Re: Yandangornis

["Mickey Mortimer" <mickey_mortimer@email.msn.com>]

Nick Longrich wrote-

> I dragged up the Yandangornis paper just now. My thoughts-
> This is a maniraptoran.

I concur.  It came out as the sister group to pygostylians in my latest
analysis (see my recent post).

Oviraptorosauria, Caudipteryx, and their probable sister-taxon
> Protarchaeopteryx all have symmetrical feet in which the fourth toe is
> subequal to the second.

How odd.  Just a few hours ago, my newest analysis gave me a cladogram in
which Protarchaeopteryx and oviraptorosaurs are sister groups.  I figured it
wasn't very trustworthy, but now I think we may be on to something...

Although they are not
> hyperelongate as in Archaeopteryx, troodonts, and Rahonavis (something I
> think could argue for a Deinonychosauria-Rahonavis Archaeopteryx clade I
> suspect might exist) they are too long and slender to be from the
> therizinosauroid-oviraptorosaurian clade.

Good call on the caudal vertebra elongation- I have several characters
relating to this in my database that support various combinations of
troodontids, dromaeosaurids, Archaeopteryx, Rahonavis, Ornitholestes and
Compsognathus.

> It is maniraptoran based on:
>  * reduced number of transverse processes (12-13 or fewer)
>  * very low chest/femur length ratio
>  * elongate digit IV
>  * ?semilunate
>  * ?bowed ulna
>
>  It appears to be more derived than velociraptor-archaeopteryx grade
> animals in having:
>  * elongate sternal ribs (actually, not in Confuciusornis so maybe not a
> good character)
>  * reduced manual unguals
>  * shortened manual phalanx II-2,
>  * posteriorly pointing sternal processes.
>
> it appears to fall outside of Confuciusornithidae+Ornithothoraces in
lacking:
> * pygostyle
> * nublike manual ungual II
> * flattened manual digit II

Here's my character analysis (based on the phylogeny from my latest
analysis):

maniraptoran:
- more than two pairs of ventral ribs attach to sternum
- sternal plates exceed coracoids in size (absent in Mononykus,
Sinornithoides lacks ossified sterna)
- opisthopubic pelvis (not synapomorphic of maniraptorans, but only occuring
in them, this is not certain in Yandangornis)
- lesser trochantor not wing-like (it appears to be fused into a
trochanteric crest, which would place it with pygostylians, among other
things- troodontids, Bagaraatan, mononykines, Rahonavis, etc.)

non-segnosaur-oviraptorosaur:
- symphysis not medially inflected (as noted by Nick)

non-oviraptorosaur:
- retroarcticular process not elongate
- transition point present in caudal series

more derived than Bagaraatan:
- less than twelve caudal vertebrae with transverse processes (also in
compsognathids)
- less than nine elongate chevrons (not known in Bagaraatan, but defines the
same group in DELTRAN)
- fourth trochantor absent (present in Velociraptor, Achillobator, Avimimus
and the Patagonykus-Mononykinae group among this clade, but only known in
Microvenator outside of it)

more derived than alvarezsaurs:
- pedal phalanx II-1 less than 90% of pedal phalanx III-1
- pedal phalanx II-2 more than 85% of pedal phalanx II-1 (not present in
Avimimus)

avian:
- less than twenty-five caudal vertebrae (paralleled in Caudipteryx and
mononykines, possibly indicative of a Rahonavis-Aves clade)
- less than nine caudal vertebrae with transverse processes (as noted by
Nick)
- less than seven elongate chevrons (also in troodontids, possibly
indicative of a Rahonavis-Aves clade as well)
- metatarsus fused (also in caenagnathids and Patagonykus, not in Rahonavis)

more derived than Archaeopteryx:
- sternal plates fused (also in Mononykus, uncertain in Archaeopteryx, but
certainly absent in dromaeosaurs)
- sternum longer than wide (same as above)
- fibula does not reach calcaneum (also in troodontids and mononykines, is
again present in Rahonavis)
- tibiotarsus completely fused
- note that the third metatarsal is not compressed proximally, as in
non-tyrannoraptorans, Compsognathus and early birds (confuciusornithids,
enantiornithines, Patagopteryx)
- toothless premaxilla (The way my cladogram comes out, this is more
parsimonious as a reversal in some enantiornithines than as lost in parallel
multiple times within Aves.  If anyone knows of an ornithurine with
premaxillary teeth, please rell me!)
- toothless dentary (The same situation here, it comes out as reversed in
ornithothoracines)

non-pygostylian:
- cervical vertebrae not heterocoelous
- more than twenty caudal vertebrae
- no pygostyle (as noted by Nick)
- no ossified keel on sternum (present in only some specimens of
Confuciusornis)

In addition, it lacks certain characters of more exclusive groups such as:
non-alvarezsaurid (caudals not procoelous)
non-dromaeosaurid (prezygapophyses and chevrons not extremely elongate)

Mickey Mortimer