Temporal range: Miocene-Early Holocene, 11.6–0.0041 Ma
|Stegodon skeleton at the Gansu Provincial Museum.|
Stegodon (meaning "roofed tooth" from the Greek words στέγειν stegein 'to cover' and ὀδούς odous 'tooth'), is a genus of the extinct subfamily Stegodontinae of the order Proboscidea. It was assigned to the family Elephantidae (Abel, 1919), but has also been placed in Stegodontidae (R. L. Carroll, 1988). Stegodonts were present from 11.6 mya to late Pleistocene, with unconfirmed records of regional survival until 4,100 years ago. Fossils are found in Asian and African strata dating from the late Miocene. They lived in large parts of Asia and East and Central Africa during the Pliocene and Pleistocene, locally in Indonesia into the Holocene epoch.
Some Stegodon species were among the largest of all Proboscidea, with adults being 4 m (13 ft) high at the shoulder, 8 m (26 ft) long, not including 3 m (10 ft) long nearly straight tusks. In some individuals, the tusks were so close together that the trunk probably did not lie between them but instead draped over.
A dwarf population survived until 12,000 years ago on the island of Flores, Indonesia. A review of 130 papers written about 180 different sites with proboscidean remains in southern China revealed Stegodon to have been more common than Asian elephants; the papers gave many recent radiocarbon dates, the youngest being 2,150 BCE (4,100 BP). However, Turvey et al. (2013) reported that one of the faunal assemblages including supposed fossils of Holocene Stegodon (from Gulin, Sichuan Province) is actually late Pleistocene in age; other supposed fossils of Holocene stegodonts were lost and their age cannot be verified. The authors concluded that the latest confirmed occurrences of Stegodon from China are from late Pleistocene, and that its Holocene survival cannot be substantiated. The name Stegodon is derived from the Greek words στεγειν stegein ('to cover') and οδον odοn ('tooth') because of the distinctive ridges on the animal's molars.
Stegodon florensis insularis is an extinct subspecies of Stegodon endemic to the island of Flores, Indonesia, and an example of insular dwarfism. The direct ancestor of S. florensis insularis is a larger-bodied S. florensis florensis, from Early Pleistocene and early Middle Pleistocene sites on Flores . Remains of S. florensis insularis are known from the cave of Liang Bua.
Similar to modern-day elephants, stegodonts were likely good swimmers[original research?], as their fossils are frequently encountered on Asian islands (such as Sulawesi, Flores, Timor, Sumba in Indonesia; Luzon and Mindanao in the Philippines; Taiwan; and Japan), which even during periods of low sea-level (during the cold phases of the Pleistocene) were not connected by land bridges with the Asian continent. A general evolutionary trend in large mammals on islands is island dwarfing. The smallest dwarf species, S. sondaari, known from 900,000 year old layers on the Indonesian island of Flores, had an estimated body weight of 300 kg (661 lb), smaller than a water buffalo. A medium to large sized stegodont, S. florensis, with a body weight of about 850 kg (1,874 lb), appeared about 850,000 years ago, and then also evolved into a dwarf form, Stegodon florensis insularis. The latter was contemporaneous with the hominin discovered in 2003, Homo floresiensis, and disappeared about 12,000 years ago.
In the past, stegodonts were believed to be the ancestors of the true elephants and mammoths, but it is currently believed that they have no modern descendants. Stegodon may be derived from Stegolophodon, an extinct genus known from the Miocene of Asia. Stegodon is considered to be a sister group of the mammoth, as well as the elephants. Some taxonomists consider the stegodonts a subfamily of Elephantidae. Both Stegolophodon and primitive elephants were derived from the Gomphotheriidae. The most important difference between Stegodon and (other) Elephantidae can be observed in the molars. Stegodont molars consist of a series of low, roof-shaped ridges, whereas in elephants each ridge has become a high-crowned plate. Furthermore, stegodont skeletons are more robust and compact than those of elephants.
In Bardia National Park in Nepal, there is a population of Indian elephants that, possibly due to inbreeding, exhibit many Stegodon-like morphological features. Some dismiss these primitive features as recent mutations rather than atavisms.
- PaleoBiology Database: Stegodon, basic info
- H. Saegusa, "Comparisons of Stegodon and Elephantid Abundances in the Late Pleistocene of Southern China", The World of Elephants -- Second International Congress, (Rome, 2001), 345-349.
- Samuel T. Turvey, Haowen Tong, Anthony J. Stuart and Adrian M. Lister (2013). "Holocene survival of Late Pleistocene megafauna in China: a critical review of the evidence". Quaternary Science Reviews 76: 156–166. doi:10.1016/j.quascirev.2013.06.030.
- Van Den Bergh, G.D., Aweb, R.D., Morwoodc, M.J., Sutiknab, T., Jatmikob and Saptomo, E. W. 2008. The youngest stegodon remains in Southeast Asia from the Late Pleistocene archaeological site Liang Bua, Flores, Indonesia. Quaternary International 182(1): 16-48.
- Van Den Bergh, G. D.; Rokhus Due Awe; Morwood, M. J.; Sutikna, T.; Jatmiko; Wahyu Saptomo, E. (May 2008). "The youngest Stegodon remains in Southeast Asia from the Late Pleistocene archaeological site Liang Bua, Flores, Indonesia". Quaternary International 182 (1): 16–48. Bibcode:2008QuInt.182...16V. doi:10.1016/j.quaint.2007.02.001. Retrieved 2011-11-27.
- Ben S. Roesch. "Living Stegodont or Genetic Freak?". Retrieved 2008-06-18.
- Yoshikawa, S; Kawamura, Y.; Taruno, H. "Land bridge formation and proboscidean immigration into the Japanese Islands during the quaternary". Journal of Geosciences, Osaka City University 50: 1–6.
- Shoshani, J.; Tassy, P. (2005). "Advances in proboscidean taxonomy & classification, anatomy & physiology, and ecology & behavior". Quaternary International. 126–128: 5. Bibcode:2005QuInt.126....5S. doi:10.1016/j.quaint.2004.04.011.
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