Open Paleo

Duonychus

Kobayashi et al., 2025 ju-oh-NI-kuss

From Greek duo (two) + onychos (claw): 'two claws', referring to the two-fingered hand bearing large curved claws.

100.5–83.6 million years ago Cenomanian–Santonian, Late Cretaceous
Late Cretaceous stages

Duonychus is an extinct genus of therizinosaurid theropod dinosaurs that lived during the Late Cretaceous (Cenomanian to early Coniacian age) of what is now Mongolia. It is known from a partial skeleton, including several vertebrae, most of the forelimbs, and part of the pelvic girdle, found in outcrops of the Bayanshiree Formation. The remains were discovered in 2012 by the Mongolian Academy of Sciences and briefly mentioned in later conference abstracts. The genus contains a single species, Duonychus tsogtbaatari, which was formally described in 2025.

Diagnosis

  1. Didactyl manus with complete absence of digit III (digit formula 2-3-0) and a reduced metacarpal III forming a splint.
  2. Fused distal carpals 1 and 2 semilunate-shaped with a mediodorsal process and a small angle (~15°) between articular surfaces of the radiale for the semilunate carpal and the radius.
  3. Equally sized manual unguals I-2 and II-2, with absence or reduction of the flexor fossa in manual phalanges.
  4. Dorsal vertebrae with long neural spines, a thick centrodiapophyseal lamina without additional laminae, and lacking pleurocoels; sacral vertebrae (2-4) with flat ventral surfaces.
  5. Reduced dorsal process at the proximal end of manual phalanges and pneumatic dorsal ribs.
  6. Entepicondyle reduced with a markedly narrow groove separating it from the ulnar condyle; deltopectoral crest positioned more proximally than in Erlikosaurus.

Species

Duonychus tsogtbaatari Kobayashi et al., 2025

Type species

Named for Mongolian paleontologist Khishigjav Tsogtbaatar, a former director of the Institute of Paleontology of the Mongolian Academy of Sciences.

Holotype
MPC-D 100/85 , Paleontological Center, Mongolian Academy of Sciences
Material
Partial skeleton including six articulated dorsal vertebrae, six articulated sacral vertebrae with sacral ribs, anterior-most caudal vertebra, dorsal ribs, partial left scapula and coracoid, humeri, ulnae, radii, carpals, metacarpals, left and right manus, right ilium, both pubes, and proximal end of left ischium.
Horizon
Bayanshiree Formation, Cenomanian–Santonian, Late Cretaceous , 100.5–83.6 million years ago The age of the containing rock unit; no finer age has been published.
Locality
Urlibe Khudak, Ömnögovi, Mongolia

References

  1. Kobayashi, Y.; Zelenitsky, D. K.; Fiorillo, A. R.; Chinzorig, T. (2025). Didactyl therizinosaur with a preserved keratinous claw from the Late Cretaceous of Mongolia. iScience 28(4). Elsevier BV. doi:10.1016/j.isci.2025.112141 kobayashi2025a