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Re: Yet more on pterosaur quad arm posture



David, that bird was successfully feeding on what I believe are
Corynocarpus fruits about a meter off the ground. I am trying to discuss
the benefits to animals of very limited elevated habitats such as these.
So, yes, it counts as what I am calling climbing.


As for the 40 million year interval, that is surely an artifact. By the
time we see anything with a fully reversed hallux it is the Barremian, and
birds have already radiated and diversified. Basal avialans,
enantiornithines and ornithurines all had memebres with reversed halluces
already. I would bet most workers imagine the radiation beginning in the
Lat Jurassic, closer to these basal paravians.

You make  a good point about parallel halluces. They are very close to
parallel in Epidendrosaurus, right? And in Turner et al. 2012 they find
Epidexipteryx may be very close to the last common ancestor of Paraves
(figure 57).

>> It counts as climbing.
>
>Hopping from branch to branch (and repeatedly falling off) counts as
>climbing?
>
>...
>
>*lightbulb moment*
>
>...Uh, sorry. This might be a linguistic misunderstanding. In English you
>"climb" stairs, and you can "climb" a mountain by just walking up instead
>of pulling yourself up a rock face; German has a more specialized word,
>and that's what I had in mind all this time.
>
>> Again, for perching adaptations to evolve, there was a population of
>>animals that went into elevated perches WITHOUT such adaptations, and
>>that provided the selection pressure for them to evolve. Were basal
>>paravians all doing that, and did it take until, say the Sapeornis node
>>in Avialae for the arboreal adaptations to arise?
>
>Well, if they were all doing that for 40 million years till that node,
>I'd expect some adaptations to arise earlier than that.
>
>> The only other way it could have happened is if there were exaptations,
>>such as gripping feet (Fowler et al. 2011), that allowed elevated
>>perches and were later replaced by reversed halluces. This exaptation is
>>reported for dromaeosaurs, which are also paravians.
>
>And it makes plenty of sense. Indeed, the hallux already isn't perfectly
>parallel to the 3rd toe in those dromaeosaurs -- all claw tips converge
>during flexion.
>
>> And, when we ask what good the intermediate stages of flapping flight
>>would be, a valid answer is "to get 1 meter off the ground into a low
>>roost", because living basal birds (tinamous, galliforms, anatids) still
>>share the character of roosting this way.
>
>Very good point.