More than 20 years ago, a skeleton called Little Foot turned up in a South African cave. The nearly complete skeleton was a hominid, or member of the human family. Now researchers have freed most of the skeleton from its stony shell and analyzed the fossils. And they say 3.67-million-year-old Little Foot belonged to a unique species.
Ronald Clarke and his colleagues think Little Foot belonged to Australopithecus prometheus (Aw-STRAAH-loh-PITH-eh-kus Pro-ME-thee-us). Clarke works at the University of the Witwatersrand in Johannesburg, South Africa. As an paleoanthropologist, he studies fossilized humans and our relatives. The scientists shared their findings in four papers. They posted them at bioRxiv.org between November 29 and December 5. Scientists have suggested the species A. prometheus might exist. But many researchers have challenged that claim.
Clarke, however, has believed in that species for more than a decade. He found the first of Little Foot’s remains in 1994. They were in a storage box of fossils from a site called Sterkfontein (STARK-von-tayn). People began excavating the rest of the skeleton in 1997.
Many other researchers instead argue that Little Foot likely belonged to a different species. This hominid is known as Australopithecus africanus. Anthropologist Raymond Dart first identified A. africanus in 1924. He was studying the skull of an ancient youngster called the Taung Child. Since then, people have turned up hundreds more A. africanus fossils in South African caves. Those include Sterkfontein, where Little Foot was found.
The braincase is the part of the skull that holds the brain. And researchers found a partial braincase that Dart thought belonged to a different species in Makapansgat, one of those other caves. In 1948, Dart called this other species A. prometheus. But Dart changed his mind after 1955. Instead, he said that braincase and another fossil at Makapansgat belonged to A. africanus. There was no A. prometheus after all, he concluded.
Clarke and his colleagues want to bring back the rejected species. They say Little Foot’s distinctive skeleton, an adult female that is at least 90 percent complete, is solid evidence for it. Says Clark: “Little Foot fits comfortably in A. prometheus.”
The scientists estimated the ages of Little Foot and other fossils from Sterkfontein and Makapansgat. Based on those ages, Clarke says A. prometheus survived for at least one million years. And, he adds, this species would have lived along with the younger A. africanus for at least a few hundred thousand years. The new papers will appear in an upcoming issue of the Journal of Human Evolution. The journal will also publish several other new analyses of Little Foot’s skeleton.
Walking into an argument
Still, the team’s claims remain controversial. The papers “fail to make a sound case” for a second Sterkfontein species, says Bernard Wood. He’s a paleoanthropologist at George Washington University in Washington, D.C.
Two other paleoanthropologists agree. They’re Lee Berger at the University of the Witwatersrand and John Hawks of the University of Wisconsin–Madison. Their comments will be published in the American Journal of Physical Anthropology. These researchers argue that Dart was right to get rid of A. prometheus. He never showed a clear difference between that species and A. africanus, they say. “I’m keeping an open mind, but I haven’t seen data [in the papers] to support any grand ideas about Little Foot,” Hawks says.
Clarke says Little Foot does have skull features that set it apart from A. africanus. He and a Witwatersrand colleague, Kathleen Kuman, describe those features in one new study. They point to the sides of Little Foot’s braincase. They’re more vertical than the sides of the one in A. africanus. And Little Foot has heavily worn teeth, from the front of the mouth to the first molars. That suggests Little Foot ate tubers, leaves and fruits with tough skins, Clarke says. A. africanus, in contrast, ate a larger variety of foods, he adds — ones that were gentler on teeth.
Robin Crompton works the University of Liverpool in England. He is an evolutionary biologist who led a second new study. It found that Little Foot had humanlike hips. And her legs were longer legs than her arms. That’s also a humanlike trait and hints that Little Foot walked upright. Such features are most similar to a 3.6-million-year-old skeleton dubbed Big Man. That skeleton, from East Africa, belonged to the species Australopithecus afarensis. The researchers think the ability to walk upright may have evolved at the same time in different parts of Africa.
Little Foot walked well but also was a good tree climber, the researchers say. She might have moved across tree branches upright while lightly grabbing branches with her arms for support. This is similar to how orangutans move. Crompton thinks this upright movement through trees later evolved into full-time, two-legged walking.
Owen Lovejoy led the analysis of Big Man’s skeleton. He’s a paleoanthropologist at Kent State University in Ohio. Lovejoy doubts that Little Foot did much walking across tree branches. And he disagrees with Crompton’s idea of how upright walking evolved. Big Man and Little Foot had bodies built for upright walking, he thinks. And they would have walked on the ground, not through trees.
Lovejoy says that one of the new papers supports his idea. That paper shows that Little Foot fell from a short height as a child. This caused a bone-bending forearm injury. (Clarke was an author of that study.) The injury would have made it hard to climb trees. If Little Foot was able to survive into adulthood with this arm injury, upright walking must have been especially important to her species, Lovejoy says.
Small brained woman
Carol Ward is a paleoanthropologist at the University of Missouri in Columbia. She predicts that more studies of Little Foot’s body parts will help to resolve these debates about her way of life. Yet another new study has just come out in the January Journal of Human Evolution. It focused on Little Foot’s brain size.
