MicroCT scans of a 3.67-million-year-old Australopithecus fossil, known as “Little Foot,” have provided scientists with unprecedented insights into how this early hominin lived and moved. This fossil, discovered in the Sterkfontein Caves of South Africa, is one of the most complete hominin skeletons ever found, offering a glimpse into the distant past. The latest research, led by scientists at the University of the Witwatersrand’s Evolutionary Studies Institute, focused on the inner ear of Little Foot, revealing important clues about her locomotion, hearing capabilities, and how she may have interacted with her environment. The results were published in the Journal of Human Evolution as part of a special issue dedicated to Little Foot’s near-complete skeleton.
The Role of the Inner Ear in Understanding Evolution
The inner ear, specifically the semicircular canals and cochlea, plays a vital role in our understanding of how ancient hominins lived. These structures not only help with balance and movement but also contribute to auditory processing. By examining these parts in fossilized remains, researchers can deduce important information about a species’ mobility, behavior, and even its sensory capabilities. The research team, including Dr. Amélie Beaudet and Professor Ronald Clarke, virtually extracted Little Foot’s inner ear using MicroCT technology, which allowed them to study the fossil in incredible detail without damaging it.
The team compared Little Foot’s inner ear with 17 other hominin specimens from different sites in South Africa, such as Sterkfontein, Swartkrans, and Makapansgat, dating between three and 1.8 million years ago. These specimens came from several genera, including Australopithecus, Paranthropus, and early Homo, as well as modern humans and chimpanzees. What emerged from this comparative analysis was a fascinating mixture of both ape-like and human-like features in Little Foot’s inner ear.
Locomotion and Balance
One of the most striking findings from this study was the structure of the semicircular canals in Little Foot’s inner ear. These canals, which are essential for balance and orientation during movement, exhibited characteristics that were more similar to those of chimpanzees than modern humans or Paranthropus. “By contrast, we found that the Little Foot inner ear canals are close to those of chimpanzees,” says Dr. Beaudet. This is significant because it suggests that, like chimpanzees, Little Foot’s movements were not fully adapted for the kind of bipedal running seen in modern humans. Instead, Little Foot’s anatomy indicates a species that engaged in bipedal walking on the ground but likely retained some ability to move through the trees.
This difference in inner ear structure suggests that the transition to fully upright bipedalism was a gradual process. The semicircular canals of modern humans have evolved for running and upright walking over long distances, but Little Foot’s canals were adapted for a more varied range of movements. This may imply that species in the Australopithecus genus were versatile in their locomotion, capable of moving both on the ground and in the trees. The diversity in the shape of the inner ear canals among Australopithecus species further supports this idea, suggesting that there was considerable variation in how different hominins within this genus moved and interacted with their environment.
Cochlea and Sound Perception
Another key aspect of the inner ear examined in the study was the cochlea, the spiral-shaped structure responsible for translating sound vibrations into neural signals. Little Foot’s cochlea, which is essential for hearing, bore a strong resemblance to that of other Australopithecus specimens, as well as Paranthropus, but differed significantly from the cochlea of early Homo specimens. This finding provides important information about the auditory capabilities of different hominin species and suggests that Little Foot’s hearing was distinct from that of modern humans.
The shape and size of the cochlea are closely linked to the range of frequencies an individual can hear. Fossil Homo specimens exhibited a cochlea that suggested a greater capacity for detecting low-frequency sounds, a feature that may have been related to adaptations for communication or environmental awareness. In contrast, Little Foot’s cochlea, like those of other Australopithecus species, had a more limited range of frequency detection, which could indicate differences in how they communicated or interacted with their surroundings.
“This organ is related to sound perception and ecological factors such as diet, habitat, or communication,” explains Dr. Beaudet. The shape of Little Foot’s cochlea suggests that she did not have the same hearing abilities as early Homo species, possibly reflecting a difference in behavior or ecological adaptation. The research team is still exploring the implications of these differences, as they may provide valuable insights into how early hominins adapted to their environments, particularly in terms of communication or social interaction.
Comparing Little Foot to Other Fossils
One of the most exciting aspects of the study was the comparison of Little Foot’s inner ear with other hominin fossils, particularly a specimen from the Jacovec Cavern in the Sterkfontein Caves. This specimen, which dates to a similar period as Little Foot, provided a crucial reference point in identifying specific traits that might be unique to early humans. “Having a reference point such as comparing Little Foot to the Jacovec specimen is important in detecting which traits are specific to us (humans), and whether humans evolved more distinct characteristics,” says Dr. Beaudet.
This comparison is vital because it allows scientists to trace the evolution of specific features, such as the shape of the inner ear, that distinguish humans from other hominin species. By understanding when certain traits emerged in the fossil record, researchers can gain a clearer picture of how human beings evolved over time. For example, the inner ear of Little Foot and other Australopithecus fossils may indicate that early humans had not yet developed the specialized balance adaptations seen in modern human anatomy.
Implications for Hominin Evolution
The findings from this study contribute to our understanding of hominin evolution, particularly in terms of how our ancestors adapted to different environments and modes of locomotion. While the study focused on the inner ear, its implications extend to broader questions about human evolution, including the transition from tree-dwelling to ground-dwelling behaviors, the development of communication, and the diversification of hominin species.
For instance, the fact that Little Foot and other Australopithecus species displayed characteristics related to both terrestrial and arboreal movement suggests that the path to modern bipedalism was not linear. Rather, early hominins likely adapted to a variety of habitats, using different forms of locomotion as needed. This study also raises interesting questions about the role of hearing in the evolution of hominins. The differences in cochlear structure between Australopithecus, Paranthropus, and early Homo suggest that auditory perception may have been an important factor in social behavior and communication during the early stages of human evolution.
More information: Amélie Beaudet et al. The bony labyrinth of StW 573 (“Little Foot”): Implications for early hominin evolution and paleobiology, Journal of Human Evolution (2018). DOI: 10.1016/j.jhevol.2018.12.002