Re: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur

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

Tim Williams <twilliams_alpha@hotmail.com> wrote:

<Maybe I'm being limited by my own imagination, but I do not see how being
"small" and "long-armed" is enough for natural selection to act upon in order
to convert a non-flier into a powered flier.  The way I see it, the process was
far more complicated at that.  I see a far bigger role for exaptation in the
evolution of avian flight, and I cannot accept that *all* flight-related
features only appeared when the animal was already a powered flier, or very
close.>

  Indeed, it has already been argued that many of the features seen in flying
animals are related not to flying but factors that aid flight, but are seen in
other animals as well. Even looking at different groups of flying amniotes, we
have found that many of them consistently lack the same features that are
considered flight related, a debate that lasted for 200 years in the case of
pterosaurs, which many including GSP have argued were powerful fliers, but
which lack many of the features GSP infers must be present for flying animals.
Indeed, Ostrom back in the early 70's proposed the predation-driven mechanics
of arm-function that Gishlick has recently been reiterating, and enforcing the
idea that predation-related features of the shoulder and arm, and Carrier, and
Carrier and Farmer, have argued that activity-related increase in metabolism
and related pelvic and thoracic anatomy are convergent if it arose as
activity-related (e.e.g., being a faster hunter, grappling with prey, etc.).
Today, we see cats employing similar arm mechanics to that of birds, and we see
the WAIR model explaining increase in non-flying activity effectiveness in
chukars among other birds without the animals needing to fly, arguing that
flight may have been a related outcome of these features, but no animal was
trying to fly while pushing its genome to select for these features, and such a
premise in fact argues for directed development, which seems odd coming from
GSP. If one argues that flight arose as an exaptation, then all features must
be considered equally in that light, rather than dismissed as some kind of
preposterous notion that isn't as viable as one's own theory.

  Indeed, Tim offers that there were oviraptorosaurs with limited digital
flexibility, and "*Ingenia*", *Conchoraptor* and *Heyuannia* enforce this by
possessing digits 2 and 3 of the manus with reduced trochlea and phalanges
that, unlike other maniraptorans, gradually decrease in size before the ungual.
If digit 2 inflexibility is a symptom of flight related activities, then
oviraptorids should ahve gone through a flight state after diverging from their
common ancestor with caenagnathids, which possess very flexible digits compared
to *Heyuannia*, or in fact all the "basal" oviraptorids such as *Oviraptor*, GI
100/42, and *Citipati*. That *Caudipteryx*, the earliest oviraptorosaur for
which we have a detailed manus to compare, has relatively large trochlea on its
manual phalanges yet exhibits an extremely shortened arm compared to, say,
dromaeosaurids, segnosaurs, argues that the short arm we see in troodontids and
oviraptorosaurs is a basal state which was elongated in birds, segnosaurs, and
dromaeosaurids. Furthermore, oviraptorids possess a more avian shoulder than
does *Caudipteryx*, and a more avian skull than does either *Caudipteryx* or
*Protarchaeopteryx* (incl. *Incisivosaurus*, _sensu_ Senter), and a primitive
hip design that speaks that these were not particularly "avian" dinosaurs to
begin with, as one might expect if they were not secondarily flightless. Senter
has also proposed that basal dromaeosaurids were separated from the main
dromaeosaurids as part of Microraptoria, and this might include *Graciliraptor*
as well. Makovicky et al. have further proposed yet another split in
dromaeosaurids by putting *Unenlagia* with the troodontid-like *Buitreraptor*,
so that the common ancestor of *Microraptor*, *Dromaeosaurus*, and *Unenlagia*
if the content remains the same, would not neccessarily look like
*Microraptor*. As Tim writes, the Late Jurassic and Early Cretaceous seem to be
periods of experimentation in flight, rather than serial loss from a single
development of it.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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