| Bistahieversor | |
|---|---|
 | |
| Skull and vertebra at theNew Mexico Museum of Natural History and Science | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | †Eutyrannosauria |
| Genus: | †Bistahieversor Carr & Williamson, 2010 |
| Species: | †B. sealeyi |
| Binomial name | |
| †Bistahieversor sealeyi Carr & Williamson, 2010 | |
Bistahieversor (meaning "Bistahi destroyer"), also known as the "Bisti Beast", is agenus of basaleutyrannosauriantheropoddinosaur. The genus contains only a single known species,B. sealeyi, described in 2010, from theLate Cretaceous[1] of New Mexico. Theholotype and a juvenile were found in the Hunter Wash Member of theKirtland Formation, while other specimens came from the underlying Fossil Forest member of theFruitland Formation. This datesBistahieversor approximately 75.5 to 74.5 million years ago during theCampanian age, found in sediments spanning a million years.
The first remains now attributed toBistahieversor, a partial skull and skeleton, were described in 1990 as a specimen ofAublysodon.[2] Additional remains, consisting of the incomplete skull and skeleton of a juvenile, were described in 1992.[3] Another complete skull and partial skeleton were found in theBisti/De-Na-Zin Wilderness Area ofNew Mexico in 1998,[4] known colloquially as the "Bisti Beast".[5]
In a 2000 paper, Thomas Carr and Thomas Williamson re-examined these four specimens and suggested that they did not belong toAublysodon, but rather to one or more new species ofDaspletosaurus.[6] 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 itBistahieversor sealeyi.[1] The nameBistahieversor comes from theNavajoBistahí, or "place of the adobe formations" in reference to theBisti/De-Na-Zin Wilderness Area where it was found.Eversor, the latter part of the name, means "destroyer."[1]
Material from both juveniles and adults has been found in theKirtland andFruitland formations ofNew Mexico. AdultBistahieversor are estimated to have been around 9 meters (30 ft) long and weigh at least a ton. The snout is deep, indicating that the feature is not unique to morederived tyrannosaurs, such asTyrannosaurus. Geographical barriers, such as the newly formingRocky Mountains, may have isolated the more southerlyBistahieversor from more derived northern tyrannosaurs.[7] 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).[8] 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).[9]
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.[10]
Bistahieversor is a genus of derived tyrannosaur often classified in the subfamilyTyrannosaurinae. Different datasets have recovered varying placements for it withinEutyrannosauria.
In 2020, Voris et al. recoveredBistahieversor as a basal member ofEutyrannosauria, rather than atyrannosaurine, diverging later thanDryptosaurus andAppalachiosaurus. These results are displayed in thecladogram below:[11]
| Eutyrannosauria |
| |||||||||||||||||||||
In 2024, Rivera-Sylva & Longrich described new remains likely belonging to a novel species ofLabocania. Their new data allowed for the reanalysis ofBistahieversor as a member of the tyrannosaurine cladeTeratophoneini, in addition toLabocania,Dynamoterror,Teratophoneus, and two unnamed specimens from theAguja andTwo Medicine formations. Their results are displayed in thecladogram below:[12]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
A 2020 study of the endocranial morphology ofBistahieversor 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, whileBistahieversor had small optic lobes, this was not a strong indicator of whether or not this dinosaur possessed poor vision.[13]
.png)
.jpg)
.jpg)
.png)
.jpg)
