Pachycephalosaur nasal airflow

[Ben Creisler <bcreisler@gmail.com>]

Ben Creisler
bcreisler@gmail.com

A new paper:

Jason M. Bourke, WM. Ruger Porter, Ryan C. Ridgely, Tyler R. Lyson,
Emma R. Schachner, Phil R. Bell and Lawrence M. Witmer (2014)
Breathing Life Into Dinosaurs: Tackling Challenges of Soft-Tissue
Restoration and Nasal Airflow in Extinct Species.
The Anatomical Record 297(11): 2148–2186
Special Issue: Special Issue The Vertebrate Nose: Evolution,
Structure, and Function
DOI: 10.1002/ar.23046
http://onlinelibrary.wiley.com/doi/10.1002/ar.23046/abstract




The nasal region plays a key role in sensory, thermal, and respiratory
physiology, but exploring its evolution is hampered by a lack of
preservation of soft-tissue structures in extinct vertebrates. As a
test case, we investigated members of the “bony-headed” ornithischian
dinosaur clade Pachycephalosauridae (particularly Stegoceras validum)
because of their small body size (which mitigated allometric concerns)
and their tendency to preserve nasal soft tissues within their
hypermineralized skulls. Hypermineralization directly preserved
portions of the olfactory turbinates along with an internal nasal
ridge that we regard as potentially an osteological correlate for
respiratory conchae. Fossil specimens were CT-scanned, and nasal
cavities were segmented and restored. Soft-tissue reconstruction of
the nasal capsule was functionally tested in a virtual environment
using computational fluid dynamics by running air through multiple
models differing in nasal soft-tissue conformation: a bony-bounded
model (i.e., skull without soft tissue) and then models with soft
tissues added, such as a paranasal septum, a scrolled concha, a
branched concha, and a model combining the paranasal septum with a
concha. Deviations in fluid flow in comparison to a phylogenetically
constrained sample of extant diapsids were used as indicators of
missing soft tissue. Models that restored aspects of airflow found in
extant diapsids, such as appreciable airflow in the olfactory chamber,
were judged as more likely. The model with a branched concha produced
airflow patterns closest to those of extant diapsids. These results
from both paleontological observation and airflow modeling indicate
that S. validum and other pachycephalosaurids could have had both
olfactory and respiratory conchae. Although respiratory conchae have
been linked to endothermy, such conclusions require caution in that
our re-evaluation of the reptilian nasal apparatus indicates that
respiratory conchae may be more widespread than originally thought,
and other functions, such as selective brain temperature regulation,
could be important.