La Trobe archaeologists have described 18 new hominin fossils including a second Homo erectus skull fragment confirming the species’ first appearance was in southern Africa 2.0 million years ago – 200,000 years earlier than traditionally thought.
The fossils also include representatives of another species, P. robustus, and show that it was undergoing microevolutionary change in response to climatic pressures.
The Drimolen Main Quarry in South Africa’s ‘Cradle of Humankind’ is one of the richest deposits of human ancestors in the world, yet many of the fossils excavated between its discovery in 1992 and 2019 were unpublished and therefore unknown to science.
La Trobe archaeologists, together with colleagues from South Africa and the United States, have now described a further 18 fossils from this site and attributed them to Homo erectus and P. robustus.
In a paper published today in Annals of Human Biology, the scientists reveal they have identified the first fossil from an adult Homo erectus at Drimolen, dated 2 million years old. This is 200,000 years older than other Homo erectus adult fossils found in other parts of the world like Dmanisi in Georgia which are dated at 1.8 million years old.
“Homo erectus is the first species of hominin that researchers broadly agree fits within our own genus Homo and is likely directly ancestral to us. Drimolen preserves evidence for the first appearance of this species 2 million years ago, however the original fossil, DNH 134, belonged to a child aged between two and four, and there was uncertainty about what the adult version may have looked like,” lead researcher Dr Jesse Martin said.
“This paper publishes a new adult fossil attributed to Homo erectus, DNH 127, providing further confirmation that this species first appeared in southern Africa 2 million years ago.”
The researchers have also been able to confirm that P. robustus underwent micro-evolution, and evolved larger teeth and chewing muscles between 2 million and 1.8 million years ago.
Dr Martin said while Homo erectus were evolving larger brains and smaller molar teeth, possibly associated with meat eating, P. robustus maintained a brain size slightly larger than chimpanzees and evolved massive molar teeth to process tough and hard foods – like a mortar and pestle.
“These two human species shared the same landscape and are both preserved in Drimolen cave. While we know that Homo erectus and the lineage leading to us was ultimately the successful one, 2 million years ago P. robustus outnumbered Homo erectus at Drimolen by more than 10 to one. During this time period it was our ancestors that looked like the outside long-odds chance to survive,” Dr Martin said.
“This paper confirms that the P. robustus fossils from the 2 million-year-old Drimolen Cave are slightly but importantly different from the P. Robustus fossils at the 1.8 million-year-old Swartkrans cave.
“During this 200,000 year period, P. Robustus teeth became even larger, and so did the muscles associated with chewing. Hominin fossils are so rare that generally the differences between them are huge, and researchers are left to make educated guesses regarding what existed in the missing parts of the fossil record.
“However, the large number of fossils from Drimolen, some of which are published in this paper, allow an unprecedented insight into the micro-evolutionary changes that shaped human ancestors.
Dr Martin said the uniqueness of the Drimolen P. Robustus population had previously been recognised with a new sub-species name, P. Robustus ukusa, and the fossils described in the research paper support this formal recognition.
The study was conducted by scientists from the Palaeoscience Labs, Department of Archaeology and History, La Trobe University, Palaeo-Research Institute, University of Johannesburg, Evolutionary Studies Institute, University of the Witwatersrand, and Department of Anthropology, Washington University.
Read the full paper: New hominin cranial and mandibular remains from Drimolen Main Quarry, South Africa
