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Scutarx, new aetosaur from Late Triassic of North America + Aetosauria phylogenetic analysis (free pdf)

Ben Creisler

A new paper in open access:

William G. Parker  (2016)
Revised phylogenetic analysis of the Aetosauria (Archosauria:
Pseudosuchia); assessing the effects of incongruent morphological
character sets.
PeerJ 4:e1583
doi: https://doi.org/10.7717/peerj.1583


Aetosauria is an early-diverging clade of pseudosuchians
(crocodile-line archosaurs) that had a global distribution and high
species diversity as a key component of various Late Triassic
terrestrial faunas. It is one of only two Late Triassic clades of
large herbivorous archosaurs, and thus served a critical ecological
role. Nonetheless, aetosaur phylogenetic relationships are still
poorly understood, owing to an overreliance on osteoderm characters,
which are often poorly constructed and suspected to be highly
homoplastic. A new phylogenetic analysis of the Aetosauria, comprising
27 taxa and 83 characters, includes more than 40 new characters that
focus on better sampling the cranial and endoskeletal regions, and
represents the most comprenhensive phylogeny of the clade to date.
Parsimony analysis recovered three most parsimonious trees; the strict
consensus of these trees finds an Aetosauria that is divided into two
main clades: Desmatosuchia, which includes the Desmatosuchinae and the
Stagonolepidinae, and Aetosaurinae, which includes the Typothoracinae.
As defined Desmatosuchinae now contains Neoaetosauroides engaeus and
several taxa that were previously referred to the genus Stagonolepis,
and a new clade, Desmatosuchini, is erected for taxa more closely
related to Desmatosuchus. Overall support for some clades is still
weak, and Partitioned Bremer Support (PBS) is applied for the first
time to a strictly morphological dataset demonstrating that this weak
support is in part because of conflict in the phylogenetic signals of
cranial versus postcranial characters. PBS helps identify homoplasy
among characters from various body regions, presumably the result of
convergent evolution within discrete anatomical modules. It is likely
that at least some of this character conflict results from different
body regions evolving at different rates, which may have been under
different selective pressures.