Open Paleo

Nemegtonykus

Lee et al., 2019 Disputed

Named after the Nemegt Formation of Mongolia where it was found, combined with Greek 'onyx' (claw); meaning 'Nemegt claw'.

72.2–66.0 million years ago Maastrichtian, Late Cretaceous
Late Cretaceous stages

Nemegtonykus is a genus of alvarezsaurid dinosaur from the Late Cretaceous ( Maastrichtian) Nemegt Formation of Mongolia. The type and only species is Nemegtonykus citus. It is the second alvarezsaurid known from the Nemegt Formation, preceded by Mononykus.

Under dispute

Nemegtonykus citus was described as a parvicursorine forming a polytomy with other Gobi alvarezsaurids (Lee and colleagues, 2019). Its position is unsettled: Kubo and colleagues (2023) recovered it outside Parvicursorinae as a successive sister taxon, and Meso and colleagues (2024) found it unstable and treated it as a junior synonym of Mononykus — a synonymy rejected by Lee and colleagues (2019) and by the reference-work treatment of Jones (2026), which retain it as a valid genus.

Diagnosis

  1. Anteroposteriorly elongate and subtrapezoidal lamina on first sacral vertebra, co-ossified with preacetabular ilium
  2. Second sacral centrum directly co-ossified with ilium without sacral rib contribution
  3. Posterodorsally oriented postacetabular process of ilium
  4. Partial plantar co-ossification between distal shafts of metatarsals II and IV
  5. Prominent wedge-shaped tubercle on posterolateral margin of tibiotarsus near distal end
  6. Partially co-ossified scapulocoracoid

Species

Nemegtonykus citus Lee et al., 2019 Disputed

Type species

From Latin 'citus' meaning 'the fast one', in reference to the animal's presumed speed.

Holotype
MPC-D 100/203 , Paleontological Center, Mongolian Academy of Sciences
Material
Partially disarticulated postcranial skeleton: 6 dorsal vertebrae, 2 sacral vertebrae, 21 caudal vertebrae, 5 dorsal ribs, scapulocoracoid, ilium, partial pubis, pelvic elements, complete femur, tibiotarsus, partial tibia, fibula, tarsometatarsus, pedal phalanges
Horizon
Nemegt Formation, Maastrichtian, Late Cretaceous , 72.2–66.0 million years ago
Locality
Altan Uul III, Ömnögovi, Mongolia

References

  1. Lee, S.; Park, J. Y.; Lee, Y. N.; Kim, S. H.; Lü, J.; Barsbold, R.; Tsogtbaatar, K. (2019). A new alvarezsaurid dinosaur from the Nemegt Formation of Mongolia. Scientific Reports 9(1): 15493. Springer Science and Business Media LLC. doi:10.1038/s41598-019-52021-y lee2019a
  2. Paul, G. S. (2024). The Princeton Field Guide to Dinosaurs (3rd ed.). Princeton University Press.

    Source of the body length and mass estimates.

    paul2024a
  3. Kubo, K.; Kobayashi, Y.; Chinzorig, T.; Tsogtbaatar, K. (2023). A new alvarezsaurid dinosaur (Theropoda, Alvarezsauria) from the Upper Cretaceous Baruungoyot Formation of Mongolia provides insights for bird-like sleeping behavior in non-avian dinosaurs. PLOS ONE 18(11): e0293801. Public Library of Science (PLoS). doi:10.1371/journal.pone.0293801

    New alvarezsaurid description recovered Nemegtonykus outside Parvicursorinae as successive sister taxon.

    kubo2023a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Treats Nemegtonykus as a parvicursorine alvarezsaurid.

    jones2026c
  5. 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

    Found Nemegtonykus unstable and treated it as a junior synonym of Mononykus.

    meso2024a