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Saurischian dinosaur semicircular canals (free pdf)



From: Ben Creisler
bcreisler@gmail.com


A new paper in PeerJ not yet mentioned:

Jesús Marugán-Lobón, Luis M. Chiappe & Andrew A. Farke  (2013)
The variability of inner ear orientation in saurischian dinosaurs:
testing the use of semicircular canals as a reference system for
comparative anatomy.
PeerJ 1:e124
doi: http://dx.doi.org/10.7717/peerj.124
https://peerj.com/articles/124/

The vestibular system of the inner ear houses three semicircular
canals—oriented on three nearly-orthogonal planes—that respond to
angular acceleration stimuli. In recent years, the orientation of the
lateral semicircular canal (LSC) has been regularly used to determine
skull orientations for comparative purposes in studies of non-avian
dinosaurs. Such orientations have been inferred based on fixing the
LSC to a common set of coordinates (parallel to the Earth’s horizon),
given that the orientation to gravity of this sensory system is
assumed constant among taxa. Under this assumption, the LSC is used as
a baseline (a reference system) both to estimate how the animals held
their heads and to describe craniofacial variation among dinosaurs.
However, the available data in living birds (extant saurischian
dinosaurs) suggests that the orientation of the LSC in non-avian
saurischian dinosaurs could have been very variable and
taxon-specific. If such were the case, using the LSC as a comparative
reference system would cause inappropriate visual perceptions of
craniofacial organization, leading to significant descriptive
inconsistencies among taxa. Here, we used Procrustes methods
(Geometric Morphometrics), a suite of analytical tools that compares
morphology on the basis of shared landmark homology, to show that the
variability of LSC relative to skull landmarks is large (ca. 50°) and
likely unpredictable, thus making it an inconsistent reference system
for comparing and describing the skulls of saurischian (sauropodomorph
and theropod) dinosaurs. In light of our results, the lateral
semicircular canal is an inconsistent baseline for comparative studies
of craniofacial morphology in dinosaurs.