[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Archaeopteryx cannot fly?



Richard and Jo Cowen (cowen@blueoakfarm.com) wrote:

<Lately several people have written approvingly of ?cruising flight? for
Archaeopteryx. The idea is that once airborne, it would have been capable of
staying up there. HOWEVER, all agree that take-off would have been difficult,
and that landing would have been difficult too. There have been summaries of
the reasons on this site, or go to
http://www.geology.ucdavis.edu/~cowen/HistoryofLife/noflightinArch.html>

  Unfortunately, for the stated reasons, a large grouped of well-developed
winged critters will also be "unable" to fly. The alula, a device that aids in
landing, as well as the tail fan, are not present in many birds more basal than
Ornithothoraces, this despite arboreal or scansorial features of the feet,
pygostyle, extremely opisthopubic orientation of the pelvis, and various other
features of the sternum, coracoid, and scapula, shared with *Archaeopteryx*.
The lack of an ossified sternum is a condition so far unique to *Archaeopteryx*
among these "early birds", but this does not mean a sternum was not present, as
it may have been unossified cartilage as well. The coracoid not only has a very
proximally-placed and large acrocoracoid, but is also caudally angled and takes
up a lot of the musculature aiding in the downstroke from the primitive
anterior position of the coracoid, which allows the humerus to be pulled
ANTERIORLY, but not as strongly VENTRALLY. In addition, a U-shaped furcula is
more suited to bending forces with more parallel distal rami than in other
dinosaurs, and thus can act as a compressive spring between the shoulder
girdles, a feature of much less importance and utility in more basal theropods
like *Velociraptor*. Similarly, the feet of *Archaeopteryx* are suited to both
a cursorial function and a limited ability at grasping branches, thus
scansorial. The scapula, unlike in most theropods, is also partially rotated
and "twisted" to orient onto the dorsal surface of the ribcage, though in truth
it was more or less dorsolateral in orientation, but apparently moreso than in,
say, *Velociraptor*. We see this in *Microraptor* as well; earlier
misjudgements of a lateral scapula would coincidentally orient the glenoid
laterally and a little ventrally, but the correct orientation (see Paul's 1988
_Predatory Dinosaurs of the World_ and 2002 _Dinosaurs of the Air_ for further
clarification) appears to place the glenoid not only laterally but also
dorsally. This allows the humerus to extend at least 30 degrees or so above the
horizontal and, though it may not be a "powerful" downstroke, was vastly more
sufficient than other dinobirds more basal than it, thus showing us an animal
"caught in the act of becoming a bird." Should we thus dismiss it's ability to
fly because takeoffs and landings would be difficult? Boobies have a LOT of
trouble landing, but do it fine, day after day, and many large-bodied and
water-bound birds also have difficulties taking off. Yet no one infers these
features as reasons to claim they cannot fly. The old days of Archie as a
land-bound gnat-catcher, wing-swiping non-flier are most likely over, and no,
no one is saying it was the tyrant of the air, either. That honor lies with the
pterosaurs of the day.

  Cheers,

Jaime A. Headden

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


                
__________________________________ 
Yahoo! FareChase: Search multiple travel sites in one click.
http://farechase.yahoo.com