Neogene hyperaridity in Arabia drove the directions of mammalian dispersal between Africa and Eurasia

Madelaine Böhme,Haytham El Atfy,Michael Marks,Nikolai Spassov,David R Begun,Michael Winklhofer,Andreas Gärtner,Uwe Kirscher,Gregor Uhlig,Mahmoud Reza Majidifard,Christian Dietzel

doi:10.1038/s43247-021-00158-y

Abstract

The evolution of the present-day African savannah fauna has been substantially influenced by the dispersal of Eurasian ancestors into Africa. The ancestors evolved endemically, together with the autochthonous taxa, into extant Afrotropical clades during the last 5 million years. However, it is unclear why Eurasian ancestors moved into Africa. Here we use sedimentological observations and soluble salt geochemical analyses of samples from a sedimentary sequence in Western Iran to develop a 10-million-year long proxy record of Arabian climate. We identify transient periods of Arabian hyperaridity centred 8.75, 7.78, 7.50 and 6.25 million years ago, out-of-phase with Northern African aridity. We propose that this relationship promoted unidirectional mammalian dispersals into Africa. This was followed by a sustained hyperarid period between 5.6 and 3.3 million years ago which impeded dispersals and allowed African mammalian faunas to endemically diversify into present-day clades. After this, the mid-Piacenzian warmth enabled bi-directional fauna exchange between Africa and Eurasia, which continued during the Pleistocene.

Highlights

The evolution of the present-day African savannah fauna has been substantially influenced by the dispersal of Eurasian ancestors into Africa
The evolution of the present day African savannah fauna has been strongly influenced by the dispersal of faunal elements from a late Miocene Eurasian precursor, the Pikermian palaeobiome, and it has been suggested that many lineages of African savannah mammals originate from the midlatitudes[21]
Our study reveals a sustained period of hyperaridity in the Pliocene and a number of transient hyperaridity intervals in the late Miocene, which coincide with lake-level lowstands of the Paratethys, and explain observed temporal changes in AfroEurasian mammal dispersals

Summary

Results and discussion

Macroscopic salt crystals, salt crusts or pans, halite pseudomorphs, or other signs of leaching and reprecipitations have not been observed within this (and younger salt-bearing) sediment, suggesting that the salt (mostly halite) is finely dispersed in the mud and was not leached after deposition Above this saline horizon a package of the most dominant fluvial channels of the entire Agha Jari Formation appears (Fig. 3i, three sandstone bodies of 60-m total thickness), dated to between 6.15–5.95 Ma. Afterwards sandstones became rare and disappear at 5.6 Ma, marking the top of lower Member of Agha Jari Formation. The Lahbari Member is characterised by structureless and uniformly beige (hue 5–10R, 2.5YR) coloured saline mud sedimentation without palaeosol development (e.g., absence of rubification, lessivation, redoximorphic features, and accumulations of carbonates, sulphates or chlorides) It shows infrequent fluvial channels (Fig. 4) of very fine sandy grainsize (in contrast to fine-to-medium sized sand in the lower Agha Jari Member), where sandstone layers are clay-rich, less consolidated and thinner than 5 m. ABased on actual PET at sampling site of 2000 mm (Flint et al.126). bBased on data from Rosenthal et al.[37] and Ewing et al.[36]

12 Gachsaran

Methods

Code availability