New prehistoric elephant ancestor found in China
In the main Proboscidean taxon of Elephantiformes, a huge pair of developed top incisors (ivories) has become a distinctive feature of this taxon. The structure is usually made as a tool for individual foraging and a weapon for males to compete for mating.
|Selected individuals of the fossil accumulation of Aphanobelodon zhaoi gen. et sp. nov. |
showing the age-sex structure [Credit: Chinese Academy of Sciences]
The researchers were always interested in the weird evolution direction. Many hypotheses and studies have been made about the functional and morphologic significances of shovel-shaped lower jaws in Amebelodontidae.
Recently, researchers Shiqi Wang, Tao Deng and Jie Ye, in IVPP, together with collaborators in Hezheng Palaeozoological Museum, Gansu, have found the conserved delicate Amebelodontidae fossil group in Middle Miocene in Dingjiaergou, Tongxin, Ningxia and published it on Journal of Systematic Palaeontology online.
reconstruction of Aphanobelodon zhaoi gen. et sp. nov. of the
Dingjiaergou Fauna |
during the early Middle Miocene [Credit: Yu Chen]
The critical significance of discovering the Aphanobelodon zhaoi lies in revealing the diversified morphological and ecological differentiation of Elephantiformes during the early evolution. The studies and verification of branching system showed that Aphanobelodon zhaoi existed as the sister group of Platybelodon in the systematic evolution.
However, the internal structure of its lower incisor is very different from the Platybelodon, but similar to the other Protanancus in the Amebelodontidae. So, the same structure of lower incisors is not made as a distinguishing criterion for inner members of Amebelodontidae, but it is a parallel evolution under the selection pressure.
Studies by microwear and mechanics analyses maintained that the group representated by Aphanobelodon zhaoi and Platybelodon in Amebelodontidae were specialized into a group that fed on the tender leaves and its wide-shovel-shaped lower jaw was mainly used to cut the tender shoots and leaves; and the other group represented by Protanancus had a broad spectrum of food, had a narrow-shovel-shaped lower jaw used to dig the shallow-layer underground plants whilst its ivories played an important role in foraging. The inner systematic differentiation of Amebelodontidae represents the ecological differentiation as well.
The top incisor missing in the male Aphanobelodon zhaoi suggests that the fights between males might be not fierce. Therefore, the social structure of Aphanobelodon zhaoi is supposed to be different from other elephants. Perhaps, the males and females in Aphanobelodon zhaoi composed a stable breeding colony and co-nursed the minor offspring. This is vastly different from the matriarchal society that forms a large scale of colony by females to nurture the offspring in the existing elephants.
Source: Chinese Academy of Sciences [October 22, 2016]