Re: Campbell's even crazier than a MANIAC? (archeopteryx

[Mike Habib <habib@jhmi.edu>]

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).

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280-0181
habib@jhmi.edu