The Mulefa in the Dark Material Series by Philip Pullman

The mulefa are the sentient species in one of philip pullman's books. They have a diamond shaped body structure and use two legs side by side to propel themselves using their two side legs, almost like living bicycles. The creatures also co evolved with a tree species that produces very hard and nearly perfect round seeds. These seeds have a hole down the centere, which the muleFA are able to stick their front and back feet through, basically becoming wheels.