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RE: Our current understanding of Mesozoic bird phylogeny
I coded Enaliornis based on Galton and Martin (2002) and it came out as
sister to Ornithurae sensu Chiappe. This is due to it lacking dorsal
central fossae, having a shallow tibiotarsal intercondylar fossa, and a
rounded distal articular surface of metatarsal II. Placing it in
Hesperornithes is one step longer, and as several hesperornithine characters
it has weren't in the matrix (short broad femur; elongate triangular cnemial
crest; proximally deep tarsometatarsus; dorsolateral ridge on metatarsal
IV), it is most parsimoniously a hesperornithine. When constrained to be a
hesperornithine, synapomorphies of that clade are- dorsal series completely
heterocoelous; intercotylar eminence on tarsometatarsus; metatarsal IV
projects distally past III. Gansus has the same position (sister taxon of
Carinatae) whether Enaliornis is a hesperornithine or not.
I also decided to code Potamornis and Asiahesperornis. Asiahesperornis is
sister to Hesperornis based on the wide metatarsal IV; while Potamornis is
at least as derived as Apsaravis, but outside Gansus+Carinatae.
evelyn sobielski wrote-
What about _Yungavolucris_? The specimen does not look
like it walked a lot but IIRC it's neither too well
adapted for perching. Is there anything Mesozoic
around which has similar proportions? (Is there
*anything* with similar proportions?)
Hesperornithines, Boluochia and Longipteryx all have metatarsal IV longer
than III (as was probably the case for Yungavolucris), though the former was
opposite in what metatarsals it reduced in width. Of course, what reason is
there to think Yungavolucris was an avisaurid?
Geography suggests against it though, or else
ocean-crossing ability would have been present before
the full mobility of the shoulder girdle evolved (it
was not yet present in _Confuciusornis_, preventing an
effective, modern-bird-type recovery stroke).
We really don't have an idea of the geographical range of confuciusornithids
outside of Liaoning and North Korea. What really suggests the
enantiornithine identity is the presence of so many other apparently
enantiornithine elements in the El Brete assemblage, though I think an
ornithurine bone was found there too.