Scientists discover bizarre dinosaur fossil with sloth-like arms and deadly claws that lived 95 million years ago

Time of India

21-04-2025

Every fossil tells a story, and some have the power to rewrite entire chapters of our understanding of prehistoric life. Over the past few decades, dinosaur fossils have changed from being just rare discoveries into interesting and novel windows into evolution, behaviour, and the diversity of ancient ecosystems.
A recently found fossil in Mongolia is opening yet another door to discoveries which is about sloth-like dinosaurs with massive claws and an unusual hand structure. Palaeontologists working in the Gobi Desert have discovered a brand-new species which is a group of peculiar, plant-eating theropods that lived 90to 95 million years ago and surprisingly , this one breaks even the rules of its own kind.
This newly discovered
Duonychus tsogtbaatari
fossil adds up to the lineage of
therizinosaurs
, that have been known for their long necks, small heads, rotund bellies, and huge claws, this fossil breaks the mould with its reduced two-fingered hands. Its name 'Duonychus' means "two claws" in Greek and clearly highlights this special feature and sets the dino apart from the ones of its kind. The name also honours Mongolian palaeontologist Khishigjav Tsogtbaatar.
These dinos are different from their kind
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"Therizinosaurs are some of the weirdest dinosaurs ever. They were theropods - so, related to meat-eaters - but they looked like giant feathered sloths," explained Yoshitsugu Kobayashi, a palaeontologist at the Hokkaido University Museum in Japan and lead author of the study, as quoted by Reuters.
But the newly discovered Duonychus takes that strangeness up a notch. While it had sharp, curved claws similar to those of a raptor, it didn't use them for hunting. Instead, this dinosaur used its short, two-fingered hands to eat plants.
"Duonychus takes that weirdness even further. It had this short, two-fingered hand with claws like a raptor (swift meat-eating dinosaurs), but it used them to eat plants. It's like evolution said, 'Let's try something totally new.' And it worked," Kobayashi added.
The skulls and legs were missing..
According to the study published on March 25 in iScience, the skeleton was incomplete, missing the skull and legs, but the arms and claws were remarkably well-preserved. One claw even retained its keratin sheath, the material found in human fingernails, making it 40% longer than the underlying bone.
'These were big, sharp and nasty claws,' said palaeontologist Darla Zelenitsky of the University of Calgary, co-author of the study, as quoted by Reuters. The preserved keratin is a rare discovery and gives researchers new information about the functionality of the claws. Kobayashi added that the hands showed 'fused wrist bones, stiff joints and the two massive claws,' which could indicate a specialized feeding method.
Digit reduction is of special interest in evolutionary biology. Most early dinosaurs had five fingers, but over time, many lost digits. The discovery of Duonychus makes it the fifth known theropod lineage to evolve with just two fingers independently, which places it among Tyrannosaurus rex.
As reported by Reuters, 'With dinosaurs that grasped vegetation during foraging, one would think more fingers would be better,' Zelenitsky said. 'That was obviously not the case with Duonychus… I suspect it may have had a specialized feeding behavior or food source.'