ORBIT RIGHT! What do the Platypus and Echidna, both mammals, have in common? They both lay eggs. They both spend as much time in the water as on land. They both live underground Next Question The Platypus and Echidna both lay eggs. These are the only 2 mammals that lay eggs. Since you've been enjoying the site, it's time to get into ORBIT! Join now for super cool DOWNLOADS, MIND BENDERS that spark your curiousity, action-packed GAMES, and BRAIN BUZZ challenges to make you a big thinker! © 2013 High Touch Entertainment, LLC All Rights Reserved Tweet