Some 3.6 million years ago, in Laetoli, Northern Tanzania, a volcano erupted, spewing ash and soot that came to settle in the plains below and, for a period of perhaps a few days, thickened into a layer of mud. This pyroclastic goo would prove a boon for archaeologists millions of years later, thanks to the thousands of animal tracks found pressed into it, each of which offers a tantalising snapshot of a day lived in the deep past.
Most famously, the Laetoli trackways would produce the earliest evidence of bipedalism in hominins, thanks to a set of footprints at Laetoli site G, excavated in the late 1970s. These prints belonged to an individual Australopithecus afarensis, the hominin ancestor most famously known from the fossilised specimen called Lucy.
Now, a re-analysis of footprints at Laetoli site A, long thought to have been laid down by an upright bear, has revealed they almost definitely belonged to another bipedal hominin ancestor – albeit one with a strange and shuffling gait. The new study, out today in the journal Nature, cements the reality that Africa 3.5 million years ago was populated by a far more diverse range of human ancestors than once thought.