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

[Jaime Headden <qi_leong@hotmail.com>]

  Mickey and I had an extensive conversation on the nature of the hallucial 
orientation of *Scansoriopteryx heilmanni* (including the type of 
*Epidendrosaurus ningchengensis*), mostly offlist. We were, at the time, 
running the specimens through various matrices and discussed the codings each 
was doing (our analyses each differed on the position, but both of us presented 
our data on the list). 

  The pes of CAGS02-IG-gausa-1, holotype of *Scansoriopteryx heilmanni* 
preserves a distinct hallux; it is positioned very distally on the pes and is 
about as far from the distal end of MTII as the distal end of MTII is from 
MTIII, and those are pretty close in length and relative position; the distal 
end is NOT twisted, and the authors illustrate the medial ligament pit exposed 
in dorsal (extensor) view and it preserves no trace of a transverse ridge that 
indicates it would have faced in any direction other than the normal; there is 
no space between MTI and MTII to imply the two are reasonably dislocated, 
although it is possible as similar features have occluded the hallucial 
orientation in *Archaeopteryx lithographica* (although resolved using 
Middleton's unpublished criteria); pdI-1 is oriented with the dorsal margin 
apparently rotated slightly medially and thus as it is splayed outward also 
proximal to the metatarsus, and the dorsal extent of the extensor groove 
between condyles is visible, such that the phalanx is disarticulated and 
slightly rotated, but MTI is not.

  The hallux is elongated, with pdII-1 nearly the same length as both pdII-1 
and pdIII-1, and longer than pdIV-1; it is longer than pdII-2, pdIII-3 and 
pdIV-4, and thus conforms to many scansorial proportions of the pes, although 
the unguals are shallowly curved. The penultimate phalanges are as long or 
longer than the proximalmost phalanges, an indicator of scansorial and arboreal 
adaptations (but these have nothing to do with flight, and occurs in extant 
tree sloths and brachiating apes).

  The pes of IVPP V12653 (holotype of *Epidendrosaurus ningchengensis*) is 
nearly identical, although the hallucial ungual is oriented the opposite of the 
other three digits, and is articulated to the proximal phalanx, although MTI 
appears to be somewhat separated distally to MTII.

  Both specimens are juveniles, and do not represent what may be inferred for 
adults (as we all know, adults and juveniles have sometimes divergent modus 
habiti).

  While larger, the holotype of *Epidexipteryx hui* (IVPP V15471) lacks most of 
its phalanges and one pes, preserving a single pdI-1, although there is no 
indication of a MTI, and the phalanx is oriented alongside and parallel to the 
metatarsals and not divergent as in the other two specimens.

  I want to stress some things about the evolution of scansoriopterygids 
because, while I have no opinion of whether they _can_ be avialaeans, avians, 
or whatever, several features of their anatomy point in odd directions, most 
notably that un-dromaeosaur-like pelvis (short pubis, LONG ischium, what 
appears to be a broad brevis shelf with little or not cuppedicus shelf of the 
ilium, no or very proximal obturator process of the ischium rather than distal 
and large, a propubic or mesopubic orientation of the pubis), but also a 
broadly expanded distal end of the scapula without any hint of becoming 
strap-like and actually quite different from most *Maniraptora*, while the 
coracoid possesses both a large proximal acrocoracoid tubercle positioned 
midwall along the coracoid length (position-neutral orientation) and what may 
be a lack of a laterally oriented coracoid glenoid (Mickey and I differed on 
this issue, which led to different codings for the orientation of the coracoid 
as we also both perceived the scapular fragment of CAGS02-IG-gausa-1 different, 
and which IVPP V15471 implies may be resolved as something that looks more 
compsognathid-like than maniraptoran-like); the femoral caput has no 
differentiated neck, and was likely fully parasagittal, the fibula is extremely 
reduced in diameter distal to the fibular crest of the tibia, although the 
proximal tarsals are not clearly differentiation; and then there's the 
abbreviated caudal series, although it is shorter in IVPP V15471 than in 
CAGS02-IG-gausa-1 and lacks any trace of a pygostyle, or elongated 
prezygapophyses in IVPP V15471.

  I don't know where these taxa sit in the theropodan tree (although clearly 
*Coelurosauria* and likely *Maniraptoriforms*, but some particularly basal 
features mixed with derived imply that it can be degenerate to an earlier 
condition in some portions of its anatomy, "experimented" in high school with 
the chem lab, or convergent with other taxa in some features. Some features are 
not known to "reverse" in flightless birds, especially features of the pelvis, 
while others are peculiar on their own and highly divergent (as in the arms). 

  All taxa are pretty derived with regards to virtually any position, and I 
think this strongly hampers results in placing them. Almost certainly many 
things that link them to avialaean maniraptorans and/or somewhere within or 
nearby include proportions of the limbs, the tail abbreviation, and as with my 
discussion with Mickey, assumptions about the shoulder girdle. I am, I think, 
the only one who has reconstructed the coracoid in a more primitive way. We 
will see when IVPP V15471 is described in more detail, along with 
CAGS02-IG-gausa-1.

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
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


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> Date: Wed, 17 Aug 2011 11:31:41 +0200
> From: david.marjanovic@gmx.at
> To: dinosaur@usc.edu
> Subject: Re: Ah ha! That's where therizinosaurs came from
>
> > fossil paravians like _Archaeopteryx_ and _Microraptor_ (which
> > retained a medially-directed hallux)
>
> Oh no. They retain a _cranially_ directed hallux. A medially directed
> one is found in *Confuciusornis* (and for instance the kiwis).
>
> Somebody should have a look at *Changchengornis* and the
> scansoriopterygids. The latter have a pretty long and fully descended
> hallux...