The Late Quaternary palaeogeography of mammal evolution in the Indonesian Archipelago

Abstract

The Quaternary faunal evolution for the Indonesian Archipelago reflects the unique relationship of each island with SE Asian mainland. The recent sub faunas of Sundaland (Kalimantan, Sumatra, Java, and Bali) preserved broad connections with the SE Asian mainland during the latest glacial. They are all balanced and show many mainland components. Alternatively, Wallacea (Sulawesi and the Lesser Sunda Islands) has always been geographically isolated from the mainland. Wallacea faunas thus remain unbalanced (they lack large carnivores) and endemic. A significant turnover arrives throughout the region with pronounced global sea level recessions around 0.8 Ma, during the transition from Early Pleistocene (EP) to the Middle Pleistocene (MP). By way of comparison, the palaeontological records of Japan and Taiwan also preserve this turnover, with EP–MP recessions bringing East Asian mainland immigrants. On Java, the earliest, Late Pliocene to early Pleistocene Satir fauna indicates island conditions. Java became connected to the SE Asian mainland towards the end of the early Pleistocene. Global cooling brought open woodlands on Java, an environment evidently preferred by Homo erectus in the Ci Saat fauna and Trinil H.K. fauna. As EP–MP sea level recessions created a wide corridor across the Sunda Shelf, Siwaliks and the SE Asian mainland terrestrial mammals invaded, as is seen in the Kedung Brubus fauna. The succeeding Ngandong fauna maintains an open woodland character but shows some endemism ( Homo erectus and Stegodon trigonocephalus, among others, can be distinguished on a subspecies level). The Late Pleistocene marks the earliest known tropical rainforest, and the corresponding Punung fauna is of Chinese affinity (with Pongo, Hylobates, and Elephas maximus). Homo sapiens probably arrives at this point as well. The youngest fossil faunas known from Java are the still poorly known Cipeundeuy Fauna (ca. 30 ka) and the Holocene faunas from Wajak and Sampung. While Sulawesi and Flores remained isolated throughout the Quaternary, only a limited number of terrestrial vertebrates arrived by crossing sea barriers. Endemic island faunas with pygmy elephantoids and giant tortoises were present during the Early Pleistocene. EP–MP sea level recessions allowed large to medium sized elephantoids to replace the dwarf species. Around the same time, Homo erectus appears on the island of Flores. Modern faunas eventually replaced the Middle Pleistocene island faunas, but the time frame has yet to be pinpointed. Sulawesi presents a unique case. Its current fauna holds no Walanae representatives. Apart from the phalangers, which must have come from the east. The ancestors of all other large Sulawesi land vertebrates, fossil and extant, reached the island by crossing the Sunda Sea. As the South Sulawesi fauna was stable until the Middle Pleistocene, this area must have constituted a separate palaeo-island. Some localized developments can be observed (e.g. shortening of the metapodials in Celebochoerus, increasing hypsodonty in Stegodon).