[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
RE: Compiled theories of flight's origin
Anthony Docimo wrote:
> * Ground Up - a ground-dwelling maniraptor flaps arms covered in
> protofeathers, and after a thousand or so
> generations, it gets off the ground an appreciable amount.
> * Trees Down - a tree-dwelling maniraptor spreads its protofeathered arms to
> slow its leap from the branches
> to the ground/prey.
Traditionally, most scenarios concerning the origin of vertebrate flight have
fallen into these broad categories ("Ground Up" or "Trees Down". However, this
can be potentially misleading.
Firstly, the "Ground Up" vs "Trees Down" dichotomy focuses on the role of
gravity in the incipient stages - if the animal is working with it or against
it. The former is usually associated with an arboreal ecology and the latter
is usually associated with a terrestrial ecology. But there are exceptions.
For example, the "Pouncing Proavis" model proposes that pro-avians leaped
downward, but were not arboreal (they launched themselves from rocks, etc). On
the other hand, somebody (might have been GSP) suggested that pro-avians lived
in trees, but leaped upward from branch to branch ("Trees Up").
Secondly, there is no reason to assume that the "Ground Up" vs "Trees Down"
scenarios are mutually exclusive. Both behaviors may have played a role in the
incipient stages of flight. I supect this is especially relevant to the origin
of avian flight; but probably not for the evolution of bat flight. Dunno about
Thirdly, it helps to remember that for the evolution of powered flight, the
development of the flight stroke is equally important as the development of the
wing. Many hypothetical pre-flight scenarios focus on one and neglect the
other - irrespective of whether they fall into the Ground Up" or "Trees Down"
Peek-a-boo FREE Tricks & Treats for You!