Daspletosaurus (/dæsˌpliːtəˈsɔːrəs/ das-PLEET-ə-SOR-əs; meaning "frightful lizard") is a genus of tyrannosaurid dinosaur that lived in Laramidia between about 78 and 74.4 million years ago, during the Late Cretaceous Period.

D. wilsoni has been suggested as an intermediate species between D. torosus and D. horneri that evolved through anagenesis, though further research may be required to definitively support the theory.

It was not until 1970 that the specimen was fully described by Dale Russell, who made it the type of a new genus, Daspletosaurus, from the Greek δασπλής (dasplēs, stem and connective vowel resulting in dasplēto-) ("frightful") and σαυρος (sauros) ("lizard").

He based this referral on features of its limb and pelvic girdle, as well as the curvature of the hand claws, which he interpreted as traits matching Daspletosaurus.

This reassignment was not universally accepted, and thorough re-examination of the specimen favored its initial referral to Albertosaurus sarcophagus, despite lacking many of the diagnostic skeletal traits used to identify mature tyrannosaurids.

[7][8] An additional maxilla and various teeth from an Edmontosaurus-dominated bonebed in the Horseshoe Canyon Formation was also mistakenly referred to Daspletosaurus, but all the tyrannosaurid material has all since been confirmed to belong to Albertosaurus.

It was mounted for display in Chicago and labeled as Albertosaurus libratus for many years, but after several skull features were later found to be modeled in plaster, including most of the teeth, the specimen (FMNH PR308) was reassigned to Daspletosaurus torosus by Thomas Carr in 1999.

[14] A new tyrannosaurid specimen (OMNH 10131), including skull fragments, ribs, and parts of the hindlimb, was reported from New Mexico in 1990 and assigned to the now-defunct genus Aublysodon.

[7][10][16] However, research published in 2010 showed that this species, from the Hunter Wash Member of the Kirtland Formation, is actually a more primitive tyrannosauroid, and was classified in the genus Bistahieversor.

[17] In 1992, Jack Horner and colleagues published an extremely preliminary report of a tyrannosaurid from the upper parts of the Campanian Two Medicine Formation in Montana, which was interpreted as a transitional species between Daspletosaurus and the later Tyrannosaurus.

In 2009, preliminary preparation of a Daspletosaurus specimen from the Coal Ridge Member of the Judith River Formation measuring about 11 metres (36 ft) long was reported.

A specimen in the collections of Triebold Paleontology excavated between 2002 and 2004, known as "Sir William" (RMDRC 2002.MT-001), shows some characteristics of Daspletosaurus suggesting a new earlier species to the genus.

[24] In 2017, John Wilson discovered the bones of a tyrannosaurid, including a partial disarticulated skull, cervical, sacral, and caudal vertebrae, and a rib, chevron, and first metatarsal, from the "Jack’s B2" site of the Judith River Formation.

[10][37] On the other hand, Phil Currie and colleagues find Daspletosaurus to be more closely related to Tarbosaurus and other Asian tyrannosaurids like Alioramus than to the North American Tyrannosaurus.

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.

[23] Alioramus remotus Alioramus altai Qianzhousaurus Lythronax Teratophoneus Dynamoterror Thanatotheristes Daspletosaurus horneri Daspletosaurus wilsoni Dinosaur Park and Oldman formations taxon (TMP 2001.36.1) Zhuchengtyrannus Tarbosaurus In the same year, Warshaw and colleagues supported the anagenesis theory by referring other specimens to D. wilsoni (including the Dinosaur Park specimen) which they considered as a valid taxon, and by reanalysing the previous study of Scherer and Voiculescu-Holvad (2024).

[26] There are indications of D. horneri possessing integumentary sensory organs, possibly used in touch, modulation of precise jaw movements, temperature reading, and prey detection.

Darren Tanke and Phil Currie hypothesize that the bites are due to intraspecific competition for territory or resources, or for dominance within a social group.

[40] A young specimen of the tyrannosaurid (TMP 1994.143.1), initially identified as the Dinosaur Park Daspletosaurus but subsequently referred to Gorgosaurus libratus, also shows bite marks on the face that were inflicted by another tyrannosaur.

Erickson has shown that after a long time as juveniles, tyrannosaurs underwent tremendous growth spurts for about four years midway through their lives.

[48] By tabulating the number of specimens of each age group, Erickson and his colleagues were able to draw conclusions about life history in a population of Albertosaurus.

However, the uplift of the Rocky Mountains in the Laramide Orogeny to the west, which began during the time of Daspletosaurus, forced the seaway to retreat eastwards and southwards.

[55] Volcanic eruptions from the west periodically blanketed the region with ash, also resulting in large-scale mortality, while simultaneously enriching the soil for future plant growth.

Fluctuating sea levels also resulted in a variety of other environments at different times and places within the Judith River Group, including offshore and nearshore marine habitats, coastal wetlands, deltas, and lagoons, in addition to the inland floodplains.

[53] The excellent vertebrate fossil record of Two Medicine and Judith River rocks resulted from a combination of abundant animal life, periodic natural disasters, and the deposition of large amounts of sediment.

The Judith River Group preserves the remains of many aquatic amphibians and reptiles, including frogs, salamanders, turtles, Champsosaurus and crocodilians.

Azhdarchid pterosaurs, and birds like Apatornis and Avisaurus flew overhead, while several varieties of mammals coexisted with Daspletosaurus and other types of dinosaurs in the various formations that make up the Judith River wedge.

[5][10][57][58] A Saurornitholestes dentary has been discovered in the Dinosaur Park Formation that bore tooth marks left by the bite of a young tyrannosaur, possibly Daspletosaurus.

[19] The higher and broader muzzles of tyrannosaurines like Daspletosaurus are mechanically stronger than the lower snouts of albertosaurines like Gorgosaurus, although tooth strengths are similar between the two groups.

Holtz notes that, at the end of the later Maastrichtian stage, tyrannosaurines like Tyrannosaurus rex, hadrosaurines and chasmosaurines like Triceratops were widespread throughout western North America, while albertosaurines and centrosaurines became extinct, and lambeosaurines were very rare.