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Feathers of the Mesozoic
Can't say as I couldn't resist.
Just my view on what Zhang and Zhou are purporting for their new
genus et species novem: *Protopteryx fengingensis,* a mouthful if I
ever heard one.
Zhang F.-c. & Zhou Z.-g. 2000. A primitive enantiornithine bird and
the origin of feathers. _Science_ 290: 1955-1959. [w/ supp. info.]
The taxon is from the Yixian Formation of Fenging County, Hebei
Province, which borders Chaoyang County in Liaoning Province, of course
both in China. The name means "primitive feather from Fenging
[County]," with the root of proto- (Lat., before, at the start, thus
preimitive) + pteryx (Grk., feather or wing, in this case the former).
The holotype, IVPP V11665, is a perfectly complete skeleton with
feathers and true down interspersed ovr its body. It is clear that
looking at this fossil and other Yixian-Jiufotang fossils that the
often perpendicular and "sprayed" looked of the down, contours, and
fuzz is resultant from the pressures of sedimentation and the effect of
being pressed in water. Hair sticks out, as you may notice next time
you go jump in a pool (considering your not bald, and certainly these
fossils weren't). So you get a long "crest" of what would otherwise lay
flat forming the common "halo" as seen in countless hundreds of
confuciusornithid birds down there.... Looking at the feather
variation, we see a sort of down/contour that covers the bird, with
faint carbon traces and impressions of the true pennaceous feathers in
the arm and parts of the tail. Finally, the tail bears a strange
morphology that has been loaded in the paper with a very subjective
meaning: scale-like. It is descibed as an enantiornithine, and a few
conditions of the tarsus and the shoulder girdle are the supportive
qualities, similarly the manus resembles enantiornithine manus in the
primitive state. The bird has a particularly large head, and there are
a few other features which bear noting, but I'll get to these later.
IVPP V11844 is the paratype, and is mostly comprised of impressions.
The holotype lies on its belly, whereas the paratype lies on its back.
To continue on a general note, the paper was written with a certain
perspective, which a great majority of the readers of this post are
aware of as being in the minority. The authors are careful, in their
way, of making statements on the line of Jones et al. 2000 [_Science_
288: 2202-2205] about the nature of the integumentary structures of
*Longisquama*. Needless to say, the paper followed a controversial
presentation of the identification of an early feather homologue by
Ruben at the SVP in Denver, last year. What is on *Longisquama's* back
are open to a considerable amount of interpreatation, as debate has
shown with the refutation of Jones' et al's evidence by Reisz and Sues,
2000 [_Nature_ 408: 428]. Previous to this, only some acknowledged the
possibility that the pennaceous structures of *Longisquama* were
similar to feather's. Feduccia's book, _The Origin and Evolution of
Birds_ (1st ed., 1996; 2nd ed., 1999), contained some heretical
statements on the nature of *Longisquama* as a focus on the evolution
of birds. Further publications went on as it suddenly became available
to study *Longisquama* in 1999 to Ruben, Jones, Martin, and Feduccia,
as well as others included Sues and Reisz. But let me emphasize
something: debate on the development of feathers has gone on for a long
time, with the first opinion extending back into the late 1800's, with
the proposal that feathers were modifications of the scales in reptiles
(Huxley, 1886, and further publications). A competing veiwpoint is the
neotenic concept that the feathers originated without a previous
biological structure. And this is not to get into methods of
development, a kettle in and of itself!
Zhang and Zhou (2000) make known their concept of the scale-origin of
feathers: from the abstract, "This type of feather may suggest that
modern feathers evolved through the following stages: (i) elongated
scale, (ii) central shaft, (iii) barbs, and finally (iv) barbules and
barbicel." This favored with comparison to *Longisquama*, though to
their credit the implication is less vocal as in Jones et al., and
there are resurgent comments on the prescence of feathers in
"dinosaurs" such as *Caudipteryx.* Thus the issue is raised that
suggests feathers in dinosaurs and birds developed independantly (p.
1957). Who am I to judge?
Now, back to the bird. *Protopteryx* is a smallish, starling-sized
bird, with a largish head and very few teeth [one pair of premaxillary,
two pair of dentary teeth; conical, unserrate, waisted, with large
resorption pits]. It is described as a basal enantiornithine, but it is
clear that this is a very derived morphology, for there are more
advanced enantiornithines with more teeth, such as *Sinornis*, and
*Iberomesornis* which may or may not be enantiornithine. Thus
*Protopteryx* probably lost its teeth in a separate event than
Enantiornithines _sensu praeteritum_ [past sense]. The sternum is huge,
with a small carina; there are indications that the lateral sternal
processes are separate from the sternal plate proper, which would
indicate that the lateral processes of the sternum in *Oviraptor,*
*Ingenia,* and *Velociraptor* (see Barsbold, Osmolska, and Maryanska,
1990, in the _Dinosauria_) are not homologous, but analogous. Primitive
and advanced features are apparent: there's a hypocleidium, a
procoracoid, proximal to distal metatarsal fusion, reduced third manal
digit to a broad triangular "prong," reduced dentition, huge arms and
head, lateral sternal processes, a very short hallux (nonetheless
retroverted, and the pes was indicatively anisodactyl). I bring the
last point up because of the novelty of the feathers in the tail which
prompt this post, so let me jump over to that. They are described as
long scale-like feathers "without barbs or rami at their proximal part
... the proximal end of the tail feathers also remains unified without
branching." (pg. 1957) These statements are not well-made, as they are
horribly open to interpretation; for instance, I could add: "but with
differentiation more distally?" This would be the most likely
statement, as I see it, but it is not obvious from the figures in the
paper. The development of the tail as long, structurally strong-looking
feathers brings to mind the tail of woodpeckers, and their "third leg"
utility when scansors like the honeycreeper traverse tree trunks. These
birds operate with zygodactyl feet for better security when about, but
the pedal structure in *Protopteryx* does not relate this, and truly,
the foot resembles a non-perching but more terrestrial-type foot, and
this may have analogies to a lifestyle.
I'm sure there are more comparisons to draw from when regarding the
fossils, but I've drawn the comparisons I've wanted to make so far.
Peace, please: this is not an invitation to war.
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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