As shown by newly discovered fossils, scientists now know that three hominid species lived in the south of Africa circa two million years ago. This finding signaled an evolutionary event -- the distribution of a human-like, highly successful species propelled. It is still unclear, however, if these three populations occupied that region at the same time.
Two braincases were discovered at Drimolen, a set of South African caves. One of these belonged to Paranthropus robustus and the other from Homo erectus. This finding was revealed by the team led by La Trobe University paleoanthropologist Andy Herries. The discoveries range from 2.04 million to 1.95 million years ago. The scientists recently reported their findings in a paper published in Science. The fossil of Homo erectus was a child, with the low and long braincase typically seen in H. erectus adults. Meanwhile, the P. robustus fossil belonged to an adult.
Scientists have previously known of two Australopithecus species that inhabited nearby regions, particularly A. sediba and A. africanus. The former had a strange anatomical configuration that has both ape-like and human-like features. The two species lived in the area around two million years ago.
With all these findings, Herries and his colleagues discovered the occurrence of a major evolutionary transition in hominids in the south of Africa roughly around 2.1 million years ago to 1.9 million years ago. During that time, fluctuations in habitat and climatic conditions caused the extinction of Australopithecus, while P. robustus and H. erectus survived. The scientists speculate that they may have outcompeted Australopithecus for resources. The researchers are not sure if these three hominid species encountered one another during this transition period.
Texas A&M University paleoanthropologist Darryl de Ruiter, who was not part of the research team, noted that the discoveries confirmed what some scientists have predicted for some time, that three hominid genera co-existed in the south of Africa.
In other South African caves, earlier excavations suggested that A. sediba, H. erectus, and P. robustus all lived nearly two million years ago. However, many of the fossils unearthed from the latter two species have been fragmentary, making it difficult to date the cave sediments where those bones were found precisely.
Herries and his team estimated the date of the Drimolen braincases with two techniques that calculated the time of formation of the cave sediments above and just below the specimens. Data on the reversals of the Earth's magnetic field in the Drimolen sediments were instrumental in confirming the estimated fossil ages.
Paleoanthropologist de Ruiter further notes that it is still controversial which of H. erectus or A. sediba was older. It has been proposed that A. sediba was a Homo ancestor. Scientists still do not know how long A. sediba existed earlier than two million years ago. They also do not know its range, as only one fossil site has been discovered in South Africa. Nonetheless, some researchers think that A. sediba is a dead-end species, regarding East Africa instead as the best possible origin of Homo.