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[1] Hunter Wash member of the Kirtland Formation, which has been dated to 74.55 ± 0.29 Ma.[2]

Bistahieversor
Temporal range: Late Cretaceous, 74.5 Ma
↓
Skull and vertebra at the New Mexico Museum of Natural History and Science
Scientific classification
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

The name Bistahieversor comes from the Navajo Bistahí, or "place of the adobe formations" in reference to the Bisti/De-Na-Zin Wilderness where it was found, and eversor, meaning "destroyer."[1]

History of discovery
Wall-mounted fossil

The first remains now attributed to Bistahieversor, a partial skull and skeleton, were described in 1990 as a specimen of Aublysodon.[3] Additional remains, consisting of the incomplete skull and skeleton of a juvenile, were described in 1992.[4] Another, complete, skull and partial skeleton were found in the Bisti/De-Na-Zin Wilderness of New Mexico in 1998,[5] known colloquially as the "Bisti Beast".[6] 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.[7] 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.[1]

Description
Size comparison with a juvenile

Material from both adolescent and adult individuals has been found in the Kirtland Formation of New Mexico, United States. Adult Bistahieversor are estimated to have been around 9 meters (30 ft) 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.[8] In 2010 Gregory S. Paul estimated a length of 8 m (26 ft) and a weight of 2.5 tonnes (2.75 short tons).[9] In 2016 Molina-Pérez and Larramendi gave a length of 9 m (29.5 ft) and a weight of 3.3 tonnes (3.6 short tons).[10]

Bistahieversor differs from other tyrannosaurs in the possession of 64 teeth, an extra opening above the eye, and a keel along the lower jaw. 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.[11]

Classification
Restoration

Bistahieversor is a genus of derived dinosaur currently classified in the subfamily Tyrannosaurinae. It is more derived than Teratophoneus but less derived than Lythronax.[12] It forms the sister taxon of a group including Lythronax, Nanuqsaurus, Tyrannosaurus, Tarbosaurus and Zhuchengtyrannus.[13]

Below is a cladogram illustrating the relationships of all tyrannosaurid genera:[13]

Tyrannosauridae
Albertosaurinae
 

Albertosaurus

 
 

Gorgosaurus

 
 
Tyrannosaurinae
 
 

Daspletosaurus torosus

 
 

Daspletosaurus horneri

 
 
 
 

Teratophoneus

 
 
 

Bistahieversor

 
 
 

Lythronax

 
 
 

Nanuqsaurus

 
 
 
 

Tarbosaurus

 
 

Zhuchengtyrannus

 
 
 

Tyrannosaurus

 
 
 
 
 
 
 
 

Below is a phylogenetic analysis found by Voris et al., in which they recovered Bistahieversor as a basal member of Eutyrannosauria instead of a tyrannosaurine:[14]

Eutyrannosauria
 
 

Dryptosaurus aquilunguis

 
 
 

Appalachiosaurus montgomeriensis

 
 
 

Bistahieversor sealeyi

 
 
Tyrannosauridae
Albertosaurinae
 

Gorgosaurus libratus

 
 

Albertosaurus sarcophagus

 
 
Tyrannosaurinae
Alioramini
 

Qianzhousaurus sinensis

 
 
 

Alioramus remotus

 
 

Alioramus altai

 
 
 
 
 
 

Teratophoneus curriei

 
 

Dynamoterror dynastes

 
 

Lythronax argestes

 
 
 
 

Nanuqsaurus hoglundi

 
 
 
Daspletosaurini
 

Thanatotheristes degrootorum

 
 
 

Dinosaur Park Formation Taxon (FMNH PR308)

 
 

Daspletosaurus torosus

 
 

Daspletosaurus horneri

 
 
 
Tyrannosaurini
 

Zhuchengtyrannus magnus

 
 
 

Tarbosaurus bataar

 
 

Tyrannosaurus rex

 
 
 
 
 
 
 
 
 
 
 
 
 
 

See also

References
  1. Carr, Thomas D.; Williamson, Thomas E. (2010). "Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea". Journal of Vertebrate Paleontology. 30 (1): 1–16. doi:10.1080/02724630903413032.
  2. Sullivan, Robert M.; Lucas, Spencer G. (2006). "The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America". Bulletin. New Mexico Museum of Natural History and Science. 35: 7–29.
  3. Lehman, Thomas M.; Carpenter, Kenneth (November 1990). "A partial skeleton of the tyrannosaurid dinosaur Aublysodon from the Upper Cretaceous of New Mexico" (PDF). Journal of Paleontology. 64 (6): 1026–1032. doi:10.1017/S0022336000019843. JSTOR 1305741.
  4. Archer, Brad; Babiarz, John P. (July 1992). "Another tyrannosaurid dinosaur from the Cretaceous of northwest New Mexico". Journal of Paleontology. 66 (4): 690–691. doi:10.1017/S0022336000024598.
  5. "New Species of Tyrannosaur Discovered in Southwestern U.S." Newswise. January 28, 2010. Retrieved February 1, 2010.
  6. "ABQJOURNAL NEWS/STATE: N.M. Tyrannosaur Is Officially Dubbed Bistahieversor sealeyi". www.abqjournal.com. Retrieved January 27, 2017.
  7. Carr, Thomas D.; Williamson, Thomas E. (2000). "A review of Tyrannosauridae (Dinosauria: Coelurosauria) from New Mexico". Bulletin. New Mexico Museum of Natural History and Science. 17: 113–145.
  8. Rettner, Rachael (January 28, 2010). "New Tyrannosaur Species Discovered". LiveScience. Retrieved February 1, 2010.
  9. Paul, Gregory S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 103.
  10. Molina-Pérez & Larramendi (2016). Récords y curiosidades de los dinosaurios Terópodos y otros dinosauromorfos. Barcelona, Spain: Larousse. p. 265.
  11. Viegas, J. (January 28, 2010). "New Tyrannosaur Had More Teeth Than T. rex". Discovery News. Retrieved February 1, 2010.
  12. Loewen, Mark A.; Irmis, Randall B.; Sertich, Joseph J. W.; Currie, Philip J.; Sampson, S. D. (2013). Evans, David C (ed.). "Tyrant Dinosaur Evolution Tracks the Rise and Fall of Late Cretaceous Oceans". PLoS ONE. 8 (11): e79420. doi:10.1371/journal.pone.0079420. PMC 3819173. PMID 24223179.
  13. Fiorillo, Anthony R.; Tykoski, Ronald S. (2014). Dodson, Peter (ed.). "A Diminutive New Tyrannosaur from the Top of the World". PLoS ONE. 9 (3): e91287. doi:10.1371/journal.pone.0091287. PMC 3951350. PMID 24621577.
  14. Voris, Jared T.; Therrien, Francois; Zelenitzky, Darla K.; Brown, Caleb M. (2020). "A new tyrannosaurine (Theropoda:Tyrannosauridae) from the Campanian Foremost Formation of Alberta, Canada, provides insight into the evolution and biogeography of tyrannosaurids". Cretaceous Research. 110: 104388. doi:10.1016/j.cretres.2020.104388.
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