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Re: Question about Archaeopteryx's (non) reversed hallux

Jaime Headden wrote:

Yeah, even *Confuciusornis* has a retroverted hallux.

Somewhat. _Confuciusornis_ has an intermediate morphology, with the hallux directed medially or slightly posteromedially - according to Middleton's thesis.

So this attribution holds for pretty much all of Pygostylia.

I'm not so sure about that. Most basal euornithines (ornithuromorphs) do not have a retroverted hallux. I think _Gansus_ has one (although the hallux is too short to be have been much use for perching), but _Yixianornis_ does not. It doen't help that the hallucal condition is unknown or undescribed for most non-neornithean euornitheans.

Non-avisaurid enantiornitheans (including _Sinornis_ & _Concornis_) have a similar hallucal morphology to confuciusornithids, suggesting a medial (or slightly posteromedial) orientation. Avisaurids show a unique condition, in which the end of metatarsal I is bent and the shaft is not twisted as in neornitheans.