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Re: Deinonychus claw use and origin of flapping

K Kripchak <saurierlagen1978@gmail.com> wrote:

> Hmmmmm.... I'm glad I was still mulling over writing follow-up
> responses to Tim, Dave, etc in the Catch-22 thread
> (http://dml.cmnh.org/2011Nov/msg00436.html). Fowler et al basically
> pulled back the curtain concealing the revelation I was trying to
> tease out from hiding via my questioning: Exaptation fits the bill
> nicely.
> My concern is that we were painting ourselves into a corner and
> setting ourselves up for future ridicule.
> The situation is hauntingly reminiscent of the days of old, when
> Feduccia would claim that although they looked very much alike, one
> could not go from a theropod manus to a bird manus... Yet in that same
> breath, he had no trouble accepting a horse's foot was derived from a
> basal five-digit eutherian manus... or that the manus of something
> that looked like Longisquama’s evolved into a bird's manus...
> Arguments against even partial arboreality based on difficulties in
> climbing down from a tree? This hands are too loose/too stiff to climb
> stuff?  Etc, etc, etc... What would one expect to see in intermediate
> steps??? Seriously... We actually are trying to sell the line,
> Feduccia-style, that goats... GOATS... could start to climb trees and
> then be selected for better climbing traits, but not theropods.
> It’s basic; Selection only works if there is a need. How did the need
> for the traits we deem as “requirements” for arboreality begin if
> protobirds weren’t up in the trees before they needed the traits to be
> up in the trees???  Where’s the logic? Awfully convenient that many
> ended up in the trees only AFTER they were evolved to allow such
> behaviour, right?
> So, we end up with arguments that boil down to saying;
> "Birds/theropods were unlikely to have become arboreal without
> cursorial basal birds/theropods possessing the capabilities, traits,
> and behaviours for becoming arboreal.  However, the capabilities,
> traits, and behaviours for becoming arboreal wouldn't have been
> selected for until cursorial basal birds/theropods became arboreal."
> A Catch-22.

This is a good point.  As you say, exaptation can be invoked for this
terrestrial-to-arboreal transition.  For example, arboreal adaptations
might have begun as characters that originally evolved for
non-arboreal functions (such as predation), but could be co-opted for
climbing or perching.

The trouble with this hypothesis is that the overall morphology of
theropods (their bauplan, if you will) was so poorly adapted for
arboreality.  Even if (and it is still an *if*) certain characters in
the hands and feet improved trunk-climbing or branch-holding ability,
these characters must be set against the rest of the skeleton, which
remained resolutely terrestrial.  Theropod backbones and joints lack
even the most basic requirements for arboreality.

This is why comparisons between theropods and mammals are so inapt -
including goats.  The much-vaunted tree-climbing abilities of goats
are a partly a product of their heritage (placentals began as small
arboreal mammals) and partly a consequence of their current ecology
(negotiating steep and uneven terrain).  Theropods lacked the flexible
vertebral columns and range of motion at the joints which, by and
large, are present in mammals.

So the question becomes: Were the changes to the distal limb elements
(= the putative incipient scansorial/arboreal characters) adequate to
allow theropods to climb trunks or grasp branches, given the
constraints imposed by the rest of the body?  This is a tricky
question, because it is difficult to frame and test hypotheses that
specifically address this issue.

> Granted, I don’t agree with all aspects/extensions of the scenario,
> but the RPR theory offers a road to an escape from that Catch-22. In
> addition, it fits right in with something that Matt Wedel recently
> stated on SVPOW in a review of Sideshow's Apatosaurus maquette; “It is
> worth keeping mind, however, that anatomy is not destiny (Smith and
> Redford 1990); the behavior of living animals is often more varied
> than their skeletal form might suggest, and in some cases
> morphological specialization can lead to ecological generalization....
> Just pointing out that certain kinds of morphological specializations
> broaden, rather than narrow, the ecological opportunities of the
> animals that bear them."
> I’ll raise a full stein of Leffe to that.
> Theories like RPR, coupled with the theme of morphological
> specializations broadening ecological opportunity, successfully gnaw
> away arguments about theropods automatically being banned from
> arboreal or scansorial behaviours unless they had the exact required
> claw geometry, or the perfect toe placement, or the perfect limb
> length ratios, or the perfect joint flexibility, or the perfect
> anything... especially since these arguments are often based on
> standards using highly derived or specialized forms.
> What’s sexy about all of this is that it culminates as an inescapable
> conclusion; the search for "refined" arboreal/scansorial adaptations
> in protobirds is just a tad bit premature. We are so driven to find
> that neat, orderly pattern... that elusive “trajectory” composed of
> straight-forward, categorizable, easily defined, dot-connecting, steps
> that our poor brains so desperately want to recognize... that we
> forget nature isn’t always so predictable, orderly, or neat.
> “Novelties” like exaptation really toss in a monkey wrench... but this
> type of crazy thing shouldn’t be unexpected. After all, how more
> radical can you get than taking a cursorial animal and putting it into
> the air???
> Kris
> On Thu, Dec 15, 2011 at 8:31 AM, Jaime Headden <qi_leong@hotmail.com> wrote:
>>   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 online here: 
>> http://qilong.wordpress.com/2011/12/14/i-cannot-compel-to-reason-triceratops-we-done-it-again/)
>>  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.
>> Cheers,
>>  Jaime A. Headden
>>  The Bite Stuff (site v2)
>>  http://qilong.wordpress.com/
>> "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 
>> Backs)
>> ----------------------------------------
>>> Date: Thu, 15 Dec 2011 17:52:41 +1100
>>> From: tijawi@gmail.com
>>> To: dinosaur@usc.edu
>>> 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
>>> troodontids.
>>> (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?
>>> Cheers
>>> Tim