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Eutheria : Proboscidea

The Stegodontidae

Stegodon tooth
A tooth of Stegodon from Java, Indonesia; specimen no. 33658 from the UCMP collections.
Stegodontidae is another family of Proboscideans, however there is debate on whether it is a valid family or if it belongs to Elephantidae (Shoshani and Tassy, 1996; Saegusa et al., 2005). The group is comprised of two genera Stegolophodon and Stegodon which are thought to have evolved from gomphotheres. They were among the largest proboscideans to roam the planet. They had low crowned teeth (brachyodont) with peaked ridges indicating they were browsers or mixed feeders in a forested environment. This is in contrast to the high crowned plated molars of mammoths and elephants. In general Stegodon had long, nearly straight tusks while Stegolophodon had four tusks, two on top and two on the bottom. Their bones were generally more robust than mammoths and elephants.

The earliest Stegolophodon fossil is from the early to middle Miocene in Thailand. The genus spread from its southeast origins along the coastline of East Asia. It is thought that this northward movement of the genus is a result of the mid-Miocene climatic warming (Saegusa, 1996). The genus Stegodon evolved from Stegolophodon. It most likely originated during the Pliocene in South China based on the high diversity of this genus in the area, however there is a reported record of the genus from Kenya, Africa dated at 6.5 million years ago. From South China, Stegodon rapidly diversified and spread through Asia (Saegusa, 1996). They were able to swim and reached many islands in southeastern Asia (even islands that were not connected during low sea levels of glaciation periods). Stegodon diversified on the Japan islands resulting in several endemic species (Saegusa et al., 2005).

Elephants reached Asia during the Pliocene and by this time stegodontids were very diverse suggesting that elephants and stegodontids may have co-existed. The loss of stegodontids in Africa may have been the result of increasing grassland on the continent.

New content researched and written by Kaitlin Maguire, 11/2010; Stegodon tooth photo by Dave Smith, UCMP