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Lewisuchus (Middle Triassic archosaur) osteology



From: Ben Creisler
bcreisler@gmail.com

A new online paper:

Jonathas S. Bittencourt, Andrea B. Arcucci, Claudia A. Marsicano & Max
C. Langer (2014)
Osteology of the Middle Triassic archosaur Lewisuchus admixtus Romer
(Chañares Formation, Argentina), its inclusivity, and relationships
amongst early dinosauromorphs.
Journal of Systematic Palaeontology (advance online publication)
DOI:10.1080/14772019.2013.878758
http://www.tandfonline.com/doi/full/10.1080/14772019.2013.878758#.UzmMiPldXeI

Lewisuchus admixtus is an enigmatic early dinosauriform from the
Chañares Formation, Ladinian of Argentina, which has been recently
considered a member of Silesauridae. Yet, it differs markedly from
Late Triassic silesaurids in dental and vertebral anatomy. Indeed, a
detailed redescription of its holotype allowed the identification of
several features of the skeleton previously unrecognized amongst
silesaurids. These include pterygoid teeth, a dorsomedial posttemporal
opening on the otoccipital, foramina associated with cranial nerves
X-XII on the caudal region of the prootic-otoccipital, and postaxial
neck/trunk vertebrae with craniocaudally expanded neural spines. The
presence of a single row of presacral scutes was also confirmed. Some
elements previously referred to, or found associated with, the
holotype, including a lower jaw, pedal elements and an astragalus,
more probably correspond to proterochampsid remains. The anatomical
information available for the holotype of L. admixtus was rescored
into a new phylogenetic dataset for dinosauromorphs, mostly based on
previous works. Lewisuchus admixtus and Pseudolagosuchus major are
treated as distinct OTUs because their preserved skeletons mostly lack
overlapping parts. The parsimony analysis supports the basal position
of L. admixtus within dinosauriforms, prior to the silesaurid-dinosaur
split, rather than at the base of Silesauridae. This suggests that a
higher number of early dinosauriform clades branched in the Middle and
Late Triassic than previously suggested.