''Bistahieversor'' (meaning "Bistahi destroyer"), also known as the "Bisti Beast", is a genus of eutyrannosaurian tyrannosauroid dinosaur; the genus contains only a single known species, ''B. sealeyi'', described in 2010, from the Late Cretaceous of New Mexico. The holotype and a juvenile were found in the Hunter Wash Member of the Kirtland Formation, while other specimens came from the underlying Fossil Forest member of the Fruitland Formation. This dates ''Bistahieversor'' approximately 75.5 to 74.5 million years ago, 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''. 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 The Bisti/De-Na-Zin Wilderness is a wilderness area located in San Juan County in the U.S. state of New Mexico. Established in 1984, the Wilderness is a desolate area of steeply eroded badlands managed by the Bureau of Land Management, exc ...

of New Mexico 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 79.5 and 74 million years ago, during the Late Cretaceous Period. The genus ''Daspletosaurus'' contains three species ...

''. 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, which they named ''Bistahieversor sealeyi''. The name ''Bistahieversor'' comes from the

Navajo The Navajo (; British English: Navaho; nv, Diné or ') are a Native American people of the Southwestern United States. With more than 399,494 enrolled tribal members , the Navajo Nation is the largest federally recognized tribe in the United ...

, or "place of the adobe formations" in reference to the

where it was found, and ''eversor'', meaning "destroyer."

Description

Material from both adolescent and adult individuals has been found in the Kirtland and Fruitland formations of New Mexico, United States. Adult ''Bistahieversor'' are estimated to have been around long, weighing at least a ton. The snout is deep, indicating that the feature is not unique to more

derived Derive may refer to: * Derive (computer algebra system), a commercial system made by Texas Instruments * ''Dérive'' (magazine), an Austrian science magazine on urbanism *Dérive, a psychogeographical concept See also * *Derivation (disambiguatio ...

tyrannosaurs such as '' Tyrannosaurus''. Geographical barriers such as the newly forming Rocky Mountains may have isolated the more southerly ''Bistahieversor'' from more derived northern tyrannosaurs. In 2010 Gregory S. Paul 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'' 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, preventing movement at the joint.

Classification

''Bistahieversor'' is a genus of derived dinosaur currently classified in the subfamily Tyrannosaurinae. It is more derived than ''

Teratophoneus ''Teratophoneus'' ("monstrous murderer"; Greek: ''teras'', "monster" and ''phoneus'', "murderer") is a genus of tyrannosaurid dinosaur which lived during the late Cretaceous period (late Campanian age, about 77 to 76 million years ago) in what i ...

'' but less derived than ''

Lythronax ''Lythronax'' () is a genus of tyrannosaurid dinosaur that lived in North America around 81.9-81.5 million years ago during the Late Cretaceous period. The only known specimen was discovered in Utah in the Wahweap Formation of the Grand Stairca ...

''. It forms the sister taxon of a group including ''Lythronax'', ''

Nanuqsaurus ''Nanuqsaurus'' (meaning "polar bear lizard") is a genus of carnivorous tyrannosaurid theropod known from the Late Cretaceous period (early Late Maastrichtian stage) Prince Creek Formation of the North Slope of Alaska, United States. It contains ...

'', '' Tyrannosaurus'', '' Tarbosaurus'' and '' Zhuchengtyrannus''. Below is a cladogram illustrating the relationships of all tyrannosaurid genera: The cladogram below is based on a phylogenetic analysis conducted by Voris ''et al.'' in 2020. Here, ''Bistahieversor'' was recovered as a basal member of Eutyrannosauria rather than as a tyrannosaurine:

Paleobiology

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

References

External links

Article about ''Bistahieversor'' on ''DinosaurusBlog'' webpage
(in Czech) {{Taxonbar, from=Q132622 Tyrannosaurs Late Cretaceous dinosaurs of North America Fossil taxa described in 2010 Monotypic dinosaur genera Taxa named by Thomas Carr Paleontology in New Mexico Campanian genus first appearances Campanian genus extinctions