The taphonomy of the Madura Strait fossil assemblage, a record of selective hunting and marrow processing by late Middle Pleistocene Sundaland hominins

The Madura Strait assemblage is the first vertebrate faunal record of submerged Sundaland. The material derives from an ancient valley of the Solo River, which was cut during the lowstand of MIS6. The geological background of the site and the taxonomy of the fossils have been described in previous publications. However, the significance of the assemblage within the Pleistocene biogeography of Southeast Asia can only be understood if we have insight into its accumulation history and homogeneity, and into the representativeness of the OSL-dated sediment for the fossils it contains. Moreover, the presence of hominin fossils raises questions on hominin subsistence strategies, which may have left traces in the fossil record. Over the past decades, similar questions have successfully been addressed by systematic taphonomic studies of fossil assemblages, notably from Africa and Europe. However, such studies are rare in Southeast Asia. Moreover, taphonomic studies of assemblages from subsea sites lag behind. Here we describe the results of a systematic taphonomic study of the Madura Strait assemblage. The fossils of terrestrial species form a homogenous assemblage, representing a steady supply of skeletal elements to the river, presumably during yearly flooding stages. OSL-dated fluvial sandstone samples point to a most likely age range of 146–131 ka. The material has been subject to fluvial size-sorting, but the absence of significant rounding points to short transportation distances and a local provenance. The skeletal remains accumulated in the fluvial valley fill or became concentrated in an overlying marine lag, as a result of tidal scour during the subsequent transition to estuarine conditions. Fossils of estuarine species derive from the estuarine sediment overlying this basal marine lag and are linked to peak-highstand conditions around MIS5e (∼123 ka). The bone remains of terrestrial species have been subject to two fracturing stages: a green-state fracturing stage prior to fluvial uptake and a sub-fossil-state fracturing stage during later marine reworking. Extensive green-state fragmentation of ruminant limb bones points to hominin bone battering and marrow processing. The age-at-death frequency distribution of bovids is indicative of selective hunting of prime adult prey. Cut marks on turtle bones show that hominins also fed on these aquatic species.