Open Paleo

Xiyunykus

Xu et al., 2018 zee-YOO-nick-us

From Mandarin xiyu meaning 'west' (referring to Western China where it was found) combined with Greek onyx meaning 'claw'; translates as 'western claw'

125.8–113.2 million years ago Barremian–Aptian, Early Cretaceous
Early Cretaceous stages

Xiyunykus is a genus of alvarezsauroid theropod from the Early Cretaceous-aged Tugulu Group of what is now China. Only one species has been described, Xiyunykus pengi.

Diagnosis

  1. Large basal tubera formed exclusively by basioccipital
  2. Basisphenoid recess with basioccipital contribution containing multiple deep fossae
  3. Cultriform process with poorly ossified dorsal margin that parallels ventral margin in lateral view
  4. Two horizontally arranged pneumatic fossae on lateral central surface of each anterior or middle cervical vertebra
  5. Distinct tubercle along ventrolateral edge of each anterior cervical centrum
  6. Deep, curved groove on scapular lateral surface immediately anterior to glenoid fossa

Species

Xiyunykus pengi Xu et al., 2018

Type species

Named in honor of Professor Peng Xiling for contributions to the study of geology in Xinjiang.

Holotype
IVPP V22783 , Institute of Vertebrate Paleontology and Paleoanthropology
Material
Partial, disarticulated skeleton
Horizon
upper Tugulu Group, Barremian–Aptian, Early Cretaceous , 125.8–113.2 million years ago
Locality
Wucaiwan area, Xinjiang, China Xu and colleagues (2018) give the horizon as "Upper Cretaceous (Barremian-Aptian?) upper part of the Tugulu Group"; both stages are Lower Cretaceous, so "Upper Cretaceous" is a slip. Zheng and colleagues' (2023) Valanginian floor dates the base of the Lianmuqin Formation at Urho, in the northwest of the Junggar Basin, not the beds at Wucaiwan.

References

  1. Xu, X.; Choiniere, J.; Tan, Q.; Benson, R. B. J.; Clark, J.; Sullivan, C.; Zhao, Q.; Han, F.; Ma, Q.; He, Y.; Wang, S.; Xing, H.; Tan, L. (2018). Two Early Cretaceous Fossils Document Transitional Stages in Alvarezsaurian Dinosaur Evolution. Current Biology 28(17): 2853-2860.e3. Elsevier BV. doi:10.1016/j.cub.2018.07.057

    Gives the holotype horizon as the upper Tugulu Group at Wucaiwan, "(Barremian-Aptian?)".

    xu2018c
  2. Fowler, D. W.; Wilson, J. P.; Freedman Fowler, E. A.; Noto, C. R.; Anduza, D.; Horner, J. R. (2020). Trierarchuncus prairiensis gen. et sp. nov., the last alvarezsaurid: Hell Creek Formation (uppermost Maastrichtian), Montana. Cretaceous Research 116. Elsevier BV. doi:10.1016/j.cretres.2020.104560

    Lists Xiyunykus from the Tugulu Group at "~Barremian–Aptian".

    fowler2020b
  3. Meso, J. G.; Pol, D.; Chiappe, L.; Qin, Z.; Díaz-Martínez, I.; Gianechini, F.; Apesteguía, S.; Makovicky, P. J.; Pittman, M. (2024). Body size and evolutionary rate analyses reveal complex evolutionary history of Alvarezsauria. Cladistics 41(2): 135-155. Wiley. doi:10.1111/cla.12600

    Places Xiyunykus "from the upper section of the Barremian–Aptian Tugulu Group".

    meso2024a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the body length, mass, and hip height estimates.

    jones2026c