Stegodon
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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. It was originally assigned to the family Elephantidae along with modern elephants but is now placed in the extinct family Stegodontidae. Like elephants, Stegodon had teeth with plate-like lophs that are different from those of more primitive proboscideans like gomphotheres and mammutids.<ref name=":2">Template:Cite journal</ref> Fossils of the genus are known from Africa and across much of Asia, as far southeast as Timor (with a single record in southeast Europe). The oldest fossils of the genus are found in Late Miocene strata in Asia, likely originating from the more archaic Stegolophodon, subsequently migrating into Africa.<ref name=":3">Template:Cite journal</ref> While the genus became extinct in Africa during the Pliocene, Stegodon persisted in South, Southeast and Eastern Asia into the Late Pleistocene.<ref>Template:Cite journal</ref>
Morphology
The skull of Stegodon is relatively tall but short,<ref name=":2" /> and similar in many respects to those of living elephants.<ref name=":72" /> The lower jaw in comparison to early elephantimorphs and its ancestor Stegolophodon is shortened (brevirostrine), and lacks lower tusks/incisors. The molar teeth are superficially like those of elephants, consisting of parallel lamellae that form ridges but are generally relatively low crowned (brachydont),<ref name=":2" /><ref>Template:Cite journal</ref> the numbers of ridges are greater in later species.<ref name=":7">van der Made, J. The Evolution of the Elephants and Their Relatives in the Context of Changing Climate and Geography. In Elefantentreich—Eine Fossilwelt in Europa; Verlag Beier & Beran: Langenweißbach, Germany, 2010; pp. 340–360. Template:ISBN.</ref> Members of the genus lack permanent premolars.<ref>Template:Cite journal</ref> The tusks are proportionally large, with those of the biggest species being among the largest known tusks in proboscideans, with a particularly large tusk of S. ganesa from the Early Pleistocene of India measured to be Template:Convert long, with an estimated mass of approximately Template:Convert, substantially larger than the largest recorded modern elephant tusk.<ref>Template:Cite journal</ref> These tusks have a slight upward curvature, and project forwards and parallel to each other, with the tusks often so close together that they are almost touching, such that the trunk would probably have had to rest on top of the tusks rather than be freely hanging between them as in living elephants.<ref name=":72">Template:Cite journal</ref>{{#invoke:Gallery|gallery}}
Size
The Chinese S. zdanskyi is suggested to be the largest species, and is known from an old male (50-plus years old) from the Yellow River that is Template:Cvt tall and would have weighed approximately Template:Convert in life. It had a humerus Template:Cvt long, a femur Template:Cvt long, and a pelvis Template:Cvt wide. The Indian S. ganesa is suggested to have a shoulder height of about Template:Cvt, and a body mass of around Template:Convert. The Javanese species S. trigonocephalus is suggested to have been around Template:Cvt tall, with a body mass of around Template:Convert.<ref name="proboscideans">Template:Cite journal</ref> S. orientalis was around the size of an Asian elephant (Elephas maximus).<ref name=":9" />
Similar to modern-day elephants, stegodonts were likely good swimmers,<ref>Simpson, G. (1977). "Too Many Lines; The Limits of the Oriental and Australian Zoogeographic Regions". Proceedings of the American Philosophical Society, 121(2), 107–120. Retrieved from http://www.jstor.org/stable/986523</ref><ref>Template:Cite journal</ref> allowing them to disperse to remote islands in Indonesia, the Philippines and Japan. Once present on the islands, due to the process of insular dwarfism, as a result of decreased land area and the reduction of predation and competition pressure, they reduced in body size, with the degree of dwarfism varying between islands as the result of local conditions. One of the smallest species, Stegodon sumbaensis from Sumba in Indonesia, is estimated at around 8% of the size of mainland Stegodon species, with a body mass of Template:Convert.