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Stenomyti, new aetosaur from the Upper Triassic Chinle Formation



From: Ben Creisler
bcreisler@gmail.com


A new online paper:


Bryan J. Small and Jeffrey W. Martz (2013)
A new aetosaur from the Upper Triassic Chinle Formation of the Eagle
Basin, Colorado, USA.
Geological Society Special Publications 379:  Anatomy, Phylogeny and
Palaeobiology of Early Archosaurs and their Kin (advance online
publication)
doi:10.1144/SP379.18
http://sp.lyellcollection.org/content/early/2013/06/07/SP379.18.abstract


A small aetosaur skull and skeleton and referred material from the
Chinle Formation, Eagle Basin of Colorado, USA, is described as a new
taxon, Stenomyti huangae gen. et sp. nov, distinguished from other
aetosaurs by the following autapomorphies: three premaxillary teeth;
four palpebrals; pronounced midline ridge on frontals and parietals;
paired ridges flanking midline ridge on parietal and frontal;
exclusion of quadratojugal from ventral margin of skull by contact
between jugal and quadrate; exclusion of postorbital from
infratemporal fenestra; infratemporal fenestra a horizontally oriented
oval that embays the posterior edge of the jugal; retroarticular
process longer than distance between articular glenoid and posterior
edge of external mandibular fenestra; oval to irregularly shaped
ventral osteoderms that do not contact each other. Paramedian and
lateral osteoderms of S. huangae are nearly identical to those of
Aetosaurus ferratus, and other shared cranial characters suggest that
these taxa are closely related and lie outside the clade
Typothoracisinae+Desmatosuchinae. This discovery indicates that other
reports of Aetosaurus across Laurasia based on osteoderms should be
reassessed. Similar confusion with the osteoderms of other
non-typothoracisine/desmatosuchine aetosaurs such as Aetosauroides,
Stagonolepis and Calyptosuchus suggests that osteoderms are not always
reliable taxonomic indicators.