23 January 2019
The grass was definitely greener for hominins in Arabia
Published online 2 November 2018
Homo species dispersed into the green grasslands of the Arabian Peninsula between 300,000 and 500,000 years ago.
The Arabian Peninsula has only recently become a focus of paleontological exploration, partly owing to the difficulties of working in a desert environment and partly because researchers thought it unlikely that Homo species, or hominins, would migrate into arid lands. Unlike our own species, Homo sapiens, who appear to be uniquely adaptable to new and extreme environments, pre-Homo sapiens hominins may not have been as able to cope with different ecological settings.
Now, analyses of fossilised animal bones and newly discovered stone tools from Ti’s al Ghadah in northern Saudi Arabia suggest that hominins dispersed into the region 100,000 years earlier than previously thought. At the time, the Peninsula was covered in savannah-like grasslands and experienced a wetter climate than today.
“Direct evidence indicating how green Arabia once was has been lacking,” says Patrick Roberts at the Max Planck Institute for the Science of Human History in Germany, who led the study alongside his colleague Michael Petraglia and Mathew Stewart of the University of New South Wales, Australia. “We undertook renewed archaeological excavations and analysis of fossil fauna from Ti’s al Ghadah — the only dated collection of middle Pleistocene fossil animals in this region — to try to find out more.”
The team found stone tools and cut marks on bones suggestive of the butchery of animals, confirming a hominin presence in association with these animals 500,000 to 300,000 years ago. This is the earliest fossil assemblage associated with hominins ever found on the Arabian Peninsula.
The researchers examined animal tooth remains using carbon and oxygen isotope analysis to confirm the types of vegetation the animals lived off.
“Carbon isotopes from herbivore tooth enamel track the abundance of different plants with different photosynthesis pathways present in their diet,” explains Roberts. “The main distinction is between C3 plants — trees, shrubs, and shade-loving grasses — and C4 plants — arid-adapted grasses and sedges with warmer growing seasons. C4 dominated in our samples, suggestive of warm, savannah-like grasslands, like East Africa today.”
“These findings are significant on two fronts,” says Brian Stewart, paleoanthropologist at the University of Michigan, who was not involved in the study. “Firstly, Roberts’ team provide valuable empirical confirmation, including precipitation and vegetation details, of local and regional paleoenvironmental conditions. Secondly, and more importantly in my view, they suggest that when pre-Homo sapiens hominins moved into a green Arabia, they likely required few specific innovative adaptations to live there. This reinforces an emerging pattern of contrast between these hominins and our own species with regards to adaptive elasticity.”
Roberts, P. et al. Fossil herbivore stable isotopes reveal middle Pleistocene hominin palaeoenvironment in ‘Green Arabia’. Nat. Ecol. Evol. http://dx.doi.org/10.1038/s41559-018-0698-9 (2018).