and Sulawesi, Wallacea is marked by a transition zone of flora and fauna first described by Alfred Russel Wallace. The complicated history of island formation on the Sunda Shelf and changing landbridge connections with mainland Southeast Asia have resulted in a high degree of endemism and local distribution discontinuities, discussed at Sundaland, the biogeographical province that has resulted from these changes. The exposure of the Sunda Shelf during eustatic sea level changes has effects on the El Niño oscillation. W. Earle in 1845 was the first to describe the general features of the Sunda and Sahul Shelves, which he termed the "Great Asiatic Bank" and the "Great Australian Bank" respectively. Submerged river systems The paleo river systems of the Sunda Shelf are vast submerged river systems that extend present-day river systems and may be interpreted to follow topographic lows in a down-slope direction. During the driest period of the Pleistocene era (about 17,000 years BP) some four distinct catchment areas form the Malacca, Siam and Sunda river systems. The Siam river system consists of a northern and a western arm. The northern arm extends the Chao Phraya River to drain the Gulf of Thailand. The western arm forming out of some rivers in central Sumatra flows through the Singapore Straits before joining up with the northern arm to empty into an estuary and the South China Sea to the north of North Natuna Island. The Malacca Straits river system is formed by a joining of waters from northeastern Sumatra and the western Malay Peninsula, draining into the Andaman Sea. The Northern Sunda river system, also known as the Great Sunda river system, or Molengraaff river system, was named after a Dutch biologist and geologist who traveled the region extensively in the late 19th century and first proposed the existence of this river system based on his observations in Borneo. The river, arising between Belitung Island and Borneo, flowed in a northeasterly direction, where it collected waters from some rivers in Central Sumatra and the rivers in Western and Northern Borneo, before flowing into the South China Sea between the North and South Natuna Islands. Finally the Eastern Sunda river system emptied northern Java and southern Borneo, flowing in an easterly direction between Borneo and Java into the Java Sea. See also Sahul Shelf Sundaland Sunda Shelf mangroves - (ecoregion) References External links Voris, H., and C. Simpson, 2000 and 2006,