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Re: Deinonychus claw use and origin of flapping
From: Ben Creisler
The press release from Montana State University (with links, art, photos):
New in PLoS ONE:
Fowler, D.W., Freedman, E.A., Scannella, J.B.& Kambic, R.E. (2011)
The Predatory Ecology of Deinonychus and the Origin of Flapping in Birds.
PLoS ONE 6(12): e28964.
Most non-avian theropod dinosaurs are characterized by fearsome serrated teeth
and sharp recurved claws. Interpretation of theropod predatory ecology is
typically based on functional morphological analysis of these and other
physical features. The notorious hypertrophied ‘killing claw’ on pedal digit
(D) II of the maniraptoran theropod Deinonychus (Paraves: Dromaeosauridae) is
hypothesized to have been a predatory adaptation for slashing or climbing,
leading to the suggestion that Deinonychus and other dromaeosaurids were
cursorial predators specialized for actively attacking and killing prey several
times larger than themselves. However, this hypothesis is problematic as extant
animals that possess similarly hypertrophied claws do not use them to slash or
climb up prey. Here we offer an alternative interpretation: that the
hypertrophied D-II claw of dromaeosaurids was functionally analogous to the
enlarged talon also found on D-II of extant
Accipitridae (hawks and eagles; one family of the birds commonly known as
“raptors”). Here, the talon is used to maintain grip on prey of subequal body
size to the predator, while the victim is pinned down by the body weight of the
raptor and dismembered by the beak. The foot of Deinonychus exhibits morphology
consistent with a grasping function, supportive of the prey immobilisation
behavior model. Opposite morphological trends within Deinonychosauria
(Dromaeosauridae + Troodontidae) are indicative of ecological separation.
Placed in context of avian evolution, the grasping foot of Deinonychus and
other terrestrial predatory paravians is hypothesized to have been an
exaptation for the grasping foot of arboreal perching birds. Here we also
describe “stability flapping”, a novel behaviour executed for positioning and
stability during the initial stages of prey immobilisation, which may have been
pivotal to the evolution of the flapping stroke.
These findings overhaul our perception of predatory dinosaurs and highlight
the role of exaptation in the evolution of novel structures and behaviours.