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RE: vaulting pterosaur launch, questions
Scott Hartman wrote:
> Sorry, but VERY. In fact, that was the entire point of my post, that
> the popular image of Archaeopteryx is not consistent with the
> peer-reviewed literature. For example, it's been observed that Archie
> did not have the shoulder mobility of a flapper:
> Senter, P. (2006). Scapular orientation in theropods and basal birds
> and the origin of flapping flight. Acta Palaeontologica Polonica.
> 51(2): 305–313.
There are differing opinions on this in the peer-reviewed literature. For
example, very recently Dial &c argued that the excursion of the forelimbs
remained fairly constant during the non-avian to avian transition, in terms of
its 3D motion. In other words, motion of the forelimb at the shoulder did not
change in an *absolute* sense, although its motion relative to the rest of the
body did change.
Dial, K.P., B.E. Jackson & P. Segre. (2008). A fundamental avian wing-stroke
provides a new perspective on the evolution of flight.
Nature 451: 985-989.
Specifically (from Dial, 2008): "The shoulder joint (glenoid) is thought to
have evolved from a primitive ventro-lateral orientation allowing a
cranial–caudal excursion (as observed in theropod ancestors) to the derived
dorso-lateral orientation allowing a dorso-ventral excursion (among extant
flying birds). Jenkins suggested the 90° rotation of the glenoid's excursion
axis relative to the body was to accommodate the derived wing-stroke angle of
extant birds. We agree with the character states Jenkins eloquently describes
and offer a novel perspective about the process underlying the evolutionary
sequence. We suggest the orientation of the shoulder joint remained relatively
fixed in 3D space (in the global and gravitational frames of reference) over
evolutionary time. Living ground birds exhibit a slinging of the torso about
the shoulder (Fig. 3a). We suggest this same feature allowed proto-birds to
use a functional wing-stroke (even with proto-wings) aligned to gravity which
assisted their hindlimbs as they scaled increasingly pitched obstacles,
allowed controlled flapping descent and powered rudimentary flight in the
transitional stages leading to level flapping flight (Fig. 1). In other words,
the gravity-based wing-stroke did not come about through a long series of
migrational stages of the forelimb (from ventro-lateral to lateral to
dorso-lateral): rather, the primitive wing-stroke started in a similar
orientation as we see it today in hatchlings using their proto-wings."
I don't know who's 'right'; but note that Dial &c's work does not contradict
Senter's biomechanical work, merely its conclusions in terms of the inferred
flight abilities (or lack thereof) of _Archaeopteryx_ and other
non-ornithothoracean birds. BTW, Senter's study also posits that
jeholornithids, confuciusornithids, and sapeornithids were also incapable of
flapping flight, for the same reasons as _Archaeopteryx_.
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