Hmm, the Taun Taun looks pretty mammilian to me. I know in the early concepts of it it was more reptilian (definately a "snow lizard" there), but I can't tell it's a "lizard" in ESB now...
The thing Obi-Wan rides looks like a large version of an earth lizard with a feathery headdress glued on (straight out of those old B-movies that used similar cheap effects, though they didn't have CG!). The Taun Taun doesn't look like any earth animal (a cross between a mountain goat, a camel and a kangaroo?).