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Re: 11th specimen of Archaeopteryx‏



On Nov 7, 2011, at 4:17 PM, Jaime Headden wrote:

> 
>   Manning et al. say nothing about "perching." That paper noted that when 
> used to penetrate a relatively persistent substrate (using flesh but also 
> projecting to wood, and tested against flesh), the claw is useful for 
> climbing and was not necessarily effective for "slashing." This is not 
> entirely consistent with arboreality, although that is possible, because 
> climbing birds do not use just one ungual for climbing, they use all 
> forward-projecting unguals, and this is not evident in dromaeosaurids. In 
> birds, while the unguals are graded largest to smallest moving from toe two 
> through toe four, then toe one, the unguals even in raptorial birds are 
> relatively similar in size (cassowaries are freaks with straight pdII-3u's, 
> ignore them); in dromaeosaurids, the pdII-3u is often twice the length of any 
> other ungual, a suspiciously bizarre distinction that enforces a functional 
> difference, especially in the strong curvature relative to the other unguals. 
> And recall, despite the huge!

And yet would we expect transitional forms - say basal avialans or basal 
paravians, if either or both of them were experimenting with tree climbing - to 
have the precise same adaptations as their later descendants? At first wouldn't 
we would expect a radiation of different adaptations and then a winnowing down 
to a large diversity of species but only a subset of the former disparity?

In other words, transitional forms that were adapting to tree climbing would 
not be expected to instantly possess a fully reversed hallux and toe claws with 
all the same proportions as in neornithines. We would expect them to have some 
changes from the ancestral morphology, and in fact Paravians and, especially, 
basal avialans do.

> 
> 
> pdII-3u, the other pedal unguals are _terrestrially_ adapted, even in 
> *Archaeopteryx lithographica*. Moreover, it is questionable how one arrives 
> at a conclusion that the highly recurved, huge forward ungual is indicative 
> of "perching" or arboreality to begin with, merely that climbing is _not_ 
> excluded.

No one should decide that the second toe of Microraptor is indicative of 
perching. However, it is possible that the well - documented hypertrophied 
flexor processes and hypertrophied ungual could allow the animal to clamp a 
branch between the point of the claw and the metatarsals. It is surprising to 
me that, despite all the debate about arboreality in Microraptor, no one seems 
to have analyzed the range of motion in the foot for maximum flexion.

> 
> 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: Mon, 7 Nov 2011 20:23:22 +0000
>> From: ssselberg@hotmail.com
>> To: dinosaur@usc.edu
>> Subject: RE: 11th specimen of Archaeopteryx‏
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> 
>> Sorry, I had a copy of the Manning study (Manning et al. (2006, "Dinosaur 
>> killer claws or climbing crampons?")at home but had lost the title 
>> page...But my question still stands: IF the sickle claw allowed the animal 
>> to perch, " wouldn't that have made a reversed hallux redundant, and also 
>> allowed the third and fourth toes to retain their more corsorial 
>> proportions?" This is important because if, as is now being postulated, the 
>> ancestors of birds were or were in the process of becoming herbivores, the 
>> sickle may have been lost. This could tip the balance in favor of a reversed 
>> hallux and a more "bird shaped" foot and eventually, the loss of clawed 
>> hands.
>> 
>> 
>> 
>> In spite of the tone of the rest of my letter, my real interest wasn't 
>> whether or not deinonychosaurs were arboreal. Personally I think that 
>> various species exhibited a wide range of behaviors, of course. I'm more 
>> interested in the deinonychosaur foot as a sort of all-purpose tool, good 
>> for but not specialized in any one task. I mean, are a cat's retractable 
>> claws “for” gripping prey, climbing, or fighting off predators and rivals( 
>> or burying poop)? I do think however that too much importance has been 
>> placed on a reversed hallux as evidence of whether or not an animal spent 
>> time in trees.
>> 
>> Scott Selberg
>                                         

Jason Brougham
Senior Principal Preparator
American Museum of Natural History
jaseb@amnh.org
(212) 496 3544