<ref name=":22">Template:Cite journal</ref> Sometimes the same island was colonised multiple times by Stegodon, as in Flores, where the Early Pleistocene strongly dwarfed species Stegodon sondaari, which was Template:Convert tall at the shoulder and weighed about Template:Convert,<ref name="proboscideans" /> was replaced by the species Stegodon florensis during the Middle Pleistocene which was initially substantially larger, but progressively reduced in size over time, with the earlier subspecies Stegodon florensis florensis from the Middle Pleistocene estimated to be around 50% the size of mainland Stegodon species with a shoulder height of around Template:Convert and a body mass of around 1.7 tons, while the later Stegodon florensis insularis from the Late Pleistocene is estimated to be around 17% the size of mainland Stegodon species, with a shoulder height of around Template:Convert, and a body mass of about Template:Convert.<ref name=":22" /><ref name="ro.uow.edu.au">Puspaningrum, Mika; Van Den Bergh, Gerrit; Chivas, Allan; Setiabudi, Erick; Kurniawan, Iwan; Brumm, Adam; and Sutikna, Thomas, "Preliminary results of dietary and environmental reconstructions of Early to Middle Pleistocene Stegodons from the So'a Basin of Flores, Indonesia, based on enamel stable isotope records" (2014). Faculty of Science, Medicine and Health - Papers: part A. 2035.</ref>
During Pliocene-Early Pleistocene (from around 4-1 million years ago), a succession of endemic dwarf species of Stegodon, probably representing a single lineage lived in the Japanese archipelago, probably derived from the mainland Chinese S. zdanskyi. In chronological succession these species are Stegodon miensis (4-3 million years ago) Stegodon protoaurorae (3-2 million years ago) and Stegodon aurorae, (2-1 million years ago) which show a progressive size reduction through time, possibly as a result of reducing land area of the Japanese archipelago.<ref>Template:Cite journal</ref> The latest and smallest species S. aurorae is estimated to be 25% the size of its mainland ancestor with a body mass of around Template:Convert.<ref name="Geer-2016">Template:Cite journal</ref> S. aurorae also shows morphological straits associated with dwarfism, like shortened limbs.<ref name=":11" />
Palaeobiology
Palaeoecology
Like modern elephants, but unlike more primitive proboscideans, Stegodon is thought to have chewed using a proal movement (a forward stroke from the back to the front) of the lower jaws. This jaw movement is thought to have evolved independently in elephants and stegodontids.<ref name=":2" /> Stegodon populations from the Late Pliocene of the India (including Stegodon insignis) are suggested to have been variable mixed feeders, while those from the earliest Pleistocene (including Stegodon ganesa) of the same region are suggested to have been nearly pure grazers based on isotopic analysis.<ref>Template:Cite journal</ref> Based on dental microwear analysis, populations of Stegodon from the Pleistocene of China (Stegodon orientalis and Stegodon huananensis) and mainland southeast Asia (S. orientalis) were found to be browsers, with clear niche differentiation from sympatric Elephas populations, which tended towards mixed feeding (both browsing and grazing),<ref>Template:Cite journal</ref><ref name=":5">Template:Cite journal</ref> though isotopic analysis of Stegodon cf. orientalis specimens from the late Middle Pleistocene of Thailand suggests that these individuals were mixed feeders that consumed a significant amount of C4 grass.<ref>Template:Cite journal</ref> Specimens of Stegodon trigonocephalus from the Early-Middle Pleistocene of Java were found to be mixed feeders to grazers, with a diet similar to that of sympatric Elephas hysudrindicus.<ref name=":8">Template:Cite journal</ref> The dwarf species from Flores, Stegodon sondaari and Stegodon florensis, are suggested to have been mixed feeders and grazers, respectively, based on stable carbon isotopes.<ref name="ro.uow.edu.au"/> Specimens of Stegodon kaiesensis from the Pliocene of East Africa were found to be browsers to mixed feeders, based on mesowear analysis.<ref name=":0">Template:Cite journal</ref>
On Flores, where dwarf Stegodon species were the only large herbivores, they were likely the main prey of the Komodo dragon.<ref>Diamond, Jared M. (1987). "Did Komodo dragons evolve to eat pygmy elephants?". Nature. 326 (6116): 832.</ref>
