So I've written a guide to converting animals between the third and fourth editions. Constructive criticism is welcome and requested, though I'm not going to argue about the basic approach, and responses of "But GURPS Animalia..." are kind of missing the point.
People often ask how to convert animal stats, and the responses "they're pretty close already" and "use
GURPS Update" fail to notice the fundamental problems of either approach. My guide tries to be a happy medium between just shoving third-edition stats into the fourth edition and getting a degree in animal biology to discover the stats by experiment.
http://trimboli.name/convanimal.html