Open Paleo

Lythronax

Loewen et al., 2013 LY-thro-nax

From Greek 'lythron' (λύθρον) meaning 'gore' and 'anax' (ἄναξ) meaning 'king', hence 'gore king'. The species name is from Greek 'argestes' (ἀργεστής), Homer's name for the wind from the southwest, referring to where the specimen was found in North America.

83.6–72.2 million years ago Campanian, Late Cretaceous
Late Cretaceous stages

Lythronax is a genus of tyrannosaurid dinosaur that lived in North America around 81.9-81.5 million years ago during the Late Cretaceous period. The only known specimen was discovered in Utah in the Wahweap Formation of the Grand Staircase-Escalante National Monument in 2009, and it consists of a partial skull and skeleton. In 2013, it became the basis of the new genus and species Lythronax argestes; the generic name Lythronax means "gore king", and the specific name argestes originates from the Greek poet Homer's name for the wind from the southwest, in reference to the specimen's geographic provenance in North America.

Diagnosis

  1. Sigmoidal lateral margin of maxilla
  2. Ratio of transverse width of anterior portion of nasal to transverse width of middle portion greater than 2.5
  3. Prefrontal and postorbital contact surfaces on frontal separated only by narrow dorsoventral groove
  4. Distinct subocular flange on jugal
  5. 11 maxillary alveoli (vs 14-16 in other tyrannosaurids)
  6. Concave lateral margin of dentary with broad postorbital process of jugal
  7. Laterally expanded caudal skull with rostrodorsally directed orbits
  8. Large distally expanded pubic boot with anteroposterior length at least 60% of total pubic length
  9. Dorsally expanded ascending process of astragalus

Species

Lythronax argestes Loewen et al., 2013

Type species

From Ancient Greek 'argestes', a name used by the poet Homer for the wind from the southwest, in reference to where the specimen was found within North America.

Holotype
UMNH VP 20200 , Utah Museum of Natural History
Material
Partial skull and skeleton including skull bones, dorsal rib, caudal chevron, both pubic bones, left tibia, fibula, and left second and fourth metatarsals
Horizon
lower Reynolds Point Member, Wahweap Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality
Nipple Butte, Utah, United States Beveridge and colleagues (2022) place the skeleton in "mudstone horizons in the lower Reynolds Point Member", the unit Loewen and colleagues (2013) call the middle member.

References

  1. Loewen, M. A.; Irmis, R. B.; Sertich, J. J. W.; Currie, P. J.; Sampson, S. D. (2013). Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans. PLoS ONE 8(11): e79420. Public Library of Science (PLoS). doi:10.1371/journal.pone.0079420 loewen2013a
  2. Beveridge, T. L.; Roberts, E. M.; Ramezani, J.; Titus, A. L.; Eaton, J. G.; Irmis, R. B.; Sertich, J. J. W. (2022). Refined geochronology and revised stratigraphic nomenclature of the Upper Cretaceous Wahweap Formation, Utah, U.S.A. and the age of early Campanian vertebrates from southern Laramidia. Palaeogeography, Palaeoclimatology, Palaeoecology 591: 110876. Elsevier BV. doi:10.1016/j.palaeo.2022.110876

    Formalizes the Wahweap members and places the holotype quarry in the lower Reynolds Point Member.

    beveridge2022a
  3. Jones, B. (2026). The Princeton Encyclopedia of Dinosaurs: Theropods. Princeton University Press.

    Source of the hip height estimate.

    jones2026c