New Materials Of Chalicotheres From The Tunggur Formation, Inner Mongolia

This paper describes and studies in detail the new materials of chalicotheres found from the late Middle Miocene Tunggur Formation of the Tunggur Tableland, Inner Mongolia, China. They are assigned to three taxa respectively, e.g. Chalicotherium cf. brevirostris, Anisodon gobiensis sp. nov., and Chalicotheriinae gen. et sp. indet. After the study of the new materials and revision of old collections, characters of Chalicotherium cf. brevirostris was complemented as: the corpus increases in height posteriorly, the angulus mandibulae expands ventrally, there exists retromolar space; the symphysis extends to P3 or P4; the diastema between the canine and P2 is long; the mental foramen is big, oval shaped, and located at the lateral side of the anterior diastema; the mandible foramen locates posterior to the dental row below the coronoid; there are incisors and canine; three incisors increase from the mesial to the distal; the talonid is more elongated than the trigonid on the lower molars, and the trigonid is U-shaped but the talonid is V-shaped; the buccal cingulum is developed while the lingual cingulum is weak or undeveloped; the posterior cingulum of M3 is well developed, and slopes labially. The new species, Anisodon gobiensis sp. nov., is characterized by having: strong mandible; the symphysis extends to the level of P2; the diastema between the canine and P2 very long; two small mental foramina nearly round and positioned at the posterior part below the canine alveolus; a blunt apex on the canine crown with a strong and long root; on the lower molar, the metastylid very weak; the buccal cingulum developed but the lingual cingulum weak; both trigonid and talonid V-shaped; the lower premolars much smaller than the lower molars, and short lower premolar row.Till now, five genera can be assigned to Chalicotheriinae, e.g. Anisodon, Chalicotherium, Butleria, Kalimantsia, and Hesperotherium. The characters of Chalicotherium and Anisodon of Chalicotheriinae are also discussed. They are very closely related and possibly be a sister group. However, the possibility of congeneric is still waiting for further evidence. By their geological and geographical distribution, they were possibly competitors living in a similar ecological niche, and Chalicotherium cf. brevirostris from China maybe the ancestor of Hesperotherium.The indication of the chalicotheres to climate and environmental changes is also discussed. This paper affirms the former climate and environmental reconstruction by the analysis of faunal composition, ecomorphology and sporopollen data. During the late Middle Miocene, the habitat in the Tunggur region of Inner Mongolia is suggested to be temperate plain zone with more arbors and shrubs. This period, the climate is warm and wet, and getting dry and cool. It's not obvious that the Globe Cooling Event after Middle Miocene climate optimum affect this region which may be controlled by the terrestrial regional environment.