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Stygivenator

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Stygivenator
Temporal range: Late Cretaceous, 66 Ma
↓
Cast of the holotype specimen of S. molnari, LACM 28471
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Superfamily: †Tyrannosauroidea
Genus: †Stygivenator
Olshevsky, 1995
Species:
†S. molnari
Binomial name
†Stygivenator molnari
(Paul, 1988)
Synonyms
  • Aublysodon molnaris
    Paul, 1988
  • Aublysodon molnari
    Paul, 1988 emend Paul, 1989

Stygivenator, also known as the "Jordan theropod" is a dubious genus of tyrannosauroid dinosaur from the Hell Creek Formation, containing the type and only species Stygivenator molnari. Originally considered a species of Aublysodon, another dubious genus, and then a juvenile of Tyrannosaurus, its specific identity can not presently be determined due to its poor preservation making it impossible to rule out an identity as either a specimen of Tyrannosaurus or Nanotyrannus.

Discovery and naming

LACM 28471 on display at the Natural History Museum of Los Angeles County

Skull material of a theropod dinosaur was discovered by Harley Garbani in 1966 near Jordan, Montana, Garfield County, Montana, Montana. Found alongside the skull of a Triceratops, it is from rock layers of the Hell Creek Formation. The specimen was returned to Garbani's institution, the Natural History Museum of Los Angeles County in California and given the specimen number LACM 28471. It's a portion of the snout consisting of both maxillae, teeth, nasals, frontals, a parietal, and portions of the surangular and dentaries.[1] Though originally considered to include one tooth from the unpreserved premaxilla, later studies have reinterpretted this element as a maxillary tooth.[2][3]

In 1978 it was scientifically described by Ralph E. Molnar, who noted similarities to both tyrannosaurids and dromaeosaurids but considered it most likely to represent a large dromaeosaur. Considering the material too lacking to give it a name, he simply referred to it as the "Jordan theropod".[3][4] Gregory S. Paul, in the 1988 book Predatory Dinosaurs of the World, instead identified as a tyrannosaurid belonging to the genus Aublysodon due to the anatomy of its supposed premaxillary tooth. He considered it a new species, and named it Aublysodon molnaris after Molnar.[5] This was later corrected by Paul to the correctly formed Aublysodon molnari.[6][7] Independently, Molnar returned to the specimen alongside Kenneth Carpenter in a 1989 study, independently concluding it was similar to Aublysodon based on the "premaxillary" tooth. However, they assignined it to the type species of that genus, Aublysodon mirandus, rather than a distinct species.[1][8]

In modern research, Aublysodon is considered to be a dubious genus, as the features of its teeth are common amongst tyrannosaurs.[2][3] Due to the doubtful nature of Aublysodon, George Olshevsky gave it a distinct genus Stygivenator in a 1995 publication. This name was derived from the Underworld river Styx of Greek mythology, referring to the Hell Creek Formation, as well as -venator, the Latin word for hunter. Together, it formed the intended meaning "Hell Creek hunter". The name came from Molnar, who would have used it in his original 1978 were he more certain of its identity at the time.[6][7]

Classification

In 2000, Thomas Carr and Thomas Williamson suggested that the proposed diagnostic features of LACM 28471 listed by Molnar and Carpenter in 1989 are actually typical of juvenile tyrannosaurids, and identified the specimen as an indeterminate juvenile tyrannosaurid pending examination.[9] In 2003, Chistopher Brochu and Philip J. Currie independently referred LACM 28471 to as an immature T. rex in each of their studies.[10][11] In 2004, Carr and Williamson identified the Stygivenator holotype (LACM 28471) and the Dinotyrannus holotype (LACM 23845) as a juvenile and subadult T. rex respectively after examination.[2] In 2013, Peter Larson suggested that LACM 28471 could be a younger specimen of Nanotyrannus lancensis, which he argued to be a valid taxon closely related to T. rex.[12] In 2016, Joshua Schmerge and Bruce Rothschild supported the validity of Nanotyrannus, but considered LACM 28471 as a juvenile T. rex.[13]

