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Europasaurus postcranial axial skeleton



From: Ben Creisler
bcreisler@gmail.com

A new online paper:


José L. Carballido & P. Martin Sander (2013)
Postcranial axial skeleton of Europasaurus holgeri (Dinosauria,
Sauropoda) from the Upper Jurassic of Germany: implications for
sauropod ontogeny and phylogenetic relationships of basal Macronaria.
Journal of Systematic Palaeontology (advance online publication)
DOI:10.1080/14772019.2013.764935
http://www.tandfonline.com/doi/full/10.1080/14772019.2013.764935


Neosauropods are well represented in the Late Jurassic fossil record,
both in Laurasia and Gondwana. Among Macronaria, Europasaurus
represents one of the most basal forms of this group. In addition to
its systematic importance, Europasaurus is also the first unequivocal
dwarf sauropod from which adult and juvenile material is available.
Despite the abundance of sauropods in the fossil record, early
juvenile specimens are rare, limiting knowledge about sauropod
ontogeny. Therefore, the great amount of material of Europasaurus
provides an excellent opportunity to improve our knowledge on the
early evolution of Macronaria, as well as to shed light on some
morphological changes through ontogeny. The postcranial axial skeleton
of sauropods is extremely modified with respect to the anatomy
observed in its ancestors, the ‘prosauropods’, proving to be one of
the most informative regions of the body. Here we provide a detailed
description of the axial skeleton of Europasaurus, including adult and
juvenile elements, discussing its systematic and ontogenetic
importance. We also analyse the phylogenetic position of Europasaurus
through a cladistic analysis using TNT, which retrieves this taxon in
a basal position among Camarasauromorpha. Additionally, the
presence/absence of discrete characters and the comparison of juvenile
elements with adult specimens allowed us to recognize different
morphological ontogenetic stages (MOS). Whereas early stages lack
derived characters (e.g. spinodiapophyseal lamina and prespinal lamina
on dorsal vertebrae), all derived characters (including
autapomorphies) are present in late immature specimens. Therefore,
while late immature specimens provide the same phylogenetic signal as
adult specimens of Europasaurus, more immature stages are recovered in
a basal position among sauropods. Finally, we apply the MOS to other
maturity criteria (e.g. neurocentral closure, sexual maturity) in a
search for a wider definition of maturity.