• For the first time we demonstrate that C4 grasses were the dominant herbaceous element of the Pikermi Formation. Our habitat reconstruction suggests fire-prone woody grasslands and woodlands within a savannah biome for Pikermi and Pyrgos and, thus, provides unambiguous evidence for the early environmental conjectures of Gaudry.

• The classical Pikermi fauna is terminated at the beginning of the Messinian (7.25–7.10 Ma) by a significant faunal turnover (post-Pikermi turnover), accompanied by massive increase of Saharan dust and salt accumulation with profound effects on soil salinity and nutrition.

• Furthermore, mineral dust in Attica was rich in soluble evaporites (halite, gypsum) in the earliest Messinian and especially during two pronounced insolation seasonality minima at 7.18 and 7.157 Ma, which suggests an orbitally driven progressive Sahara desertification. We suppose that a latest Tortonian to early Messinian dust- and salt-laden atmosphere over the Mediterranean may have further accelerated cooling and aridification via absorption of incoming solar radiation and, thus, may partially explain regionally accentuated Mediterranean cooling

• We subdivide Upper Miocene sediments of the Athens and the Mesogea Basins (Figs 1 and 2) into the terrestrial to alluvial Pikermi Formation (new formation) and the palustrine to lacustrine Rafina Formation (new formation). The Pikermi Formation represents an up to 30-mthick sequence of predominantly reddish silts with subordinate clastic channels of conglomerates and sandstones, which contains a rich and exclusively terrestrial vertebrate fauna. The formation rests discordantly upon the ‘lower limestone unit’[9] (palustrine to lacustrine grey marls and coals) and is concordantly overlain by the Rafina Formation (palustrine to lacustrine clay, coal, and platy limestone). Based on transport mechanisms, sediment colour, and palaeosol development, the Pikermi Formation can be subdivided into two members: the Red Conglomeratic Member (new member) characterized by debris flows and the fluvio-alluvial Chomateri Member (new member). The lower part of the Pikermi Formation (Red Conglomeratic Member) represents an alternation of red silts with a weak pedogenic overprint and debris flow deposits (Fig 3). These debris flows contain clasts of the nearby Attica unit of Mt. Pendeli, which indicates a strong topographic gradient. Silts from the lower Red Conglomeratic Member include the classical Pikermian bone accumulations. The upper Pikermi Formation (Chomateri Member) represents an alternation of reddish to yellowish silts with fluvial channels and channel-fill trains (Fig 3) that are indicative of small migrating streams during times of increased surface run-off. Away from channels, silts can contain well developed calcareous palaeosols rich in mammalian fossils. In both basins, the Pikermi Formation is concordantly overlain by palustrine clays and coals, and lacustrine marls and limestones of the Rafina Formation