"No Name Saurus," the Case of NGMC 91

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

[HP] Mickey Mortimer writes that the possible reference of NGMC
91 to *Sinornithosaurus* should have forced the authors to
ascribe it to a named taxon or just simple establish a new
taxon.

  First, the specimen is most likely a juvenile. It is
reasonable to expect that, as discussed on this list, only an
adult taxon can justly provide characters on which to establish
taxonomy, as juveniles of similar taxa can share almost _every_
feature of each other (sensu Centrosaurinae and Lambeosaurinae)
whereas only through ontogeny can the taxa be differentiated
substantially.... Thus the possible juvenility can provide a
basis for resemblance, and any features relating to proportions
should be forgiven; features found in later onteogeny are not
known, and *Sinornithosaurus* _could_ have looked like this, but
so could any other species of the mophological trend that
Mickey, Pete Buchholz, and I have [all independently] found in
*Bambiraptor*, *Microraptor*, *Sinornithosaurus*, *Rahonavis*,
and *Unenlagia* from "typical" Dromaeosauridae [*Droameosaurus*
+ *Velociraptor*]. All dromaeosaurids, for instance, have
enormously large heads, and most have large orbits. The temporal
region in this specimen is almost completely obfuscated and thus
not telling in some intra-dromaeosaur relationships....
Triangular snouts with ovate nares (even restricted caudally)
occur in juveniles of a multitude of maniraptoran taxa,
including [esp.] troodontids, purportedly forming a mono- or
paraphyletic Deinonychosauria. Juveniles of closely related taxa
_will_ resemble one another....

  It would be all fine and that should the authors of the
_Nature_ paper have referred the specimen to a "genus" (as if
that meant anything) but they dis ascribe it to the most
reasonable taxon they could without providing assumptions on an
ontogeny they did not know, which was the safest bet they could
offer.... Better to get rid of all the *Cheneosaurus*es of the
world than continue to describe juveniles whose natures and
relationships depend on final ontogeny, and we cannot be sure of
their true [or most likely, adult] affinities.

  Thus I disagree with Mickey in his ascription of NGMC 91 as
cf. *Sinornithosaurus* on the single point that it is most
likely a juvenile, and its relationships are putative to
*Sinornithosaurus* (Ji et al., 2001 state this) but cannot be
reasonably demonstrated except by comparison of an ontogenic
sequence we don't have; resemblances can be plesiomorphic, and
thus throwing the taxa into confusion. As Mark Norell noted, the
Jehol biota is not done throwing us surprises and fantastic
discoveries, so we can "savor the anticipation" as Caitlin
Kiernan remarks.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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