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Re: On the Issue of Sprawling Dromaeosaurs



David Marjanovic wrote:

I still don't know why everyone seems to assume that *Microraptor* and the
like were arboreal. The 1st toe was a bit longer than usual, but still
short, and its position is unknown; the phalangeal proportions are still on
the terrestrial side;

I don't know that "everyone" assumes that _Microraptor_ was arboreal, but a lot of people believe it probably spent at least part of its time in trees (including myself). The elongate penultimate phalanges and the slender and recurved pedal claws are comparable to modern perching birds; and although the orientation of the hallux is unclear, the first metatarsal and the first pedal digit have shifted further down on the foot. This allowed improved opposability, but it is not specialized for anisodactyl perching. Then again, a specialized perching pes had to come from something, and the pedes of _Microraptor_ and _Archaeopteryx_ show an incipient stage in its development.


the body size means nothing; and the foot feathers
could or could not have hindered running, we don't know, because we don't
know if the feathers were foldable (among other things).

The "foot feathers" might or might not have hindered running. But what were they there for, if not for aerial locomotion? Even those who argue that _Microraptor_ might have been a powered flier have not gone so far as to suggest that _Microraptor_ was capable of a ground-level takeoff. Therefore, _Microraptor_ required an elevated platform from which to launch itself into the air. In light of the derived pedal morphology, trees appear to me to be a pretty good candidate for this.


True, body size alone means nothing. Until we find a _Microraptor_ specimen with its foot wrapped around a fossilized tree-branch, we have no direct 'proof' that _Microraptor_ spent time in the trees. But combining all the characters mentioned above (small body size; pedal moprhology; plumage), one has to wonder if all these *derived* theropod characters might be tuned toward the same ecomorphology. I think we can build a highly circumstantial and parsimonious case that they are - in this case, tree-climbing + aerial locomotion.


Tim

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