Stegosaurus

Stegosaurus is one of the most recognisable dinosaurs in history, famous for its alternating rows of large, diamond-shaped back plates and spiked tail. Thriving during the Late Jurassic across western North America and Portugal, it shared its floodplains with predators like Allosaurus. Growing up to nine metres long, Stegosaurus had an arched back, tiny head, and hindlegs that were significantly longer than its front limbs. Its iconic plates were not embedded in the skeleton but set directly in the skin; their exact function continues to be debated, with proposals ranging from thermoregulation to sexual display. At the end of its muscular tail lay four sharp spikes capable of delivering crippling blows. Stegosaurus possessed relatively small teeth and relied on low-growing ferns, cycads, and conifers.

Its famous tail spikes, arranged in two pairs, are informally known in paleontology as a 'thagomizer'.

Where and when

Stegosaurus lived in the Late Jurassic, from 155 to 149 million years ago (Kimmeridgian-Tithonian age). Its remains come from United States and Portugal, in the Morrison Formation.

The numbers

Length 8 m (estimates run from 7 to 9 m). Mass about 5.3 t. Hip height about 2.8 m. That is 4.7 human-lengths, or 0.71 of a double-decker bus. These are estimates from near-complete skeleton; fields marked estimated by the site are length, mass, hip height.

Compare Stegosaurus with a bus Place on the timeline