"Mystery" prehistoric footprints re-excavated for second look: Were they left by bears or human ancestors?

Prehistoric footprints that have puzzled scientists since the 1970s are getting a second look: Were they left by extinct animals or by human ancestors?

When famed paleontologist Mary Leakey first uncovered the footprints in Tanzania 40 years ago, the evidence was ambiguous.

Leakey focused her attention instead on other fossil footprints that could be more clearly linked to early humans. Those footprints, found at a site called Laetoli G, are the first clear evidence of early humans walking upright.