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Balaur, predatory dromaeosaurid or omnivorous flightless bird? (free pdf)

Ben Creisler

A new open access paper:

Andrea Cau, Tom Brougham &  Darren Naish (2015)
The phylogenetic affinities of the bizarre Late Cretaceous Romanian
theropod Balaur bondoc (Dinosauria, Maniraptora): dromaeosaurid or
flightless bird?
PeerJ 3:e1032
doi: https://dx.doi.org/10.7717/peerj.1032

The exceptionally well-preserved Romanian dinosaur Balaur bondoc is
the most complete theropod known to date from the Upper Cretaceous of
Europe. Previous studies of this remarkable taxon have included its
phylogenetic interpretation as an aberrant dromaeosaurid with
velociraptorine affinities. However, Balaur displays a combination of
both apparently plesiomorphic and derived bird-like characters. Here,
we analyse those features in a phylogenetic revision and show how they
challenge its referral to Dromaeosauridae. Our reanalysis of two
distinct phylogenetic datasets focusing on basal paravian taxa
supports the reinterpretation of Balaur as an avialan more crownward
than Archaeopteryx but outside of Pygostylia, and as a flightless
taxon within a paraphyletic assemblage of long-tailed birds. Our
placement of Balaur within Avialae is not biased by character
weighting. The placement among dromaeosaurids resulted in a suboptimal
alternative that cannot be rejected based on the data to hand.
Interpreted as a dromaeosaurid, Balaur has been assumed to be
hypercarnivorous and predatory, exhibiting a peculiar morphology
influenced by island endemism. However, a dromaeosaurid-like ecology
is contradicted by several details of Balaur’s morphology, including
the loss of a third functional manual digit, the non-ginglymoid distal
end of metatarsal II, and a non-falciform ungual on the second pedal
digit that lacks a prominent flexor tubercle. Conversely, an
omnivorous ecology is better supported by Balaur’s morphology and is
consistent with its phylogenetic placement within Avialae. Our
reinterpretation of Balaur implies that a superficially
dromaeosaurid-like taxon represents the enlarged, terrestrialised
descendant of smaller and probably volant ancestors.