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RE: Gansus Bird-Dino Connection - Penn Press Release

"The enantiornitheans had the best adaptations for perching, so they were able to dominate the ecological niche that we would associate with songbirds, cuckoos, woodpeckers or birds of prey," Harris said. "Gansus appears to have had adaptations for a lifestyle centered around water, based on things like the proportions of the leg and foot bones."
While the enantiornitheans are now long gone, their perching lifestyle has now been taken over by the descendents of birds like Gansus.

I don't think this point gets emphasized enough. There is precious little evidence for perching in the vast majority of Mesozoic birds - the perching enantiornitheans are the exception. The feet of certain enantiornitheans (avisaurids) show perching specializations, though the retroverted hallux was achieved in a very different manner to that of modern perching birds. Confuciusornithids (maybe) show some adaptations for perching. But the rest (including _Archaeopteryx_, other enantiornitheans, basal ornithuromorphs, basal ornithurans) show no perching adaptations at all.

For ornithuromorphs, a perching pes does not appear until quite late in their evolution, well into the crown-group Neornithes. The most basal neornithean group to exhibit perching might be certain galloanserine birds that roost in trees - like modern tree-ducks, or guans. Either perching ornithuromorphs were around in the Mesozoic, and the fossil record is doing a really good job keeping them secret; or this is a relatively recent innovation for this group, and ornithurans (as neognaths) did not venture into the trees until the Cenozoic.