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

Re: Phytodinosauria status





David Marjanovic wrote (in response to George):

> The basalmost dinosaur could well have
> been an obligate semisprawling quadruped (and arboreal into the bargain).
> If,
> as I think, the forelimb evolved gradually into a functioning wing
> (progressively losing its outermost digits in the process) in a lineage of
> arboreal dinosaurs,


Here you IMHO run into the same problems as Feduccia -- why should the
forelimbs (and only they) evolve into wings in a quadruped, and why should
they lose digits in an arboreal animal???


IMHO too. Modern gliders are arboreal and quadrupedal, and all are likely to have evolved from arboreal and quadrupedal ancestors: "flying" frogs, "flying" squirrels, "flying" possums, "flying" lemur (colugo)...

Most gliding mammals have the gliding membrane (patagium) strung between the forelimbs and hindlimbs. This gives the largest possible extent for the gliding surface. This is important for generating lift.

Among gliding mammals, the only exception are "flying" primates, such as sifakas. Primates are primitively quadrupedal, and most primates move around on the ground using all four limbs. However, they progress from tree to tree by bipedal leaps -
most lemurs (and relatives) are "vertical clingers and leapers". The purpose of the sifaka's gliding surface (small "armpit" patagium and brachial "mat" of hair) is as much maneverability as lift.


There is no evidence that the ancestors of birds were anything other than bipedal - unless George is advocating a "Tetrapteryx"-like stage in the evolution of birds.


Tim

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com