Avian remains from the Early/Middle Pleistocene of the So'a Basin, central Flores, Indonesia, and their palaeoenvironmental significance

The So'a Basin in central Flores contains the earliest known evidence for hominins on this remote Indonesian island, with stone tools from this region dating back at least 1.0Ma. At least 16 late Early to early Middle Pleistocene terrestrial fossil localities record evidence for highly insular endemic faunas and proxy evidence for hominins. The hominin presence in the So'a Basin raises many questions as to how, when, and from where hominins arrived on the island, and key issues regarding their adaptation to this insular environment remain poorly understood. Here, we provide palaeoenvironmental data based on avian remains recovered during recent, systematic excavations of late Early to early Middle Pleistocene deposits at Mata Menge and Bo'a Leza in the So'a Basin. At least six species of birds in five avian orders were recovered, forming the oldest bird remains recovered from Wallacea. Two species, a swan (Cygnus sp.) and an eagle owl (Bubo sp.), no longer occur on Flores. The avian assemblage from Mata Menge and Bo'a Leza described here is indicative of an open environment with a strong open, freshwater component and nearby grasslands, and with forests at a distance. In that, it differs from the Late Pleistocene limestone cave site of Liang Bua, the find locality of Homo floresiensis, and is more similar to the Early Pleistocene Homo erectus sites of the Sangiran Dome on Java. Although little is known regarding the identity of the So'a Basin toolmakers, the presence of an open, savannah-type environment in the late Early to early Middle Pleistocene of Flores may have facilitated their dispersal from the Asian shelf into Wallacea. •The So'a Basin (Flores) contains the earliest evidence for hominins in Wallacea.•We identified six bird species from Early/Middle Pleistocene deposits at So'a.•Two taxa, a swan Cygnus sp. and an eagle owl Bubo sp., no longer occur on Flores.•The avian assemblage indicates an open lake environment and forests at a distance.•An open environment in the So'a Basin may have facilitated hominin dispersal.