Early synapsid evolution and fossil record sampling bias

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com


A new advance paper:



Neil Brocklehurst , Christian F. Kammerer , and Jörg Fröbisch (2013)
The early evolution of synapsids, and the influence of sampling on
their fossil record.
Paleobiology 39(3):470-490. 2013
doi: http://dx.doi.org/10.1666/12049
http://www.bioone.org/doi/abs/10.1666/12049
Supplementary materials deposited at Dryad: doi 10.5061/dryad.cq376

Synapsids dominated the terrestrial realm between the late
Pennsylvanian and the Triassic. Their early evolution includes some of
the first amniotes to evolve large size, herbivory, and
macro-predators. However, little research has focused on the changes
in diversity occurring during this early phase in their evolutionary
history, with more effort concentrating on later events such the
Permo-Triassic extinction. Here we assess synapsid diversity, at both
the species and genus levels, between the Carboniferous (Moscovian)
and the Middle Permian (Capitanian). A raw, taxic diversity (richness)
estimate is generated, and we use two separate methods to correct for
sampling biases in this curve. To remove the effect of anthropogenic
sampling bias, we apply a recently published modification of the
residual diversity method, and then generate a supertree, using matrix
representation with parsimony to infer ghost lineages and obtain a
phylogenetic diversity estimate. The general diversity pattern
reflects the initial diversification of synapsids in the late
Pennsylvanian and early Cisuralian, which was followed by an
extinction event during the Sakmarian. Diversity recovered during the
Artinskian and Kungurian, coinciding with the radiation of Caseidae,
although other families begin to decline. A second extinction event
occurred across the Kungurian/Roadian boundary, in which
Edaphosauridae and Ophiacodontidae died out although Caseidae and
Therapsida diversified. The sampling-corrected curves reveal further
extinction during the Roadian, although therapsids were again
unaffected. Pelycosaurian-grade synapsids survived during the Wordian
and Capitanian, but were a minor part of an otherwise
therapsid-dominated fauna. Evidence of significant anthropogenic
sampling bias calls into question previous diversity studies that have
not employed sampling correction.