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Gracilisuchidae, new pseudosuchian archosaur clade (free pdf)



Ben Creisler
bcreisler@gmail.com


A new paper not yet mentioned:

Richard J. Butler, Corwin Sullivan, Martín D. Ezcurra, Jun Liu,
Agustina Lecuona and Roland B. Sookias (2014)
New clade of enigmatic early archosaurs yields insights into early
pseudosuchian phylogeny and the biogeography of the archosaur
radiation.
BMC Evolutionary Biology 2014, 14:128
doi:10.1186/1471-2148-14-128
http://www.biomedcentral.com/1471-2148/14/128/abstract

pdf:
http://www.biomedcentral.com/content/pdf/1471-2148-14-128.pdf

Background
The origin and early radiation of archosaurs and closely related taxa
(Archosauriformes) during the Triassic was a critical event in the
evolutionary history of tetrapods. This radiation led to the
dinosaur-dominated ecosystems of the Jurassic and Cretaceous, and the
high present-day archosaur diversity that includes around 10,000 bird
and crocodylian species. The timing and dynamics of this evolutionary
radiation are currently obscured by the poorly constrained
phylogenetic positions of several key early archosauriform taxa,
including several species from the Middle Triassic of Argentina
(Gracilisuchus stipanicicorum) and China (Turfanosuchus dabanensis,
Yonghesuchus sangbiensis). These species act as unstable 'wildcards'
in morphological phylogenetic analyses, reducing phylogenetic
resolution.

Results
We present new anatomical data for the type specimens of G.
stipanicicorum, T. dabanensis, and Y. sangbiensis, and carry out a new
morphological phylogenetic analysis of early archosaur relationships.
Our results indicate that these three previously enigmatic taxa form a
well-supported clade of Middle Triassic archosaurs that we refer to as
Gracilisuchidae. Gracilisuchidae is placed basally within Suchia,
among the pseudosuchian (crocodile-line) archosaurs. The approximately
contemporaneous and morphologically similar G. stipanicicorum and Y.
sangbiensis may be sister taxa within Gracilisuchidae.

Conclusions
Our results provide increased resolution of the previously poorly
constrained relationships of early archosaurs, with increased levels
of phylogenetic support for several key early pseudosuchian clades.
Moreover, they falsify previous hypotheses suggesting that T.
dabanensis and Y. sangbiensis are not members of the archosaur crown
group. The recognition of Gracilisuchidae provides further support for
a rapid phylogenetic diversification of crown archosaurs by the Middle
Triassic. The disjunct distribution of the gracilisuchid clade in
China and Argentina demonstrates that early archosaurs were
distributed over much or all of Pangaea although they may have
initially been relatively rare members of faunal assemblages.