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Re: Campbell's even crazier than a MANIAC? (archeopteryx
Augusto Haro wrote:
Perhaps you are right in this, but i think we can see it other way,
without the derogatory word "poor". It seems that galliforms and
tinamous share a short-range flight. Thus, we should hypothesize that
to be the basal condition based on parsimony alone (I'm basing this
reconstruction of basal character states in Livezey and Zusi, 2007).
The Galliformes may later get special adaptations while maintaining
the plesiomorphic short-range flight.
The catch is that this burst-specialist, short-range flight morphology
is quite distinctive - it is actually a highly derived state, compared
to the morphology of more basal, fossil taxa. The short range comes
from the expansion of the anaerobic capacity at the expense of aerobic
capacity, which produces very high power outputs. Without the
forelimb strength and shoulder excursion see in modern burst flyers,
it is unlikely that more basal birds used a similar dynamic. The
sternal complex is also altered in burst launchers, with a reduced
plate and deepened keel (to make room for an expanded p. minor) -
again, we do not see such adaptations in more basal birds. Thus, the
short-ranged specialization of galliforms is clearly derived. Same
goes for tinamous, though the trend is less extreme. The upshot is
that trying to apply short-range restrictions on birds outside the
crown group, on the basis of an apparent EPB, is probably misleading.
Short-ranged specialists could indeed form the base of crown-group
birds, based purely on the in-group bracket, but none of the outgroup
fossil taxa yet found appear to have been burst specialists - so a
more detailed EPB is essentially equivocal.
However, I know, Anseriformes, which seem to be the sister-group of
Galliformes, can engage in sustained flight, so the Galliform
short-range flight can be an apomorphic reversal.
It's almost certainly apomorphic, and likely not a reversal, since the
required shoulder morphology and pectoral structure (not to mention
load capacity in the forelimb) is lacking in taxa outside Neornithines
(also lacking in most of the in-group, of course, appearing as a
convergent apomorphy in Galliformes, Columbiformes, and (to some
extent) Passeriformes). The ancestral state for the Galloanserae is
equivocal: the two living groups within this clade are each on
opposite ends of a continuous morphological/physiological spectrum.
Short and long ranged flight are not discrete characters, and probably
should not be mapped as simple gains and losses.
But, according to the EPB, we should posit that sustained flight may
be a sinapomorphy
of Neognathae (with an apomorphic reversal in galliforms), as only
short-range fliers or non-fliers are found basal to Neognathae (i.e.,
Palaeognathae). Alternatively, sustained flight should independently
appear in Anseriformes and the sister group of Galloanserae, which
however also indicates sustained flight has to be inferred as being
restricted to the Neognathae.
But not all fossil paleognaths are short-range specialists.
Lithornithids, for example, do not appear to be burst specialists (at
least, based on the material I've looked at in our collections here
and at the NMNH). Besides, with their limited diversity, living
Paleognaths are probably not informative for reconstructing the state
basal to Neognathae. The flightless forms don't give us any
information in this regard (short-ranged flyers are not more prone to
flightlessness), and that leaves a single group (tinamous), which
appear to have an apomorphic flight condition.
Anseriforms are also highly derived with regards to locomotion, having
taken sustained flight to the extreme (almost entirely aerobic flight
power, very rapid flight, continuous flapping, and running launch -
which encompass a whole suite of derived flight characters). The EPB
resolution more or less breaks down for reconstructing basal
locomotion in Neornithines - we can tell because the traits in
question have mechanical signals which can be tested for directly in
fossil taxa. So, for example, we don't seem to have any fossil taxa
outside Neornithines with the speed or sustained power of a duck, nor
the burst launch specializations of galliform birds. There might be
rapid, aerobic flight showing up near the base of the Ornithuran
phylogeny, based on Gansus, but I say that tentatively because I
haven't had a chance to work on the animal directly (and I don't think
anyone that has worked up a flight analysis). Might be some rapid
flight species within Enantiornithines, as well, but also tentative.
The fact that the Galloanserae contains both extremes of the spectrum,
nested together, at the base of the Neognathae phylogeny ends up
producing some weird EPB results in this case. This is further
complicated by the limited living diversity in Paleognaths, which are
mostly uninformative (flightless), with one living group that happens
to be short-range adapted (but likely doesn't represent the
plesiomorphic state for Paleognathae).
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205