''Bistahieversor'' (meaning "Bistahi destroyer"), also known as the "Bisti Beast", is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of basal eutyrannosaurian

theropod Theropoda (; from ancient Greek , (''therion'') "wild beast"; , (''pous, podos'') "foot"">wiktionary:ποδός"> (''pous, podos'') "foot" is one of the three major groups (clades) of dinosaurs, alongside Ornithischia and Sauropodom ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic Geological period, period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the #Evolutio ...

. The genus contains only a single known species, ''B. sealeyi'', described in 2010, from 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 ...

of New Mexico. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

and a juvenile were found in the Hunter Wash Member of the

Kirtland Formation The Kirtland Formation (originally the Kirtland Shale) is a Sedimentary rock, sedimentary geological formation. Description The Kirtland Formation is the product of alluvial muds and overbank sand deposits from the many channels draining the ...

, while other specimens came from the underlying Fossil Forest member of the

Fruitland Formation The Fruitland Formation is a geologic formation found in the San Juan Basin in the states of New Mexico and Colorado, in the United States of America. It contains fossils dating it to the Campanian age of the late Cretaceous.

. This dates ''Bistahieversor'' approximately 75.5 to 74.5 million years ago during the

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 ...

age, found in sediments spanning a million years.

Discovery and naming

The first remains now attributed to ''Bistahieversor'', a partial skull and skeleton, were described in 1990 as a specimen of ''

Aublysodon ''Aublysodon'' (“backwards-flowing tooth") is a dubious genus of carnivorous dinosaurs known only from the Judith River Formation in Montana, which has been dated to the late Campanian age of the late Cretaceous period (about 75 million years ...

''. Additional remains, consisting of the incomplete skull and skeleton of a juvenile, were described in 1992. Another complete skull and partial skeleton were found in the Bisti/De-Na-Zin Wilderness Area of

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

in 1998, known colloquially as the "Bisti Beast". In a 2000 paper, Thomas Carr and Thomas Williamson re-examined these four specimens and suggested that they did not belong to ''Aublysodon'', but rather to one or more new species of ''

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 ...

''. However, it was not until 2010 that Carr and Williamson published a thorough re-description of the specimens and found that they belonged to a new genus and species of more generalized tyrannosauroid. They named it ''Bistahieversor sealeyi''. The name ''Bistahieversor'' comes from the

Navajo The Navajo or Diné are an Indigenous people of the Southwestern United States. Their traditional language is Diné bizaad, a Southern Athabascan language. The states with the largest Diné populations are Arizona (140,263) and New Mexico (1 ...

, or "place of the adobe formations" in reference to the Bisti/De-Na-Zin Wilderness Area where it was found. ''Eversor'', the latter part of the name, means "destroyer."

Description

Material from both juveniles and adults has been found in the Kirtland and Fruitland formations of

. Adult ''Bistahieversor'' are estimated to have been around long and weigh at least a ton. The snout is deep, indicating that the feature is not unique to more derived tyrannosaurs, such as ''

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 ...

''. Geographical barriers, such as the newly forming

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

, may have isolated the more southerly ''Bistahieversor'' from more derived northern tyrannosaurs. In 2010,

Gregory S. Paul Gregory Scott Paul (born December 24, 1954) is an American freelance researcher, author and illustrator who works in paleontology. He is best known for his work and research on theropoda, theropod dinosaurs and his detailed illustrations, both l ...

estimated a length of 8 meters (26 ft) and a weight of 2.5 metric tons (2.75 short tons). In 2016, Molina-Pérez and Larramendi gave a length of 9 meters (29.5 ft) and a weight of 3.3 metric tons (3.6 short tons). Bistahieversor sealeyi life restoration

''Bistahieversor'' differs from other tyrannosaurs in the possession of 64 teeth, an extra opening above the eye, and a keel along the lower jaw, among many other unique traits. The opening above the eye is thought to have accommodated an air sac that would have lightened the skull's weight. ''Bistahieversor'' also had a complex joint at its "forehead" that would have stabilized the skull to prevent movement at the joint.

Classification

''Bistahieversor'' is a genus of derived tyrannosaur often classified in the subfamily

Tyrannosaurinae 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 L ...

. Different datasets have recovered varying placements for it within

Eutyrannosauria Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent be ...

. In 2020, Voris et al. recovered ''Bistahieversor'' as a basal member of

, rather than a

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 ...

, diverging later than ''

Dryptosaurus ''Dryptosaurus'' ( ) is a genus of eutyrannosaurian theropod dinosaur that lived on the island continent of Appalachia approximately 67-66 million years ago during the end of the Maastrichtian age of the Late Cretaceous period. ''Dryptosaurus'' ...

'' and ''

Appalachiosaurus ''Appalachiosaurus'' ( ; "Appalachian lizard") is a genus of tyrannosaurian theropod dinosaur from the Late Cretaceous period of what is now eastern North America. It was a basal member of the Eutyrannosauria clade meaning it was rather close i ...

''. These results are displayed in 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: In 2024, Rivera-Sylva & Longrich described new remains likely belonging to a novel species of ''

Labocania ''Labocania'' is a genus of carnivorous theropod dinosaur of disputed affinities from the Late Cretaceous of Mexico. Initially regarded as an indeterminate theropod, later studies mentioned possible affinities with tyrannosaurids, abelisaurids, o ...

''. Their new data allowed for the reanalysis of ''Bistahieversor'' as a member of the tyrannosaurine clade

Teratophoneini 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 ...

, in addition to ''Labocania'', ''

Dynamoterror ''Dynamoterror'' (meaning "powerful terror") is a monospecific genus of tyrannosaurid dinosaur from New Mexico that lived during the Late Cretaceous (lower Campanian age, 78 Ma) in what is now the upper Allison Member of the Menefee Formation. Th ...

'', ''

Teratophoneus ''Teratophoneus'' ("monstrous murderer"; Greek: ''teras'', "monster" and ''phoneus'', "murderer") is a genus of Tyrannosaurinae, tyrannosaurine Theropoda, theropod dinosaur that lived during the late Campanian age of the Late Cretaceous period, ...

'', and two unnamed specimens from the Aguja and

Two Medicine Two Medicine is the collective name of a region located in the southeastern section of Glacier National Park (U.S.), Glacier National Park, in the U.S. state of Montana. It has a campground alongside Two Medicine Lake. From the period starting in ...

formations. Their results are displayed in the

below:

Paleobiology

A 2020 study of the endocranial morphology of ''Bistahieversor'' shed some light on its hunting behaviors. Its large olfactory bulbs indicate a very heightened sense of smell, while the elongated semi-circular canals implied increased agility and sophisticated gaze stabilization while the head was moving. ''Bistahieversor'' also possessed binocular vision, allowing it to see much better than more primitive predatory dinosaurs. The study noted that, while ''Bistahieversor'' had small optic lobes, this was not a strong indicator of whether or not this dinosaur possessed poor vision.

References

External links

Article about ''Bistahieversor'' on ''DinosaurusBlog'' webpage
(in

Czech Czech may refer to: * Anything from or related to the Czech Republic, a country in Europe ** Czech language ** Czechs, the people of the area ** Czech culture ** Czech cuisine * One of three mythical brothers, Lech, Czech, and Rus *Czech (surnam ...