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Kaatedocus, new diplodocid sauropod from Jurassic Morrison Formation, Wyoming

From: Ben Creisler

A new Jurassic sauropod taxon from North America:

Emanuel Tschopp & Octávio Mateus (2012)
The skull and neck of a new flagellicaudatan sauropod from the
Morrison Formation and its implication for the evolution and ontogeny
of diplodocid dinosaurs.
Journal of Systematic Palaeontology (advance online publication)

A new taxon of diplodocid sauropod, Kaatedocus siberi gen. et sp.
nov., is recognized based on well-preserved cervical vertebrae and
skull from the Morrison Formation (Kimmeridgian, Late Jurassic) of
northern Wyoming, USA. A phylogenetic analysis places it inside
Diplodocinae (Sauropoda: Flagellicaudata: Diplodocidae), as a sister
taxon to a clade uniting Tornieria africana and the classical
diplodocines Barosaurus lentus and Diplodocus. The taxon is diagnosed
by a unique combination of plesiomorphic and derived traits, as well
as the following unambiguous autapomorphies within Diplodocidae:
frontals separated anteriorly by a U-shaped notch; squamosals
restricted to the post-orbital region; presence of a postparietal
foramen; a narrow, sharp and distinct sagittal nuchal crest; the
paired basal tuber with a straight anterior edge in ventral view;
anterior end of the prezygapophyses of mid- and posterior cervical
vertebrae is often an anterior extension of the pre-epipophysis, which
projects considerably anterior to the articular facet; anterodorsal
corner of the lateral side of the posterior cervical vertebrae marked
by a rugose tuberosity; posterior margin of the prezygapophyseal
articular facet of posterior cervical vertebrae bordered posteriorly
by conspicuous transverse sulcus; posterior cervical neural spines
parallel to converging. The inclusion of K. siberi and several newly
described characters into a previously published phylogenetic analysis
recovers the new taxon as basal diplodocine, which concurs well with
the low stratigraphical position of the holotype specimen.
Dinheirosaurus and Supersaurus now represent the sister clade to
Apatosaurus and Diplodocinae and therefore the most basal diplodocid
genera. The geographical location in the less known northern parts of
the Morrison Fm., where K. siberi was found, corroborates previous
hypotheses on faunal provinces within the formation. The probable
subadult ontogenetic stage of the holotype specimen allows analysis of
ontogenetic changes and their influence on diplodocid phylogeny.