What early human relative, whose foot bones and other fossils were attributed to a recently discovered species, lived alongside Lucy?

For many years, the widely accepted view of early human evolution suggested that only one hominin species, Australopithecus afarensis—famously represented by the "Lucy" skeleton—inhabited East Africa between approximately 3.8 and 3 million years ago. However, this perspective has been challenged by the discovery of another ancient human relative, Australopithecus deyiremeda. This species lived around 3.5 to 3.3 million years ago in the same region of Ethiopia, directly overlapping in time (Review) with Lucy's kind.

The identification of Australopithecus deyiremeda was significantly bolstered by the study of a 3.4-million-year-old partial foot fossil, known as the "Burtele foot," found in Ethiopia's Afar Rift in 2009. While initially unassigned, further fossil discoveries, including jaws and teeth from the same geological layers, allowed scientists to confidently attribute the foot bones to Australopithecus deyiremeda. This species presented a fascinating mix of primitive and advanced traits, notably possessing an opposable big toe, a feature helpful for grasping branches and tree climbing, while still being capable of walking on two legs. This contrasts with Australopithecus afarensis, whose feet were more adapted for fully committed ground-walking, with a forward-pointing big toe.

The co-existence of Australopithecus deyiremeda and Lucy's species, Australopithecus afarensis, reveals a more diverse early human family tree than previously thought. Researchers suggest that these two species likely avoided direct competition by adapting to different environments and diets. Australopithecus deyiremeda appears to have relied on resources found in woodlands, such as leaves and fruits, while Australopithecus afarensis occupied more open environments and consumed a broader range of foods. This "niche partitioning" allowed multiple hominin species to thrive in the same landscape, offering valuable insights into the complex evolutionary pathways that led to modern humans.