Elephas_celebensis

<i>Stegoloxodon</i>

Stegoloxodon

Extinct genus of dwarf elephant

Stegoloxodon is an extinct genus of dwarf elephant known from the Early Pleistocene of Indonesia. It contains two species, S. indonesicus from Java, and S. celebensis from Sulawesi. Its relationship with other elephants is uncertain.

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Taxonomy

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 (which is not known outside of Africa) or to Elephas planifrons (which is known from the Late Pliocene-Early Pleistocene of South Asia).[5]

Description

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]

Ecology

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]

References

  1. [1]
    Hooijer, D.A .(1949). Pleistocene Vertebrates from Celebes. IV. - Archidiskodon celebensis nov spec. Zoologische Mededelingen, Museum Leiden 30: 205–226.
  2. [2]
    Markov, Georgi N.; Saegusa, Haruo (2008-09-01). "On the validity of Stegoloxodon Kretzoi, 1950 (Mammalia: Proboscidea)". Zootaxa. 1861 (1): 55. doi:10.11646/zootaxa.1861.1.5. ISSN 1175-5334.
  3. [3]
    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
  4. [4]
    Hooijer, D.A. (1974). Elephas celebensis (Hooijer) from the Pleistocene of Java. Zoologische Mededelingen, Museum Leiden, 48: 85–93.
  5. [5]
    Sanders, William J. (2018-02-17). "Horizontal tooth displacement and premolar occurrence in elephants and other elephantiform proboscideans". Historical Biology. 30 (1–2): 137–156. doi:10.1080/08912963.2017.1297436. ISSN 0891-2963.
  6. [6]
    Van Der Geer, Alexandra A. E. (March 2014). "Parallel patterns and trends in functional structures in extinct island mammals". Integrative Zoology. 9 (2): 167–182. doi:10.1111/1749-4877.12066. hdl:10795/3252. ISSN 1749-4877. PMID 24673761.
  7. [7]
    Alink, Gerrit; Adhityatama, Shinatria; Simanjuntak, Truman (2017-12-29). "The Descriptive Analysis of Palaeolithic Stone Tools from Sulawesi, Collected by the Indonesian-Dutch Expedition in 1970". AMERTA. 35 (2): 75. doi:10.24832/amt.v35i2.252.
  8. [8]
    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: 1-419
  9. [9]
    Puspaningrum, Mika Rizki; Chivas, Allan R.; Kurniawan, Iwan; Wibowo, Unggul P.; Zaim, Yahdi; Van den Bergh, Gerrit D. (2021-12-28). "Isotopic reconstruction of Proboscidean habitats and diets on enigmatic island of Sulawesi". Berita Sedimentologi. 47 (3): 79–80. doi:10.51835/bsed.2021.47.3.364. ISSN 0853-9413.
  10. [10]
    Puspaningrum, Mika R.; van den Bergh, Gerrit D.; Chivas, Allan R.; Setiabudi, Erick; Kurniawan, Iwan (January 2020). "Isotopic reconstruction of Proboscidean habitats and diets on Java since the Early Pleistocene: Implications for adaptation and extinction". Quaternary Science Reviews. 228: 106007. doi:10.1016/j.quascirev.2019.106007.
  11. [11]
    Vos, John de; Ostende, Lars W. van den Hoek; Bergh, Gert D. van den (2007), Renema, Willem (ed.), "Patterns in Insular Evolution of Mammals: A Key to Island Palaeogeography", Biogeography, Time, and Place: Distributions, Barriers, and Islands, vol. 29, Dordrecht: Springer Netherlands, pp. 315–345, doi:10.1007/978-1-4020-6374-9_10, ISBN 978-1-4020-6373-2, retrieved 2023-08-10
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