Bistahieversor
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 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". 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 , or "place of the adobe formations" in reference to the Bisti/De-Na-Zin Wilderness 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 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" but less derived than "Lythronax". It forms the sister taxon of a group including "Lythronax", "Nanuqsaurus", "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 on the endocranial morphology of "Bistahieversor" found it resembled tyrannosaurids in several aspects and would likely have behaved similarly. The large olfactory bulbs indicate a heightened sense of smell, while the elongate semi-circular canals imply high agility and sophisticated gaze stabilization when the head would be moving. "Bistahieversor" possessed binocular vision, allowing it to see better than other large predatory dinosaurs (excluding tyrannosaurids). The authors of the paper noted  that while "Bistahieversor" possessed small optic lobes, this was not a strong indicator on whether this dinosaur possessed poor vision.