Sumatra is an island in western Indonesia and part of the Sunda Islands. It is the largest island that is entirely in Indonesia (two larger islands, Borneo and New Guinea, are shared between Indonesia and other countries) and the sixth largest island in the world at 473,481 km2 (including adjacent islands such as the Riau Islands and Bangga Belitung Islands). The equator crosses the island at its centre on West Sumatra and Riau provinces. The climate of the island is tropical, hot and humid with lush tropical rain forest once dominating the landscape. Sumatra has a wide range of plant and animal species, including many species of animals that are critically endangered, such as the Sumatran Ground-cuckoo, Sumatran tiger, Sumatran elephant, Sumatran rhinoceros, and Sumatran orangutan.