Genetic evidence for anatomically modern humans (AMH) out of Africa before 75 thousand years ago (ka) and in island southeast Asia (ISEA) before 60 ka (93-61 ka) predates accepted archaeological records of occupation in the region. Claims that AMH arrived in ISEA before 60 ka (ref. 4) have been supported only by equivocal or non-skeletal evidence. AMH evidence from this period is rare and lacks robust chronologies owing to a lack of direct dating applications, poor preservation and/or excavation strategies and questionable taxonomic identifications. Lida Ajer is a Sumatran Pleistocene cave with a rich rainforest fauna associated with fossil human teeth. The importance of the site is unclear owing to unsupported taxonomic identification of these fossils and uncertainties regarding the age of the deposit, therefore it is rarely considered in models of human dispersal. Here we reinvestigate Lida Ajer to identify the teeth confidently and establish a robust chronology using an integrated dating approach. Using enamel-dentine junction morphology, enamel thickness and comparative morphology, we show that the teeth are unequivocally AMH. Luminescence and uranium-series techniques applied to bone-bearing sediments and speleothems, and coupled uranium-series and electron spin resonance dating of mammalian teeth, place modern humans in Sumatra between 73 and 63 ka. This age is consistent with biostratigraphic estimations, palaeoclimate and sea-level reconstructions, and genetic evidence for a pre-60 ka arrival of AMH into ISEA. Lida Ajer represents, to our knowledge, the earliest evidence of rainforest occupation by AMH, and underscores the importance of reassessing the timing and environmental context of the dispersal of modern humans out of Africa.

Abstract:Caves have been an important source of vertebrate fossils for much of Southeast Asia, particularly for the Quaternary. Despite this importance, the mechanisms by which vertebrate remains accumulate and preserve in Southeast Asian caves has never been systematically reviewed or examined. Here, we present the results of three years of cave surveys in Indonesia and Timor-Leste, describing cave systems and their attendant vertebrate accumulations in diverse geological, biogeographical, and environmental settings. While each cave system is unique, we find that the accumulation and preservation of vertebrate remains are highly dependent on local geology and environment. These factors notwithstanding, we find the dominant factor responsible for faunal deposition is the presence or absence of biological accumulating agents, a factor directly dictated by biogeographical history. In small, isolated, volcanic islands, the only significant accumulation occurs in archaeological settings, thereby limiting our understanding of the palaeontology of those islands prior to human arrival. In karstic landscapes on both oceanic and continental islands, our understanding of the longterm preservation of vertebrates is still in its infancy. The formation processes of vertebratebearing breccias, their taphonomic histories, and the criteria used to determine whether these represent syngenetic or multiple deposits remain critically understudied. The latter in particular has important implications for arguments on how breccia deposits from the region should be analysed and interpreted when reconstructing palaeoenvironments.

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We employ high-throughput thermal-neutron tomographic imaging to visualise internal diagnostic features of dense fossiliferous breccia from three Pleistocene cave localities in Sumatra, Indonesia. We demonstrate that these seemingly homogeneous breccias are an excellent source of data to aid in determining taphonomic and depositional histories of complex depositional sites such as tropical caves. X-ray Computed Tomographic (CT) imaging is gaining importance amongst palaeontologists as a non-destructive approach to studying fossil remains. Traditional methods of fossil preparation risk damage to the specimen and may destroy contextual evidence in the surrounding matrix. CT imaging can reveal the internal composition and structure of fossils contained within consolidated sediment/rock matrices prior to any destructive mechanical or chemical preparation. Neutron computed tomography (NCT) provides an alternative contrast to X-rays, and in some circumstances, is capable of discerning denser matrices impenetrable to or yielding no contrast with CT imaging. High-throughput neutron imaging reduces neutron fluence during scanning which means there is less residual neutron-induced radioactivation in geological samples; allowing for earlier subsequent analyses. However, this approach remains unutilised in palaeontology, archaeology or geological surveys. Results suggest that the primary agents in the formation of the breccias and concentration of incorporated vertebrate remains are several rapid depositional phases of water and sediment gravity flow. This study highlights the potential for future analyses of breccia deposits in palaeontological studies in caves around the world.

We provide the first numerical age constraints for the palaeontological assemblage and associated sediment from Ngalau Sampit, Sumatra, one of M. Eugène F.T. Dubois' noted sites that he excavated in 1889, and of which we present a transcript of his unpublished report. A combination of U-series, Electron Spin Resonance (ESR) and Luminescence (pIR-IRSL) methods was employed. The three tooth samples yield 1σ consistent combined U-series/ESR ages (mean age of 105 ± 9 ka, 1 s.d.), supporting the chronological integrity of the fossil assemblage at Ngalau Sampit. Three breccia samples yield internally 1σ consistent pIR-IRSL age estimates (mean age of 93 ± 6 ka, 1 s.d.), suggesting that the breccia may represent one single depositional event. All these results are compatible with the U-series age estimates previously obtained on post-depositional carbonate formations. We cannot exclude that the existing, and systematic, age difference between ESR and pIR-IRSL methods (~12 ka on average) may reflect the difference in the dated events (death of the animals vs. sediment burial). However, this apparent deviation is most likely not significant (mean ages are in close agreement a 1σ) and results from the existing uncertainty around the evaluation of the gamma dose rate, which partly arises from the absence of in situ dosimetry. Despite this uncertainty, all the numerical ages consistently and systematically correlate the breccia and associated fossil assemblage to MIS 5 (a finer correlation to sub-stages within MIS 5 would most likely be too speculative at this stage). Ngalau Sampit represents only the third site from the Pandang Highlands to be radiometrically dated, after Lida Ajer and Ngalau Gupin, and the second site explored and recorded by Dubois to have associated dates. Finally, Ngalau Sampit is the only site in Sumatra that chronologically correlates to MIS 5, and thus with the regionally important site of Punung in Java.