A newly discovered Paranthropus robustus fossil documents small-scale evolutionary changes. The fossil cranium shows evidence for micro-evolution and suggests environmental conditions drove rapid changes, says University of Johannesburg Palaeo-Research Institute project co-director Stephanie Baker.

Paranthropus robustus is a big toothed, extinct species of hominin from South Africa. Scientists believed that male Paranthropus robustus were much larger than females. A new fossil from Drimolen, South Africa, suggests that the species evolved rapidly because of climate change about two-million years ago.

"This specimen shows the Drimolen Paranthropus robustus looks different to those from nearby Swartkrans."

Evolution within a species can be difficult to see in the fossil record. The record usually shows large patterns, such as when species appear or go extinct. The new male from Drimolen, DNH 155, provides researchers a chance to look at this species with a magnifying lens. The DNH 155 cranium is one of the best-preserved Paranthropus robustus specimens known to science.

Paranthropus are known for their huge teeth and thick skulls, and they could eat very hard foods. As the climate became drier and cooler, they were able to survive on less desirable food stuffs.

"This wasn't the case for the Drimolen Paranthropus. The position of their chewing muscles meant they couldn't chew with as much force as the later populations. That means that the population from Drimolen was not as well adapted to a dry landscape as the later Swartkrans population. We can say that, in only 200 000 years, this species was able to adapt to the climate," explains Baker.

Drimolen is fast becoming a hotspot for early hominin discoveries. The site has a very constrained date of 2.04-million to 1.95-million years old, she says.

"Earlier this year, we announced the oldest Homo erectus in the world, DNH 134 or 'Simon'. This means there were three species of fossil hominin two-million years ago. The Drimolen team - a group of specialists from around the world - hope to expand our understanding of early human evolution.

“It is important to know how these early species adapted to the changing climate. We ourselves are facing rapid climate changes. This study shows how detailed research can give us insight into ancient populations," concludes Baker.

The team's research paper, entitled 'Drimolen cranium DNH 155 documents microevolution in an early hominin species', was published in the journal Nature Ecology & Evolution on November 9.