A new Therizinosaurus dinosaur with only two fingers has been discovered in the Gobi Desert of Mongolia. This dinosaur is a herbivore that lived in the late Cretaceous period, between 72 million and 68 million years ago, in the Nemegt Basin of Mongolia. It is known to have had enormous feathers.
Professor Kobayashi Yoshitsugu of Hokkaido University Museum and researchers from the Mongolian Academy of Sciences announced on the 25th that they excavated a bipedal theropod dinosaur known as "Duonychus tsogtbaatari" in the Gobi Desert. The results of this study were published in the international journal iScience.
The Duonychus fossil was accidentally discovered by workers at a construction site for a water pipeline in southern Mongolia in 2012. At that time, the pelvis, both arms, hands, and spine were excavated together. The name Duonychus means "two claws" in Greek, while tsogtbaatari is named after Mongolian paleontologist Hishigjav Tsogtbaatar.
The most notable feature of this fossil is that it has only two fingers. There had been no cases of Therizinosaurus dinosaurs with two fingers among those discovered so far. Most theropod dinosaurs have three fingers. Although there are some carnivorous dinosaurs like Tyrannosaurus with only two, Duonychus is a herbivore that belongs to a completely different lineage than Tyrannosaurus.
The research team explained that having two fingers is a result of evolution aimed at efficiently grasping plants, rather than a mutation. Duonychus appears to have used its arms in a manner distinct from existing dinosaurs, with a much sturdier structure in its elbow, wrist, and finger joints compared to typical theropods. It is especially believed to have specialized in pulling branches or plants using its two fingers and approximately 30 cm long curved claws.
Another remarkable aspect of this fossil is that the "claw cover" on the first finger of the left hand is preserved in perfect condition. The claw cover is made of tough keratin, similar to human nails, but usually decays quickly, making it hard to leave a fossil. Cases where a three-dimensional structure is fully preserved, as with this fossil, are rare, and this is the first time it has been confirmed in Therizinosaurus. Thanks to this, scientists are now able to analyze the actual length, curvature, and function of the claws much more precisely.
The research team pointed out the limitation that only partial skeletal remains of this fossil were recovered, rather than a complete skeleton. They also added that the rapid excavation caused by time constraints due to construction work limits the precision of anatomical interpretation.
References
iScience (2025), DOI: https://doi.org/10.1016/j.isci.2025.112141