The Quaternary fossil assemblage of Layang Mawas Cave (Merapoh, Pahang) in Peninsular Malaysia: context, formation, composition and age constraints

Abstract

Layang Mawas Cave represents the first numerically-dated Middle to Late Pleistocene fossil site in the eastern part of Peninsular Malaysia. Previous research mostly focused on the Quaternary fossil sites located in the western part of the peninsula that is distinctly separated from the east by the granitic Main Range batholith. A survey of the fossil-bearing breccia in Layang Mawas Cave yielded 21 remains, mostly tooth fragments and isolated teeth, from at least eight taxa. Stratigraphic and sedimentological evidence suggest that all the fossils found in different areas of the cave relate to the same breccia formation event. The faunal assemblage is comparable with those from five other Middle and Late Pleistocene West Malaysian sites. It also includes a new biogeographic record for Pleistocene orangutan and the first directly-dated occurrence of a Proboscidea in the region. The polymictic nature of both allochthonous and autochthonous clasts with large grain size difference in the breccia indicates an intense mixing of fauna through successive episodes of deposition and post-depositional erosion. Our study suggest that the fossils were deposited as part of natural sedimentary processes over a long history of hydraulic or gravitational transportation and reworking, possibly after being accumulated by rodents. Direct dating of a few selected teeth from the fossil assemblage using U-series and ESR methods was quite challenging given the existing uncertainty around the dose rate evaluation. Despite some apparent scatter possibly partly resulting from this intrinsic uncertainty, our results nevertheless return a Late Pleistocene (MIS 5 to 4) age for most of the fossil teeth, while a last tooth coming from another area within the chamber most likely shows an older Middle Pleistocene age (MIS 7 or older). Although all dated specimens may be in first instance related to the same breccia formation event, we cannot reasonably exclude that some of them may have been reworked from significantly older deposits or correspond to various phases of fossil accumulation.