Re: Microraptor also ate fish

[Tim Williams <tijawi@gmail.com>]

David Marjanovic <david.marjanovic@gmx.at> wrote:

> Maybe what should be researched first is whether *M.* was capable of powered
> flight and whether it was capable of gliding. (And the same, actually, holds
> all the way to *Confuciusornis*.)


I wonder how practicable this would be.  Let's say the purpose of
early aerodynamic wings was to achieve control during descents more so
than the distance travelled.  Not that these two parameters are
mutually exclusive - in modern gliding mammals, orientational control
during the glide is critically important to a safe landing (e.g.,
Byrnes &c's work on colugos; the glide is not actually "passive").
_Microraptor_ might have used its wings purely for orientational
control.  In that case, it might be difficult to categorize the wing
morphology as consistent with either "powered flight" or "gliding",
but a third option that incorporates elements of both.


I certainly agree that the flight capabilities of basal avialans
(including _Confuciusornis_) are as problematic as those of
microraptorines.  The origin of powered flight in avialans might have
had a "long fuse", with only Ornithothoraces acquiring true powered
flight.  BTW, this is the exact opposite of what GSP advocates (flight
being primitive for all maniraptorans).


> If it was capable of powered flight, it didn't need trees to take off. It
> used to be thought that the ability to take off from the ground is special
> and must have been the last step in the evolution of flight -- but, as Mike
> Habib just reminded us, it's not special at all: all extant birds capable of
> powered flight take off by jumping, no matter from where -- even
> hummingbirds derive 80 % of the necessary energy that way. No bird just
> stands there and flaps till it takes off.


As your example of the hummingbird demonstrates, you do need to have a
fairly advanced flight apparatus for this.  A 'flapping-start' model
for the origin of flight requires that the incipient wing is capable
of generating thrust.  IMHO, that's a tall order.


> At the same time, if it was capable of powered flight, it could have been
> able to spend a lot of time in trees _anyway_, _without_ being able to climb
> up a tree! Very few birds today are able to start at the ground and climb up
> a tree trunk, and, AFAIK, all of them have very special adaptations to this.
> Even juvenile hoatzins, with their finger claws, have strong perching feet
> and additionally use the beak, options denied to *Microraptor* or
> *Archaeopteryx*. Most arboreal birds are able to perch in a tree but more or
> less unable to climb.


Yes - and thank you for mentioning the hoatzin.  The wing-claws of
juveniles are just part of the equipment they use to clamber through
trees.  And juveniles of certain other bird species have wing-claws
for the same reason.  In all cases, the feet are superbly adapted for
grasping branches.


> If it was instead a glider, it _must_ have used some elevated perch (pretty
> obviously a tree given the landscape it lived in), and it _must_ have been
> able to climb there from the ground.


Unless it climbed other animals (e.g., large prey)...?  Look at Fig.
49 in the Brusatte et al. (2013) description of _Balaur_ to see what I
mean.  Or those illustrations of _Deinonychus_ riding a bucking
_Tenontosaurus_.  But this puts us well into the realm of speculation.


> If neither of these worked, and all those asymmetric feathers had _another_
> purpose _instead_ (display, brooding, quick turns during running, whatever),
> then it doesn't need to have had any climbing abilities (beyond those
> required simply by its size) and could have been exclusively terrestrial.


The "stability flapping" model of Fowler et al. (2011) also proposes
an entirely terrestrial route for the evolution of incipient wings.
However, the "stability flapping" model, as with the models you
mention (display, brooding, quick turns during running), needs to
provide an adaptive rationale for why the animal became airborne.
These exaptive models provide a template for the evolution of wings,
but not for why these wings came to be used for flight.

One advantage of a gliding/parachuting model is that the adaptive
rationale behind powered flight is essentially continuous: improved
(or more refined) aerial performance.  For example, if a small winged
maniraptoran in a dense habitat leaps from a tree, and uses the wings
to help guide its way down to open ground, then improved orientational
control would be paramount. This could be achieved initially by a
combination of drag and lift, and later by a combination of lift and
thrust (i.e., flapping).  Not that I'm advocating this route; not at
all.  But any scenario for the origin of avian flight has to provide
both a morphological rationale and an ecological rationale for how and
why theropods became airborne.  Every "how" needs a "why", even though
we may never actually know the "why".






Cheers

Tim