Duonychus
"two claws"
- Lived
- 101 to 84 million years ago, Late Cretaceous
- Diet
- Herbivore
- Group
- Theropods, Therizinosauridae
- Found in
- Mongolia
- Named by
- Kobayashi et al. 2025
Where its fossils were found
The evidence
Today
90 million years ago
Habitat
The Baynshire Formation records river floodplains in what is now Mongolia. Segnosaurus, Erlikosaurus and Talarurus are also known from these rocks.
Field notes
About Duonychus
What it was like
Duonychus was a therizinosaur, a pot-bellied plant eater with a long neck and big claws. Unlike its relatives, which had three fingers, Duonychus had only two fingers on each hand, each tipped with a large, curved claw.
One of its claws still has its horny sheath preserved, which shows that the claw in life was even longer than the bone inside. It may have used its hands to pull branches toward its mouth.
Its world
It lived in the Late Cretaceous in what is now Mongolia. Its fossil comes from the Baynshire Formation, where it shared the land with other therizinosaurs, Segnosaurus and Erlikosaurus, the raptor Achillobator and the armored Talarurus.
How it was found
Kobayashi and colleagues named Duonychus in 2025, from a single partial skeleton.
Field gallery
More views of Duonychus
Scenes reconstructed from the available fossil evidence.
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 Duonychus.
The evidence
The science behind Duonychus
Which parts of the picture come from its own bones, and which come from its relatives.
From its own fossils
- The partial skeleton preserves the trunk, shoulders, arms, hands and parts of the pelvis.
- Each hand had two fingers with large curved claws; a small leftover hand bone marks the lost third finger.
- A preserved horny claw sheath extends beyond the bone inside it.
Borrowed from relatives
- Erlikosaurus guides the missing head and neck, while Nothronychus guides the legs and tail.
- Feathers in Beipiaosaurus suggest that Duonychus may also have had a coat of simple feathers.
Still unknown
- Its skull shape and teeth.
- Its exact tail length and which toes carried its weight.
- Its feather covering and color.
Often drawn wrong
- Giving it three clawed fingers copies other therizinosaurs; Duonychus had only two.
- Drawing the claws only as long as their bones leaves out the longer horny sheath.
Discovery timeline
- 2009SkinXu, Zheng & You
- 2015Close relativeHedrick et al.
- 2025Named itKobayashi et al.
Key papers
The research behind what we know of Duonychus
Skin
Reported broad, simple feathers in Beipiaosaurus, providing a comparison for a possible feather coat in Duonychus.
A new feather type in a nonavian theropod and the early evolution of feathers. Proceedings of the National Academy of Sciences 106: 832-834
Read the paper : A new feather type in a nonavian theropod and the early evolution of feathers (opens in a new tab)Close relative
Described the bones of Nothronychus, a useful comparison for the missing legs and tail of Duonychus.
The Slothful Claw: Osteology and Taphonomy of Nothronychus mckinleyi and N. graffami (Dinosauria: Theropoda) and Anatomical Considerations for Derived Therizinosaurids. PLOS ONE 10: e0129449
Read the paper : The Slothful Claw: Osteology and Taphonomy of Nothronychus mckinleyi and N. graffami (Dinosauria: Theropoda) and Anatomical Considerations for Derived Therizinosaurids (opens in a new tab)Named it
Described a two-fingered therizinosaur with a preserved horny claw sheath and interpreted its hands as effective grasping tools.
Didactyl therizinosaur with a preserved keratinous claw from the Late Cretaceous of Mongolia. iScience 28: 113214
Read the paper : Didactyl therizinosaur with a preserved keratinous claw from the Late Cretaceous of Mongolia (opens in a new tab)
Close relatives
Other members of Therizinosauridae
Sources: Wikidata