[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Yixianosaurus in Holtz, 2000
I recently added *Yixianosaurus* for the hell of it, into Holtz (2000) to see
what incarnation of a phylogeny I could get out of it. Of this analysis, only 44
of 386 characters could be coded, roughly 16% of the total. This resulted in
1560 steps, and some few thousand trees. Needless to say, i won't bore you with
the details of the tree valuies, because they don't seem at all parsimonious.
Oddly enough, *Yixianosaurus* fell consistently in as the sister group to the
Alvarezsauridae, as a near-avian. This is distinguished by numerous cranial,
vertebral, and hindlimb features obviously not present in *Yixianosaurus*, but
of the pectoral and forelimb features, some features do relate to the
relationship that are of note:
219.0 - coracoid biceps tubercle absent or poorly developed, and this has a
lot to do with the way I coded it, as the element is tiny, apical on the
caudoventral fossa, and not at all knobby or prominent otherwise.
220.0 - coracoid angle with scapula at the glenoid fossa moderate.
231.1 - humeroulnar ratio less or equal to 100%; the humerus is 36% longer
than the ulna.
232.0 - radiohumeral ratio less than 75% but greater than 50%; the ratio is
262.0 - metacarpal II much less than 50% humerus length; for obvious reasons,
this is inordinately basal to birds in general; all theropods have this that are
not themselves avian, as well as a few other critters like *Epidendrosaurus* and
*Scansoriopteryx,* as well as *Sinosauropteryx.*
264.0 - metacarpal III not very much narrower than mcII; as in
265.0 - metacarpal III straight.
274.1 - first phalanx of pollex (digit 1) greater than the length of mcII.
283.1 - manual ungual length extremely long.
Rather than involve some extraordinary analysis, topological differences in
the tree only involve the placement of *Yixianosaurus.* In regards to my earlier
considerations, is appears to be a basal maniraptoran/maniraptoriform; and as in
Xu et al. (2002) and Makovicky et al. (2003), Alvarezsauridae also lies at this
position of the tree, as the basal-most member of Maniraptora. Perhaps this
means something significant, who knows.
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)