Late Quaternary Sea-Level Changes and the Palaeohistory of Palawan Island, Philippines

Palaeogeographic reconstructions of Palawan Island using Geographic Information Systems based on present-day bathymetry show extensive changes in land area with respect to sea-level fluctuations during the Late Quaternary. Our analysis shows that a lowering of at least 135 meters from present-day levels is needed in order to expose a narrow land connection between Palawan and Sundaland. This most likely last occurred during OIS 12 (ca. 440 Ka) and probably OIS 16 (ca. 630 Ka), facilitating overland colonization between the two islands. The reconstructions further illustrate the extent of land exposed, which was likely covered by open savannah vegetation during the LGP and inhabited by several large mammal species now extinct on the island. Sea-level rise at the end of the Pleistocene caused the inundation of shallow shelves of Palawan, and this, accompanied by a conversion to closed rainforest environments, was probably responsible for the disappearance of most of the large mammal fauna of Palawan. Coastline reconstructions demonstrate that the appearance of mid-Holocene shell middens in the Philippine archaeological record is due to the formation and proximity of mangrove forests during sea-level high-stand, rather than a consequence of changes in human subsistence strategies.