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Re: Iguanodon(?) sp. and Jixiangornis



Nick Gardner wrote-

> The premaxilla is not tapered rostrally.  The maxilla contacts external
> naris. Nasals are rostrodorsally depressed (?). Premaxillary teeth absent
> are absent.  Maxillary teeth are absent.  The antorbital fenestra has not
> been lost.

A very strange skull.  Reminds me of Caudipteryx, with the unbird-like
rounded premaxilla.  Funny how all these oviraptorosaur-like basal birds are
showing up now (Shenzhouraptor, Omnivoropteryx), alongside the
dromaeosaur-like ones.  The skull is seems to resemble nemegtosaurs in the
orbit's position and shape, and laterotemporal fenestra extending anteriorly
below the orbit.  The antorbital fenestra is also shown extending below the
orbit, with a large maxillary fenestra anteriorly.  Nasals are short, as
expected, but the narial region is obscure.  No less than three possible
narial openings are present, and the configuration of bones around them is
uncertain.  The naris seems not to be above the maxillary fenestra, unlike
oviraptorosaurs, if everything here is properly identified and articulated.
The orbit is really much too small for a maniraptoriform and located far too
high up.  There is a supposed jugal wrapping caudally around the antorbital
fenestra and possessing a prominent dorsal process that would make part of a
complete postorbital bar.  Now, I think the skull is misinterpreted.  The
orbit and antorbital fenestra are probably both part of a larger crushed
orbit.  The maxillary fenestra would then be the real antorbital fenestra,
and the jugal would be a palatal bone (ectopterygoid and/or pterygoid).

> The dentary teeth are absent.  The dentary is rostroventrally curved.  The
> external mandibular fenestra is present.  The dentary is ~60-75% of
> mandibular length.  The posteroventral process of the dentary is very
long,
> and extends for most of the length of the external mandibular fenestra.

An enlarged surangular foramen is also there.  There seem to be nine
cervicals reported, eight dorsals, seven sacrals and twenty-seven caudals.

> There are quadrangular lateral processes on sternum.  The sternal plates
are
> ossified and co-fused with a midline keel.  The furculae is robust and
> U-shaped.  The acromion process of the scapula appears to be prominent,
> triangular, and perhaps cranioventrally directed.  The superficial
surfaces
> of coracoid face anteriorly.  There are ossified uncinate processes.

No hypocleideum on the furcula, but a surprisingly small interclavicular
angle.  Coracoids are more strut-like than Jeholornis, being comparable to
Eoenantiornis (not convex laterally though).  I think the coracoids are
displaced posteriorly compared to the sternum, so that their true
orientation is uncertain.  Very small anteriorly projecting pointed
acromion, probably not contacting the coracoid.  There are 4-5 sternal ribs
and 13-14 rows of gastralia.

> The metacarpals are not fused to each other or to the semilunate carpal.
> The semilunate carpal covers the proximal bases of metacarpals I, II, and
> III.  Metacarpal I is 10% or less the length of metacarpal II.  Metacarpal
> III is bowed posterolaterally.  Manual phalanx I-1 is slightly bowed.
Manual
> ungual I is shorter than manual ungual II, and less curved.  Manual
> phalanges II-1 and II-2 are nearly subequal.  Only III-3 and the ungual as
> far as the phalanges go for manual digit III.  Manual phalanx II-1 is
> expanded transversely.  The ulna is longer than the humerus.  The humerus
> appears to have a hatchet-shaped deltopectoral crest.

The first digit is subequal mcII, like Omnivoropteryx and Sapeornis.
Phalanx II-1 is slightly longer than II-2 (22.7 mm vs. 21.1).  Metacarpal
III actually reaches slightly past metacarpal II.  Digit III seems very
reduced in width, with a tiny ungual.

> The astragalus and calcaneum are proximally fused to the tibia, but I
> presume not to each other since they are referred to as separate elements?
> The metatarsus is proximally fused to each other and to the distal
tarsals.
> The hallux is retroverted.  Pedal ungual II is larger and more curved than
> III.  Pedal phalanx II-1 is shorter (~75%) than II-2.  Pedal digit IV is
> nearly as long as III and much longer than II.  The distalmost phalanges
are
> the longest in all the digits.  I cannot tell if pedal digit II is
> hyperextendible.  The tibia is longer than femur.

The hallux is also disarticulated from the metatarsal, making the
retroversion suspect.

> -- Avialae
>       |-- Archaeopteryx
>       `-- Orthavialae
>           |-- Shenzhouraptor
>           `-- Euavialae
>               |-- Jixiangornis
>               `-- Pygostylia
>                   |-- Confuciusornithidae
>                   `--+-- Enantiornithes
>                      `-- Ornithurae
>                          `-- Aves

At least Orthavialae will be a useful term for the clade containing
Rahonavis, Shenzhouraptor (=Jeholornis), Yandangornis, Jixiangornis,
Sapeornis, Omnivoropteryx and Pygostylia.  Euavialae might just contain the
last five.  I'd place Jixiangornis in the Yandangornithidae pending a
phylogenetic analysis.

Mickey Mortimer