For years, we've been asking, "Which came first: the chicken or the egg?" Maybe what we should have been asking is, "Which came first: the frog or the tadpole?" A new paper in the journal Nature details the oldest known tadpole fossil. Ringing in 20 million years earlier than scientists previously had evidence of, this fossil might get us closer to an answer.Have another scientific discovery you want us to cover on a future episode? Email us at shortwave@npr.org — we might feature your idea on a future episode! Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy