Re: Yixianosaurus longimanus, a Peculiarly Normal Yixian Theropod

["Jaime A. Headden" <qilongia@yahoo.com>]

Luis Rey (luisrey@ndirect.co.uk) wrote:

<One thing that so far I don't think has been stressed enough is that the
overall length of the arms is extremely short . It may be compared to the
actual hands, but .... And those claws... enormous!  I have the PDF of the
paper and it is just remarkable. I do think it is important because this
is yet another variant missing from the puzzle. We have seen it all
(almost) in the enormous mosaic of bird evolution that is coming from the
Liaoning Province. Long tails and incipiently fused digits, fully
functional clawed hands and pygostiles, beaks and jaws with teeth mixed
with primitive and advanced bird features; aye aye-like creatures (with
elongated third finger),  four winged creatures and now typical
dinosaurian long hands and short arms.  The more discoveries the more the
picture of avian evolution gets complicated.>

  I think as more fossils are found, the basal maniraptoran branches will
show more complex variations than will the basal avian branches. This is
largely because at the base of Maniraptora, we have short arms,
large-handed, slightly-folding wristed, "normal"-hipped animals that have
complex cranial variations. Rather, basal birds vary in their cranial
features and limb proportions more than anything else. Long tails mix with
short, but in more basal maniraptorans, we get short, long, mid-length
tails, all within single groups such as Oviraptorosauria, specializations
to climbing, gliding, and cursors, as in Dromaeosauridae, and even more
specializations than basal birds show. The root of the maniraptoran tree
seems more prone to full skeletal variation than does the basal bird
group, and the evolution of flight seems to have begun and formed in its
mosaic prior to birds, and this is an aspect that has been and should be
stressed. Luis is right, the arms are really rather short with just huge
hands and claws, perhaps recalling the proportions of segnosaurs like
*Beipiaosaurus* (from which *Yixianosaurus* differs in various significant
manual and humeral and carpal ways).

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

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

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