QUATERNARY MAMMALS WEST AND EAST OF WALLACE'S LINE

by

D. A. HOOIJER (Rijksmuseumvan Natuurlijke Historie, Leiden, The Netherlands)

Wallace's Line marks the edge of the in : it separates from Celebes, and from . At the height of Pleistocene glaciations the shelf area, , was dry or mostly so, and land mammals could make their way from Southeast to what are now the islands of , , and Borneo. Macassar Strait between Borneo and Celebes is so wide and deep that it acted as an effective barrier in the dispersal of a number of mammalian species of Asiatic origin, but the chain extending east from Bali was more easily accessible: some of the water gaps now separating these islands dried up in the Pleistocene, and Indo-Malayan species penetrated to Flores and Timor. On the other hand, Australian elements coming in from the east had to jump the water gaps between and (Sahulland) to Timor and the islands in the Banda Sea, which were considerable even in times of glacially lowered sealevels. Cuscuses (genus Phalanger) got to Timor, and spread through the Moluccas, establishing two endemic species in Celebes. They never crossed Wallace's Line. As a whole, the recent fauna of Celebes is three-fourth Asiatic in origin (MAYR, 1945). If we look into the fossil record, we find that many of the extant species of the Indo-Malayan area already existed in the Pleistocene, and that the fauna of Sundaland was more uniformly distributed over Java, Sumatra, and Borneo (Table 1). As far as the ten well-known, terrestrial Asiatic mammals enumerated there are concerned, Java has less than half of them today, but Sundaland species now extinct in Java do occur as fossil remains in the Djetis and Trinil faunas of that island, post-Villafranchian assemblages made world-renowned by Pithecanthropus, Java Man, first found at Trinil by DUBOIS in 1891/92. In 1890 he already unearthed a juvenile mandibular fragment of a hominid at Kedungbrubus in what we now know is the Djetis fauna, in beds called the Putjangan Beds underlying the Kabuh Beds with the Trinil fauna, both exposed in the area of the Sangiran dome where VON KOENIGSWALD made further discoveries of fossil hominids between 1936 and 1941. The Djetis fauna has more extinct species than has the Trinil fauna, of which I will mention a few. First of all a species originally described from the Pinjor horizon of the Upper Siwaliks of 47

India as Elephas planifrons Falconer & Cautley, which survives in the post-Villafranchian Djetis beds just as it does in the Lang Son fauna of Indo China, where it is associated with more advanced elephants like Elephas namadicus Falconer & Cautley (HOOIJER, 1955: 94, 95: Karang Jati, Tritik; PATTE, 1955). The earliest occurrence of Elephas planifrons in Java is at Tjijulang in the western part of the island (VON KOENIGSWALD, 1951; HOOIJER, 1953c: 225, 227), where it occurs in a fully extinct faunal assemblage antecedent to the Djetis fauna and generally considered to represent a Villafranchian stage. The Villafranchian is a type of fauna we now know to have ranged from about 4 to about 2 million years ago: the earliest Villafranchian faunas such as those of Vialette and Etouaires are dated at 3.8 and 3.4 million years, and the latest, at Chilhac and Coupet, at 1.9 to 1.8 million years (VAN COUVERING, 1972). If, with VAN COUVERING (1972) and MAGLIO (1973), we place the Plio/Pleistocene boundary at roughly 2 million years, then Mount Coupet emerges as earliest Pleistocene, and older Villafranchian faunas are Pliocene. For long years Elephas planifrons was held to be the most primitive species of true elephant and was believed to have inhabited Europe and Africa as well as Asia. Its sudden appearance in European and Asiatic deposits was taken as a marker for the beginning of the Villafranchian and was used for faunal correlation (e.g., HOOIJER, 1956). We know better now, thanks to the epoch-making studies of MAGLIO (1970, 1973). The true elephants originated in Africa, several million years before their emergence in Europe and Asia. The African origin of the elephants was expounded by OSBORN (1934), who held Archidiskodon subplanifrons Osborn (including A. proplanifrons Osborn) from South Africa to be indubitably ancestral to Archidiskodon planifrons. As pointed out by MAGLIO, subplanifrons is on the Mammuthus lineage, and planifrons belongs to Elephas. Elephas planifrons, then, is a strictly Asiatic species, derived from Primelephas gomphotheroides Maglio of Africa via Elephas ekorensis Maglio at the 4 million year level in Kenya (see fig. 1, taken from MAGLIO, 1973, fig. 19), with occurrences of primitive stages along the expansion route from Africa such as the Bethlehem elephant, the earliest stage of Elephas recorded outside Africa (HOOIJER, 1958a; MAGLIO, 1973: 44/45). In the Siwaliks it occurs first in the Tatrot horizon, and in Java in the Tjijulang Beds. In the Djetis Beds, but also in the area of the Sangiran dome, there is a pygmy elephant originally named Stegodon hypsilophus Hooijer but which, in concurrence with MAGLIO (1973: 46/47), I now regard as belonging to Elephas celebensis (HOOIJER, 1974b). It is less advanced in the process of size reduction and relative crown heightening than the