Hylaeosaurus

Hylaeosaurus holds an esteemed position in the history of science as the third creature used by Sir Richard Owen to establish the clade Dinosauria in 1842. Discovered by Gideon Mantell in West Sussex, England, the primary specimen consists of the front half of an armoured skeleton embedded in a large slab of Wealden sandstone. Living during the Early Cretaceous, this medium-sized quadrupedal herbivore grew to roughly four to five metres long. Its neck and shoulders carried sharp, flattened spikes, complemented by rows of circular dermal scutes running down its back. Like other early ankylosaurians, it lacked a bony tail club and relied entirely on its low-slung, spiked armour for protection. While its skull remains poorly known, Hylaeosaurus remains a crucial historical milestone in palaeontology.

It was the third genus Richard Owen used to define the Dinosauria in 1842, alongside Megalosaurus and Iguanodon.

Where and when

Hylaeosaurus lived in the Early Cretaceous, from 139.8 to 132.9 million years ago (Valanginian age). Its remains come from United Kingdom, in the Tunbridge Wells Sand Formation.

The numbers

Length 4.5 m (estimates run from 4 to 5 m). Mass about 1.2 t. Hip height about 1.1 m. That is 2.6 human-lengths, or 0.4 of a double-decker bus. These are estimates from partial skeleton; fields marked estimated by the site are length, mass, first ma, last ma, hip height.

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