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Re: Enantiornithines and Iberomesornis



Jaime Headden wrote-

> Mickey Mortimer (Mickey_Mortimer111@msn.com) wrote:
>
> <Regardless of the likely paraphyly of enantiornithines as currently
> conceived, the characters used by Sanz (1988, 1995) and Chiappe (1995) to
> place Iberomesornis below their level have been nicely eliminated by
> Sereno (2000).
>
>  - The posterior cervicals of enantiornithines (eg. Eoalulavis, Catalan
> nestling) are also amphicoelous.>
>
>   This is true of many birds, as in *Confuciusornis* and more advanced
> birds.

Actually, Confuciusornis has semi-heterocoelous posterior cervicals (Chiappe
et al., 1999), similar to the anterior cervicals of the Catalan nestling.
Yandangornis has been reported to have amphicoelous cervicals in Cai and
Zhao's rather poor description of the taxon.  The only other birds I know of
with supposedly amphicoelous cervicals are described by Hou (Jibeinia,
Longchengornis, Chaoyangia).  As he does not distinguish the
semi-heterocoelous centra of Confuciusornis from amphicoely either, and as
more basal taxa (Sapeornis, Jeholornis) have the semi-heterocoelous
condition, I do not trust that these taxa actually have fully amphicoelous
cervicals.
What's important is that since Chiappe's and Sanz's older studies were done,
it's been shown that partial heterocoely developed first in birds more basal
than Iberomesornis (probably at the Jeholornis level), while full
heterocoely seems to have first evolved in ornithuromorphs.  So this is not
a valid character to keep Iberomesornis below enantiornithines.

> <- Prominent hypapophyses are present on the last cervical and the first
> three dorsals.>
>
>   This is a synapomorphy of the Oviraptorosauria + bird clade, is it not?
> With significant appearance in later birds, suggesting multiple loss to
> reduce neck flexibility or length, as in possibly dromaeosaurids, etc..

Probably, but lots of members of that clade lack it (segnosaurs,
Microvenator, Sinovenator, Deinonychus, Microraptor, Archaeopteryx,
Sinornis, Apsaravis).  It's also probably found in Ornitholestes, and in
mononykines (which may be members of this clade).  It doesn't seem
correlated to neck length.  Again, it's not a valid character to keep
Iberomesornis below enantiornithines.

> < - There are eight, not five sacrals.>
>
>   Lü et al. pointed out that nearly all pygostylians have more than seven
> sacrals at adulthood.

Yes, all except Protopteryx and perhaps Cuspirostrisornis.

> < - The scapulacoracoid articulation is not preserved.
>   - The transverse groove across the humeral head is not definitely
>  present, but is variable in enantiornithines anyway.
>   - The radial condyle is not preserved, and the ulnar condyle seems to
> round on to the anterior side of the humerus.
>   - Pelvic fusion is variable in enantiornithines, and partially developed
> in Iberomesornis.>
>
>   This data tells us nothing, unfortunately.

Agreed.

> <- The proximal tarsals are completely fused to the tibia.
>   - There are no free distal tarsals.>
>
>   As in most ornithurines, I beleive.

Not only ornithurines, but nearly all pygostylians.  Jibeinia, Protopteryx
and Longipteryx retain unfused tarsals though, making their fusion in
confuciusornithids most parsimoniously considered a convergence.

> <Thus, the "alternate hypothesis" of placing Iberomesornis basal to
> classic enants like Sinornis, Eoalulavis and Concornis is effectively
> dead.>
>
>   I beg to differ. And the Enantiornithiformes has been considered the
> only stable clade within the group, whereas the others are easily unstable
> and may reflect the reason why cladistics has found such weak evidence for
> placing them there. Have you looked at the bootstrap values?

Well, you've presented no evidence that Ibermesornis is more basal than
"classic enants", and have not refuted Sereno's objections to Sanz's and
Chiappe's pre-2001 characters suggesting such.
An "Enantiornithiformes" has never been described from a cladistic analysis.
Have you looked at the literature? ;-)

Mickey Mortimer