Actually, Pikia had no legs, but one of it's descendants dis - oops!

Don - I got to thinking about this after I posted; palaeontologists and zoologists often enjoy speculation about how evolution might have played out if the variables had been different; check out these speculative zoology blogs:

Metazoica

Speculative Dinosaur Project - scroll down to see the excellent sketches on how penguins (extant dinosaurs of course) might have developed.