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So last year my friend Jared Voris named both Thanatotheristes degrootorum and Daspletosaurini (as you all probably know). For the past year a few others and I been studying this clade (you probably all know as well) and have been able to put up a good argument for two unnamed and controversial Daspletosaurus species, one from the Dinosaur Park Formation of Alberta and the other from the Judith River Formation of Montana. This presents that there’s most likely 4 Daspletosaurus species, there’s also been evidence of a possible (note possible, just kind of a guess based of age and location) Thanatotheristes from the early Judith River Formation. Along with Thanatotheristes degrootorum that’s 6 species of Daspletosaurini. Though there has been some recent news of a new Tyrannosaur that seems to fit perfectly in this lineage that my friend discovered, I can’t say much on it though until the paper is out. Careful radiometric and geological dating has shown the species don’t overlap. In order that unnamed species my friend discovered is 83.4-80 million years old, Thanatotheristes degrootorum is 80-79.5 million years old, the Judith Rivers possible Thanatotheristes sp. is 79.5-78 million years old, the Judith River Daspletosaurus sp. is 78-77 million years old, Daspletosaurus torosus is 77-76.5 million years old, the Dinosaur Park Formation Daspletosaurus sp. is 76.5-74.8 million years old, and Daspletosaurus horneri is 74.6-74 million years old (note that through time the features on these species change and flow perfectly together) (there’s also a gap there of 100,000 years I’ll get to soon) (and there might be another species in the Horseshoe Canyon Formation of Alberta but for now we suspect they went extinct 74 million years ago due to absence of diagnostic fossils and the Elkhorn range volcanoes in Montana experiencing huge volcanic events and the Western Interior Seaway rising causing an extinction and faunal turnover in North Western North America) anyways that gap of 100,000 years between the Dinosaur Park Formation Daspletosaurus sp. and Daspletosaurus horneri is pretty special as it contains three mysterious specimens from the upper Two Medicine Formation (Currie, P.J., Trexler, D., Koppelhus, E.B., Wicks, K., Murphy, N., 2005 An Unusual Multi-Individual Tyrannosaurid Bonebed in the Two Medicine Formation (Late Cretaceous, Campanian) of Montana (USA). pp. 313-324 In: The Carnivorous Dinosaurs. Carpenter, K. (ed.) Indiana University Press, 371 pp.) Interestingly, now that Daspletosaurus horneri has been described, TA.1997.002 (which is one of the specimens) instead seems to share characters with D. torosus plus the Dinosaur Park Formation species. In particular, the maxillary fenestra is longer than tall, the upper half of the lacrimal orbital margin is convex, the lacrimal horn is tall, the dorsal margin of the posterior postorbital process is convex, and the surangular shelf overhangs the posterior foramen. And this adding on that the sediments it was found in were between the Dinosaur Park Formation Daspletosaurus sp. and Daspletosaurus horneri in age, along with some Daspletosaurus horneri features (more research has to be done on these features) shows it’s most likely a transitional form! Especially since it’s the right age to be and shares features of both its predecessor and ancestor! Along with a transitional form this shows possibly our first complete Anagenetic lineage! I’m quite interested to hear everyone’s thoughts on this subject.

Hi, Since the group Daspletosaurini has just be established. Wouldn’t Nanuqsaurus be part of it, it is known as a Tyrannosaurinae but since the clade/group Daspletosaurini has been established wouldn’t it be a Daspletosaurini? Since it shares some features with the Daspletosaurini.