Stegodon

Palaeobiology

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. 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. 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), 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. 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. 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. Specimens of Stegodon kaiesensis from the Pliocene of East Africa were found to be browsers to mixed feeders, based on mesowear analysis.

The East-Southeast Asian species Stegodon orientalis is thought to have primarily inhabited densely forested environments though it may have also inhabited somewhat more open forested habitats, while the Javanese Stegodon trigonocephalus is thought to have primarily lived in a mix of open savannah woodland and forest.

On Flores, where dwarf Stegodon species were the only large herbivores, they were likely the main prey of the Komodo dragon. Members of Stegodon florensis and perhaps other Stegodon species may have deliberately entered caves to mourn the dead or for water and minerals.

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.

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.

Taxonomy

Stegodon was named by British palaeontologist Hugh Falconer in 1857, originally as a subgenus of Elephas, the genus which today contains the Asian elephant. Among the first described remains of the genus by Falconer were from the Siwalik Hills of the northern Indian subcontinent, which he assigned to the species Stegodon insignis and Stegodon ganesa, which have since become the subject of taxonomic confusion because of the lack of clearly assigned type specimens and the uncertain stratigraphic provenance of Falconer's collected material. 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, with transitional fossils between the two genera known from the Late Miocene of Southeast Asia and Yunnan in South China, with Stegodon and Stegolophodon collectively placed into the family Stegodontidae. Stegodontidae is placed within the clade Elephantimorpha within Proboscidea, with its exact position in the group being uncertain. Many studies have supported stegodontids as more closely related to modern elephants than to true mastodons of the family Mammutidae, though some studies have found other positions, with one 2025 study finding (albeit with weak support) stegodontids more closely related to Mammutidae than to elephants. Stegodontids are believed to have derived from gomphotheres, with Gomphotherium annectens having been suggested to be the ancestor of Stegolophodon by some authors.

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. Indeterminate remains are also known from the Early Pleistocene and early Middle Pleistocene of Israel.

Relationship with humans

Remains at a number of sites suggest that humans (in a broad sense, including archaic humans) interacted with Stegodon. 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. At the late Middle Pleistocene Panxian Dadong cave site in southern Guizhou Province, southwest China, dating to around 300–190,000 years ago, 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. 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. 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.

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. A 2026 study suggested that H. floresiensis likely only consumed Stegodon remains in the cave that had already been primarily consumed by Komodo dragons.

Evolution and extinction

The oldest fossils of Stegodon in Asia date to the Late Miocene, around 8–11 million years ago, with the oldest fossils of the genus in Africa being around 7–6 million years old. Stegodon became extinct in Africa during the late Pliocene, around 3 million years ago suggested to be the result of expansion of grassland habitats. The earliest records of Stegodon in Java date to the Early Pleistocene, over 2 million years ago. On the islands of the Philippines, remains of Stegodon are suggested to span from at latest 0.8–1 million years ago until at least 400,000 years ago.

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. 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.

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, though in India records of Stegodon may date as recently as 35–30,000 years ago, and to at least 30–20,000 years ago for S. orientalis in China, with young records of this age including those from Guangxi southwest China, as well as southern Shaanxi in northern China. The harsh climate of the Last Glacial Maximum may have contributed to the decline of S. orientalis. 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. Although some authors have claimed a Holocene survival in China for S. orientalis, these claims cannot be substantiated due to loss of specimens and issues regarding dating.