In June 2025, Gregory S. Paul supported a basal eutyrannosaurian (non-tyrannosaurid) position for Nanotyrannus and argued for the validity of Stygivenator, referring NCSM 40000 to as S. sp.[14] In October 2025, Lindsay Zanno and James Napoli formally described NCSM 40000 as a skeletally mature specimen of N. lancensis, and considered Stygivenator as a nomen dubium potentially synonymous with N. lancensis based on firsthand examination.[3]

References

  1. ^ a b Molnar, R. E.; Carpenter, K. (1989). "The Jordan theropod (Maastrichtian, Montana, USA) referred to the genus Aublysodon". Geobios. 22 (4): 445–454.
  2. ^ a b c Carr, T.D.; Williamson, T.E. (2004). "Diversity of late Maastrichtian Tyrannosauridae (Dinosauria: Theropoda) from western North America". Zoological Journal of the Linnean Society. 142 (4): 479–523. doi:10.1111/j.1096-3642.2004.00130.x.
  3. ^ a b c d Zanno, L.E.; Napoli, J.G. (2025-10-30). "Nanotyrannus and Tyrannosaurus coexisted at the close of the Cretaceous". Nature. doi:10.1038/s41586-025-09801-6.
  4. ^ Molnar, R. E. (1978). "A New Theropod Dinosaur from the Upper Cretaceous of Central Montana". Journal of Paleontology. 52 (1): 73–82.
  5. ^ Paul, G. S. (1988). Predatory Dinosaurs of the World. Simon and Schuster. p. 325. ISBN 978-0671619466.
  6. ^ a b Olshevsky, G. (1995). "The origin and evolution of the tyrannosaurids (Part 1)". Kyoryugaku Saizensen. 9: 92–119.
  7. ^ a b Olshevsky, G. (1995). "The origin and evolution of the tyrannosaurids (Part 2)". Kyoryugaku Saizensen. 10: 75–99.
  8. ^ Lehman, T. M.; Carpenter, K. (1990). "A partial skeleton of the tyrannosaurid dinosaur Aublysodon from the Upper Cretaceous of New Mexico". Journal of Paleontology. 64 (6): 1026–1032.
  9. ^ Carr, Thomas D.; Williamson, Thomas E. (2000). "A review of Tyrannosauridae (Dinosauria: Coelurosauria) from New Mexico". Bulletin. 17. New Mexico Museum of Natural History and Science: 113–145.
  10. ^ Brochu, C. R. (2003). "Osteology of Tyrannosaurus rex: insights from a nearly complete skeleton and high-resolution computed tomographic analysis of the skull". Society of Vertebrate Paleontology Memoirs. 7: 1–138. doi:10.2307/3889334. JSTOR 3889334.
  11. ^ Currie, Philip J. (2003). "Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia" (PDF). Canadian Journal of Earth Sciences. 40 (4): 651–665. Bibcode:2003CaJES..40..651C. doi:10.1139/e02-083. Archived (PDF) from the original on December 23, 2023. Retrieved January 21, 2023.
  12. ^ Larson, P.L. (2013). "The case for Nanotyrannus". In Parrish, J.M.; Molnar, R.A.; Currie, P.J.; Koppelhus, E.B. (eds.). Tyrannosaurid Paleobiology. University of Indiana Press. pp. 15–53. ISBN 978-0253009302.
  13. ^ Schmerge, Joshua D.; Rothschild, Bruce M. (2016). "Distribution of the dentary groove of theropod dinosaurs: Implications for theropod phylogeny and the validity of the genus Nanotyrannus Bakker et al., 1988". Cretaceous Research. 61: 26–33. Bibcode:2016CrRes..61...26S. doi:10.1016/J.CRETRES.2015.12.016. S2CID 85736236.
  14. ^ Paul, Gregory S. (2025). "A presentation of the current data on the exceptionally diverse non-tyrannosaurid eutyrannosaur and Tyrannosaurini genera and species of western North America during the end Cretaceous North American interchange". Mesozoic. 2 (2): 85–138. doi:10.11646/mesozoic.2.2.1.
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