Stegoloxodon

S. celebensis was originally described as Archidiskodon celebensis in 1949 by Dirk Albert Hooijer.[1] S. indonesicus was originally described by Miklós Kretzoi based on a molar found near Bumiayu, originally attributed to Elephas planifrons, who coined the genus Stegoloxodon to contain the species.[2] A 1973 paper argued for the synonymy of the two species,[3] which was later rejected, though they are usually considered closely related.[2] Some later papers referred the species to Elephas.[4] A paper by Paul Yves Sondaar in 1984 started a trend of referring to the two species to the genus "Elephas" with quotation remarks, reflecting uncertainty about their placement in the genus. A 2008 review by Markov and Saegusa resurrected the genus Stegoloxodon to house the two species.[2]

The relationship with other elephants has been considered uncertain, which has been suggested to be the result of dwarfism-caused changes to its morphology.[2][5] Some authors have suggested a close relationship to Loxodonta or to Elephas planifrons.[5]

Both S. indonesicus and S. celebensis were dwarf elephants substantially smaller than mainland elephant species[5] as a result of insular dwarfism,[6] with S. celebensis estimated to have been around 150 cm (4.9 ft) tall.[7] The molar plates of both species are low-crowned with thick enamel, with the lamellae frequency being notably higher in S. celebensis than in S. indonesicus.[2] Both species retained permanent premolars.[5] Lower tusks are present in some adult individuals of S. celebensis, unlike modern elephants, which is either suggested to have been a retained ancestral trait lost in modern elephants,[8] or the result of paedomorphosis as a consequence of dwarfism,[3] with the mandibular symphysis of S. celebensis being downwardly turned. The skull of S. celebensis is short and tall, with fronto-parietal crests, and slightly curved upper tusks.[8]

Isotope analysis suggests that S. celebensis was a flexible feeder,[9] while S. indonesicus is suggested to have been a dedicated browser on C3 vegetation in forested habitats.[10] S. celebensis inhabited the island alongside the similarly sized dwarf Stegodon species Stegodon sompoensis, and a larger unnamed Stegodon species[8][11] while Stegoxolodon indonesicus co-existed alongside the gomphothere Sinomastodon bumiajuensis, and an unnamed dwarf species of Stegodon.[10]