Deinonychus claw use and origin of flapping

[Ben Creisler <bscreisler@yahoo.com>]

From: Ben Creisler
bscreisler@yahoo.com
 
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. 
doi:10.1371/journal.pone.0028964
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0028964

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.