Thanatotheristes degrootorum "De Groot's Reaper of Death," was named by Voris et al. in February 2020 based on partial upper and lower jaws of a tyrannosaurid from around 80 million years ago in Alberta, Canada. The paper described not only a new genus of dinosaur but also proposed the tyrannosaurids of that area represented two different evolutionary lineages: one northern group of tyrannosaurs that differed from their southern group by a number of skeletal features. These differences, to the authors, meant different dinosaur genera roamed about simultaneously.
A paper released in September 2020 concludes Thanatotheristes isn't a valid genus but is a species of Daspletosaurus, thus creating a new (and oldest) Daspletosaurus, D. degrootorum. The new paper "sinks" Thanatotheristes by demonstrating that most characters used to declare Thanatotheristes as a valid taxon are found in other specimens of Daspletosaurus. In paleontology, to be considered a legitimate dinosaur genus, there must be characters belonging only to that genus and no other animal. This allows paleontologists to know when they have discovered a new dinosaur versus one already known. Both are important as finding more of known dinosaurs permits paleontologists to better understand the range of variation present. Variation is one of the most vexing problems of paleontology, when a single dinosaur is discovered one sometimes wonders if a "unique" character is actually a character tied to age (a juvenile male gorilla has a smooth skull, an adult has a large keel, without having both specimens one might think they belong to different animals), or to injury, or genetic anomalies, or just plain variation like how humans have varying hair and eye color, if one's earlobes are free standing or attached to the side of the head, and numerous other variables that make each of us unique, but still part of the same species.
The collapsing of Thanathotheristes into Daspletosaurus likely will be contested. The original authors will seek more material, evaluate the claims that the characters they used are not unique, and after more re-search (to search again, I love that word!) they will publish a counter-publication.