Daspletosaurini is an extinct

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

(

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

) of

tyrannosaurine Tyrannosaurinae (or tyrannosaurines) is one of the two extinct subfamilies of Tyrannosauridae, a family of coelurosaurian theropods that consists of at least three tribes and several genera. All fossils of these genera have been found in the Late ...

dinosaurs that lived in

Laramidia Laramidia was an island continent that existed during the Late Cretaceous period (99.6–66 Year#SI prefix multipliers, Ma), when the Western Interior Seaway split the continent of North America in two. In the Mesozoic era, Laramidia was an island ...

during the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

(Middle

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

) period. It consists of two genera: ''

Daspletosaurus ''Daspletosaurus'' ( ; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 77 and 74.4 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three named ...

'' and '' Thanatotheristes''. Four species have been described in the two genera, namely ''Daspletosaurus torosus'', ''Daspletosaurus horneri'', ''Daspletosaurus wilsoni'', and ''Thanatotheristes degrootorum''. At one point all of them were assigned as specimens of ''D. torosus'', but several papers since 2017 have found them to represent distinct species. Some researchers found

anagenesis Anagenesis is the gradual evolution of a species that continues to exist as an interbreeding population. This contrasts with cladogenesis, which occurs when branching or splitting occurs, leading to two or more lineages and resulting in separate ...

in the group, whether contained in a daspletosaurin clade or paraphyletic in respect to the lineage of tyrannosaurines leading up to ''

Tyrannosaurus ''Tyrannosaurus'' () is a genus of large theropod dinosaur. The type species ''Tyrannosaurus rex'' ( meaning 'king' in Latin), often shortened to ''T. rex'' or colloquially t-rex, is one of the best represented theropods. It lived througho ...

'', but a 2023 study refuted this theory on the basis of morphological and stratigraphical data.

Description

Daspletosaurins were large predators, reaching around in length. However, they were not the largest tyrannosaurids, as more derived taxa, such as ''

'', could reach lengths of more than . Daspletosaurini is diagnosed by characteristics such as the presence of an extremely coarse subcutaneous surface of the maxilla anteroventral to the antorbital fossa; a constricted jugal ramus of maxilla; the anteroventral corner of the maxilla tapers into a shallow angle (<65°) as measured between the alveolar margin of the first two alveoli and the anterior margin of the subcutaneous surface; a prefrontal that is broad in dorsal view and strongly dorsomedially arced in anterior view; a dentary chin located ventral to either the third alveolus or third interdental plate and possessing no fewer than 14 maxillary teeth.

Classification

In the 2020

description Description is any type of communication that aims to make vivid a place, object, person, group, or other physical entity. It is one of four rhetorical modes (also known as ''modes of discourse''), along with exposition, argumentation, and narr ...

of '' Thanatotheristes'', Voris et al. erected Daspletosaurini as a new clade within Tyrannosauridae, as a sister taxon to a clade comprising ''

Zhuchengtyrannus ''Zhuchengtyrannus'' (meaning "Zhucheng tyrant") is a genus of Tyrannosauridae, tyrannosaurid theropod dinosaur known from the Campanian stage of the Late Cretaceous of Shandong Province, China. It belongs to the subfamily Tyrannosaurinae, and co ...

'', ''

Tarbosaurus ''Tarbosaurus'' ( ; meaning "alarming lizard") is a genus of large tyrannosaurid dinosaur that lived in Asia during the Late Cretaceous epoch, about 70 million years ago (Maastrichtian age). It contains the single type species: ''Tarbosaurus ...

'', and ''

''. The

cladogram A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...

below shows the results of the

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

performed by Voris et al. (2020): In 2022, Warshaw & Fowler proposed that the three ''Daspletosaurus'' species evolved through

in the Tyrannosaurinae in a line leading to ''Zhuchengtyrannus'', ''Tarbosaurus'', and ''Tyrannosaurus''. Due to their more fragmentary nature, ''Thanatotheristes'' and ''Nanuqsaurus'' were excluded from this analysis. The cladogram below shows the results of the phylogenetic analysis performed by Warshaw & Fowler (2022). In 2023, Scherer and Voiculescu-Holvad argued that the stratigraphic ranges of ''D. torosus'', ''D. wilsoni'' and an unnamed species from the

Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 7 ...

and

Oldman Formation The Oldman Formation is a stratigraphic unit of Late Cretaceous (Campanian stage) age that underlies much of southern Alberta, Canada. It consists primarily of sandstones that were deposited in fluvial channel and floodplain environments. It was ...

show a clear overlap, indicating that anagenesis may not be the predominant factor of speciation within the genus, since all species of ''Daspletosaurus'' were contemporaneous with each other at some point during its evolution. Phylogenetic analyses resolved ''D. horneri'' as the most basal species, in spite of the fact that it's stratigraphically the youngest. While the authors did not completely refute the possibility that anagenesis was the main driver of ''Daspletosaurus'' evolution based on the intermediate morphological features, they also suggested that ''D. wilsoni'' may be a junior synonym of ''D. torosus'', since there is a near lack of autapomorphic characters that can differentiate this species. They also claimed that ''Daspletosaurus'' did not evolve from ''Thanatotheristes'', since they found no support on the basis of morphological and stratigraphical data, and that anagenesis will not be supported unequivocally due to the limited sample and nature of the fossil record which doesn't show a great degree of variation in morphology. The cladogram presented for their phylogenetic analysis is shown below.

References

{{Taxonbar, from=Q84050109 Tyrannosauridae Dinosaur tribes Campanian dinosaurs Dinosaurs of North America