Revised age and stratigraphy of the classic Homo erectus-bearing succession at Trinil (Java, Indonesia)

Obtaining accurate age control for fossils found on Java (Indonesia) has been and remains challenging due to geochronologic and stratigraphic uncertainties. In the 1890s, Dubois excavated numerous faunal fossilsdincluding the first remains of Homo erectusdin sediments exposed along the Solo River at Trinil. Since then, various, and often contradictory age estimates have been proposed for the Trinil site and its fossils. However, the age of the fossil-bearing layers and the fossil assemblage remains inconclusive. This study constructs a chronostratigraphic framework for the Trinil site by documenting new stratigraphic sections and test pits, and by applying 40Ar/39Ar, paleomagnetic, and luminescence (pIRIR290) dating methods. Our study identifies two distinct, highly fossiliferous channel fills at the Trinil site. The stratigraphically lower Bone-Bearing Channel 1 (BBC-1) dates to 830e773 ka, while Bone-Bearing Channel 2 (BBC-2) is substantially younger with a maximum age of 450 +/- 110 ka and an inferred min-imum age of 430 +/- 50 ka. Furthermore, significantly younger T2 terrace deposits are present at similar low elevations as BBC-1 and BBC-2. Our results demonstrate the presence of Early and Middle Pleisto-cene, and potentially even late Middle to Late Pleistocene fossiliferous sediments within the historical excavation area, suggesting that Dubois excavated fossils from at least three highly fossiliferous units with different ages. Moreover, evidence for reworking suggests that material found in the fossil-rich strata may originate from older deposits, introducing an additional source of temporal heterogeneity in the Trinil fossil assemblage. This challenges the current assumption that the Trinil H.K. fauna ewhich includes Homo erectus-is a homogeneous biostratigraphic unit. Furthermore, this scenario might explain why the Trinil skullcap collected by Dubois is tentatively grouped with Homo erectus fossils from Early Pleistocene sediments at Sangiran, while Trinil Femur I shares affinities with hominin fossils of Late Pleistocene age. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Automated summary

This study aims to establish an accurate age control for the fossils found at the Trinil site in Java, Indonesia. By applying various dating methods and documenting new stratigraphic sections, the researchers identified two distinct fossil-rich channel fills with ages ranging from 830-773 ka to 450 +/- 110 ka. The presence of fossils from different time periods challenges the assumption of a homogeneous biostratigraphic unit at the Trinil site.