Bistahieversor
Name: Bistahieversor
(Bistahi Destroyer).
Phonetic: Bis-tah-hee-eh-ver-sore.
Named By: Thomas Carr & Thomas Williamson
- 2010.
Classification: Chordata, Reptilia, Dinosauria,
Saurischia, Theropoda, Tyrannosauroidea.
Species: B. sealeyi (type).
Type: Carnivore.
Size: Estimated 9 meters long.
Known locations: USA, New Mexico - Kirtland
Formation.
Time period: Campanian of the Cretaceous.
Fossil representation: Two sets of remains
representing juvenile and adult individuals.
The
skull of Bistahieversor has many features that are
considered primitive
for the tyrannosaurid
group, but most importantly, a noticeable
depth that is lacking in other, and later, tyrannosaurid species.
This is significant because it was once thought that only the later
and more advanced tyrannosaurids, like Tyrannosaurus
itself, had
deeper snouts. The fact that the fossil record can show us
tyrannosaurid snouts that were deep in Bistahieversor,
getting
narrower in others like Gorgosaurus
and Albertosaurus,
and going deep
again in Tyrannosaurus, suggests that skull depth
was an evolutionary
adaptation to predatory styles and prey animals, as opposed to
tyrannosaurid advancement.
Increased
skull depth is often taken as an indication for larger jaw muscles,
in turn capable of inflicting significantly more bite force. The
skull also features an extra opening above the orbital fenestra,
which has considered to have been an air sac for reducing skull
weight. This opening is absent from the juvenile specimen,
suggesting that it was a sign of maturity. This also reinforces the
weight reduction theory, as it would have helped to lighten the skull
as it grew bigger, and heavier. Bistahieversor
had around
sixty-four teeth, a lot for a tyrannosaurid when you consider that
Tyrannosaurus had fifty-four.
At
roughly nine meters long, Bistahieversor would
have been comparable
to the tyrannosaurid Daspletosaurus
in size, which was active in the
Northern reaches of Campanian USA, while Bistahieversor
was in the
south. Bistahieversor was also joined by the
tyrannosaurid
Teratophoneus,
another of its kind that seems to have been restricted
to the Southern US even though it also lived during the Campanian.
Both
Bistahieversor and Teratophoneus
display more basal tyrannosaurid
morphology, and both are known only from the southern area of what
was once called Laramidia. This was the western half of North America
that was separated from the eastern half by the Western Interior
Seaway. Rising sea levels combined with mountain ranges being pushed
up could have isolated the southern tyrannosaurids from the North,
causing the retention of the more basal features seen in
Bistahieversor, so late in the geological
timescale.
Further reading
- 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). - Thomas D. Carr, Thomas E.
Williamson - 2010.
- Neurosensory and sinus evolution as tyrannosauroid dinosaurs
developed giant size: insight from the endocranial anatomy of
Bistahieversor sealeyi. - The Anatomical Record. -
Matthew McKeown,
Stephen L. Brusatte, Thomas E. Williamson, Julia A. Schwab, Thomas D.
Carr, Ian B. Butler, Amy Muir, Katlin Schroeder, Michelle A. Espy,
James F. Hunter, Adrian S. Losko, Ronald O. Nelson, D. Cort Gautier
& Sven C. Vogel. - 2020.
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