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Euparkeriids (Archosauriformes) from Triassic of China (free pdf)

Ben Creisler

New in open-access PeerJ:

Roland B. Sookias, Corwin Sullivan, Jun Liu & Richard J. Butler (2014)
Systematics of putative euparkeriids (Diapsida: Archosauriformes) from
the Triassic of China.
PeerJ 2:e658
doi: http://dx.doi.org/10.7717/peerj.658

The South African species Euparkeria capensis is of great importance
for understanding the early radiation of archosauromorphs (including
archosaurs) following the Permo–Triassic mass extinction, as most
phylogenetic analyses place it as the sister taxon to crown group
Archosauria within the clade Archosauriformes. Although a number of
species from Lower–Middle Triassic deposits worldwide have been
referred to the putative clade Euparkeriidae, the monophyly of
Euparkeriidae is controversial and has yet to be demonstrated by
quantitative phylogenetic analysis. Three Chinese taxa have been
recently suggested to be euparkeriids: Halazhaisuchus qiaoensis,
‘Turfanosuchus shageduensis’, and Wangisuchus tzeyii, all three of
which were collected from the Middle Triassic Ermaying Formation of
northern China. Here, we reassess the taxonomy and systematics of
these taxa. We regard Wangisuchus tzeyii as a nomen dubium, because
the holotype is undiagnostic and there is no convincing evidence that
the previously referred additional specimens represent the same taxon
as the holotype. We also regard ‘Turfanosuchus shageduensis’ as a
nomen dubium as we are unable to identify any diagnostic features. We
refer the holotype to Archosauriformes, and more tentatively to
Euparkeriidae. Halazhaisuchus qiaoensis and the holotype of
‘Turfanosuchus shageduensis’ are resolved as sister taxa in a
phylogenetic analysis, and are in turn the sister taxon to Euparkeria
capensis, forming a monophyletic Euparkeriidae that is the sister to
Archosauria+Phytosauria. This is the first quantitative phylogenetic
analysis to recover a non-monospecific, monophyletic Euparkeriidae,
but euparkeriid monophyly is only weakly supported and will require
additional examination. Given their similar sizes, stratigraphic
positions and phylogenetic placement, the holotype of ‘Turfanosuchus
shageduensis’ may represent a second individual of Halazhaisuchus
qiaoensis, but no apomorphies or unique character combination can be
identified to unambiguously unite the two. Our results have important
implications for understanding the species richness and
palaeobiogeographical distribution of early archosauriforms.