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Re: Feathered Dragons: Studies on the Transition from Dinosaurs to Birds
>>>I would also like to say that unless there was a special novel muscular
>>>anatomy of the legs not seen in any bird, croc, lizard, or other tetrapod
>>>known today that would have been able to control such feather-moving
>>>structures, this is one of the more unparsimonious arguments to assume that
>>>these animals were particularly terrestrial _and_ capable of maintaining
>>>leg-feather security.<<<
Um, no. The hindleg feathers are themselves totally novel from
any "bird, croc, lizard, or other tetrapod known today," so no matter what the
attachement or musculature you assume (moveable or not) you are making a
third-level EPB inference. And even if they were totally arboreal, the
feathers would still get destroyed if they could not fold back when not in use.
Because the feathers had to be tucked back regardless of arboreal/terrestrial
status, their presence makes not an iota of difference in the debate, unless
one assumes a priori their function. So what did they do? Mor on that later...
>>>Avian femoral orientation laterally from the belly has been explained not as
>>>a climbing adaptation, or even particularly
arboreal, but as an accomodation of the visera beneath the pelvis and the
requisite widening of the thorax and pelvis ... the femora had to orient
laterally to accomodate.<<<
The typical theropod everted femur, which becomes more everted as it is
protracted and less so as it is retracted, in no way allows lateral splay. In
dromaeosaurs it simply everts a bit more as it is protracted; Unless
Microraptor has a pelvis and/or femur totally different from that of say,
Bambiraptor and Deinonychus, there is no way for it to employ the hind-limb
remigies as a "butt-fan," or as to generate lift furing gliding.
>>the feathers also show the same increasing distal symmetry of their brachial
>>remiges, implying a direct aerodynamic connection...<<<
I totally agree, but:
>>>...and likely for some form of flight advantage, whether they were flapping
>>>or not.<<<
Well maybe, depending on how you mean that. I apologize if I am misreading you
here, but it sounds like you are making Feduccia's classic mistake of
associating aerodynamic function with lift generation in flight. With the
limbs tucked up during a glide-leap or powered flight (not taking a position
here at the moment) the limbs become stabilizers/rudders, they could not
generate lift. The aerodynamic shape would reduce drag from the rudders, and
make them more effective. Unless someone can demonstrate a unique morphology
that would allow the rear remiges to be used in a manner sub-horizontal
relative to the line of the body, they cannot be butt-fans and/or passive lift
generators.
Note that I am not saying that Microraptor wasn't gliding or even flying,
it likely was. And it may have gotten up in trees to take advantage of
gravity. But if it did so, the lack of specializations to an arboreal
lifestyle suggests it was a secondary spread to the trees allowed by their
partial mastery of the air, not the remnents of a lineage of arboreal scansors
that birds evolved from.
Everyone please stop drawing spread-eagle sinornithosaurs until there is
convincing osteological evidence for a unique hind-limb locomotor use.
Scott Hartman
Zoology & Physiology
University of Wyoming
Laramie, WY 82070
(307) 742-3799