Segnosaurus

Segnosaurus was a peculiar, heavy-bodied herbivorous theropod from the Late Cretaceous Bayan Shireh Formation of Mongolia. First described in 1979, its unusual combination of an extraordinarily broad pelvis, short four-toed feet, and toothless beak baffled palaeontologists for years, leading to the creation of the enigmatic Segnosauria. Today, Segnosaurus is understood as an advanced therizinosaur, demonstrating how some meat-eating dinosaurs completely transitioned to plant-eating lifestyles. Reaching around six to seven metres in length, it possessed a large gut cavity to ferment tough vegetation, balanced upon sturdy hind legs. Its jaws held small, closely spaced serrated teeth alongside a keratinous beak for snipping foliage. Segnosaurus likely used its formidable, elongated forearm claws to pull high branches within reach, occupying a unique ecological niche in its ancient semi-arid floodplain environment.

It gave its name to Segnosauria, the group now known as the herbivorous therizinosaurs.

Where and when

Segnosaurus lived in the Late Cretaceous, from 96 to 89 million years ago (Cenomanian-Turonian age). Its remains come from Mongolia, in the Bayan Shireh Formation.

The numbers

Length 6.5 m (estimates run from 6 to 7 m). Mass about 1.6 t. Hip height about 2.5 m. That is 3.8 human-lengths, or 0.58 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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