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Tromerosaurus solumons Powers, Napoli, Coppock, Sharpe, Garros, Demers-Potvin, Raun, Stock, Miyashita & Currie, 2026 |
ABSTRACT
Tyrannosaurid species have often been considered to have high longevity and low diversity relative to contemporaneous megaherbivores. Recent chronospecies assertions around tyrannosaurid lineage evolution have reinforced this idea. An albertosaurine, Tromerosaurus solumons, from the Oldman Formation of Alberta, Canada, shares features with Daspletosaurus and Gorgosaurus, and prompts reassessment of tyrannosaurid characteristics and the Late Cretaceous radiation of Tyrannosauridae. Maxillary morphometrics reveal clear intermediate morphologies in Tromerosaurus between Daspletosaurus and Gorgosaurus, including an anteroposteriorly longer maxillary fenestra and narrower pila promaxillaris than in Gorgosaurus libratus. An anatomical diagnosis of Tromerosaurus solumons allowed referral of specimens previously attributed to Gorgosaurus. Restricted stratigraphic overlap between Tromerosaurus and Gorgosaurus offers support to this distinction. A modified recent character-taxon dataset recovers Tromerosaurus as the earliest diverging member of Albertosaurinae under parsimony or Tyrannosaurinae under Bayesian inference. The difference in topologies along with reduced node support values for clades such as Lythronax + Teratophoneus, or Bistahieversor and other derived tyrannosaurines, suggests uncertainty as to their recovery within Albertosaurinae or Tyrannosaurinae. Together, these results support a younger divergence of the two main tyrannosaurid lineages with rapid character acquisition and transition during the Late Cretaceous (Santonian–Maastrichtian).
SYSTEMATIC PALEONTOLOGY
THEROPODA, Marsh 1881
TYRANNOSAUROIDEA, Walker 1964
TYRANNOSAURIDAE, Osborn 1906
ALBERTOSAURINAE, Currie et al. 2003
Clade Definition—A group of tyrannosaurid theropods that are more closely related to Albertosaurus than Tyrannosaurus (Currie et al., 2003).
TROMEROSAURUS, gen. nov.
TROMEROSAURUS SOLUMONS, gen. et sp. nov.
Albertosaurus libratus TMP 1985.011.0003 (Table 1); Carr 1999
Gorgosaurus libratus TMP 1994.012.0602 and TMP 1995.005.0001 (Table 1); Currie 2003b.
Daspletosaurus torosus UALVP 52981 (Table 1); Rhodes et al. 2021.
Gorgosaurus libratus TMP 1985.011.0003 (Fig. 3B), TMP 1994.012.0602 (Figs. 3K, 7D and 8C), and TMP 1995.005.0001 (Fig. 5B); Voris et al. 2021.
Daspletosaurus UALVP 52981 (Table 1); Paul et al. 2022.
Etymology—The genus name derives from Ancient Greek for terrible or frightful (tromerós) lizard (saûros) with regard to the taxon having a mosaic of characteristics between Gorgosaurus (terrible lizard) and Daspletosaurus (frightful lizard). The specific epithet (solumons) derives from Latin for lonely (solus) and mountain (mons), pertaining to the isolation of the lacrimal horn by a broad flat shelf of the posterior process of the lacrimal. This also pays homage to the infamous fictional dragon Smaug (in particular, to his lair in The Hobbit (Tolkien, 1937), recognizing the visual similarities between tyrannosaurids and iconography of dragons.
Mark J. Powers, James G. Napoli, Colton C. Coppock, Henry S. Sharpe, Christiana W. Garros, Alexandre V. Demers-Potvin, Gorm S. Raun, Jordan C. Stock, Tetsuto Miyashita and Philip J. Currie . 2026. A new albertosaurine from the Oldman Formation, Alberta, Canada, illuminates ambiguity between albertosaurine and tyrannosaurine characteristics. Journal of Vertebrate Paleontology. e2728669. DOI: doi.org/10.1080/02724634.2026.2728669 [02 Oct 2026]
