Dinosaur With Two Massive, Sloth-Like Claws Is on ‘Another Level’ of Weird—Even Among Its Unusual Group of Relatives
Paleontologists discovered Duonychus tsogtbaatari from fossils uncovered in 2012. It was a giant, feathered creature adapted to grasp and feed on vegetation
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Paleontologists have discovered a strange new dinosaur species that may have looked like a giant, feathered mix of a sloth and giraffe. It had only two raptor-like clawed fingers per hand, which the creature used not to maul other prey, but to snack on vegetation.
Two fossilized claws, as well as parts of the dinosaur’s tail, arms, ribs, hips, legs and backbone were uncovered in Mongolia’s Gobi Desert in 2012. Now, in a study published Tuesday in the journal iScience, paleontologists describe the new species based on these 90-million-year-old remains. They called it Duonychus tsogtbaatari in honor of Mongolian paleontologist Khishigjav Tsogtbaatar and because “Duonychus” means “two claws” in Greek.
Surprisingly, the team discovered that one of the two giant bony claws has its keratin sheath—comparable to a human nail—still preserved. Normally, keratin “doesn’t fossilize,” study lead author Yoshitsugu Kobayashi, a paleontologist at Hokkaido University in Japan, tells New Scientist’s James Woodford.
“This is by far the biggest claw preserved for a dinosaur that has that keratinous sheath on it,” Darla Zelenitsky, a paleontologist at the University of Calgary in Canada and co-author of a study, tells CNN’s Katie Hunt. “It’s close to a foot in size.” The fossil also shows the claw was much longer than the internal bone beneath it.
Hello to Duonychus, the newest dinosaur. And a weird one at that.
— Steve Brusatte (@SteveBrusatte) March 26, 2025
A two-fingered therizinosaur with hands that remind me of oversized BBQ tongs.
Congrats Yoshi Kobayashi, Darla Zelenitsky, @Paleo_Fiorillo & crew!
My thoughts for @CNN https://t.co/yIlZ3Q2COG
Duonychus tsogtbaatari stood around ten feet tall and weighed approximately 573 pounds. It was a member of the Therizinosaurs, a group of dinosaurs that existed in Asia and North America between 66 million and 100 million years ago. They are typically known for their small heads, long necks, feathered bodies and bipedalism, as well as three long claws on each hand—a trend that Duonychus breaks. While they belong to the theropods, a subgroup of dinosaurs that includes all meat-eaters, therizinosaurs were likely herbivores.
“Therizinosaurs are already some of the most unusual dinosaurs out there, but Duonychus tsogtbaatari takes it to another level,” Kobayashi tells Live Science’s Jess Thomson. “This newly discovered species from Mongolia breaks the mold with just two fingers instead of the typical three, offering a rare glimpse into how theropod hands evolved and adapted.”
“It’s like evolution said, ‘Let’s try something totally new.’ And it worked,” Kobayashi adds to Reuters’ Will Dunham.
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Duonychus tsogtbaatari is the only known therizinosaur with two claws, but other theropod dinosaurs, including the Tyrannosaurus rex, also evolved to have two fingers instead of three. Kobayashi and his colleagues suggest that the Duonychus tsogtbaatari would have used these claws and flexible wrists to pull plant and tree branches closer to munch on their vegetation, similarly to today’s two-toed sloths.
“Three fingers might have just gotten in the way,” Kobayashi explains to New Scientist, “while two provided a more precise and efficient grasp.” The claws may have also helped defend the dinosaurs or provide “powerful weapons in intraspecific competition,” Zichuan Qin, a paleontologist at the University of Birmingham in England who was not involved in the study, tells National Geographic’s Riley Black.
Ultimately, “this is yet another example of a wonderful new dinosaur that we couldn’t have dreamed ever existed if we didn’t find its fossils,” Steve Brusatte, a paleontologist at the University of Edinburgh who did not participate in the study, tells CNN.
