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Re: 11th specimen of Archaeopteryx



On 11/1/2011 3:00 AM, Tim Williams wrote:
The selection pressure
for paravians to evolve a perching pes cannot have been very strong,
given that it is not until long after wings first appeared that we see
even incipient development of a reversed hallux (around the
confuciusornithid/sapeornithid level of avian evolution).


1) Perching came prior to reversal (repeating Jason's point).
2) An animal that forages cursively has cursively foraging feet, so to speak -- one would not expect the basal pes condition to be rapidly re-arranged while a cursorial lifestyle was still conserving it -- especially just to get a good night's sleep. A slow transition to full-on arboreality, which is what reversal of the toe represents, is not surprising, any more than the gradual transition to the knee-walking condition is. Implied is that all modern cursorial birds are secondarily so -- which hardly seems controversial. 3) The difficulty an Archie-type animal would encounter not-falling-while-sleeping has been wildly exaggerated. 4) The negative consequences of an occasional fall by a feathered animal that could likely fly at least a little and could certainly glide seem minimal -- much less negative than being stomped or eaten on a dark night. 5) Perhaps Archie was alone on his island, but I think it a safe assumption that Archie's ancestors/siblings had predators -- and not ones that stood 8m tall, either.

Looking at the generic theropod skeleton and wondering what modifications you could install to make the poor thing arboreal w/out starving him leads to this -- give him wings. Once he can fly, then you can mess around w/ his feet.