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Asperoris, new archosauriform from Middle Triassic Manda beds of Tanzania



From: Ben Creisler
bcreisler@gmail.com

New in PLoS ONE:

Sterling J. Nesbitt, Richard J. Butler & David J. Gower (2013)
A New Archosauriform (Reptilia: Diapsida) from the Manda Beds (Middle
Triassic) of Southwestern Tanzania.
PLoS ONE 8(9): e72753.
doi:10.1371/journal.pone.0072753
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0072753


Background

Archosauria and their closest relatives, the non-archosaurian
archosauriforms, diversified in the Early and Middle Triassic, soon
after the end-Permian extinction. This diversification is poorly
documented in most Lower and Middle Triassic rock sequences because
fossils of early groups of archosauriforms are relatively rare
compared to those of other amniotes. The early Middle Triassic (? late
Anisian) Manda beds of southwestern Tanzania form an exception, with
early archosaur skeletons being relatively common and preserved as
articulated or associated specimens. The Manda archosaur assemblage is
exceptionally diverse for the Middle Triassic. However, to date, no
non-archosaurian archosauriforms have been reported from these rocks.

Methodology/Principal Findings

Here, we name a new taxon, Asperoris mnyama gen. et sp. nov., from the
Manda beds and thoroughly describe the only known specimen. The
specimen consists of a well-preserved partial skull including
tooth-bearing elements (premaxilla, maxilla), the nasal, partial skull
roof, and several incomplete elements. All skull elements are covered
in an autapomorphic highly rugose sculpturing. A unique combination of
character states indicates that A. mnyama lies just outside
Archosauria as a stem archosaur within Archosauriformes, but more
precise relationships of A. mnyama relative to other early
archosauriform clades (e.g., Erythrosuchidae) cannot be determined
currently.

Conclusions/Significance

Asperoris mnyama is the first confirmed non-archosaurian
archosauriform from the Manda beds and increases the morphological and
taxonomic diversity of early archosauriforms known from the Middle
Triassic. The direct association of A. mnyama with species referable
to Archosauria demonstrates that non-archosaurian archosauriforms were
present during the rise and early diversification of Archosauria.
Non-archosaurian archosauriforms and archosaurs co-occur in fossil
reptile assemblages across Pangaea from the late Early Triassic to the
end of the Late Triassic.