Triceratops and Anhanguera forelimb posture

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

A new online paper:


Shin-ichi Fujiwara and John R. Hutchinson (2012)
Elbow joint adductor moment arm as an indicator of forelimb posture in
extinct quadrupedal tetrapods.
Proceedings of the Royal Society B (advance online publication)
doi: 10.1098/rspb.2012.0190
http://rspb.royalsocietypublishing.org/content/early/2012/02/17/rspb.2012.0190.abstract


Forelimb posture has been a controversial aspect of reconstructing
locomotor behaviour in extinct quadrupedal tetrapods. This is partly
owing to the qualitative and subjective nature of typical methods,
which focus on bony articulations that are often ambiguous and
unvalidated postural indicators. Here we outline a new, quantitatively
based forelimb posture index that is applicable to a majority of
extant tetrapods. By determining the degree of elbow joint
adduction/abduction mobility in several tetrapods, the carpal flexor
muscles were determined to also play a role as elbow adductors. Such
adduction may play a major role during the stance phase in sprawling
postures. This role is different from those of upright/sagittal and
sloth-like creeping postures, which, respectively, depend more on
elbow extensors and flexors. Our measurements of elbow muscle moment
arms in 318 extant tetrapod skeletons (Lissamphibia, Synapsida and
Reptilia: 33 major clades and 263 genera) revealed that sprawling,
sagittal and creeping tetrapods, respectively, emphasize elbow
adductor, extensor and flexor muscles. Furthermore, scansorial and
non-scansorial taxa, respectively, emphasize flexors and extensors.
Thus, forelimb postures of extinct tetrapods can be qualitatively
classified based on our quantitative index. Using this method, we find
that Triceratops (Ceratopsidae), Anhanguera (Pterosauria) and
desmostylian mammals are categorized as upright/sagittally locomoting
taxa.