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The Middle Eocene Arshanto fauna (Mammalia) of Inner Mongolia

1987; Volume: 56; Linguagem: Inglês

10.5962/p.215164

1943-6300

Tao Qi,

Animal Ecology and Behavior Studies

Review of the Eocene deposits in Inner Mongolia has shown that the classic "Arshanto Formation" forms the lower beds of the Irdin Manha Formation.Mammalian faunas from the Arshanto beds as well as from the overlying Irdin Manha beds are middle Eocene in age, roughly equivalent to the early and late Bridgerian, respectively.Two other units, formerly included in the "Arshanto Formation" are the Lower Eocene Bayan Ulan beds and the Upper Paleocene Nomogen beds, both here referred to the Nomogen Formation.Comparisons between the Inner Mongolian Arshanto fauna and the approximately time equivalent faunas of eastern and southern Asia suggest the existence of two Asiatic paleobiogeographic districts during the middle Eocene. Annals of Carnegie Museumvol. 56 fauna (under study by Zhai), which is quite similar to but shows some differences from the Nomogen fauna, was found in Bayan Ulan above the level of the Nomogen beds.Fossil mammals also were found in the Arshanto beds in several other areas such as Arshanto Obo, Irdin Manha, Bayan Ulan, Huhe Bulak, and Ulan Bulak in 1976 and 1977.These are the main materials described in this paper, and these faunas comprise the Arshanto fauna.2. The composition of the Arshanto fauna bears some resemblance to that of the Irdin Manha fauna.The ages of both are close, i.e., middle Eocene.Therefore, three middle Eocene mammalian faunas are recognized in the eastern part of China: the earliest, Xintai (Sintai) fauna (Zhou and Qi, 1982), the Arshanto fauna, and the latest, Irdin Manha fauna.The Arshanto and Irdin Manha faunas are quite different from the Inner Mongolian Shara Murun fauna in composition.The age of the latter is unquestionably late Eocene, on the basis of such mammals as the hyaenodontid Pterodon, the perissodactyl Deperetella, and the artiodactyl Archaeomeryx.3. The age of the Arshanto fauna seems to compare most closely with that of the early middle Eocene Bridger fauna (Bridger A and B) of North America, especially on the basis of the helaletids and the brontotheriids.It must be noted, however, that some elements of the Arshanto fauna are more typically associated with older faunas (Harpagolestes, Homogalax ), whereas at least Forstercooperia is more typically younger.4. Based on the known fossils, the east and central Asiatic middle Eocene faunas belong to the same paleogeographic district, and both are quite different from those of the south Asiatic district.The southern fauna has some marine mammals, such as Cetacea, and some terrestrial animals, such as Proboscidea and Artiodactyla, which never or very rarely appear in the Arshanto fauna and in central Asia.Some relatives (Anthracotheriidae) of middle Eocene mammals found in south Asia were discovered in late Eocene beds in south China and Burma, but are rare in northern Asia.Therefore, southern and southeast Asia appear to belong to another paleogeographic district.