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Hi everyone. Today I came across the
Evolutionary Origin of Feathers volume that was recently mentioned. I
figured I would give a rundown of the articles and comment on a few (okay,
so it's mostly poking holes through the birds-aren't-dinosaurs claims :-)
). All of these are in American Zoologist (volume 40, number 4) and were
originally presented at the Evolutionary Origin of Feathers Symposium presented
at the Annual Meeting of the Society for Integrative and Comparative Biology,
Jan. 6-10 at Denver, Colorado.
Maderson and Homberger, 2000. The evolutionary
origin of feathers: A problem demanding interdisciplinary communication.
455-460.
Stettenheim, 2000. The integumentary morphology of
modern birds- an overview. 461-477.
Bock, 2000. Explanatory history of the origin of
feathers. 478-485.
Sumida and Brochu, 2000. Phylogenetic context for
the origin of feathers. 486-503.
This is a great comparison of the various
hypotheses for bird origins and rightly concludes theropod dinosaurs are the
best choice. There's a couple references in the bibliography I haven't
heard of before. One by Holtz on the Arctometatarsalia and one by the AMNH
team on coelurosaur phylogeny :-) . Apparently both are coming out in a
new book. I can't wait!
Dodson, 2000. Origin of birds: The final solution?
504-512.
Maderson and Alibardi, 2000. The development of the
sauropsid integument: A contribution to the problem of the origin and evolution
of feathers. 513-529.
Sawyer, Glenn, French, Mays, Shames, Barnes, Rhodes
and Ishikawa, 2000. The _expression_ of Beta keratins in the epidermal appendages
of reptiles and birds. 530-539.
Menon and Menon, 2000. Avian epidermal liquids:
Funtional considerations and relationship to feathering. 540-552.
Homberger and de Silva, 2000. Funtional
microanatomy of the feather-bearing integument: Implications for the evolution
of birds and avian flight. 553-574.
Wolf and Walsberg, 2000. The role of the plumage in
heat transfer processes of birds. 575-584.
Ruben and Jones, 2000. Selective factors associated
with the origin of fur and feathers. 585-596.
This paper is the first in the volume to refute the
feathered theropods from Liaoning. They dismiss the integumentary
filaments of Sinosauropteryx as macerated collagen fibers. Notable is the
fact the authors state the fibers constitute a "continuous midline frill", which
has been disproven by Currie and others. They say the theropod status of
Protarchaeopteryx and Caudipteryx is dubious. Protarchaeopteryx is "too
poorly preserved for definitive taxonomic analysis", though "its long forelimbs
are not inconsistant with an avian status". I suppose that since a
flightless bird might reduce its forelimb length, this is true. It's
equally true however that Ornitholestes, some oviraptorids and dromaeosaurs
have arms of equal or greater length. Ruben and Jones argue against the
theropod status of Caudipteryx by refuting the three "unambiguous characters"
cited by Ji et al. (1998) that birds have and it lacks. They say the
quadratojugal cannot be proven to have been sutured with the quadrate,
as they do not contact in the holotype and show a photo of the
specimen which differs in this aspect from the figure in Ji et al..
Oviraptorid specimens GIN B and ZPAL MgD-I/96 (Maryanska and Osmolska, 1997)
show a cotylar articulation between the two bones and Velociraptor has
a reduced loose contact (Barsbold and Osmolska, 1999), so even if Ruben and
Jones are right, it would mean nothing. They claim the quadratojugal is
far too short to contact the squamosal. Again, I see no evidence of this,
but even if true, Sinornithoides shows this character as well (Russell and Dong
1994). Finally, "an obturator process may or may not exist in Caudipteryx,
but, in any case, a similar structure is also known to have occured in some
birds (e.g., Concornis)." May or may not exist? That cracked me up
:-D . First of all, the ischia are clearly visible in two specimens and
obviously show obturator processes (learn how they get past this small detail
later). Secondly, they misstate the character, which was to have a
reduced or absent obturator process. I personally don't think
Archaeopteryx has a reduced obturator process, but Concornis has a very reduced
process. Basically, Ruben and Jones present no convincing evidence
Protarchaeopteryx or Caudipteryx is a bird.
Porter, Budaraju, Stewart and Ramankutty, 2000.
Calculating climate effects on birds and mammals: Impacts on biodiversity,
conservation, population parameters, and global community structure.
597-630.
Brush, 2000. Evolving a protofeather and feather
diversity. 631-639.
Farlow, Gatesy, Holtz, Hutchinson and Robinson,
2000. Theropod locomotion. 640-663.
Another wonderful paper. Covers footprints,
cursoriality of large theropods, etc. Avimimus is listed in the back as
being a tentative alvarezsaurid. How very interesting...
Geist and Feduccia, 2000. Gravity defying
behaviors: Identifying models for protoaves. 664-675.
Another amusing read. Theropods cannot be
bird ancestors due to:
- size too large. This is amusing not only
because of Microraptor, but also because they advocate the body of Rahonavis is
theropod in the very next paragraph!
- deep, laterally compressed body. Is
Archaeopteryx dorsoventrally compressed or something?
- long, narrow, vertical to subvertical pubes.
What's great about this is that they ignore Norell and Makovicky (1997), who
showed Velociraptor has a strongly opisthopubic pelvis, yet show figure 14 from
that article on the very next page.
- long, stiffened, counterbalancing tail.
Sinornithoides has an almost identical tail to Archaeopteryx, and Rahonavis' is
even closer. They might have had better luck just calling Rahonavis a
bird.
- forelimbs shorter than hindlimbs.
