''Stegoloxodon'' is an extinct genus of

dwarf elephant Dwarf elephants are prehistoric members of the order Proboscidea which, through the process of allopatric speciation on islands, evolved much smaller body sizes (around shoulder height) in comparison with their immediate ancestors. Dwarf elephant ...

known from the

Early Pleistocene The Early Pleistocene is an unofficial epoch (geology), sub-epoch in the international geologic timescale in chronostratigraphy, representing the earliest division of the Pleistocene Epoch within the ongoing Quaternary Period. It is currently esti ...

of Indonesia. It contains two species, ''S. indonesicus'' from

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

, and ''S. celebensis'' from

Sulawesi Sulawesi ( ), also known as Celebes ( ), is an island in Indonesia. One of the four Greater Sunda Islands, and the List of islands by area, world's 11th-largest island, it is situated east of Borneo, west of the Maluku Islands, and south of Min ...

. Its relationship with other elephants is uncertain.

Taxonomy

''S. celebensis'' was originally described as ''Archidiskodon'' ''celebensis'' in 1949 by Dirk Albert Hooijer. ''S. indonesicus'' was originally described by

Miklós Kretzoi Miklós Kretzoi (9 February 1907 – 15 March 2005) was a Hungarian people, Hungarian geologist, paleontologist and paleoanthropologist and Széchenyi Prize winner. Exhibition in the Hungarian National Museum, 9 February - 24 May 2004 Kr ...

based on a molar found near Bumiayu, originally attributed to ''Elephas planifrons'', who coined the genus ''Stegoloxodon'' to contain the species. A 1973 paper argued for the synonymy of the two species,Maglio, V.J. (1973). ''Origin and evolution of the Elephantidae''. Transactions of the American Philosophical Society Philadelphia Volume 63. American Philosophical Society, Philadelphia. Pp. 149 which was later rejected, though they are usually considered closely related. Some later papers referred the species to ''Elephas''. 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. The relationship with other elephants has been considered uncertain, which has been suggested to be the result of dwarfism-caused changes to its morphology.'''' Some authors have suggested a close relationship to '' Loxodonta'' (which is not known outside of Africa) or to '' Elephas planifrons'' (which is known from the Late Pliocene-Early Pleistocene of South Asia).''''

Description

Both ''S. indonesicus'' and ''S. celebensis'' were

s substantially smaller than mainland elephant species as a result of

insular dwarfism Insular dwarfism, a form of phyletic dwarfism, is the process and condition of large animals evolving or having a reduced body size when their population's range is limited to a small environment, primarily islands. This natural process is disti ...

, with ''S. celebensis'' estimated to have been around tall. 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''. Both species retained permanent

premolars The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mout ...

. 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, or the result of

paedomorphosis Neoteny (), also called juvenilization,Montagu, A. (1989). Growing Young. Bergin & Garvey: CT. is the delaying or slowing of the Physiology, physiological, or Somatic (biology), somatic, development of an organism, typically an animal. Neoteny i ...

as a consequence of dwarfism, with the

mandibular symphysis In human anatomy, the facial skeleton of the skull the external surface of the mandible is marked in the median line by a faint ridge, indicating the mandibular symphysis (Latin: ''symphysis menti'') or line of junction where the two lateral ha ...

of ''S. celebensis'' being downwardly turned. The skull of ''S. celebensis'' is short and tall, with fronto-parietal crests, and slightly curved upper tusks.Bergh, G.D. van den, 1999. The Late Neogene elephantoid-bearing faunas of [Indonesia and their palaeozoogeographic implications; A study of the terrestrial faunal succession of Sulawesi, Flores and Java, including evidence for early hominid dispersal east of Wallace's line, Scripta Geologica 117: 1-41

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Ecology

Isotope analysis suggests that ''S. celebensis'' was a flexible feeder, while ''S. indonesicus'' is suggested to have been a dedicated browser on C3 vegetation in forested habitats. ''S. celebensis'' inhabited the island alongside the similarly sized dwarf ''

Stegodon ''Stegodon'' (from the Ancient Greek στέγω (''stégō''), meaning "to cover", and ὀδούς (''odoús''), meaning "tooth", named for the distinctive ridges on the animal's molars) is an extinct genus of proboscidean, related to elephants ...

'' species ''Stegodon sompoensis,'' and a larger unnamed ''Stegodon'' species'''' while ''Stegoxolodon indonesicus'' co-existed alongside the gomphothere '' Sinomastodon bumiajuensis,'' and an unnamed dwarf species of ''Stegodon''.''''

References

{{Taxonbar, from=Q21353505 Prehistoric elephants Pleistocene extinctions Cenozoic mammals of Asia Extinct animals of Indonesia Fossil taxa described in 1949