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Re: New Jeholornis specimen
Gregory S. Paul wrote:
Yet another example that cladistics is at best hard pressed to handle the
degree of reversal, parallalism, and convergence going on in the mosaic
development of basal birds that had not yet evolved far from the
dinosaurian grade, and were often losing and perhaps even reevolving
I see what you're driving at - and having read both PDW and DA, I'm
sympathetic. It is conceptually difficult to distinguish the incipient
flight apparatus of "pre-flight" theropods, with the "post-flight" apparatus
of secondarily flightless birds close to the origin of flight. Some of the
latter may be unfairly pigeonholed into the former under the invocation of
Cladistics is one important tool for restoring paleophylogentics, but not
the only one, and in this case is inferior to assessing the relative
derived degree of flight adaptations that are present.
I sense a subjectiveness in this method, which relies too heavily on
assessing the "flightworthiness" of individual osteological characters.
Take the more lateral orientation of the glenoid (for more anterolateral
excursion of the humerus) or the broader second manual digit (for attachment
of primaries). Both *might* be directly related to the inception of powered
flight, specifically the flight stroke.
However, these and other maniraptoran / avepectoran characters may initially
have evolved for other purposes. For example, the lateral glenoid allowed
the arms to sweep forward to an improved degree - an advantage when grabbing
large prey with both hands, or snatching flying prey out of the air with one
or both hands. The improved attachment of primaries to the hand may not
necessarily be an adaptation for resisting torsional forces during flapping
flight, but for resisting the rigors of other behaviors that involved the
hands. Grappling prey, for example. Or more rudimentary forms of aerial
locomotion than flapping flight - ground-to-air leaps, or tree-to-tree (or
Long story short, I think your model understates the role of exaptation in
the assembly of the avian flight apparatus. As I said before, I don't
dismiss the idea that many non-flighted maniraptorans / avepectorans were
secondarily flightless. But proposing a volant pedigree for all these taxa
is throwing the baby out with the bathwater, IMHO. Personally, I think
maniraptorans underwent a long period of experimentation with aerial and
arboreal behavior prior to the advent of powered flight; and that
oviraptorosaurs, therizinosaurs, and deinonychosaurs are relicts of this
process. But only birds took this process to the next (and most demanding)
level of aerial locomotion: powered flight.
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