Duonychus tsogtbaatari: Mongolia’s Bizarre Two-Clawed “Therizinosaur” Shakes Paleontology to Its Core

In a discovery that has rocked the dinosaur world, scientists have named Duonychus tsogtbaatari — a medium-sized therizinosaurid with only two functional fingers and a spectacularly preserved keratinous claw — from Mongolia’s Gobi Desert.

Described in March 2025 in iScience by Yosнιтsugu Kobayashi and colleagues, the partial skeleton comes from the Upper Cretaceous Bayanshiree Formation (Cenomanian–Santonian, ~96–90 million years ago). At roughly 3 metres long and 260 kg, this derived therizinosaur stands out for its didactyl (two-fingered) hands — a rare reduction among theropods that evolved independently from the famous two-fingered tyrannosaurids.

The star feature is the exceptionally preserved hand: fused distal carpals forming a semilunate shape, a reduced metacarpal III as a splint, complete absence of digit III, and two equally large manual unguals sheathed in a mᴀssive keratin claw with extreme flexion (nearly 90°). These adaptations made the hands powerful, flexible grapplers ideal for stripping vegetation or possibly even climbing.

The find provides the first three-dimensional insight into therizinosaur hand evolution and digit reduction in avetheropods. Kobayashi noted the claws were “adept at grasping vegetation,” suggesting a specialised herbivorous lifestyle with sophisticated forelimb function.

Now the subject of intense study and striking life reconstructions, Duonychus proves that therizinosaurs continued to experiment with extreme anatomy deep into the Cretaceous — delivering one of the strangest and most illuminating theropod hands ever found.