Early evidence of continental aridity and open-habitat grasslands in Europe as revealed by the Middle Miocene microflora of the Madrid Basin

In this study we present a new, extensive palaeobotanical and palaeoclimatic record from 85 microfloral assemblages of Middle Miocene (late Langhian-early Serravallian) age recovered from ten localities in the Madrid Basin. A large, shallow, slightly saline lacustrine system developed in the study area, promoting the occurrence of salt-tolerant plant communities on the lake margin. The regional landscape of the basin was characterised by grass-dominated, savannah-like vegetation under a warm (MAT: 13.8-18.8 degrees C) and semi-arid (MPwet: 151-71 mm, MPdry: 45-4 mm) climatic regime with marked seasonality of temperature and precipitation. These data reopen the debate on the origin of grasslands linked to dry conditions in Europe. Overall increased cooling and aridity through the Miocene led to the onset of grass-dominated habitats at the expense of forests, a process that in eastern Europe has been shown to occur from the Late Miocene. Our results, together with previous palaeobotanical and fossil mammal data from southern and central Spain, strongly indicate that open habitats were already prevalent in the Iberian Peninsula in the Middle Miocene, suggesting an earlier establishment here than in eastern Europe, possibly following a temporal pattern like the Anatolian Peninsula. The taxonomic diversity yielded by the samples from the Madrid Basin contributes to the understanding of the floristic composition of these early open habitats which were dominated by Poaceae, Amaranthaceae and Asteraceae with scattered shrubby and arboreal plants adapted to dry conditions such as Ricinus, Ephedra, Olea, Quercus, Acacia and Pinus. The age of the studied samples, coincident with the Middle Miocene Climatic Transition, indicates that this climatic episode marked an important step towards the establishment of open vegetation.

Automated summary

The study presents a new palaeobotanical and palaeoclimatic record from the Madrid Basin during the Middle Miocene period, indicating the existence of open grassland habitats under warm and semi-arid climatic conditions. The data suggest that the onset of grass-dominated habitats was influenced by increased cooling and aridity throughout the Miocene, leading to changes in landscape and vegetation composition. The taxonomic diversity of plant species in the region contributes to a better understanding of the floristic composition of early open habitats dominated by grasses, suggesting an earlier establishment of open habitats in the Iberian Peninsula compared to eastern Europe.