Palaeopathology
In the Siwalik Hills assemblage, the Pliocene S. insignis shows a relatively low frequency of enamel hypoplasia, likely due to the relative stability of regional climate during this epoch. The Pleistocene S. ganesha, on the other had, had high rates of enamel hypoplasia that have been attributed to a highly unstable environmental dynamics during the epoch.<ref>Template:Cite journal</ref>
Social behaviour
Ichnofossils of a group of Stegodon from the Late Pliocene of Japan suggest that like modern elephants, Stegodon were highly social animals and lived together in herds.<ref>Template:Cite journal</ref>
Taxonomy
In the past, stegodonts were believed to be the ancestors of the true elephants and mammoths, but currently they are believed to have no modern descendants. Stegodon is likely derived from Stegolophodon, an extinct genus known from the Miocene of Asia,<ref name=":3" /> with transitional fossils between the two genera known from the Late Miocene of Southeast Asia and Yunnan in South China.<ref name=":2" /> Stegodon is more closely related to elephants and mammoths than to mastodons.<ref name=":4" /> Like elephants, stegodontids are believed to have derived from gomphotheres.<ref>Template:Cite journal</ref>
Phylogeny
The following cladogram shows the placement of the genus Stegodon among other proboscideans, based on hyoid characteristics, following Shoshani and Tassy (2005):<ref name=":4">Template:Cite journal</ref>
List of species
- Stegodon kaisensis Late Miocene – Pliocene, Africa
- Stegodon zdanskyi Late Miocene – Pliocene, China
- Stegodon huananensis Early Pleistocene, China
- Stegodon orientalis Middle – Late Pleistocene, China, Southeast Asia, Japan, Taiwan
- Stegodon namadicus/S. insignis/S. ganesa Pliocene – Late Pleistocene, India
- Stegodon miensis Pliocene, Japan
- Stegodon protoaurorae Late Pliocene – Early Pleistocene, Japan
- Stegodon aurorae Early Pleistocene – early Middle Pleistocene, Japan
- Stegodon sondaari Early Pleistocene, Flores, Indonesia
- Stegodon florensis Middle – Late Pleistocene, Flores, Indonesia
- Stegodon luzonensis Middle Pleistocene, Luzon, Philippines
- Stegodon trigonocephalus late Early Pleistocene – early Late Pleistocene, Java, Indonesia
- Stegodon sompoensis Late Pliocene – Early Pleistocene, Sulawesi, Indonesia
- Stegodon sumbaensis Middle – Late Pleistocene, Sumba, Indonesia
- Stegodon timorensis Middle Pleistocene, Timor, Indonesia
- Stegodon mindanensis Pleistocene Mindanao, Philippines
An indeterminate Stegodon molar of an uncertain locality and age is known from Greece, representing the only record of the genus in Europe.<ref>Template:Citation</ref> Indeterminate remains are also known from the Early Pleistocene and early Middle Pleistocene of Israel.<ref>Template:Cite journal</ref>
Relationship with humans
Remains at a number of sites suggest that humans (in a broad sense, including archaic humans) interacted with Stegodon.<ref>Template:Cite journal</ref> At a cave deposit on Gele Mountain near Chongqing in southwest China, a mandible of Stegodon orientalis was used to make a handaxe, with dating suggesting the bone is around 170,000 years old.<ref>Template:Cite journal</ref> At the late Middle Pleistocene Panxian Dadong cave site in southern Guizhou Province, southwest China, dating to around 300-190,000 years ago,<ref>Template:Cite journal</ref> numerous remains of juvenile (0-12 years of age) and a much smaller number of adult remains of adult Stegodon orientalis, representing a minimum of 12 individuals were found at the site in association with stone tools and human remains. It suggested that Stegodon remains were brought to the cave by humans though none of the elements show clear evidence of processing.<ref name=":9">Schepartz, Lynne, and Sari Miller-Antonio. 2010. "Large Mammal Exploitation in Late Middle Pleistocene China: A Comparison of Rhinoceros & Stegodonts at Panxian Dadong." Before Farming 4: 1–14.</ref><ref>Template:Cite journal</ref> At the Xinlong Cave site in the Three Gorges area of Chongqing, suggested to date to around 200-130,000 years ago, two Stegodon cf. orientalis tusks have been found along with human remains. These tusks appear to have been delibrately engraved with patterns and are suggested to have been brought into the cave by humans.