A newly discovered dinosaur species found in Mongolia is challenging what scientists thought they knew about a rare group of ancient plant-eaters.
Researchers uncovered the fossil in the Gobi Desert during the construction of a water pipeline in the Bayanshiree Formation, located in the Ömnögovi Province of southern Mongolia.
The dinosaur has been named Duonychus tsogtbaatari, which means “two fingers” and honors Mongolian paleontologist Khishigjav Tsogtbaatar.
What makes Duonychus so unusual is that it had only two fingers on each hand – unlike other therizinosaurs, which typically have three.
This group of dinosaurs, known for their large claws and plant-based diets, lived during the Late Cretaceous Period, roughly 100 million to 66 million years ago, in areas that are now Asia and North America.
“Many species of therizinosaurs have been discovered, and this group had pretty much been defined by their three-fingered hands sporting large claws,” said Darla Zelenitsky, a paleontologist at the University of Calgary in Canada.
“To find a specimen with only two fingers/claws was surprising as this was so out of the ordinary for this group of dinosaurs.”
The fossil remains were remarkably well-preserved. Scientists recovered parts of the arms, spine, and hips. Most notably, the hands were nearly intact, including a rare feature – a keratin sheath covering the claw.
DINO NEWS!!!
Meet Duonychus tsogtbaatari the Khishigjav Tsogtbaatar´s 2 claws.
A 90 mya 2 fingers Therizinosaurid who was 3 m. long and like 270 kg.Giving us amazing, bizarre and iconic species from Mongolia.#dinosaurs #Mongolia #Science #paleoart #paleo pic.twitter.com/ecNQTAQbhm
— The Darknix (@TheDarknix) March 20, 2025
This sheath, made of the same material as human fingernails, helped experts understand the size and shape of the claws when the animal was alive.
“The hands, a hallmark of therizinosaurs, are exquisitely preserved,” Zelenitsky said. “Even the keratinous sheath of the claw is preserved revealing how big and sharp its claws really were.”
Lead study author Yoshitsugu Kobayashi from Hokkaido University in Japan described the new dinosaur species in Mongolia, Duonychus, as one of the most unusual members of an already strange group.
While some meat-eating dinosaurs like Tyrannosaurus rex had two fingers, this marks the first time a therizinosaur has been found with fewer than three.
Kobayashi believes the dinosaur may have evolved this hand structure to help it grip plants better. The shape of the claw suggests it could pull branches closer in a hook-like motion, similar to how modern-day chameleons use their feet.
Skeletal reconstruction of Duonychus tsogtbaatari holotype MPC-D 100/85.
Scale bar is 1 m. pic.twitter.com/R1i2Ntjcm9— らえらぷす@「恐竜のきほん」発売中 (@GET_AWAY_TRIKE) March 25, 2025
“The loss of the third finger in Duonychus tsogtbaatari might actually have made its remaining two fingers even better at what they were designed for — grasping,” Kobayashi said.
“Based on the shape of its well-preserved claw and how it curved, Duonychus was likely using its hands to grab onto branches and pull vegetation closer, kind of like how chameleons do today.”
Researchers also suggest the claws might have had other uses, such as protection, attracting mates, or even play.
This discovery not only adds a new member to the therizinosaur family but also marks the fifth known case of a theropod dinosaur evolving to lose a finger. Scientists believe Duonychus shows a true shift in dinosaur evolution rather than a rare mutation.
“It’s a remarkable find that reshapes our understanding of therizinosaurs and theropod evolution as a whole,” Kobayashi said.
