Tromerosaurus

Tromerosaurus Temporal range: Late Cretaceous (mid-Campanian), ~ B V H B Apt. Albian C T C S Cam. M
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Superfamily:	†Tyrannosauroidea
Family:	†Tyrannosauridae
Subfamily:	†Albertosaurinae
Genus:	†Tromerosaurus Powers et al., 2026
Species:	†T. solumons
Binomial name
†Tromerosaurus solumons Powers et al., 2026

Tromerosaurus (lit. 'terrible lizard') is an extinct genus of tyrannosaurid theropod dinosaur known from the Late Cretaceous (Campanian age) of Canada. The genus contains a single species, Tromerosaurus solumons, known from at least three partial skulls and skeletons. Previous work had regarded one of these, deriving from the Oldman Formation, as belonging to Daspletosaurus, and two of them, from the Dinosaur Park Formation, as belonging to the closely related Gorgosaurus. A placement within the subfamily Albertosaurinae is preferred, though some anatomical features of Tromerosaurus are reminiscent of tyrannosaurines.

Discovery and naming

In 2010, Stuart Plotkin discovered the remains of a tyrannosaur skeleton in outcrops of the upper Oldman Formation (quarry Q258) in eastern Dinosaur Provincial Park in Alberta, Canada. A team from the University of Alberta (UA) assisted in excavating the specimen in 2010 and 2011. The specimen is now housed in the UA Laboratory for Vertebrate Paleontology (UALVP), where it is accessioned as specimen UALVP 52981. It consists of a partially articulated, albeit incomplete, skeleton including most of the skull (missing the splenials and some components of the right half) and much of the postcranium (vertebrae from the neck and trunk, gastralia, ribs, both humeri, the pelvis, and most of the right hindlimb). Initial reports identified this specimen as belonging to Daspletosaurus without discussion. The discovery of this specimen prompted the reanalysis of two partial skeletons from the lower rock layers of the Dinosaur Park Formation, which overlies the Oldman Formation. Both of these specimens, housed in the Royal Tyrrell Museum of Palaeontology (TMP), had been previously mentioned in the scientific literature as belonging to the closely related genus Gorgosaurus. TMP 1994.012.0602, which includes much of the skull and tail, in addition to gastralia, ribs, most of both hindlimbs, and the pelvis, has been regarded as the largest and most mature adult specimen of G. libratus. TMP 1995.005.0001, a smaller partial skeleton, comprises an incomplete, disarticulated skull and an unprepared pelvis.

In 2026, Mark J. Powers and colleagues described Tromerosaurus solumons as a new genus and species of tyrannosaurid theropod based on these fossil remains, designating UALVP 52981 as the holotype specimen. TMP 1994.012.0602 and TMP 1995.005.0001 were referred to this species based on shared anatomical features with the holotype. Two isolated maxillae from unknown localities were tentatively also referred, one of which (UALVP 56605) belongs to a mature individual, while the other (TMP 1985.011.0003) belongs to a small juvenile. The generic name, Tromerosaurus, is combines the Ancient Greek words τρομερός (tromerós), meaning 'terrible' or 'frightful', and σαῦρος (saûros), meaning 'lizard'. This alludes to the combination of anatomical traits it shares with Gorgosaurus (lit. 'terrible lizard') and Daspletosaurus (lit. 'frightful lizard'). The specific name, solumons, is derived from the Latin words solus, meaning 'lonely', and mōns, meaning 'mountain'. This references the anatomy of the lacrimal horn, which is isolated by a wide, flattened shelf of the bone's posterior process. It also alludes to the dragon Smaug and his lair on Lonely Mountain in J. R. R. Tolkien's 1937 fantasy novel The Hobbit, hinting at the visual parallels between dragon iconography and tyrannosaurids.