Post-Cretaceous origin for rodents

[Ben Creisler <bcreisler@gmail.com>]

From: Ben Creisler
bcreisler@gmail.com

A new article in PLoS ONE that may be of interest to some:

Shaoyuan Wu, Wenyu Wu, Fuchun Zhang, Jie Ye, Xijun Ni, Jimin Sun,
Scott V. Edwards, Jin Meng, Chris L. Organ (2012)
Molecular and Paleontological Evidence for a Post-Cretaceous Origin of Rodents.
PLoS ONE 7(10): e46445.
doi:10.1371/journal.pone.0046445
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046445


The timing of the origin and diversification of rodents remains
controversial, due to conflicting results from molecular clocks and
paleontological data. The fossil record tends to support an early
Cenozoic origin of crown-group rodents. In contrast, most molecular
studies place the origin and initial diversification of crown-Rodentia
deep in the Cretaceous, although some molecular analyses have
recovered estimated divergence times that are more compatible with the
fossil record. Here we attempt to resolve this conflict by carrying
out a molecular clock investigation based on a nine-gene sequence
dataset and a novel set of seven fossil constraints, including two new
rodent records (the earliest known representatives of Cardiocraniinae
and Dipodinae). Our results indicate that rodents originated around
61.7–62.4 Ma, shortly after the Cretaceous/Paleogene (K/Pg) boundary,
and diversified at the intraordinal level around 57.7–58.9 Ma. These
estimates are broadly consistent with the paleontological record, but
challenge previous molecular studies that place the origin and early
diversification of rodents in the Cretaceous. This study demonstrates
that, with reliable fossil constraints, the incompatibility between
paleontological and molecular estimates of rodent divergence times can
be eliminated using currently available tools and genetic markers.
Similar conflicts between molecular and paleontological evidence
bedevil attempts to establish the origination times of other placental
groups. The example of the present study suggests that more reliable
fossil calibration points may represent the key to resolving these
controversies.