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Archosauromorph remains from Early−Middle Triassic, Argentina

Ben Creisler

A new online paper:

Martín Ezcurra, Agustín G. Martinelli, Lucas E. Fiorelli, Atila A.S.
Da-Rosa & Julia B. Desojo (2015)
Archosauromorph remains from the Tarjados Formation (Early−Middle
Triassic, NW Argentina).
Ameghiniana (advance online publication)

The Agua de la Peña Group of the Ischigualasto−Villa Unión Basin
(northwestern Argentina) documents the evolution of archosauromorph
assemblages in western Gondwana during the late Middle and Late
Triassic. However, the South American archosauromorph record in the
aftermath of the Permo-Triassic mass extinction (Early−early Middle
Triassic) is remarkably scarce and restricted to isolated bones. Here,
we describe a recently collected isolated second sacral vertebra and
rib that represents one of the few fossils known from the Lower−Middle
Triassic Tarjados Formation, the unit that underlies the Agua de la
Peña Group. This specimen is identified as an archosauromorph because
of the presence of a non-notochordal vertebra and a bifurcated distal
end of the second sacral rib. A quantitative phylogenetic analysis
places the new specimen as an archosauromorph more derived than
protorosaurs. In particular, this specimen resembles Pamelaria,
Prolacerta and early rhynchosaurs in the presence of a squared
posterior projection of the bifurcated second sacral rib. The new
specimen represents the first body fossil of a diapsid formally
described in the Tarjados Formation and the oldest member of the group
in the Ischigualasto−Villa Unión Basin. As a result, this specimen
increases the high-level taxonomic richness of Archosauromorpha in
South America in the aftermath of the Permo−Triassic mass extinction.