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Coloradisaurus skull redescription (Triassic sauropodomorph)



Ben Creisler
bcreisler@gmail.com

In the new JVP:

Cecilia Apaldetti, Ricardo N. Martinez, Diego Pol & Thibaud Souter (2014)
Redescription of the Skull of Coloradisaurus brevis (Dinosauria,
Sauropodomorpha) from the Late Triassic Los Colorados Formation of the
Ischigualasto-Villa Union Basin, northwestern Argentina.
Journal of Vertebrate Paleontology 34(5):  1113-1132
DOI:10.1080/02724634.2014.859147
http://www.tandfonline.com/doi/full/10.1080/02724634.2014.859147#.VA8IbPldXTo


The cranial anatomy of the basal sauropodomorph Coloradisaurus brevis
from the upper levels of the Norian Los Colorados Formation is here
redescribed and comparisons made based on the holotype skull and
mandible. Coloradisaurus brevis is diagnosed by most of the features
proposed in the original description and an additional set of
autapomorphies, such as presence of circular upper temporal fenestrae,
laminae on the ventrolateral margins of a ventral fossa of the
basisphenoid and on the ventral region of the parasphenoid, and
tab-like medial process at the posteromedial end of the mandible.
Coloradisaurus is placed within Massospondylidae, as in recent
analyses. This position is supported primarily by postcranial
characters, but some cranial features identified in this study provide
additional evidence supporting this position (e.g., jugal contribution
to the antorbital fenestra, frontal proportionately longer than
nasals). However, the cranial anatomy of Coloradisaurus also bears
several characters that are shared with plateosaurids (e.g., low
mandibular articulation, broad maxillary wall on the anterior margin
of antorbital fossa, broad prefrontals, projection of infratemporal
fenestra behind the orbit, stepped braincase, robust septum between
basipterygoid processes). Thus, Coloradisaurus is interpreted as a
massospondylid that has convergently acquired characters that are
otherwise only known in plateosaurids, highlighting the conflicting
pattern of character distribution among basal sauropodomorphs.