Two diagrams show the location of the hominid footprints found by archaeologist Mary Leakey's team at Laetoli. Other animal tracks are also visible. These tracks, at least 3.6 million years old, were the first evidence paleontologists found of upright walking, an ability unique to humans. According to Ian Tattersall: "Usually behavior has to be inferred indirectly from the evidence of bones and teeth, and there is almost always argument over inferences of this kind. But at Laetoli, through these footprints, behavior itself is fossilized."