[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Remarks on the "Chimaeric" Nature of Recent Fossil "Dino-Birds"



Dingeorge wrote:

<Why is it that any fossil that doesn't fit the
cladogram/theory of the day is called a chimera? Not
to say Archaeoraptor is or isn't one, just that this 
particular excuse is getting a little overworked
(Protoavis, Avimimus, Rahonavis, etc.).>

  [This is a general post, not just to George, who I
met at SVP and had a great pleasure in talking to him
on both Tuesday and Saturday nights, along with Tracy,
Brooks, and quite a few others]

  There is a lot of unpublished yak on the supposed
chimaeras of the dinosaurian literature, and quite a
few of them are based on some well supported theories;
some, however, are not. To explain, let me take these
animals down as I perceive the situations and opinions
(and let anyone who disagrees do so without any _ad
hominem_ comments as has been applied to some of the
authors).

  *Protoavis texasensis* -- the chimaeric nature of
this animal is supported by the apparent 4-digit, 5-mc
manus, along with "quill-knobs" on several mc's
whereas birds possess them only on the major mc (mcII
to bird/dino proponents); the skull really isn't in
the best of condition, though not having seen anything
clear on it, I must stop there on that; and several of
the vertebrae lack any features associating them to
birds, including hypopophyses, elongate cervical
centra, abnormal pubis with an anterior pubic process
(propubic process in ornithschians). Otherwise ....
<shrug>.

  *Avimimus portentosus* and *A. sp.* -- as has been
previously expounded on this animal, and partially
detailed by Nick Pharris in a recent post, the limbs
of Avi resemble most closely those of parvicursorids
(as I can hardly compare these to *Alvarezsaurus*) but
the femora and tibiae also compare well to
oviraptorosaurians and perhaps significantly to
*Kakuru* and *Microvenator*; the skull is definately
oviraptorosaurian by nature, possesses 6 unambiguous
ovi characters, 1 ambiguous one, and 9 other
characters possibly plesiomorphic for
oviraptorosaurians as a whole, but 16 characters found
in oviraptorosaurians in all [unpublished data]; the
pelvis is possibly a basal alvarezsaur or
oviraptorosaur pelvis, or a unique form, but complete
fusion of the elements in the type and refered
specimen (*A. sp.* of Kurzanov, 1985) indicates
possible avian relationships; meanwhile, I have no
idea what to make of the "carpometacarpus," but there
are some who question the inference of this fragment
as a cmc -- the rest of the forelimb can certainly be
applied to oviraptorosaurians, but these belong to the
type, along with a host of vertebrae which possess
basal oviraptorosaurian characters also found in
alvarezsaurs. My feeling is that there is either a ?
== { Alvarezsauria + Oviraptorosauria } clade, where
Avi is a derived member of the basal split, or it
really is two different animals. The type is mostly
likely, in the face of this analysis, composed of an
oviraptorosaur and an alvarezsaur.

  *Rahonavis* -- [sorry, forgot the species] is almost
certainly a single animal, and a single individual.
The Oregan Team's assertion (date?) that the type
includes forelimbs of *Vorona* fails in the face of
stratigraphic evidence where in the quarry producing
the specimens, they are from different levels in the
rock (Forster, pers. comm.) so are very likely not
missassociated.

  *Caudipteryx zoui* -- [for anyone who's seen Rogers
et al.'s poster at SVP, this won't come as a shock]
but the specimens are preserved in such a way as to
demonstrate they are from a single type of animal.
That there are two specimens preserved in nearly
identical poses makes the animals unlikely to be
missassociated, especially given the parsimony of the
different parts of the skeleton as belonging to the
same phylogenetic level, as basal avialians or basal
oviraptorosaurs (or the same thing? :) ).

  "Archaeoraptor liaoningensis" -- because the
Czerckas' haven't described it yet, but leaked the
name, and aside from the fact that it actually, by
Chinese law, belongs to China, this animal _should_ be
kept out of the discussion until such a time as would
be "proper" -- not to put a damper on things, but ....
onto the fossil, given current discussion: a lot of it
is disassociated, such as the tail, head, pes, and
such details as obscured or missing fragments,
carbonized traces which as discussed at SVP can and do
cover bone under UV light (after *Confusciousornis*)
and generally a fragmented skull proserved mostly as
the snout. Therefore, it might best be prudent to wait
until the animal is published properly to await
scientific discussion of it. Unless someone has a
differing opinion ... personally, it looks just like
many fossils of *Confusciousornis* in the position.
Also, given fears of "re-combined" fossils thanks to
improvisational Chinese farmers, see above.

  My couple dollars,


=====
Jaime "James" A. Headden

"Come the path that leads us to our fortune."

Qilong---is temporarily out of service.
Check back soon.
__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com