Study of tyrannosaur braincases shows more variation than previously
thought

Date:
August 19, 2021
Source:
Canadian Museum of Nature
Summary:
Scientists have used CT scans to digitally reconstruct the brain,
inner ear, and surrounding bones (known as the braincase) of two
well-preserved Daspletosaurus specimens. This massive tyrannosaur
lived in the coastal forest of what is now Alberta around 75 million
years ago -- preceding the more famous T. rex by about 10 million
years. Their results suggest that dinosaur brains, and the bones
enclosing and protecting, them vary more than previously thought
within species, or among closely related species.



FULL STORY ========================================================================== Among the fierce carnivores that lived during the late Cretaceous was a predator named Daspletosaurus. The massive tyrannosaur, about nine metres
long, lived in the coastal forest of what is now Alberta around 75 million years ago -- preceding the more famous T. rex by about 10 million years.


==========================================================================
For the first time, scientists in Canada and Argentina have used CT scans
to digitally reconstruct the brain, inner ear, and surrounding bones
(known as the braincase) of two well-preserved Daspletosaurus specimens.

Their results, published online today in the Canadian Journal of
Earth Sciences, counter a prevailing view that dinosaur brains and
the bones enclosing and protecting them varied little within species,
or among closely related species, especially when compared with
changes observed in other parts of the skeleton. "Our study with the
two Daspletosaurus specimens suggests otherwise," explains Dr. Tetsuto Miyashita, palaeontologist with the Canadian Museum of Nature and senior
author of the study.

"We know that tyrannosaurs had relatively good-sized brains for
a dinosaur, and this study shows that this pattern holds for
Daspletosaurus. Furthermore, based on the shapes of the brain,
ear structure, and braincase, we suggest that these two specimens
represent distinct species of daspletosaurs." Access to a braincase,
the internal part of the skull that surrounds and protects the brain,
helps unlock one of the most complex parts of dinosaur anatomy. This
requires advanced medical technology such as a CT scanner to image the
internal spaces hidden underneath thick bones, with the resulting hundreds
of hours of work to reconstruct the brain and other fleshy parts slice
by slice. Therefore, most studies on dinosaur brains have each focused on
one specimen from a representative species of the group. As an exception, Tyrannosaurus rex has several such reconstructions of their brains. Now,
this new study investigates two remarkably well-preserved skulls of Daspletosaurus, a much rarer tyrannosaur than T. rex.

One belongs to the original specimen of Daspletosaurus, which
is prominently displayed at the Canadian Museum of Nature in
Ottawa. Unearthed in 1921 along the banks of Alberta's Red Deer River,
its description in 1970 as Daspletosaurus torosus ("muscular frightful
lizard)" by Dr. Dale Russell ushered in the modern era of research on tyrannosaurids. The second specimen, uncovered in 2001, is with the Royal Tyrrell Museum of Palaeontology in Alberta. Miyashita is continuing to
study it with Dr. Philip Currie of the University of Alberta, another
author of the study.

Study of the braincase structure and its endocranial cavity provides
insights on the brain itself, as well as characteristics such as the
layout of cranial nerves, and some aspects of the sensory biology such
as auditory and visual anatomy that drove the life of the dinosaur.

Dr. Ariana Paulina Carabajal, a dinosaur braincase expert in Argentina
and study co-author at the Instituto de Investigaciones en Biodiversidad
y Medioambiente (CONICET-Universidad Nacional del Comahue), provided
the detailed models of the brain and inner ear anatomy and related
structures. Among the findings were the presence of large bony canals that would have transmitted thick nerve bundles that moved the eyeballs. The researchers also describe large air sacs that filled up most of the
braincase bones, which is in line with the limited studies known of
other tyrannosaurs.

"These cavities within the bones not only make the huge skull lighter,
but also are related to the middle region of the ear," explains Paulina Carabajal. "The cavities probably helped to amplify sound and assist
the system that communicates to the left and right ears, allowing the
brain to determine where a sound is coming from." Yet, even within the
two braincases of Daspletosaurus, there were differences.

"It was surprising to see so many variations in the braincases even though
the skeletons are similar," says Miyashita, who offers that their study provides a good reason to look at more braincases within similar groups
of dinosaurs, or even within species.

"Researchers have looked inside so few braincases in dinosaurs, typically
one each for whatever species they studied, that this reinforced
the assumption that these structures don't change much within and
among species. We just haven't looked inside enough skulls to document variation." Additional authors of the paper, entitled "Two braincases of Daspletosaurus (Theropoda: Tyrannosauridae): anatomy and comparison," are Thomas Dudgeon, and Dr. Hans Larsson of McGill University, who contributed
the scanning data for the Canadian Museum of Nature specimen. The study
authors are grateful to the Montfort Hospital in Ottawa, the University
of Alberta Hospital in Edmonton, and the Canada Diagnostic Centre in
Calgary for access to their CT scanners.

========================================================================== Story Source: Materials provided by Canadian_Museum_of_Nature. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Ariana Paulina Carabajal, Philip J. Currie, Thomas W. Dudgeon,
Hans C.E.

Larsson, Tetsuto Miyashita. Two braincases of Daspletosaurus
(Theropoda: Tyrannosauridae): anatomy and comparison. Canadian
Journal of Earth Sciences, 2021; 1 DOI: 10.1139/cjes-2020-0185 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210819102657.htm

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