[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Sharovipteryx



In a message dated 5/24/00 6:55:01 PM EST, ptnorton@email.msn.com writes:

<< Since there are species of moss that live exclusively in trees, even the
 absence of a skeleton can't be interpreted as absence of arboreality. I'm
 just curious about what characters can be pointed to as evidence for or
 against an arboreal lifestyle. >>

As far as I know, there is no skeletal feature or combination of skeletal 
features that is unique to arboreality among vertebrates; in nature, 
everything has a counterexample. If you're a vertebrate, you don't even need 
>limbs< to be arboreal.

On the other hand, here is the abstract of a paper titled "The Birds Came 
First" I was working on a while ago, as time permitted:

Two mutually exclusive scenarios currently compete to explain the origin of 
birds and avian flight. One, the "trees-down" scenario, explains avian flight 
as an arboreal adaptation, and argues that, because all known dinosaurs are 
terrestrial cursorial forms, they cannot be intimately related to birds. 
Anatomical similarities between birds and dinosaurs, particularly theropods, 
must therefore be convergent. The other scenario, "ground-up," argues that, 
because common ancestry of modern birds and non-arboreal, cursorial theropod 
dinosaurs is strongly supported by cladistic analyses, avian flight must have 
evolved in these dinosaurs--somehow--without passing through an arboreal 
stage. Overlooked in this debate is a third alternative, originally proposed 
in 1911 by Othenio Abel, that some early dinosaurs were small, arboreal 
animals, not terrestrial cursors, and that it is from such arboreal, birdlike 
dinosaurs, or "dino-birds," that both birds and certain ground-dwelling, 
cursorial theropod dinosaurs later descended. This scenario accounts for the 
close relationship of birds and dinosaurs without invoking a miraculous 
convergence hypothesis, and it accounts for the origin of avian flight 
without invoking the equally miraculous appearance and accumulation of 
flight-related anatomical features in animals not otherwise disposed to fly. 
Thus it likely provides a better account of dinosaurian and avian evolution 
than either the strict "trees-down" or "ground-up" scenarios.