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Ankylosaur Pelvic Shield Morphology

From: Ben Creisler

In the new Journal of Paleontology:

Victoria M. Arbour, Michael E. Burns, and Philip J. Currie (2011)
A Review of Pelvic Shield Morphology in Ankylosaurs (Dinosauria:
Journal of Paleontology 85(2): 298-302 (Mar. 2011) 
doi: 10.1666/10-071.1 

The pelvic shield of ankylosaurian dinosaurs refers to an area of
osteoderms lacking differentiated transverse bands over the pelvic region
and it is used as a diagnostic character for various ankylosaur groups. The
pelvic shield character varies across ankylosaur taxa but is typically
coded as a binary character or is excluded from phylogenetic analyses,
which obscures evolutionary trends and relationships. This study
investigates for the first time pelvic shield morphology in a stratigraphic
and geographic context. This paper comprehensively reviews pelvic shield
morphology with firsthand observations of specimens, and proposes three
categories of pelvic shield morphology. Category 1 pelvic shields have
un-fused but tightly interlocking osteoderms. Category 2 pelvic shields
have fused osteoderms forming rosettes and are restricted to the Late
Jurassic to mid Cretaceous of North America and Europe. Category 3 pelvic
shields have fused polygonal osteoderms of similar size, and are found in
the mid- to Late Cretaceous of North America. Although the pelvic shield is
used to characterize the Polacanthidae, an interpretation supported by this
review, the validity of such a clade is dependent upon a global parsimony
analysis incorporating this character. Future analyses of the Ankylosauria
should incorporate a more detailed treatment of the pelvic shield to
determine its diagnostic value within the group.

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