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Re: climbing dromaeosaurs and friends



Everybody,
The problem isn't simply whether or not maniraptorans could climb trees (and in this regard, I think Gishlick's analysis is pretty good) but whether they were arboreal _scannsors_. And they couldn't have been. As I mentioned (briefly) in my talk at SVP, the parasagital limbs of theropods put their center of mass too far away from the substrate (branches) to have been succesful scannsors. If they had tried to jump from branch to branch, they would have fallen on the very first try. This appears to have been true even of Archaeopteryx, and it is unlikely that early birds were arboreal themselves until they evolved a degree of control that allowed for low speed landings.
Of course it's fair to question whether perhaps some theropod limbs didn't operate in a parasagital plane; Larry Martin has suggested that Arcaheopteryx limbs were "monkey-like" in their articulation. The utter lack of acceptance of this idea is evidence itseld, but taphanomically it's also pretty unambiguous. All of the Archeo specimens, despite their myriad preservational positions, preserve the hind limbs in a parasagital plane (even when the forelimbs aren't). Yet the far majority of articulated Solenhofen pterosaurs are preserved with the hind limbs in separate planes of articulation. Clearly something functional is different between these taxa.
So what of all the papers (e.g. Feduccia) that suggest that Archeo was a percher, and now perhaps Microraptor was also a good climber? It's a load of dingos kidneys, I'm afraid. All of the pretty diagrams comparing Archeo claws to perching birds, running birds, etc. always fail to include falconiformes, which use their claws for prey manipulation. When these critter are included, as in the study presented by Kenworthy, Chapman, Holtze, and Sadlier, Archeo groups much better with prey-manipulation claws than it does with perching claws. In fact, I would go so far as to suggest that the retroverted hallux evolved for prey manipulation long before it was useful for perching, although this evolutionary novelty certainly pre-adapted birds for a perching lifestyle.


Well, that's long enough for now, I'll rant on birds and arboreality again later.

Cheers,

Scott
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