They formed in the same way our footprints do when walking on soft ground like mud. But rather than being washed away, evidence of some of these reptiles' movements has survived for millions of years.

And because the footprints fall next to each other, they indicate that the two hominids were walking side by side and close enough to each other to be touching. Apes sometimes walk on two legs.

Have you ever been for a walk and noticed a trail of footprints? Maybe you were walking ... the rain washes them away or if someone cleans the floor. Then the trail is gone for good.