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INTRODUCING Microraptor gui (or Cryptovolans pauli, or Microraptor pauli, or...)



Greetings,

Just saw that the paper is available on line, so I can talk about:

Xu, X., Z. Zhou, X. Wang, X. Kuang, F. Zhang & X. Du. 2003. Four-winged
dinosaurs from China. Nature 421: 335-340.

(If you get Nature online, check it out at:
http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v421/n6921/f
ull/nature01342_fs.html).

This paper introduces _Microraptor gui_ (after paleontologist Gu Zhiwei), a
new species of _Microraptor_ from the Juifotang Fm. at Dapingfang, Chaoyang
County, western Liaoning.  (The Juifotang is stratigraphically above the
Yixian).

There is a wonderful holotype specimen (IVPP V13352) and a number of
referred specimen.  These show that this animal clearly had long pennaceous
feathers attached to the arms AND to the legs, the latter running all the
way down the length of the metatarsus!!

Hmmm...  Sounds familiar.  Like a previously described dromaeosaur from the
Jiufotang, illustrated but unnamed by Norell et al. 2002 (Nature 416: 36-37)
and later serving as the holotype of Czerkas, Zhang, Li & Li's _Cryptovolans
pauli_. In fact, these taxa are VERY similar: in fact, I strongly suspect
they are the same taxon, and that when the taxonomic dust settles this
species will be _Microraptor pauli_ (if the Czerkas et al. paper is accepted
as valid taxonomic literature: if not, it's _M. gui_).  Unfortunately, the
_C. pauli_ type is never addressed in this new paper.

Like _Microraptor zhaoianus_ and the _C. pauli_ type, _M. gui_ has:
metacarpal III subequal to metacarpal II in length; extremely short manual
phalanx III-2 that is less than one-quarter of manual III-1 length; manual
III-3 extremely slender and shorter than III-1 in length, and small distal
articulation of manual III-3 skewed ventrally (okay, the last one can't be
evaluated in _C. pauli_).  They distinguish it from _M. zhaoianus_ by a
prominent biceps tuberocity is present close to the proximal end of the
radius (hard to interpret in the photos I have of _C. pauli_) and a
proportionately very short manual digit I (metacarpal I + phalanx
I-1/metacarpal II length ratio is 0.80?0.84).  This latter feature IS
different between _M. gui_ and _C. pauli_, so make of it what you will...

Now, for the big interpretation.  Xu et al. consider the elongated leg wing
feathers as gliding supports, and have a restoration of _Microraptor_ with
its leg splayed out to the side.  I find this very questionable, given that
there is no particular evidence that _Microraptor_ to move into this
position (which in your typical dinosaur would require popping the femoral
head out of the socket).

No, I don't have any good alternative explanation for the elongated leg
feathers.  Rudder?  Aid in prey capture?  Display?  Genetic link by serial
homology with the arm feathers?  Nevertheless, given the constraints of the
pelvic anatomy, I do not see how the leg feathers could be used as a
laterally-oriented flight surface.

There is a News & Views accompanying the article:
Prum, R.O. 2003. Palaeontology: Dinosaurs take to the air. Nature
421:323-324.

In it (as in Xu et al.'s paper), the suggestion is made that maniraptorans
went through a four-winged gliding tetrapteryx stage, as suggested 90 years
ago or so by Beebe.  However, Prum mentions an alternative: that leg "wings"
are merely a dromaeosaur trait.  I would add that given that none of the
basal birds for which wing impressions are known (_Archaeopteryx_ and the
Liaoning birds), and given that none of other non-dromaeosaurids for which
feather impressions are known, show this feature, that the current simplest
best explanation is that these were not present in a group more inclusive
than Deinonychosauria, and possibly as exclusive as _Microraptor_.

Very cool things.  And still more on the way... :-)

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796