Sinornithosaurus has forelimbs 86% as long as its hindlimbs, while my estimate
for Beipiaosaurus indicates they were subequal.
The authors dispute the avian status of Rahonavis
(besides the forelimbs) based on the lack of a hypopubic cup and the presence of
a laterally compressed subvertical pubis with a pubic foot. The
hypopubic cup of Archaeopteryx is an irregular mass of calcite with an
artifactual posterior excavation, while Velociraptor may possess a slight
hypopubic cup (Norell and Makovicky, 1999). The pubis of Archaeopteryx is
subvertical while segnosaurs and dromaeosaurs have opisthopubic pubes. The
pubic foot is present in Archaeopteryx and some enantiornithines, while reduced
in troodontids and Sinornithosaurus. It is apparent none of their evidence
holds up to examination.
A slight attempt is made to dismiss
Sinosauropteryx's integumentary filaments and the dinosaurian nature of
Caudipteryx. It's basically a shorter repeat of Ruben and Jones, but a few
new "avian" characters are presented for Caudipteryx.
- shortened, incipiently fused tail. While
the tail of Caudipteryx is shorter than any other non-avian theropod (and
Archaeopteryx, Rahonavis and Yandangornis), it is not fused at all. Now if
they want to argue Nomingia is a bird.....
- ventrally oriented foramen magnum. Odd they
can tell this from the disarticulated and incomplete braincase (the exocipital
is the only element preserved), but I don't know enough about braincase
morphology to refute it. :-(
- vaned feather structure. Circular
reasoning.......
Besides the reduced tail length, there's yet again
no compelling evidence Caudipteryx is more derived than
Archaeopteryx.
Tarsitano, Russell, Horne, Plummer and Millerchip,
2000. On the evolution of feathers from an aerodynamic and constructional
viewpoint. 676-686.
Martin and Czerkas, 2000. The fossil record of
feather evolution in the Mesozoic. 687-694.
Saving the best for last. Pelecanimimus
apparently now has pebble-like scales. It must be news to Briggs et al.
(1997) who found all purported skin except a small bare patch on the throat
pouch was actually internal tissue. Sinosauropteryx also now has scale
impressions preserved. At least that's how Martin views the filament
cross-sections. He claims feather quills would be widely separated from
each other, apparently disregarding the fact these are more primitive than
modern feathers and compressed together. The authors claim
Protarchaeopteryx could have limited flight capabilities with long enough
feathers. Bambiraptor's arms are longer, so any such statement could be
applied to it as well. Reasons it is a bird-
- teeth with waisted crown and expanded
roots. Also in troodontids, Archaeornithoides, Microraptor, alvarezsaurids
(which Martin considers ornithomimosaur relatives), etc.
- reduced serrations on teeth. Also in
Pelecanimimus, Archaeornithoides, Byronosaurus, alvarezsaurids,
etc.
- shortened tail. It's not as short as
Caudipteryx's, but rather close to oviraptorids and Nomingia.
- shortened fibula. This is unknown (Ji et
al., 1998), but mononykines, Rahonavis and troodontids all share this feature
anyway.
- reflexed hallux. Probably false, but
present in Microraptor and Rahonavis in any case.
Again, no evidence withstands scrutiny and their
assignment of Rahonavis to the Dinosauria helped (but was not neccessary for) my
case.
Caudipteryx is a bird because:
- teeth with expanded roots. See
above.
- primary feathers. See above under "veined
feather structure".
- carpus with at least four
bones. Actually, there are three, but more are present
in allosaurids, segnosaurs, tyrannosaurids and ornithomimids
anyway.
- absence of pubic foot. Completely false
(Zhou and Wang, 2000; Currie pers. comm. 1999). Mononykines and
troodontids have absent or highly reduced pubic feet even if Martin and Czerkas
were right.
- reflexed hallux. Probably true this time,
but see above for undisputed dinosaurs with it too.
- shortened tail. See above
again.
It's more derived than Archaeopteryx based
on:
- no maxillary or dentary teeth.
Enantiornithines and ornithurines primitively lack this. Is Caudipteryx
supposed to be a carinate? Many dinosaurs (ornithomimids, oviraptorosaurs)
also have this.
- external mandibular fenestra
present. Plesiomorphic and present in virtually all theropods, while
absent in a couple enantiornithines and maybe Archaeopteryx.
- enlarged premaxilla. No more than
oviraptorids.
- reduced maxilla. Correlated with the above
character and also present in oviraptorids.
- reduced hypopubic cup. Plesiomorphic
and present in nearly all dinosaurs anyway....
- ball-shaped femoral head. Plesiomorphy only
absent in Archaeopteryx and Rahonavis.
- reduced fibula. False (Ji et al., 1998),
but present in troodontids, etc. anyway.
- reduced calcaneum. Less reduced than
troodontids :-)
- greatly shortened tail with evidence of pygostyle
formation. See above.
There is also a hilarious skeletal reconstruction
of Caudipteryx in an upright posture. The ilium now has pointed
preacetabular and postacetabular processes, despite obviously being expanded
anteriorly and squared-off posteriorly. How can they get away with such
fraudulent artistry? We learn the obturator process is missing because the
ischium was upside down the whole time! ;-) It's actually the proximodorsal
process, despite both being preserved the other way in IVPP V 12344. Now I
see why it's so ambiguous... ;-) Finally, the pubis has been trimmed to make it
not pass the ischium in its extreme opisthopubic orientation.
Sigh.
Finally, there is a panal discussion at the
end.
I hope you enjoyed this and those of you curious as
to what evidence existed that Protarchaeopteryx and Caudipteryx are birds are
satisfied.
Mickey Mortimer
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