WASHINGTON (AP) — Prehistoric footprints that have puzzled scientists since the 1970s are getting a second look. Were they left by an extinct species of bear or ape, or by early human ancestors? When famed paleontologist Mary Leakey first uncovered the footprints in Tanzania 40 years ago, the evidence was ambiguous. Leakey is best known for finding the first clear evidence of early humans walking upright. Decades later, a new team of paleontologists re-excavated the enigmatic footprints and made photos and 3-D scans available for other researchers to continue the debate. The research was published Wednesday in the Nature.