On the hindfoot bones of Mammuthus trogontherii from Shanshenmiaozui in Nihewan Basin, China

Shanshenmiaozui is an open-air fossil site of Early Pleistocene age in Nihewan Basin, China. During 2006-2011, nearly 100 fossil specimens of Mammuthus trogontherii were unearthed, including some series of tarsal, metatarsal and phalange bones of immature individuals, which represent the first discovery of hindfoot bones of immature M. trogontherii. Morphologically, the new tarsals are intermediate between those of Mammuthus meridionalis and Mammuthus primigenius. However, they have some possible differences from those of Palaeoloxodon antiquus: the relatively quadrangled plantar surface of the astragalus; the relatively flat cuboid facet on calcaneum; and the special configuration of the distal facets on ectocuneiform. With reference to the age determination by teeth, the footbone remains can be categorized into three age groups: newborn calf, juvenile, and subadult, approximately corresponding to one month old, 6-7 years old, and 10-20 years old individuals, respectively. The ontogenetic changes of the hindfoot bones can be detected in their size, morphology, compact layer, and epiphyseal fusion. There are possibilities of proximal epiphyses on metatarsals and distal epiphyses on phalanges, which is unusual in other mammals, but reasonable in elephants because of their lengthy growth period.