The Saharo-Arabian Desert is one of the largest biogeographical barriers on Earth, impeding dispersals between Africa and Eurasia, including movements of past hominins. Recent research suggested that this barrier has been in place since at least 11 million years ago. However, a new Griffith University-led study shows that numerous humid intervals occurred in the Saharo-Arabian Desert over the past 8 million years.
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Markowska et al. show recurrent humid intervals in the central Arabian interior over the past 8 million years. Image credit: Paul Breeze.
Arabia is at the center of the largest near-continuous chain of drylands on Earth; a harsh and often hyperarid belt stretching from the Sahara to the Thar Desert.
The Saharo-Arabian Desert barrier limits animal dispersal, dividing Africa and Eurasia into the Afrotropical, Palaearctic and Indomalayan biogeographic realms, each characterized by distinct assemblages of plant and animal species and communities.
The permanence of this desert barrier serves as a major control on the delineation of these biogeographic realms, whereas climatic amelioration across the Saharo-Arabian region permits dispersal between them.
Consequently, this region is a ‘transition zone,’ hosting complex faunal mixtures that have African, Eurasian and South Asian features.
Recent research suggested that drying across this desert barrier may have begun in the Late Miocene with fully arid conditions in the Sahara from at least 11 million years ago and hyperaridity in the northern Arabian margins starting at 9 million years ago.
“But fossil evidence from the Late Miocene (marked by an increase in global temperatures) and Pleistocene (which contained multiple ice ages) suggests the episodic presence within the Saharo-Arabian Desert interior of water-dependent animals,” said Griffith University’s Professor Michael Petraglia, co-senior author of the study.
“Animals such as crocodiles, equids, hippopotamids, proboscideans, were likely sustained by rivers and lakes that were largely absent from today’s arid landscape.”
“These wetter conditions likely facilitated these mammalian dispersals between Africa and Eurasia, with Arabia acting as a key crossroads for continental-scale biogeographic exchanges.”
In the new study, Professor Petraglia and colleagues analyzed a set of cave speleothems (mineral deposits such as stalagtites and stalagmites) from the Arabian interior.
This represents one of the longest paleoclimatic records currently available for Arabia, as well as one of the longest speleothem paleoclimate records globally.
“Little was known about Arabia’s paleoclimate before this time,” said Northumbria University’s Dr. Monika Markowska.
“The findings highlight that precipitation during humid intervals decreased and became more variable over time, as the monsoon’s influence weakened, coinciding with enhanced northern hemisphere polar ice cover during the Pleistocene.”
“Arabia has traditionally been overlooked in Africa-Eurasia dispersals, but studies like ours increasingly reveal it central place in mammalian and hominin migrations,” added Dr. Faisal al-Jibrin, lead Saudi archaeologist of the Heritage Commission.
The results appear in the journal Nature.
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M. Markowska et al. Recurrent humid phases in Arabia over the past 8 million years. Nature, published online April 9, 2025; doi: 10.1038/s41586-025-08859-6