Amélie Beaudet is a paleoanthropologist at the University of Witwatersrand. She and her colleagues used scanning technologies to help a computer make a 3-D reconstruction, or digital cast, of Little Foot’s brain surface. They then compared it to similar digital casts of 10 other South African hominid specimens. Those fossils were between roughly 1.5 million and 3 million years old.
Little Foot had a small brain. Hers was only about one-third the volume of a modern adult woman’s, the new analyses show. In fact, Little Foot’s was more chimplike than was the brain of any other southern African hominid. That’s not surprising, the investigators add: Little Foot is also the oldest known southern African hominid.
3-D Short for three-dimensional. This term is an adjective for something that has features that can be described in three dimensions — height, width and length.
anthropology The study of humankind. A social scientist who studies different societies and cultures is called an anthropologist.
Australopithecus An extinct genus of hominids that lived in East Africa from about 4 million to 2 million years ago.
biology The study of living things. The scientists who study them are known as biologists.
braincase A part of the skull that protects the brain.
colleague Someone who works with another; a co-worker or team member.
digital (in computer science and engineering) An adjective indicating that something has been developed numerically on a computer or on some other electronic device, based on a binary system (where all numbers are displayed using a series of only zeros and ones).
evolution (v. to evolve) A process by which species undergo changes over time, usually through genetic variation and natural selection. These changes usually result in a new type of organism better suited for its environment than the earlier type. The newer type is not necessarily more “advanced,” just better adapted to the particular conditions in which it developed.
evolutionary biologist Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).
family A taxonomic group consisting of at least one genus of organisms.
fossil Any preserved remains or traces of ancient life. There are many different types of fossils: The bones and other body parts of dinosaurs are called “body fossils.” Things like footprints are called “trace fossils.” Even specimens of dinosaur poop are fossils. The process of forming fossils is called fossilization.
hominid A primate within the animal family that includes humans and their ancient upright-walking relatives. Except for humans, all other hominids are known only from fossils.
orangutan One of the great apes (which also include gorillas, chimpanzees and bonobos), this red-haired tree dweller shares 97 percent of its genes in common with humans. They can live for 60 years, with adults weighing 48 to 130 kilograms (105 to 286 pounds) depending on gender, age and health, with males being bigger. They have opposable thumbs (as humans do) and also opposable big toes, which aids in their gripping.
paleoanthropologist A scientist who studies ancient humans and hominid biology, also the behavior and evolution of hominids evolved. This field is based on the analysis of fossils, remnants, artifacts or markings created or used by hominids.
physical (adj.) A term for things that exist in the real world, as opposed to in memories or the imagination. It can also refer to properties of materials that are due to their size and non-chemical interactions (such as when one block slams with force into another).
physical anthropology The type of anthropology, or study of humankind, that deals with how humans have gradually changed over time. It includes how their look or structures might have varied.
skull The skeleton of a person’s or animal’s head.
species A group of similar organisms capable of producing offspring that can survive and reproduce.
trait A characteristic feature of something. (in genetics) A quality or characteristic that can be inherited.
unique Something that is unlike anything else; the only one of its kind.
vertical A term for the direction of a line or plane that runs up and down, as the vertical post for a streetlight does. It’s the opposite of horizontal, which would run parallel to the ground.
Journal: A. Beaudet et al. The bony labyrinth of StW 573 (“Little Foot”): Implications for early hominin evolution and paleobiology. Journal of Human Evolution. Vol. 127, February 2019, p. 67. doi:10.1016/j.jhevol.2018.12.002.
Journal: A. Beaudet et al. The endocast of StW 573 (“Little Foot”) and hominin brain evolution. Journal of Human Evolution. Vol. 126, January 2019, p. 112. doi:10.1016/j.jhevol.2018.11.009.
Journal: R.H. Crompton et al. Functional anatomy, biomechanical performance capabilities and potential niche of StW 573: an Australopithecus skeleton (circa 3.67 Ma) from Sterkfontein Member 2, and its significance for the last common ancestor of the African apes and for hominin origins. bioRxiv. Posted online November 29, 2018. doi:10.1101/481556.
Journal: L. Bruxelles et al. A multiscale stratigraphic investigation of the context of StW 573 Little Foot and Member 2, Sterkfontein Caves, South Africa. bioRxiv. Posted online November 29, 2018. doi:10.1101/482711.
Journal: R.J. Clarke and K. Kuman. The skull of StW 573, a 3.67 Ma Australopithecus skeleton from Sterkfontein Caves, South Africa. bioRxiv. Posted online December 4, 2018. doi:10.1101/483495.
Journal: A.J. Heile et al. Bilateral asymmetry of the forearm bones as possible evidence of antemortem trauma in the StW 573 Australopithecus skeleton from Sterkfontein Member 2 (South Africa). bioRxiv. Posted online December 5, 2018. doi:10.1101/486076.
Journal: L.R. Berger and J. Hawks. Australopithecus prometheus is a nomen nudum. American Journal of Physical Anthropology, in press, 2018.