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Yurgovuchia, new dromaeosaurid from Utah



From: Ben Creisler
bcreisler@gmail.com

A new theropod in PLoS ONE:


Senter, P., Kirkland, J.I., DeBlieux, D.D., Madsen, S. & Toth, N. (2012)
New Dromaeosaurids (Dinosauria: Theropoda) from the Lower Cretaceous
of Utah, and the Evolution of the Dromaeosaurid Tail.
PLoS ONE 7(5): e36790.
doi:10.1371/journal.pone.0036790
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0036790


Background

The Yellow Cat Member of the Cedar Mountain Formation (Early
Cretaceous, Barremian? – Aptian) of Utah has yielded a rich theropod
fauna, including the coelurosaur Nedcolbertia justinhofmanni, the
therizinosauroid Falcarius utahensis, the troodontid Geminiraptor
suarezarum, and the dromaeosaurid Utahraptor ostrommaysorum. Recent
excavation has uncovered three new dromaeosaurid specimens. One
specimen, which we designate the holotype of the new genus and species
Yurgovuchia doellingi, is represented by a partial axial skeleton and
a partial left pubis. A second specimen consists of a right pubis and
a possibly associated radius. The third specimen consists of a tail
skeleton that is unique among known Cedar Mountain dromaeosaurids.

Methodology/Principal Findings

Y. doellingi resembles Utahraptor ostrommaysorum in that its caudal
prezygapophyses are elongated but not to the degree present in most
dromaeosaurids. The specimen represented by the right pubis exhibits a
pronounced pubic tubercle, a velociraptorine trait that is absent in
Y. doellingi. The specimen represented by the tail skeleton exhibits
the extreme elongation of the caudal prezygapophyses that is typical
of most dromaeosaurids. Here we perform a phylogenetic analysis to
determine the phylogenetic position of Y. doellingi. Using the
resulting phylogeny as a framework, we trace changes in character
states of the tail across Coelurosauria to elucidate the evolution of
the dromaeosaurid tail.

Conclusions/Significance

The new specimens add to the known diversity of Dromaeosauridae and to
the known diversity within the Yellow Cat paleofauna. Phylogenetic
analysis places Y. doellingi in a clade with Utahraptor, Achillobator,
and Dromaeosaurus. Character state distribution indicates that the
presence of intermediate-length caudal prezygapophyses in that clade
is not an evolutionarily precursor to extreme prezygapophyseal
elongation but represents a secondary shortening of caudal
prezygapophyses. It appears to represent part of a trend within
Dromaeosauridae that couples an increase in tail flexibility with
increasing size.