Elephas celebensis

The Sulawesi dwarf elephant (Stegoloxodon celebensis or Elephas celebensis) was about half the size of Archidiskodon (=Mammuthus) planifrons to which it was initially considered to be related by Dirk Albert Hooijer in 1949.[1] The most evident difference with the latter is the presence of functional lower tusks in some individuals. This was considered as paedomorphosis, a retention of juvenile characters in the adult stage, by Vincent Maglio in his revision of the proboscideans in 1973.[2] He based his conclusion on the presence of vestigial incisive germs in mandibles of Mammuthus planifrons. This idea was followed by Hooijer in 1974.[3]

The retention of functional lower tusks is, however, not seen in juveniles of otherwise single paired tuskers, so cannot be considered a paedomorphic feature proper. It is simply a retention of a primitive character, as seen in the African elephantid genera Primelephas and Stegotetrabelodon, and possibly the earliest forms of Elephas planifrons. Between the late 1980s and early 1990s, an Indonesian-Dutch team excavated more material, including a fairly complete but rather distorted skull. All material, new as well as old, is described and revised in Van den Bergh’s thesis of 1999 on the Indonesian elephantoids, with a discussion on taxonomy.[4] He puts question marks, “Elephas”, to indicate the uncertain taxonomical position, following Paul Sondaar’s approach of 1984.[5] Van den Bergh accepts a possible relation with “Elephas” indonesicus from Ci Pangglosoran near Bumiayu on Java, dated to the same geological period. Also this specimen was originally assigned to Elephas (= Mammuthus) planifrons, but was later renamed Stegoloxodon indonesicus by Kretzoi in 1950.[6] Recently, Georgi Markov and Haruo Saegusa made a further step and synonymized “Elephas” with Stegoloxodon in 2008.[7]

The genus Stegoloxodon is restricted to Java and Sulawesi. The exact relation between the two endemic species is unclear, because the Javan species is known only by a single molar.

Fossils of the Sulawesi dwarf elephant are found in the Walanea Formation, dated to the Late Pliocene - Early Pleistocene. The single fossil of the Javanese species was found at Ci Pangglosoran near Bumiayu on Java,[8] dated to the same geological period.