Duonychus tsogtbaatari: Mongolia’s Bizarre Two-Clawed Therizinosaur Reveals Unique Hunting Tactics 90 Million Years Ago

In a March 2025 iScience paper, paleontologists led by Yosнιтsugu Kobayashi have described Duonychus tsogtbaatari — the first didactyl (two-fingered) therizinosaur ever discovered. Unearthed from the ~95–90-million-year-old Bayanshiree Formation in Mongolia’s Gobi Desert, this medium-sized herbivore (~3 metres long, 260 kg) possessed mᴀssively robust hands ending in two enormous, keratin-sheathed claws, while its third digit was reduced to a mere splint.

The exceptionally preserved holotype (MPC-D 100/85) includes complete left and right manus, revealing claws longer than those of any other therizinosaur. These weapons, combined with powerful forelimbs, suggest a versatile predatory and foraging strategy far more complex than simple leaf-stripping. The claws likely enabled climbing, grappling large branches, and precise grasping — behaviours once thought impossible for these giant-clawed herbivores.

Phylogenetic analysis places Duonychus firmly inside Therizinosauridae, proving that extreme digit reduction evolved independently within the group. The preserved keratin sheaths provide rare direct evidence of claw function, supporting a mosaic of scansorial, tensorial, and amplectorial behaviours.

“This specimen shows therizinosaur hands were far more plastic than we ever imagined,” Kobayashi noted. The discovery forces a re-evaluation of feeding ecology across Avetheropoda and demonstrates that even “gentle” giant-clawed dinosaurs continued to experiment with anatomy deep into the Late Cretaceous.

Named in honour of Mongolian paleontologist Khishigjav Tsogtbaatar, Duonychus (“two claws”) adds a striking new branch to the therizinosaur tree and proves the Gobi’s bizarre dinosaurs were even stranger — and more behaviourally sophisticated — than previously known.