RE: Ah ha! That's where therizinosaurs came from

[Jaime Headden <qi_leong@hotmail.com>]

Ron Orenstein wrote:

<That's the biggest problem with concluding that oviraptorids etc are 
secondarily flightless - where is the unquestionably volant clade into 
which they fit?  Of course it could turn up any day (and I assume Greg 
Paul will argue that it already has, but not everyone has tumbled to it 
yet.)>

  This kind of actually starts with the recovery of *Protarchaeopteryx robusta* 
as an oviraptorosaur, which has arms close to the length of its legs -- which 
are themselves not terribly short. A short tail (<30), although no evidence of 
a pygostyle, adds to the argument that whatever ancestor it had, if we take 
*Caudipteryx zoui* as a descendant, would have had a short tail, long legs, and 
potentially longer arms. Here, we place our taxa on a cline with an even 
longer-armed, short-tailed oviraptorosaur wouldhave existed. Despite that 
separate sternal plates are preserved in both taxa, with short scapulae and 
large, rounded and short coracoids, we might assume that the arm length alone 
with the short tail would be enough to infer "flightness" in the ancestor.

  As Tim Williams continually points out in this debate, and in connection with 
the Dececchia & Larsson paper just recently published by _PLoS ONE_, there must 
be a way to distinguish an actual FLIGHT-character from a character in which 
the function may be related, but not essentially for flight. This is something 
Paul has not done, and which is I think generally futile as there are few taxa 
we can actually assess the mechanical properties of which exhibit these 
features, are not themselves related to actual fliers, and thus can be used to 
discriminate "true" and "apparent" flight characters.

  That said, it has been bandied about that *Omnivoropteryx sinousaorum* 
(Czerkas & Ji, 2002) and taxa like it (*Sapeornthidae*) represent 
oviraptorosaur-like taxa. Wroteth the Mickey 
(http://dml.cmnh.org/2002Sep/msg00668.html):

"Phylogenetic Relationships- The only oviraptorosaur-like characters are the 
short snout, ventrally displaced premaxilla and anterior maxilla, decurved 
dentary and elongate external mandibular fenestra.  The first is common in 
basal birds, especially Jeholornis.  The third is also found in Jaholornis, 
while the third is seen in confuciusornithids.  The second character is not 
known in eumaniraptorans."

  Like sapeornithids, and avialaeans, and unlike oviraptorosaurs, we get things 
such as:

"more than ten
dorsal vertebrae, scapula decreases in wifth distally, acromion does not
project dorsally(?), distal scapular shaft curved to be concave dorsally,
distal humerus strongly curved anteriorly/laterally, radius about 1/2 of
ulnar width, distal radius abruptly expanded, metacarpal I ~1/7 of
metacarpal II length, phalanx I-1 ~1/2 of metacarpal II length, phalanx I-1
slender, phalanx II-2 distally expanded(?), phalanx II-2 shorter than
phalanx II-1, pubic symphysis ~1/3 pubic length, pubic shafts bent
posteriorly around midlength, pubic boot projects mostly posteriorly,
metatarsal V absent(?), elongate metatarsal I, phalanx II-2 subequal in
length to II-1, distal phalanges of pedal digits III and IV elongate
compared to penultimate phalanges.  While a few of these might be expected
in a convergently volant oviraptorosaur, many have no particular relation to
flight."

  So concludeth the Mickey: "So Omnivoropteryx is not a volant oviraptorosaur, 
but is a
eumaniraptoran instead."

  I have a hard time seeing sapeornithids (any of them) as oviraptorsaurs. The 
skulls (e.g., Zhou & Zhang, 2003) are superifically similar (and by 
superficially, I mean cherry-picking specific oviraptorosaurs and ignoring 
others, like for example *Incisivosaurus gauthieri*) but seem to differ in the 
details, or are represented broadly among maniraptorans, like *Scansoriopteryx 
heilmanni* (Czerkas & Yuan, 2002) and *Epidexipteryx hui* (Zhang et al. 2008). 
Needless to say, though, this will not be the last we will hear on this 
subject, as I am sure new future basal oviraptorosaurs will come out, and the 
skull of *Similicaudipteryx yixianensis* (He et al., 2008) has yet to be 
described from recently published new specimens (Xu et al., 2010).

  I have an image in mind which depicts my predicted basal oviraptorosaur, but 
will get into that in some future time.

Czerkas, S. A. & Ji Q. 2002. A preliminary report on an omnivorous volant bird 
from northeast China. in Czerkas (ed.) Feathered Dinosaurs and the Origin of 
Flight. The Dinosaur Museum Journal 1:127-135.
Czerkas, S. A. & Yuan C. 2002. An arboreal maniraptoran from northeast China. 
in Czerkas (ed.) Feathered Dinosaurs and the Origin of Flight. The Dinosaur 
Museum Journal 1:63-95.
He T., Wang X.-l. & Zhou Z.-h. 2008. A new genus and species of caudipterid 
dinosaur from the Lower Cretaceous Jiufotang Formation of western Liaoning, 
China. Vertebrata PalAsiatica 46(3):178-189.
Xu X., Zheng X. & You H.-l. 2010. Exceptional dinosaur fossils show ontogenetic 
development of early feathers. Nature 464:1338-1341.
Zhang, F.-ch., Zhou Z.-h., Xu X., Wang X.-l. & Sullivan, C. 2008. A bizarre 
Jurassic maniraptoran from China with elongate ribbon-like feathers. Nature 
455:1105-1108.
Zhou Z.-h. & Zhang F.-c. 2003. Anatomy of the primitive bird Sapeornis 
chaoyangensis from the Early Cretaceous of Liaoning, China. Canadian Journal of 
Earth Sciences -- Revue canadienne de sciences de la Terre 40:731-747.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
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