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Re: flying Archie

Don Ohmes wrote:

An alternative "bottleneck" evolutionary path to the gradual terrestrial transition scenario; abandonment of terrestrial locomotion entirely (perhaps/probably for an aquatic environment), and then after the avian bodystyle was well-established, re-invasion of the terrestrial environment.
Flight superiority well in wing, so to speak. No worries about center-of-mass issues relative to the hindlimbs during "remodeling" there.

Yes, that's possibly what happened. The modern avian body plan (including the short tail) appears to be primitive for the Ornithothoraces, and so precedes the Enantiornithes-Euornithes split. There are many basal euornithean birds that appear to have been adapted to an aquatic environment (_Archaeorhynchus_, _Yanornis_, _Yixianornis_, _Gansus_, _Hongshanornis_, _Ichthyornis_, Hesperornithiformes). Also, we know that that confuciusornithids fed on fish (Dalsatt et al., 2006). So an aquatic ecology might have facilitated evolution of the modern avian body plan ('remodeling', as you nicely put it) in ornithothoracean birds.

For the above to be true, the arboreal adaptations of enantiornitheans would be derived relative to the basal ornithothoracean condition. This requires that enantiornithean birds headed out of the water, and up into the trees long before the euornitheans (including neornitheans) did. In support of this, the perching adaptations of enantiornitheans (especially the avisaurids) are very different to those of neornitheans, so arboreal perching almost certainly evolved independently in these two lineages.