Fossils of this taxon are found in the Foremost Formation of Alberta, Canada, coexisting with medium-sized ceratopsids like Xenoceratops foremostensis and small pachycephalosaurids like Colepiocephale lambei.

The holotype specimen of Thanatotheristes degrootorum (TMP 2010.5.7) is based on a right maxilla, right jugal, right postorbital, right surangular, right quadrate, right laterosphenoid, left frontal, and both dentaries.

[1] T. degrootorum is characterised by:[1] The type specimen of Thanatotheristes has been estimated at 8 m (26 ft), based on the skull material and comparisons with related genera.

It includes T. degrootorum, Daspletosaurus torosus, D. horneri, and a tyrannosaurid from the Dinosaur Park Formation (FMNH PR308).

[1] The cladogram below is the result of the phylogenetic analysis performed by Voris et al. (2020):[1] Dryptosaurus aquilunguis Appalachiosaurus montgomeriensis Bistahieversor sealeyi Gorgosaurus libratus Albertosaurus sarcophagus Qianzhousaurus sinensis Alioramus remotus Alioramus altai Teratophoneus curriei Dynamoterror dynastes Lythronax argestes Nanuqsaurus hoglundi Thanatotheristes degrootorum Daspletosaurus torosus Daspletosaurus horneri Zhuchengtyrannus magnus Tarbosaurus bataar Tyrannosaurus rex An analysis of a subadult Daspletosaurus torosus frontal by Yun, 2020 suggests that features of the bone would effectively demonstrate that autapomorphies of some tyrannosaurid taxa would be inadequate, due to the broad range in morphology of frontals within particular clades.