Re: Gliders to Fliers?

[Dinogeorge@aol.com]

In a message dated 9/26/99 7:06:04 PM EST, mbonnan@hotmail.com writes:

<< I'm confused now, so please clear this up 
 for me: are you saying that each major group (clade, grade, what-have-you) 
 of dinosaurs descended in progressive order from arboreal archosaurs which 
 eventually became the birds?  For instance, the Ceratosaurs came down first, 
 followed by the early Tetanurans, then the Maniraptorans, etc.?
 >>

Yes, you've got it quite right. Secondary flightlessness occurred 
independently >many< times off the lineage leading from basal archosaurs to 
birds, and each flightless lineage thereafter evolved its own set of 
apomorphies and adaptations to cursorial terrestrial lifestyle. Makes 
cladistic analysis very difficult, for one thing, because of massive 
convergence and vestigialization. Theropods all look alike because there 
aren't many ways for a bipedal predator with a long tail and diminished 
forelimbs to look. Think of the problems we still have classifying Cenozoic 
large fossil ground-dwelling birds!