In a groundbreaking discovery during a decades-long archaeology project in northeastern Ethiopia, ancient, fossilized teeth have been unearthed that suggest the coexistence of two distinct kinds of hominins, or human ancestors, between 2.6 and 2.8 million years ago. This revelation may indicate the presence of a previously unknown species, offering fresh insights into the intricate tapestry of human evolution.
Between 2018 and 2020, researchers uncovered ten teeth belonging to the genus Australopithecus, an ancient human relative, alongside three teeth from the genus Homo, which includes modern humans, or Homo sapiens. These findings were published on Wednesday in the prestigious journal Nature. The overlap of these two hominins in the fossil record is remarkably rare, challenging previous assumptions that Homo emerged after Australopithecus.
The Australopithecus species exhibited bipedalism similar to modern humans but possessed smaller brains, akin to those of apes. The emergence of Homo species, characterized by larger brains, is often perceived as an evolutionary advancement. However, the coexistence of these two groups highlights a more complex picture of evolution. “This new research illustrates that the common perception of a linear evolution from ape to Neanderthal to modern human is misleading,” said Kaye Reed, a co-author of the study and research scientist at the Institute of Human Origins.
Reed has been a co-director of the Ledi-Geraru Research Project since 2002, which aims to uncover evidence of early Homo species. In 2015, the team made headlines by discovering the oldest known Homo jawbone, dated at 2.8 million years. Moreover, attempts to find later evidence of Australopithecus afarensis, which emerged 3.9 million years ago, have yielded no signs beyond 2.95 million years ago, indicating a potential extinction prior to the first appearance of Homo.
The newly identified Australopithecus teeth were compared to known species like afarensis and another group called garhi, revealing distinct differences. The team believes these teeth belong to a previously unknown species of Australopithecus that lived after Lucy, the famous fossil discovered in 1974. Reed expressed surprise at the discovery, emphasizing its importance in illustrating the non-linear nature of human evolution.
The teeth were uncovered in the Afar region, a critical site for paleoanthropological research. This area has yielded numerous preserved fossils and some of the earliest stone tools, thanks to its unique geological conditions. The region’s active tectonic processes expose ancient layers of sediment, vital for understanding nearly five million years of evolutionary history.
The Australopithecus teeth were dated to approximately 2.63 million years ago, while the Homo teeth date back to 2.59 and 2.78 million years ago. Researchers remain cautious about classifying these teeth into specific species until more data and fossils are available. Brian Villmoare, the lead author, emphasized the need for additional fossil evidence to clarify the distinctions between Australopithecus and Homo and understand their coexistence in the fossil record.
Finding these teeth was no easy task, as they resemble common pebbles scattered across the landscape. Local fossil hunters have played a crucial role in this endeavor, leveraging their lifelong familiarity with the terrain to identify these rare finds.
This study is significant as it sheds light on a crucial period in human evolutionary history, spanning from 3 million to 2 million years ago. Dr. Stephanie Melillo, a paleoanthropologist, pointed out that understanding this timeframe is challenging due to historical sediment deposition patterns in eastern Africa. Structural basins, like the Turkana Basin, have proven essential for gathering sediment layers that contain fossils, while the Afar Depression, the focus of this study, shows similar potential.
The research indicates that Australopithecus did not exist in isolation, as evidenced by its interaction with Homo. Reed and her team aim to investigate whether these two hominins shared or competed for resources by analyzing isotopes in their teeth. Additionally, they intend to determine which hominin was responsible for the stone tools discovered at the site. While the exact nature of their coexistence remains uncertain, Reed expressed hope for more discoveries that will provide greater clarity on our ancient ancestors.
In conclusion, the discovery of these ancient hominin teeth in northeastern Ethiopia marks a significant milestone in our understanding of human evolution. As researchers continue to explore this rich archaeological site, we may uncover even more clues about the complex interactions and adaptations of our early ancestors.
