MEANING: Two claws
PERIOD: Late Cretaceous
CONTINENT: Asia
Duonychus preserved the largest keratin hand claw sheaths of any known dinosaur, at 30 cm in length. Large claws are typical for therizinosaurs, but Duonychus only had two fingers per hand, unique among the known therizinosauria. It was herbivorous, likely using these claws to pull branches toward its mouth. Duonychus was about 3 m long in total body length.
Abstract from paper: Therizinosaurs were a group of herbivorous/omnivorous theropod dinosaurs that lived in Asia and North America during the Cretaceous Period. These theropods are notable for their three-fingered hands sporting large claw-like unguals. Here, we describe a new and unusual species of the therizinosaurid Duonychus tsogtbaatari, recovered from the lower Upper Cretaceous Bayanshiree Formation of the Gobi Desert of Mongolia. This species is different from other therizinosaurs in that the hand possesses only two fingers, rather than three fingers, the typical condition for Avetheropoda, providing further insight into forelimb/hand reduction among theropods. Phylogenetically, Duonychus reveals a broader but still limited appearance of didactyly among avetheropodans. The manual ungual of Duonychus tsogtbaatari also preserves a nearly complete three-dimensional structure covering the ungual of the left manual digit I, which represents a keratinous manual claw. The strong curvature of this large claw and high ungual flexion indicate that Duonychus was likely amplectorial (grasping) and an effective grasper of vegetation, despite having only two functional fingers.
Duonychus is from the Late Cretaceous. The Cretaceous is the third and final geological period of the Mesozoic Era, with the Late Cretaceous making up roughly the second half of it, lasting from about 100 to 66 million years ago. It was a time of significant evolutionary change, with dinosaurs reaching their greatest diversity before the mass extinction at the end of the Cretaceous.
The Cretaceous was a period with a relatively warm climate, though the Late Cretaceous experienced a global cooling trend, caused by falling levels of carbon dioxide in the atmosphere. The continents were nearing their present positions, but high sea levels flooded low-lying regions, turning Europe into an archipelago, and forming the Western Interior Seaway in North America. These seas were home to a variety of marine reptiles, including mosasaurs and plesiosaurs, while pterosaurs and birds shared the skies.
On land, dinosaurs continued to thrive and diversify during the Late Cretaceous, producing many of the most well-known goups, including tyrannosaurs, hadrosaurs, and pachycephalosaurs. Established Cretaceous dinosaur clades like the ceratopsians, ankylosaurs, and dromaeosaurs continued to flourish. Sauropod species consisted almost exclusively of titanosaurs, which seemed to be confined to the Southern Hemisphere for much of the Late Cretaceous. Flowering plants and grasses diversified and spread, becoming the dominant flora similar to what we see today.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene (K–Pg) extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs, and large marine reptiles, died out. This event, likely triggered by an asteroid impact, is marked by the abrupt K–Pg boundary, a distinct geologic layer separating the Mesozoic and Cenozoic Eras. In its aftermath, mammals and avian dinosaurs rapidly diversified, becoming the dominant land animals of the Cenozoic Era.
Duonychus is a therizinosaur. Therizinosauria is a family of large herbivorous theropod dinosaurs from the Middle Jurassic to Late Cretaceous deposits of Europe, Asia, and North America. They spanned a large range of sizes, from the Jianchangosaurus at about 2 m in length, to the 10 m long Therizinosaurus.
Therizinosaurs had a very distinctive set of characteristics. Their long necks, wide torsos, and hind four-toed feet resembled those of basal sauropodomorph dinosaurs. Among the most striking characteristics of therizinosaurs are the enormous claws on their hands, which reached lengths of around one meter in Therizinosaurus. The wide range of motion in the forelimbs also supports the idea that they were mainly herbivorous. They may have used their long reach and strongly curved claws to grasp and shear leafy branches. Skin impressions from Beipiaosaurus indicate that therizinosaurs were covered with a coat of primitive, down-like feathers, as well as longer, simpler, quill-like feathers that may have been used in display.