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New Diplodocoidea phylogenetic analysis

From: Ben Creisler

In case this advance online publication has not been 

WHITLOCK, J. A. (2011)
A phylogenetic analysis of Diplodocoidea (Saurischia: 
Zoological Journal of the Linnean Society (advance online 
doi: 10.1111/j.1096-3642.2010.00665.x

Diplodocoidea includes some of the first well-known 
sauropod dinosaurs, including such late 19th century and 
early 20th century discoveries as Apatosaurus, 
Diplodocus, and Dicraeosaurus. As a consequence of their 
long history of study, the basic set of suprageneric 
diplodocoid interrelationships is well resolved, and the 
diagnostic features of each genus are well established. 
However, intergeneric relationships are less resolved, 
including the relationships of putatively basal taxa like 
Amphicoelias and Haplocanthosaurus, the flagellicaudatan 
Suuwassea, and the highly specialized rebbachisaurids. 
For the rebbachisaurids, this uncertainty is coupled with 
a recent surge in the discovery of new taxa. Comparative 
cladistic methods demonstrate that character and taxon 
sampling need to be improved before greater phylogenetic 
resolution can be expected. Here, I present a new 
phylogenetic analysis that resolves many of the 
outstanding questions regarding the relationships within 
Diplodocoidea and examines palaeobiogeographical trends 
within the group. Suuwassea is recovered as a basal 
dicraeosaurid (the only Laurasian member of the group), 
and two distinct clades of rebbachisaurids are 
identified: a group closely allied with Nigersaurus and a 
clade associated with Limaysaurus. Amphicoelias, 
Amazonsaurus, and Haplocanthosaurus are provisionally 
placed as successively less-derived taxa at the base of 
Diplodocoidea. A North American origin for Diplodocoidea 
and Flagellicaudata is hypothesized based on the 
geographical and temporal distribution of those taxa. 
Rebbachisaurid taxa demonstrate a South American/African 
vicariance pattern, but the timing of the event pre-dates 
the proposed final rifting of those continents by c. 40 
million years; the meaning of this discrepancy is