Duonychus tsogtbaatari: Giant Two-Clawed Therizinosaur with a Preserved Keratinous “Killing Claw” Emerges from Mongolia’s Gobi Desert

A bizarre new therizinosaur, Duonychus tsogtbaatari, has stunned scientists with its didactyl hands and one of the best-preserved keratinous claws ever found in a dinosaur. This medium-sized herbivore, roughly the size of a grizzly bear, lived in what is now southeastern Mongolia during the Late Cretaceous (Cenomanian–Santonian stages, ~100–85 million years ago).

The partial skeleton was unearthed in 2012 during water-pipeline construction near Khanbogd in Ömnögovi Province, within the Bayanshiree Formation. Led by the Mongolian Academy of Sciences, the excavation yielded an exceptionally preserved right hand with only two functional digits—the first known didactyl therizinosaur. Most strikingly, a mᴀssive keratinous claw sheath (over 30 cm long when complete) remains intact, revealing the true size and curvature of the living weapon.

Published March 25, 2025, in iScience by Yosнιтsugu Kobayashi, Darla Zelenitsky, Anthony Fiorillo and Tsogtbaatar Chinzorig, the study estimates a body mᴀss of about 260 kg. The enormous claws, far larger than those of most therizinosaurs, likely served as formidable tools for pulling down vegetation, defense, or even occasional scavenging—making Duonychus a uniquely equipped member of its bizarre, sickle-clawed family.

Named “two-claw” (duo + onyx) in reference to its hands, the species honors Mongolian paleontologist Khishigjav Tsogtbaatar. The holotype is housed at the Insтιтute of Paleontology, Mongolian Academy of Sciences.

This discovery highlights the hidden diversity of therizinosaurs and shows that their iconic claws could evolve in surprising ways. With its preserved soft-tissue claw, Duonychus offers an unprecedented glimpse into how these “weirdest dinosaurs” used their mᴀssive weapons in life.