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Balaur (Theropoda: Dromaeosauridae) osteology monograph in Bulletin of AMNH :

From: Ben Creisler

A new monograph about Balaur:

Stephen L. Brusatte, Mátyás Vremir, Zoltán Csiki-Sava, Alan H. Turner,
Akinobu Watanabe, Gregory M. Erickson, and Mark A. Norell (2013)
The Osteology of Balaur bondoc, an Island-Dwelling Dromaeosaurid
(Dinosauria: Theropoda) from the Late Cretaceous of Romania.
Bulletin of the American Museum of Natural History Number 374 :1-100
doi: http://dx.doi.org/10.1206/798.1


The Haţeg Island fauna of the terminal Late Cretaceous (ca. 71–65
million years ago) of Romania is one of the most unusual dinosaur
assemblages in the global fossil record. It has long been recognized
that many herbivorous dinosaurs from the Haţeg fauna were dwarfed,
morphologically aberrant, and/or primitive relative to mainland
contemporaries, and these taxa are often considered examples of the
so-called island effect: the evolutionary phenomenon by which
island-dwelling species are often dwarfed and anatomically modified.
Very little, however, is known about the carnivorous dinosaurs that
inhabited Haţeg Island, and it is unclear whether they were also
dwarfed, aberrant, or primitive. In 2009, the discovery of the first
substantially complete theropod from the Late Cretaceous of Europe,
the holotype of the Romanian dromaeosaurid Balaur bondoc, provided the
first clear glimpse at an island-dwelling carnivorous dinosaur. Here
we describe and figure this remarkably preserved skeleton in detail.
We provide detailed descriptions and photographs of individual bones,
and make extensive comparisons with other dromaeosaurids (and other
derived coelurosaurian theropods).

This monographic description provides further evidence that Balaur is
an unusual derived dromaeosaurid, closely related to Velociraptor,
with a remarkably modified hand and foot skeleton, including a stocky
and heavily fused distal hind limb, a double set of hyperextensible
pedal claws, and a fused and atrophied hand, which are otherwise
unknown among derived coelurosaurian theropods. We present an updated
diagnosis of Balaur based on additional preparation of the holotype,
comparisons with other dromaeosaurids, and careful consideration of
postmortem crushing. Histological techniques demonstrate that both the
holotype and a referred specimen of Balaur, which is approximately 50%
larger than the holotype and from a separate locality, belong to
mature individuals. Therefore, we remove the referred specimen from
Balaur bondoc and conservatively consider it Balaur sp. We present an
updated assessment of the phylogenetic relationships of Balaur based
on a comprehensive new coelurosaurian cladistic dataset, which
corroborates the close relationship between Balaur, Velociraptor,
Deinonychus, Adasaurus, and Saurornitholestes. We review the fossil
record of European Late Cretaceous theropods and show that other
specimens from the Late Cretaceous of Romania (including the holotype
of Elopteryx), France, and Hungary either do not belong to Balaur (due
to the lack of Balaur autapomorphies) or cannot be compared to Balaur
because of a lack of overlapping material. Finally, we discuss the
biogeographic history of European terminal Cretaceous dinosaur faunas
and comment on the extreme morphological specializations of Balaur. We
conclude that the phylogenetic position of Balaur, a derived
dromaeosaurid closely related to Late Cretaceous Laurasian taxa, is
inconsistent with previous hypotheses of long-term geographic
endemicity of the Romanian island faunas, but argue that the aberrant
Bauplan of Balaur is similar to that seen in some living and recently
extinct mammals and thus likely due to the “island effect.”