Indonesia contains one of the world's most remarkable geographical boundaries in its distribution of animals. This dates back to the glacial period when sea level fell all over the world. During this period the islands of Java. Sumatra, Kalimantan and Ball on the Sunda Shelf were joined together with one another and with the Asian mainland, but Papua, Aru and the Australian continent of the Sahul Shelf were separated. This early geographical separation explains why the tropical animal species of Java, Sumatra and Kalimantan do not exist in Papua. For the same reason, the kangaroo of Papua is missing in the other region. Maluku. Sulawesi and the Lesser Sunda Islands, which lie between the Sunda and Sahul shelves, have a strikingly different fauna. Most of the eastern fauna do not exist in Sulawesi even though this island is close to Kalimantan, being just across the Makassar Strait.