Triassic terrestrial vertebrate recovery in southwestern US after Permian extinction

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

A new paper not yet mentioned on the DML:


David A. Tarailo and David E. Fastovsky (2012)
Post–Permo-Triassic terrestrial vertebrate recovery: southwestern United States.
Paleobiology 38(4):644-663. 2012
doi: http://dx.doi.org/10.1666/11054.1
http://www.bioone.org/doi/abs/10.1666/11054.1


Recovery of marine biodiversity following the Permo-Triassic
extinction is thought to have been delayed relative to other mass
extinctions. Terrestrial vertebrate biodiversity is said to have taken
as much as 15 Myr longer to recover than the marine. The present study
tests, at the scale of an individual fossil community, whether a
disparity in biodiversity existed in the American Southwest, between
the Moenkopi Formation, containing an early Middle Triassic (Anisian)
terrestrial tetrapod fauna, and the Chinle Formation, containing a
successor Late Triassic (Norian) tetrapod fauna. Taking Chinle faunal
biodiversity to represent full biotic recovery, comparison of
taxonomic and guild diversity of faunas from similar depositional and
taphonomic environments in these two formations allowed us to assess
the possibility of incipient terrestrial recovery of biodiversity in
the Anisian.

Comparisons were made between the Holbrook Member fauna of the
Moenkopi, a unit best characterized as a low-sinuosity medium- to
coarse-grained fluvial deposit, and each of four Chinle stratigraphic
units, representing fluvial settings from sandy low-sinuosity to muddy
high-sinuosity. Three metrics were applied: generic and familial
taxonomic diversity and guild diversity; these were compared by
rarefaction. Simpson and Shannon diversity metrics augmented the
analysis. Units of extraordinary preservation in the Chinle—the
so-called blue layers—were removed from the analysis. In all tests the
biodiversity of the Holbrook Member fauna is within the variation seen
in Chinle faunas.

If the results of our study represent global conditions, they suggest
that by at least early Anisian time (6 Myr after the P/T extinction)
biodiversity had reached levels comparable to those seen in the Late
Triassic. This potentially brings the terrestrial vertebrate recovery
in line with the 4–8 Myr it took for recovery in the marine realm.