Largest complete dinosaur claw found in Gobi Desert

The largest fully-preserved dinosaur claw has been discovered during construction of a water pipeline in the Gobi Desert of southeastern Mongolia. Named Duonychus tsogtbaatari, the previously-unknown Cretaceous dinosaur had two-digit hands with lethal curved claws nearly a foot long. The newly-discovered fossil preserved both of the claws of both hands, plus the keratin sheath of one of the digits. The keratin sheath adds more than 40% to the length of the claw.

“Keratin usually doesn’t fossilise. It decays long before bones do,” says [Hokkaido University paleontology professor Yoshitsugu] Kobayashi. “Most of the time, when we find dinosaur claws, we’re only looking at the bony core. But in life, the actual claw would have been covered in a thick keratin sheath, making it longer and more curved.”

The incredibly rare keratin sheath gives paleontologists new insight into how these dinosaurs used their hands in life, and the preservation of the rest of the hands is exceptional as well, including the fused wrist bones and stiff joints.

Paleontologists with Mongolia’s Institute of Paleontology also found fossilized remains of the dinosaur’s backbone, tail bone, ribs and hips. The skull and legs were missing, but based on the dimensions of the remains of the body, the dinosaur was 10 feet long and weighed 575 pounds. It was not fully grown.

Duonychus was a member of the Therizinosaur clade of herbivorous theropods which inhabited Asia and North America during the Cretaceous period (90-95 million years ago). All of the members of the group have exceptionally large claws, but Duonychus is the only one with two digits. All of the other known therizinosaurs had three.

Team member Darla Zelenitsky at the University of Calgary, Canada, says finding a two-fingered therizinosaur was extremely surprising: “We were like, wow, this is truly bizarre for one of these dinosaurs.”

“This is the largest fully preserved 3D dinosaur claw found, by far,” she says. “This claw is not preserved as an outline on the rock surrounding the bone, which is pretty typical for fossils that have the true claws preserved. This claw is actually three-dimensional and forms a sheath around the underlying finger bone, similar to what we see in the paws of dogs and cats.”

The two fingers was an adaptation that gave Duonychus more dexterity and strength when grabbing and pulling down vegetation. The curvature of the claws and the great flexion of the sheath made it easier to hook branches, and the greater size and strength of two digits instead of three made it possible for the dinosaur to target thicker branches. The third finger may have even been a disadvantage for them, just getting in the way and hindering the tightness and precision of the two-fingered grip.

The findings have been published in the journal  and can be read here.