Open Paleo

Enigmosaurus

Barsbold, 1983 ee-NIG-mo-SAWR-us

From Greek enigma (riddle/enigma) + sauros (lizard): 'enigma lizard' or 'enigmatic lizard', reflecting uncertainty about its affinities at the time of description.

100.5–89.8 million years ago Cenomanian–Turonian, Late Cretaceous
Late Cretaceous stages

Enigmosaurus is a genus of therizinosauroid that lived in Asia during the Late Cretaceous period. It was a medium-sized, ground-dwelling, bipedal herbivore that represents the third therizinosaur taxon from the Bayanshiree Formation, although it is known from the lower part. The genus is monotypic, including only the type species E. mongoliensis, known from a well-preserved pelvis and other tentative body remains.

Under dispute

Enigmosaurus is an intermediate therizinosaur that falls inside or outside Therizinosauridae according to the definition used. Zanno (2010) and Liao and colleagues (2026) recover it as a successive outgroup to the family as Zanno and colleagues (2009) define it; Kobayashi and colleagues (2022) recover it as the sister of the derived therizinosaurids, inside their stem-defined Therizinosauridae. It is placed in Therizinosauroidea. A proposed synonymy with Erlikosaurus has been rejected.

Diagnosis

  1. Pubis and ischium narrow, without lateral flattening.
  2. Distal end of pubis elongated and shoe-shaped, narrowed anteriorly and posteriorly.
  3. Anterior presymphyseal region of distal pubis bears a wide longitudinal (sagittal) indentation continuing onto the anterior shaft.
  4. Obturator process displaced distally, highly narrowed and elongated, fused tightly to the pubis, considerably higher than the distal end.

Species

Enigmosaurus mongoliensis Barsbold, 1983

Type species

Named for Mongolia, the country of discovery.

Holotype
IGM 100/84 , Paleontological Center, Mongolian Academy of Sciences
Material
Partial skeleton lacking skull: well-preserved pelvic girdle (sacral vertebrae, partial ilium, pubis, left ischium) plus tentative postcranial elements
Horizon
Bayanshiree Formation, Cenomanian–Turonian, Late Cretaceous , 100.5–89.8 million years ago
Locality
Khara Khutul, Dornogovi, Mongolia

References

  1. Barsbold, R. (1983). Khishchnye dinozavry mela Mongolii [Carnivorous dinosaurs from the Cretaceous of Mongolia]. Trudy - Sovmestnaya Sovetsko-Mongol'skaya Paleontologicheskaya Ekspeditsiya 19: 1-117. barsbold1983a
  2. Zanno, L. E. (2010). A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology 8(4): 503-543. doi:10.1080/14772019.2010.488045

    Recovered Enigmosaurus outside Therizinosauridae, as successive outgroup to that family.

    zanno2010a
  3. Kobayashi, Y.; Takasaki, R.; Fiorillo, A. R.; Chinzorig, T.; Hikida, Y. (2022). New therizinosaurid dinosaur from the marine Osoushinai Formation (Upper Cretaceous, Japan) provides insight for function and evolution of therizinosaur claws. Scientific Reports 12(1). Springer Science and Business Media LLC. doi:10.1038/s41598-022-11063-5

    Recovered Enigmosaurus as the sister of the derived therizinosaurids, inside a stem-defined Therizinosauridae.

    kobayashi2022a
  4. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Reports Enigmosaurus as a therizinosaurid or a basal therizinosauroid.

    jones2026c
  5. 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
  6. Zanno, L. E.; Gillette, D. D.; Albright, L. B.; Titus, A. L. (2009). A new North American therizinosaurid and the role of herbivory in 'predatory' dinosaur evolution. Proceedings of the Royal Society B: Biological Sciences 276(1672): 3505-3511. The Royal Society. doi:10.1098/rspb.2009.1029

    Defined Therizinosauridae as the least inclusive clade containing Nothronychus, Segnosaurus, Erlikosaurus and Therizinosaurus.

    zanno2009a
  7. Liao, C. C.; Freimuth, W. J.; Zanno, L. E.; Xu, X. (2026). A new therizinosaur from the Early Cretaceous Jehol Biota and ecomorphological patterns among early therizinosaurians. Journal of Systematic Palaeontology 24(2): 2710287. Informa UK Limited. doi:10.1080/14772019.2026.2710287

    Recovered Enigmosaurus as a successive outgroup to Therizinosauridae.

    liao2026a