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Camposaurus as oldest neotheropod



From: Ben Creisler
bh480@scn.org

In July Palaeontology:

Ezcurra, M. D. and Brusatte, S. L. (2011)
Taxonomic and phylogenetic reassessment of the early neotheropod dinosaur
Camposaurus arizonensis from the Late Triassic of North America. 
Palaeontology 54: 763?772. 
doi: 10.1111/j.1475-4983.2011.01069.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2011.01069.x/abstract

Abstract:
Camposaurus arizonensis, a small theropod dinosaur from the early?middle
Norian of Arizona (USA), is widely considered the oldest known neotheropod.
However, despite its importance, Camposaurus is the subject of taxonomic
and phylogenetic uncertainty and is often considered a nomen dubium,
largely because of a fragmentary holotype. We here reassess the holotype of
Camposaurus and identify two autapomorphies: the posterior edge of the
tibial articular surface for the fibula offset as a sharp and prominent
ridge and the absence of an anteriorly expanded medial condyle of the
astragalus. We therefore consider Camposaurus to be a valid and diagnostic
taxon of basal theropod dinosaur. For the first time, we include
Camposaurus in a phylogenetic analysis, which confirms its neotheropod
placement and recovers it as a close relative of Coelophysis rhodesiensis
within Coelophysoidea sensu stricto. The position of Camposaurus as the
oldest neotheropod provides an important calibration point, but
necessitates long ghost lineages, indicating that our knowledge of the
early evolutionary history of theropod dinosaurs is still patchy.
Furthermore, our phylogenetic analysis recovers a polytomy at the base of
Neotheropoda, as most parsimonious trees disagree in recovering a
monophyletic or paraphyletic 'traditional' Coelophysoidea. This suggests
that basal theropod phylogeny remains in a state of flux, and the monophyly
of 'traditional' Coelophysoidea remains an open question.


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