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Lusotitan (Sauropoda) osteology (free pdf)



From: Ben Creisler
bcreisler@gmail.com


A new online paper. The article is open access (free pdf!).


Philip D. Mannion, Paul Upchurch, Rosie N. Barnes & Octávio Mateus (2013)
Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan
atalaiensis (Macronaria) and the evolutionary history of basal
titanosauriforms.
Zoological Journal of the Linnean Society (advance online publication)
DOI: 10.1111/zoj.12029
http://onlinelibrary.wiley.com/doi/10.1111/zoj.12029/abstract
http://onlinelibrary.wiley.com/doi/10.1111/zoj.12029/pdf


Titanosauriforms represent a diverse and globally distributed clade of
neosauropod dinosaurs, but their inter-relationships remain poorly
understood. Here we redescribe Lusotitan atalaiensis from the Late
Jurassic Lourinhã Formation of Portugal, a taxon previously referred
to Brachiosaurus. The lectotype includes cervical, dorsal, and caudal
vertebrae, and elements from the forelimb, hindlimb, and pelvic
girdle. Lusotitan is a valid taxon and can be diagnosed by six
autapomorphies, including the presence of elongate postzygapophyses
that project well beyond the posterior margin of the neural arch in
anterior-to-middle caudal vertebrae. A new phylogenetic analysis,
focused on elucidating the evolutionary relationships of basal
titanosauriforms, is presented, comprising 63 taxa scored for 279
characters. Many of these characters are heavily revised or novel to
our study, and a number of ingroup taxa have never previously been
incorporated into a phylogenetic analysis. We treated quantitative
characters as discrete and continuous data in two parallel analyses,
and explored the effect of implied weighting. Although we recovered
monophyletic brachiosaurid and somphospondylan sister clades within
Titanosauriformes, their compositions were affected by alternative
treatments of quantitative data and, especially, by the weighting of
such data. This suggests that the treatment of quantitative data is
important and the wrong decisions might lead to incorrect tree
topologies. In particular, the diversity of Titanosauria was greatly
increased by the use of implied weights. Our results support the
generic separation of the contemporaneous taxa Brachiosaurus,
Giraffatitan, and Lusotitan, with the latter recovered as either a
brachiosaurid or the sister taxon to Titanosauriformes. Although
Janenschia was recovered as a basal macronarian, outside Titanosauria,
the sympatric Australodocus provides body fossil evidence for the
pre-Cretaceous origin of titanosaurs. We recovered evidence for a
sauropod with close affinities to the Chinese taxon Mamenchisaurus in
the Late Jurassic Tendaguru beds of Africa, and present new
information demonstrating the wider distribution of caudal
pneumaticity within Titanosauria. The earliest known titanosauriform
body fossils are from the late Oxfordian (Late Jurassic), although
trackway evidence indicates a Middle Jurassic origin. Diversity
increased throughout the Late Jurassic, and titanosauriforms did not
undergo a severe extinction across the Jurassic/Cretaceous boundary,
in contrast to diplodocids and non-neosauropods. Titanosauriform
diversity increased in the Barremian and Aptian–Albian as a result of
radiations of derived somphospondylans and lithostrotians,
respectively, but there was a severe drop (up to 40%) in species
numbers at, or near, the Albian/Cenomanian boundary, representing a
faunal turnover whereby basal titanosauriforms were replaced by
derived titanosaurs, although this transition occurred in a
spatiotemporally staggered fashion.