Hesperosaurus

Hesperosaurus was a stegosaur from the Late Jurassic Morrison Formation of Wyoming, living alongside its close cousin Stegosaurus. While superficially similar, Hesperosaurus possessed distinct cranial and armour features, including a shorter, broader skull and oval, plate-like osteoderms that were wider than they were tall. Measuring about six metres in length, it was somewhat smaller and more basal than Stegosaurus. Remarkably preserved specimens have revealed direct evidence of soft tissues, including skin impressions composed of small hexagonal scales and keratinous sheaths that significantly enlarged the visual profile of its dorsal plates. It wielded four sharp tail spikes for warding off carnivores like Ceratosaurus. Some scientists have classified it as a species of Stegosaurus, but most continue to recognise it as a valid separate genus.

Soft-tissue impressions show its back plates were covered by a thick horn-like sheath that extended beyond the bone.

Where and when

Hesperosaurus lived in the Late Jurassic, from 156 to 150 million years ago (Kimmeridgian age). Its remains come from United States, in the Morrison Formation.

The numbers

Length 6 m (estimates run from 5.5 to 6.5 m). Mass about 2.2 t. Hip height about 1.8 m. That is 3.5 human-lengths, or 0.54 of a double-decker bus. These are estimates from near-complete skeleton; fields marked estimated by the site are length, mass, hip height.

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