<ref>Template:Cite journal</ref> At the Late Pleistocene Ma'anshan site also in Guizhou, remains of Stegodon orientalis including both adults and juveniles among other animals are found in two layers, the older dating to around 53,000 years Before Present (BP), with the younger dates to around 19,295-31,155 years BP with the minimum number of individuals being 7 and 2 for the older and younger layers respectively, with the older layer containing adults and juveniles while in the younger later only juveniles are present. Bones at the site display cut marks indicating butchery, and are thought to have been accumulated at the site by people, likely by hunting or possibly scavenging in the case of the large adults found in the older layer.<ref name=":13">Template:Cite journal</ref>
At Liang Bua cave on Flores dating to around 80-50,000 years ago, remains of the dwarf Stegodon species Stegodon florensis are associated with stone tools produced by the dwarf archaic human species Homo floresiensis, with a small number of the bones bearing cut marks. The ambiguous circumstantial association between bones and stone tools, and the rarity of cut marks makes it unclear to what if to any degree, hunting of Stegodon was practiced by Homo floresiensis.<ref name=":1">Template:Citation</ref><ref>Template:Cite journal</ref>
Evolution and extinction
The oldest fossils of Stegodon in Asia date to the Late Miocene, around 8-11 million years ago,<ref name=":3" /> with the oldest fossils of the genus in Africa being around 7-6 million years old.<ref name=":11">Template:Cite journal</ref> Stegodon became extinct in Africa during the late Pliocene, around 3 million years ago suggested to be the result of expansion of grassland habitats.<ref name=":0" />
The Javanese species Stegodon trigonocephalus became extinct around 130-80,000 years ago during the latest Middle Pleistocene-early Late Pleistocene (Marine Isotope Stage 5) following a change to more humid conditions, which may have reduced grazing habitat.<ref name=":8" /> The last records of Stegodon florensis date to around 50,000 years ago, around the time of arrival of modern humans to Flores (the earliest evidence of which dates to 46,000 years ago), suggesting that effects of modern human activity were likely the cause of their extinction.<ref>Template:Cite journal</ref>
Stegodon became extinct in the Indian subcontinent (Stegodon namadicus/Stegodon sp.), mainland Southeast Asia and China (S. orientalis) at some point during the Late Pleistocene epoch, while Asian elephants, which existed in sympatry with Stegodon in these regions, are still extant. The precise timing of extinction is uncertain for these regions,<ref name=":10">Template:Cite journal</ref><ref name=":5" /><ref name=":6" /><ref name=":12">Template:Cite journal</ref> though in India records of Stegodon may date as recently as 35-30,000 years ago,<ref name=":10" /> and to at least 30-20,000 years ago for S. orientalis in Guizhou, southwest China.<ref name=":13" /> The survival of the Asian elephant as opposed to Stegodon orientalis in Southeast Asia and South China has been suggested to be due to its more flexible diet in comparison to S. orientalis.<ref name=":5" /> Although some authors have claimed a Holocene survival in China for S. orientalis,<ref name="saegusa">H. Saegusa, "Comparisons of Stegodon and Elephantid Abundances in the Late Pleistocene of Southern China" Template:Webarchive, The World of Elephants – Second International Congress, (Rome, 2001), 345–349.</ref> these claims cannot be substantiated due to loss of specimens and issues regarding dating.<ref name=":6">Template:Cite journal</ref>
References
Template:Commons category Template:Wikispecies Template:Portal Template:Reflist
- Extinct animals of Indonesia
- Pages with broken file links
- Stegodontidae
- Miocene proboscideans
- Miocene mammals of Asia
- Miocene mammals of Africa
- Pliocene mammals of Africa
- Pliocene mammals of Asia
- Pleistocene mammals of Africa
- Pleistocene mammals of Asia
- Pliocene proboscideans
- Pleistocene proboscideans
- Miocene genus first appearances
- Prehistoric placental genera
- Fossil taxa described in 1847
- Taxa named by Hugh Falconer
- Pleistocene genus extinctions