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Re: New Jeholornis specimen
Tim, like others, is making statements that expose a lack of knowledge about
the issue of bird origins.
He states that since the shoulder glenoids of Archaeopteryx and flying
dromaeosaurs face laterally they could not elevate the wings above
horizontal. As I describe and illustrate in both PDW and DA, I have
manipulated high quality casts of the similarly laterally oriented shoulder
joint of Early Jurassic Syntarsus and could easily elevate the humerus well
above horizontal, thereby describing an extensive flapping arc. Of course
basal avepods were not flying - the extensive arm motion was for predation -
this was a true exaptation that allowed small avepods to develop a flapping
wing without even trying. What Archaeopteryx and basal dromaeosaurs could not
do was elevate the humerus fully vertically, as in modern flying birds. The
ancient fliers could not fly as well as modern birds, but the same was true
of a Spad compared to a Raiden.
On to the issue of assessing the relative flight performance of dromaeosaurs
compared to Archaeopteryx. Tim, like many others, continues to fail to
understand the basic principles and methods at work here - which I describe
in detail in DA - so I will go over it briefly one more time.
If characters are exaptations for flight, then they should be present in
nonfliers or well developed or weak fliers.
If characters are flight characters then they should be present only in
If an avepod protoflier had a flight performance less than that present in
Archaeopteryx, and it had anatomical exaptations for flight, then it's flight
adaptations should be A) less developed than in the latter, or B) they should
be both less developed and no better developed, and C) few or no flight
adaptations should be better developed than in Archaeopteryx.
If an avepod had a flight performance better than present in Archaeopteryx,
then its flight adaptations should be A) better developed than in the latter,
or B) they should be both as well developed and better developed, and C) few
or no flight adaptations should be less developed than in Archaeopteryx.
That's logical enough.
The ribcage, sternal complex, hands and primary feathers of Jehol
dromaeosaurs are all far better adapted for flight than Archaeopteryx in
numerous regards. The rest of the wing complex is at least as well developed
for flight as in Archaeopteryx. In no regard is the basal dromaeosaur wing
less well developed for flight than in Archaeopteryx. The ways in which the
dromaeosaurs were better adapted for flight than Archaeopteryx are the ways
that increased the muscle power of the wings and the ability to
aerodynamically exploit that power. Ergo, Jehol dromaeosaurs enjoyed a level
of powered flight superior to that present in Archaeopteryx. It is therefore
not feasible for any of the flight adaptations present in dromaeosaurs to be
exaptations for flight.
For dromaeosaurs to have had less flight performance than Archaeopteryx they
would have had to obstinately failed to use the full power of their larger
arm muscles to power fly, instead only gliding like dinosaurian coach
potatoes. The improved wing feather attachments and stengthened
sternal-ribcage complex would go to waste.
To argue that the advanced flight adaptations of dromaeosaurs were basal
exaptations for flight means that somehow these same features disappeared in
Archaeopteryx, itself an animal fully capable of flying. In this strange
scenario the big sternum of basal dromaeosaurs evolved for predation or
something, along with the flattened finger, despite neither being known in
any none flier. Then these classic avian flight features were lost in
Archaeopteryx despite its fully developed wing array, only to reappear in
latter birds for purposes of flight. Parsimony, logic, functional and
comparative anatomy and evolutionary trends and all fly out the window.
Trying to argue that Jehol dromaeosaurs were basal protofliers less aerially
capable than Archaeopteryx with a host of advanced flight features that were
really expatations is super spin of a completely contrary data base, not
science, and is beating the dead horse of obsolete phylogentics.
BTW, it would be a good idea that before anyone contributes to this
particular discussion that they read DA, since it is the most in depth
discussion of the subject of evolution and loss of flight of dino-birds.
Take the flattening of the central finger. So far it is