Pterosaur cranial morphology and evolutionary history

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com


A new online paper:




FOTH, C., BRUSATTE, S. L. and BUTLER, R. J. (2012)
Do different disparity proxies converge on a common signal? Insights
from the cranial morphometrics and evolutionary history of Pterosauria
(Diapsida: Archosauria).
Journal of Evolutionary Biology (advance online publication)
doi: 10.1111/j.1420-9101.2012.02479.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2012.02479.x/abstract


Disparity, or morphological diversity, is often quantified by
evolutionary biologists investigating the macroevolutionary history of
clades over geological timescales. Disparity is typically quantified
using proxies for morphology, such as measurements, discrete
anatomical characters, or geometric morphometrics. If different
proxies produce differing results, then the accurate quantification of
disparity in deep time may be problematic. However, despite this, few
studies have attempted to examine disparity of a single clade using
multiple morphological proxies. Here, as a case study for this
question, we examine the disparity of the volant Mesozoic fossil
reptile clade Pterosauria, an intensively studied group that achieved
substantial morphological, ecological and taxonomic diversity during
their 145+ million-year evolutionary history. We characterize
broadscale patterns of cranial morphological disparity for pterosaurs
for the first time using landmark-based geometric morphometrics and
make comparisons to calculations of pterosaur disparity based on
alternative metrics. Landmark-based disparity calculations suggest
that monofenestratan pterosaurs were more diverse cranially than basal
non-monofenestratan pterosaurs (at least when the aberrant
anurognathids are excluded), and that peak cranial disparity may have
occurred in the Early Cretaceous, relatively late in pterosaur
evolution. Significantly, our cranial disparity results are broadly
congruent with those based on whole skeleton discrete character and
limb proportion data sets, indicating that these divergent approaches
document a consistent pattern of pterosaur morphological evolution.
Therefore, pterosaurs provide an exemplar case demonstrating that
different proxies for morphological form can converge on the same
disparity signal, which is encouraging because often only one such
proxy is available for extinct clades represented by fossils.
Furthermore, mapping phylogeny into cranial morphospace demonstrates
that pterosaur cranial morphology is significantly correlated with,
and potentially constrained by, phylogenetic relationships.