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Segnosaurus, Late CretaceousBaynshire Formation, Mongolia · named 1979
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Segnosaurus

SEG-no-SORE-us

"slow lizard"

Type species Segnosaurus galbinensis

Lived
101 to 84 million years ago, Late Cretaceous
Diet
Herbivore
Length
estimates range from 4 to 7 m (13 to 23 ft)
Group
Theropods, Therizinosauridae
Found in
Mongolia and Japan
Named by
Perle 1979

Where its fossils were found

The evidence

Today

5 finds

90 million years ago

Map: C. R. Scotese, PALEOMAP

Habitat

Its Mongolian home included river plains and lakes. Other dinosaurs in the Baynshire Formation included Erlikosaurus, Garudimimus and Talarurus.

Field notes

About Segnosaurus

What it was like

Segnosaurus was a therizinosaur, a strange theropod that gave up hunting to eat plants. It had a long neck, a small head with a beak, a pot belly, and long claws on its hands. It was about 4 to 7 meters (13 to 23 feet) long.

Its hips were broad and turned back like a bird's, a feature that puzzled scientists for years.

Its world

It lived in the Late Cretaceous, in what is now Mongolia. Its bones come from the Baynshire Formation, where it shared the land with the dromaeosaur Achillobator, the therizinosaur Erlikosaurus, the ostrich-like Garudimimus and the armored Talarurus.

How it was found

Perle named Segnosaurus in 1979. The type species is Segnosaurus galbinensis. For years it was hard to classify, and it was once thought to be a late relative of the long-necked sauropods.

Field gallery

More views of Segnosaurus

Scenes reconstructed from the available fossil evidence.

Segnosaurus in its habitat, photo 1

1 of 3

Lived alongside

Found in the same rock formations

A rock formation can hold fossils laid down millions of years apart, so not every animal here met Segnosaurus.

The evidence

The science behind Segnosaurus

Which parts of the picture come from its own bones, and which come from its relatives.

From its own fossils

  • The lower jaw curves downward toward a broad, toothless front.
  • Some teeth have extra serrated edges and folded surfaces, probably helping it break down plants in its mouth.
  • Partial skeletons preserve the shoulder, arms, hips and hindlimbs.

Borrowed from relatives

  • Erlikosaurus guides the missing upper skull and the blunt beak at the snout tip.
  • Nothronychus helps fill in the neck, broad belly and short tail.
  • Feathers in Beipiaosaurus suggest that Segnosaurus may have had a coat of simple filaments.

Still unknown

  • The shape of its upper skull.
  • Its feather covering and color.
  • Which plants it ate.

Often drawn wrong

  • Its hand claws should be curved, rather than the long, nearly straight blades of Therizinosaurus.
  • Its palms faced inward, rather than down toward the ground.
  • The toothless front of the lower jaw should not become a huge hooked beak.

Discovery timeline

  1. 1979Named itPerle
  2. 2009Close relativeXu, Zheng & You
  3. 2015Close relativeHedrick et al.
  4. 2016How it fedZanno et al.

Key papers

The research behind what we know of Segnosaurus

Close relatives

Other members of Therizinosauridae

Sources: Wikidata