Is 'Little Foot' a human ancestor—or just a distant cousin?
Jason Heaton

Is 'Little Foot' a human ancestor—or just a distant cousin?

They call him “Little Foot” but he’s a big deal to human evolution researchers. From this putative human ancestor’s beautifully preserved head (shown above) to his fairly small feet, this australopithecine—a cousin to the famous 3.2-million-year-old “Lucy,” also a candidate for a human ancestor—is the most complete australopithecine skeleton ever found. But since he was discovered in South Africa’s Sterkfontein Caves in the early 1990s, researchers have argued bitterly about how old he is, with estimates ranging from 2.2 million to 4 million years old. Now, researchers using a state-of-the-art dating technique that employs isotopes of the elements aluminum and beryllium conclude that Little Foot died 3.67 million years ago, as they report online today in Nature. If correct, it could mean that Little Foot is an ancestor of the more than 3-million-year-old human line. The team also argues that Little Foot belongs to a new species, which it calls Australopithecus prometheus. But some skeptics are not buying such an early date, arguing that the team might be dating the wrong rocks (the skeleton itself can’t be dated because it is too old for radiocarbon and techniques for dating older fossils rely on dating the rocks and sediments in which they are found), and also that the aluminum-beryllium technique might not be suitable for South Africa’s limestone caves. Researchers also question whether Little Foot represents a new species or is just a spectacularly well-preserved specimen of Australopithecus africanus, a well-known australopithecine that lived in South Africa between 3 million and 2 million years ago and was probably an evolutionary sideline and not a human ancestor. Most are withholding judgment until a detailed anatomical analysis of the skeleton is published, which won’t appear any earlier than next year.