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Re: "Flight theory has legs"
Ok, so the results are preliminary and need to be confirmed, perhaps
further study will show otherwise, but common guys, you are really special
pleading to shoe-horn the current results into the trees-down (or
trees-sideways) idea of flight origins.
>>I think we can all agree that, if theropods did enter the trees prior to the
>>advent of flight, then these first arboreal theropods would have been very
>>ungainly tree-climbers. But they had to start somewhere.<<
Yeah, they had to start somewhere, but that somewhere requires branch leaping.
Slow ungainly climbing is a perfectly plausible habitat, but not for the origin
of flight! And it is of course possible that dino-birds had a split in their
adaptations between manual and pedal claws, but it's almost as doubtful as it
is speculative. Dinobirds leaping from branch to branch would be in dire need
of pedal claws for grasping the branches the landed on. The condition is made
worse because their long columnar limbs put their center of gravity further
away from the branch, decreasing mechanical advantage for stopping their
momentum. Archaeopteryx and other dinobirds may not have even had a fully
retroverted hallux, and they certainly did not have the large flexor tubercles
and curved pedal phlanges needed for such scansoriality.
The best suggestion I've heard to get sinornithosaurs into trees was Greg
Paul's suggestion that the legs splayed, but after looking over high resolution
images of the specimens, I cannot confirm that the proximal femoral heads are
different from those of other dromeosaurs. Perhaps better specimens will clear
this up, but the bulk of the anatomical evidence for known theropods does not
support the needed degree of scansoriality.
I know that a trees-down origin is more intuitive, and I've convinced that
both bats and pterosaurs evolved flight in an arboreal context, but dinobirds
are very different.
P.S. In his excellent Dinosaurs of the Air, Greg Paul says that the only
explanation for the reduction in pelvic girdle size in archaeopterygians and
early dromeosaurs is that they were arboreal. Nonsense; it is equally
parsimonious to assume that the terminal ballistic phase during terrestrial
hunting had begun the switch from true leaping to gliding and/or active powered
flapping. Once aerodynamic power supplants leg power, reduction of hindlimb
mass would have enhanced the distance and control over this hunting style. No
trees need be involved.