Tromerosaurus

Powers et al., 2026

From Greek 'tromeros' (terrible or frightful) and 'sauros' (lizard), for its mix of traits shared with Gorgosaurus and Daspletosaurus.

83.6–72.2 million years ago Campanian, Late Cretaceous

Late Cretaceous stages

Tromerosaurus 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.

Diagnosis

A ventromedially oriented prong on the vomeropterygoid process of the palatine
A strongly arched pterygoid contact surface on the vomeropterygoid process of the palatine
The supraoccipital is excluded from the foramen magnum
The pila promaxillaris of the maxilla is medially inset from the osseous wall of the antorbital fossa
The maxillary fenestra approaches the anterior margin of the antorbital fossa
A concave posterodorsal margin on the orbital process of the lacrimal

Species

Tromerosaurus solumons Powers et al., 2026

Type species

From Latin 'solus' (lonely) and 'mons' (mountain), for the lacrimal horn isolated by a broad flat shelf of the lacrimal's posterior process; it also alludes to the lair of the dragon Smaug in The Hobbit.

Holotype: UALVP 52981 , University of Alberta Laboratory for Vertebrate Paleontology
Material: Partial skeleton of a mature individual with most skull bones (lacking the splenials, the right postorbital-squamosal and quadratojugal-quadrate complexes, and the right mandible), presacral vertebrae, gastralia, both humeri, the complete pelvis and the right hindlimb.
Horizon: Oldman Formation, Campanian, Late Cretaceous , 83.6–72.2 million years ago
Locality: Quarry Q258, Dinosaur Provincial Park, Alberta, Canada The describing paper places the quarry "4 meters below the nearest measured Oldman-Dinosaur Park Formation contact", in a massive yellow-stained sandstone below the field station bentonite.

References

Powers, M. J.; Napoli, J. G.; Coppock, C. C.; Sharpe, H. S.; Garros, C. W.; Demers-Potvin, A. V.; Raun, G. S.; Stock, J. C.; Miyashita, T.; Currie, P. J. (2026). A new albertosaurine from the Oldman Formation, Alberta, Canada, illuminates ambiguity between albertosaurine and tyrannosaurine characteristics. Journal of Vertebrate Paleontology e2728669. Informa UK Limited. doi:10.1080/02724634.2026.2728669 powers2026a