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RE: Deinonychus claw use and origin of flapping
I am going to reserve my comments in specific for a few days. I want to say
that I really like this paper, and that the other paper that came out in _PLoS
ONE_ today with John Scannella as an author (a response to Farke's discussion
on the viability of the separate *Nedoceratops hatcheri* -- my comments are now
is very well composed for its intitial points.
What really strikes me about the paper is the way it is written, something I
noted about another recent paper although for technical reasons here:
http://qilong.wordpress.com/2011/12/08/what-carbon-has-to-do-with-it/ Fowler et
al. write in a personal narrative, and the structure is at once compelling and
oft-putting because it's a little less than _de rigeur_ you'd typically expect
for in depth hypothesis testing. This is largely because the article is
proposing a scenario, and Dial's 2003 WAIR paper was written much the same way,
as were formative Ostrom papers on the topic of avian flight. Awesome,
personable stuff. So I'd like to get that off my chest.
I really, really like Fowler et al.'s explanation for tooth morphology, and
it jives nicely with the biomech work that's been done on jaws recently, as
they note. Awesome stuff.
I'd like to say that, about topics 2 and 3 below, that there is a paradoxical
element to the RPR hypothesis:
Fowler et al. propose that basal deinonychosaurs were cursors, likely pursuit
hunters. I would bring attention to Hartman's discussion of the argument that
early pre-birds could run around with their arms and tail as stabilizing
aerofoils, where the exaptation is towards an elevated forelimb that could
tangentially lead into WAIR, and a broader, shorter tail can develop more
maneuverability. Instead, the trajectory was toward an apparently
hypercursorial pes in troodontids (due to proportions and the
arctometatarsalian pes), while the dromaeosaur lineage shortened this feature
after the split with *Microraptoria*. Dromaeosaurids are short-legged, larger,
and likely ambush hunters. Yet it is not these animals have have developed
shoulder motility, broad sterna, or proportionally longer arms to body size.
They have shortened the arms, shortened the leg, and reduced shoulder mobility.
Thus, it might seem that instead of developing a should-arm "flapping"
mechanism on the lineage to birds, they did so completely isolated and parallel
to the evolution of the modern avian flight stroke. This is important when you
consider that some dromaeosaurs (esp. the unenlagiines) had particularly short
forelimbs, and form the sister group to the dromaeosaurines (sensu lato), while
at the same time retained these features at small size (*Buitreraraptor
gonzalezorum*). Depending on the order of divergence (microraptorians
(unenlagiines, dromaeosaurines)) or (unenlagiines (microraptorians,
dromaeosaurines)), thus could upset the trajectory favored in the paper that
the arms and behavior of large-bodied dromaeosaurids had anything to do with
the evolution of the avian flight strike.
... but, like I said, awesome stuff.
Jaime A. Headden
The Bite Stuff (site v2)
"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)
"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion
> Date: Thu, 15 Dec 2011 17:52:41 +1100
> From: firstname.lastname@example.org
> To: email@example.com
> Subject: Re: Deinonychus claw use and origin of flapping
> > 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
> I think people would be disappointed if there wasn't any discussion of
> this paper, in light of how revolutionary this Raptor Prey Restraint
> (RPR or "ripper") hypothesis is.
> So to get the ball rolling (so it can then slowly grind to a halt)...
> (1) I'm enthralled by the idea that basal paravians had a grasping
> pes. Unlike birds, in which an enlarged and fully reversed first
> digit opposes the third digit to achieve an anisodactyl grasping pes
> (such as for perching), _Deinonychus_ achieved a grasping pes by the
> medially directed first digit effectively opposing the fourth digit
> during flexion. The foot's grasping abilities were helped by
> elongation of the pedal digits, and a metatarsus that was held close
> to the substratum. Prey captured by the foot would be held against
> the "plantar" surface, gripped by all four toes. This certainly
> explains the descent of the hallux.
> Troodontids had a more mobile first digit, and therefore might have
> been even better at grasping small prey. The metatarsal I of the
> troodontid specimen shown in Fig. 9 actually reminds me of the
> inverted P-shaped metatarsal I of certain non-ornithurine birds -
> although it is much shorter and higher on the metatarsus in
> (2) This grasping/predatory function inferred for the paravian foot is
> regarded by Fowler &c as a possible precursor to the perching foot of
> birds, via exaptation. Thus, a "hallux reversal required for perching
> could be exapted from a predatory function in a wholly terrestrial
> predator, without invoking a hypothetical pre-flight arboreal or
> scansorial stage for non-avian theropods." Although the authors are
> skeptical of arboreality in basal paravians, I think it is possible
> that critters like _Microraptor_ could have used their feet to help
> climb trees and/or grasp branches. Fowler &c actually allow for this
> possibility, so I'm not quibbling with their work here. But I think
> one can reconstruct certain paravians such as microraptorines,
> jeholornithids and long-armed troodontids (e.g., _Jinfengopteryx_)
> venturing up trees without necessarily being arboreal.
> IMHO, in many theropods the forelimbs were not that much use in prey
> capture - either too short, or the range of motion was too limited -
> and the manus of paravians was ill-equipped for grasping small
> objects. So when it comes to grasping small prey, it made sense for
> the feet to take up the slack.
> However, if the tree presented in the _Xiaotingia_ paper is correct,
> and archaeopterygids, dromaeosaurids and troodontids form a clade that
> is the sister taxon to the bird clade... then predation might not have
> been the reason behind the evolution of a grasping pes. This tree (Xu
> et al., 2011) suggest that herbivory (and a robust skull) are
> primitive for Paraves (or the bird clade, at least), and that
> deinonychosaurs are exceptional in their carnivorous/predatory habits
> (and a gracile skull).
> (3) The "stability flapping" behavior suggested as part of RPR is
> consistent with a "flapping-first" hypothesis of the origin of avian
> flight. But isn't this at odds with Senter's (2006) work which
> inferred that flapping came late to birds, because the scapular
> orientation in non-ornithoracean paravians precluded a full stroke?