptionally long, broad tail that comprised nearly half its total body length. The tail and back were reinforced with an intricate lattice of bony tendons, giving the dinosaur a distinctively rigid posterior section whilst maintaining a relatively typical ornithopod head and torso.
Tenontosaurus likely lived in herds for protection against predators, as suggested by multiple individuals found together at some fossil sites. The dinosaur could move both bipedally and quadrupedally, probably adopting a four-legged stance when feeding on low-growing plants and rearing up on its hind legs to reach higher vegetation or when running from danger.
Tenontosaurus has appeared in several dinosaur documentaries and educational programmes, often depicted as prey for pack-hunting Deinonychus, though it remains less famous than many other dinosaurs in popular media.
Tenontosaurus was first described by John Ostrom in 1970. The original fossils were discovered at Cloverly Formation, Montana, USA.
