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Aenigmastropheus, new archosauromorph from Permian of Tanzania, and timing of lizard-crocodile split



From: Ben Creisler
bcreisler@gmail.com


New in PLoS ONE:


Martín D. Ezcurra, Torsten M. Scheyer & Richard J. Butler (2014)
The Origin and Early Evolution of Sauria: Reassessing the Permian
Saurian Fossil Record and the Timing of the Crocodile-Lizard
Divergence.
PLoS ONE 9(2): e89165.
doi:10.1371/journal.pone.0089165
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0089165


Sauria is the crown-group of Diapsida and is subdivided into
Lepidosauromorpha and Archosauromorpha, comprising a high percentage
of the diversity of living and fossil tetrapods. The split between
lepidosauromorphs and archosauromorphs (the crocodile-lizard, or
bird-lizard, divergence) is considered one of the key calibration
points for molecular analyses of tetrapod phylogeny. Saurians have a
very rich Mesozoic and Cenozoic fossil record, but their late
Paleozoic (Permian) record is problematic. Several Permian specimens
have been referred to Sauria, but the phylogenetic affinity of some of
these records remains questionable. We reexamine and review all of
these specimens here, providing new data on early saurian evolution
including osteohistology, and present a new morphological phylogenetic
dataset. We support previous studies that find that no valid Permian
record for Lepidosauromorpha, and we also reject some of the previous
referrals of Permian specimens to Archosauromorpha. The most
informative Permian archosauromorph is Protorosaurus speneri from the
middle Late Permian of Western Europe. A historically problematic
specimen from the Late Permian of Tanzania is redescribed and
reidentified as a new genus and species of basal archosauromorph:
Aenigmastropheus parringtoni. The supposed protorosaur Eorasaurus
olsoni from the Late Permian of Russia is recovered among
Archosauriformes and may be the oldest known member of the group but
the phylogenetic support for this position is low. The assignment of
Archosaurus rossicus from the latest Permian of Russia to the
archosauromorph clade Proterosuchidae is supported. Our revision
suggests a minimum fossil calibration date for the crocodile-lizard
split of 254.7 Ma. The occurrences of basal archosauromorphs in the
northern (30°N) and southern (55°S) parts of Pangea imply a wider
paleobiogeographic distribution for the group during the Late Permian
than previously appreciated. Early archosauromorph growth strategies
appear to be more diverse than previously suggested based on new data
on the osteohistology of Aenigmastropheus.