Extinct human species evolved rapidly to survive a period of climate change 2 million years ago
A species of ancient human that lived two million years ago was forced to evolve and change its physical traits in order to survive . The emergence of Paranthropus robustus happened roughly at the same time as the more primitive hominin species Australopithecus died out. It is believed this period of rapid change in occurred due to significant climate change forcing animals to adapt, or die. During this period of time the first members of the Homo genus, of which modern humans are descended, also emerged. Homo erectus and P. robustus took different approaches to the changing world, with the former developing a big brain to make tools in order to tackle the issue of hard, chewy food sources. The latter, however, underwent physical changes and evolved larger teeth and powerful chewing muscles over 200,000 years a rapid evolutionary intervention. Scroll down for video 'These two vastly different species, H. erectus with their relatively large brains and small teeth, and P. robustus with their relatively large teeth and small brains, represent divergent evolutionary experiments,' said Angeline Leece of La Trobe University, the other first author of the study. 'While we were the lineage that won out in the end, the fossil record suggests that P. robustus was much more common than H. erectus on the landscape two million years ago.' Researchers discovered a new fossil of the P. robustus species in the fossil-rich Drimolen cave system northwest of Johannesburg in the so-called Cradle of Humanity. They compared this to others of the same species which had previously been found. Existing theories claimed there was a large amount of variance in the size of the males and females of the species, a phenomenon known as sexual dimorphism seen in many living animals. However, the new specimen, called DNH 155, which is clearly male and believed to be the best preserved example of his species, dispels this. The researchers, from Washington University in St Louis and La Trobe University in Australia, now think it exemplifies the way the species physically changed. One notable trait that changed over time is its dentition. Dr Leece says: 'We now know that tooth size changes over time in the species, which begs the question of why. 'There are reasons to believe that environmental changes placed these populations under dietary stress, and that points to future research that will let us test this possibility.' Existing fossils from the time this species existed prove mammals that relied on woods and bushland went extinct while other species associated with drier, more open environments appeared in the area for the first time. P. robustus, which appeared at this time of flux, was built for the arid conditions. Professor David Strait, professor of biological anthropology at Washington University, says as a result it was well-suited to eating tough foods that grew in this new climate. 'P. robustus is remarkable in that it possesses a number of features in its cranium, jaws and teeth indicating that it was adapted to eat a diet consisting of either very hard or very tough foods,' he said. 'We think that these adaptations allowed it to survive on foods that were mechanically difficult to eat as the environment changed to be cooler and drier, leading to changes in local vegetation.' The researchers found that the earliest members of this species had chewing muscles which were weaker than their descendants. Over the course of 200,000 years, a dry climate likely led to natural selection favouring the evolution of a more efficient and powerful feeding apparatus in the species,' says Professor Strait. The findings are published in the journal