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Jinfengopteryx elegans the troodontid



A few thoughts...
Jinfengopteryx is remarkably unbirdlike in several ways.  The naris is small
and anteriorly positioned, with a short dorsal premaxillary process above
it.  The snout is more rounded than avialans.  The maxillary and
promaxillary fenestrae take up a larger percentage of the antorbital fossa
length.  There is a large amount of maxillary teeth.  The distal caudals are
less elongate than most paravians.  The scapula is distally expanded (like
scansoriopterygids).  The first manual digit is comparatively robust.  The
first metacarpal is longer than most paravians.
There are a few birdlike characters, but they are all too derived for an
archaeopterygid- twelve cervicals, eleven dorsals, fused manual phalanges
III-1 and III-2.

After entering it into my matrix, Jinfengopteryx emerges as a basal
troodontid.  Characters that may support this include the robust lacrimal
(compare to Mei), smaller and closely packed anterior teeth, apically
expanded dorsal neural spines (like Sinovenator and Mei), short pedal digit
II (Jaime noticed this), and possibly the absence of ossified uncinate
processes and sterna (if their absence in Sinornithoides is real).  This
would also fit well with the short forelimbs and slender furcula.  The snout
resembles Sinovenator fairly closely.

Ji et al. assign it to the Archaeopterygidae based on the triangular skull
(as in Sinovenator), serrationless teeth (as in Sinovenator, Mei,
Byronosaurus), shortened proximal caudals (not as much as in other
paravians), cervical ribs longer than their respective centra, and extensive
contact between the semilunate and metacarpal I (symplesiomorphy).

I'll save my final judgement until I get the data matrix of Ji et al. (since
they include Sinovenator, and Jinfengopteryx does not clade with it), but it
seems we have the most complete troodontid known, and the only one with
preserved feathers.  The matrix seems to be a modified version of Norell and
Clarke's (2001), with some added non-birds.  Perhaps it suffers from the
same problems that place oviraptorosaurs in Ornithurae in Lu et al. (2002),
i.e. analyzing non-birds in a bird matrix.

Finally, a few notes about Ji et al.'s identifications.  The labeled
"pterygoid" looks to be a parasphenoid rostrum, the "squamosal" part of the
parietal, and the first caudal is supposed to be twice the length of the
second (never happens elsewhere in theropods) and seems to have two
associated chevrons, so is probably two caudals (raising the caudal count to
24).

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html