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Microsuchus (Mesoeucrocodylia) redescribed, from the Upper Cretaceous of Argentina



Ben Creisler
bcreisler@gmail.com

A new paper:


Juan Martín Leardi, Lucas E. Fiorelli & Zulma Gasparini (2105) [2014]
Redescription and reevaluation of the taxonomical status of
Microsuchus schilleri (Crocodyliformes: Mesoeucrocodylia) from the
Upper Cretaceous of Neuquén, Argentina.
Cretaceous Research 52(A): 153–166
DOI: 10.1016/j.cretres.2014.09.007
http://www.sciencedirect.com/science/article/pii/S0195667114001712

Highlights

The type specimen of Microsuchus schilleri from Santonian of Argentina
is redescribed.
Microsuchus is a valid taxon, having unique characters in its
postcranial skeleton.
Microsuchus is depicted in a polytomy at the base of Mesoeucrocodylia.
Neuquensuchus, another taxon from the same locality, is found as a ziphosuchian.
Microsuchus and Comahusuchus might be synonymous taxa.

Abstract

Fragmentary remains of Microsuchus schilleri (Crocodyliformes:
Mesoeucrocodylia) from the Bajo de La Carpa Formation (Santonian, Late
Creteceous) of northern Patagonia, Argentina, are decribed and
reevaluated taxonomically. The type specimen is an articulated
individual with hindlimb and axial remains. Microsuchus has several
traits that allow to recognize it as a valid taxon (the presence of
bulge lateral to the prezygapophyses of the second sacral vertebra;
elongated posterior zeugopodia; proximal caudal centra with triangular
cross section). Microsuchus was originally assigned as a goniopholidid
based on the platycely of its vertebral centra, a character that is
widely distributed among fossil crocodyliforms. A phylogenetical
analysis using an expanded data matrix focusing on postcranial data
was performed in which Microsuchus and another long-limbed
crocodyliform from the same location, Neuquensuchus, were included.
Microsuchus is depicted in a politomy as a basal mesoeucrocodylian,
with its position as a neosuchian or notosuchian supported by a single
synapomorphy on the different most parsimonious trees. Additionaly,
Neuquensuchus is well nested among notosuchians, in contrast to
previous hypothesis. These findings further increase the crocodyliform
diversity of the Bajo de la Carpa Formation and emphasize the
relevance of its fauna in studies of the diversification of
mesoeucrocodylians and notosuchians. Furthermore, the occurrence of
both Microsuchus and Neuquensuchus gives evidence of a basal stock of
mesoeucrocodylians with elongated limbs that was not previously
reported for northern Patagonia.