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Proterosuchus (Triassic archosauriform) revised taxonomy

Ben Creisler

A new online paper:

Martín D. Ezcurra and Richard J. Butler (2014)
Taxonomy of the proterosuchid archosauriforms (Diapsida:
Archosauromorpha) from the earliest Triassic of South Africa, and
implications for the early archosauriform radiation.
Palaeontology (advance online publication)
DOI: 10.1111/pala.12130

Proterosuchidae is one of the first clades of Archosauriformes
(archosaurs and closely related species) to appear in the fossil
record, with the richest sample of the group coming from the
Lystrosaurus Assemblage Zone (earliest Triassic) of South Africa. Four
nominal proterosuchid species were described from South Africa during
the twentieth century (Proterosuchus fergusi, Chasmatosaurus
vanhoepeni, Chasmatosaurus alexanderi and Elaphrosuchus rubidgei), but
interpretations of their taxonomy have been widely disparate. The most
recent taxonomic revision concluded that P. fergusi is the only valid
species and that the other nominal species are junior subjective
synonyms of this taxon. This proposal was based on the interpretation
that anatomical differences between the nominal species could be
explained as a result of ontogenetic changes and/or post-mortem
deformation. The recent discoveries of multiple new South African
proterosuchid specimens provide an impetus to revisit their taxonomy.
Based upon a comprehensive re-examination of all known specimens, as
well as examination of other proterosuchid taxa in collections
worldwide, we conclude that the holotype of Proterosuchus fergusi is
undiagnostic. As a result, we propose a neotype (RC 846) for the
species. ‘Chasmatosaurus vanhoepeni’ and ‘Elaphrosuchus rubidgei’ are
considered subjective junior synonyms of P. fergusi. ‘Chasmatosaurus’
alexanderi is considered a valid species, for which we propose the new
combination P. alexanderi comb. nov. A third species, P. goweri sp.
nov., is erected on the basis of a single specimen (NMQR 880). All
three species recognized here are taxonomically distinct from a
previously described archosauriform maxilla from the lower
Lystrosaurus AZ. As a result, we recognize a minimum of four
archosauriform species following the Permo-Triassic mass extinction in
South Africa. Our results suggest a greater species richness of
earliest Triassic archosauriforms than previously appreciated, but
that archosauriform morphological disparity remained low and did not
expand until the late Early Triassic – early Mid-Triassic.