BIOGEOGRAPHY

Qiu (1997) listed several large mammals, mostly large herbivores, which are shared by early Miocene faunas in Lanzhou and in Bugti, Pakistan: a gomphothere proboscidean, the schizotheriine chalicothere Phyllotillon, giant paraceratherine rhinos, the endemic Asian rhino Aprotodon, and the large archaic artiodactyl Paraentelodon. Such faunal exchange is indicative of a lack of barriers, at least for large mammals, between the two regions in the early Miocene. This is in contrast to biogeographic differentiation observed in the middle and late Miocene of mainland Asia, commonly attributed to the uplift of the Tibetan Plateau (Qiu and Li, in press).

The carnivores from Lanzhou, on the other hand, appear to be mostly Palearctic elements and no southern Asian affinity can be detected. The Lanzhou Hyaenodon is the only Miocene survivor of the genus outside Africa. Hyaenodon is a highly hypercarnivorous (almost exclusively meat eating) and cursorial predator (Morlo 1999). This highly diverse genus is one of the most wide-ranging, highly mobile predators, occupying the entire northern hemisphere. As archaic predators, creodonts are mostly dominant in the Paleogene. By Miocene time, hyaenodonts were largely replaced by carnivorans in Eurasia and North America, and were survived by only a few relicts in Africa, Europe, and southern Asia. A single species, Hyainailouros, is left in the early Miocene of Europe (Ginsburg 1999b). In the early and middle Miocene of eastern and northern Africa, these archaic forms still thrived in relative isolation and include modest generic diversity: Teradon, Anasinopa, Metasinopa, Dissopsalis, Metapterodon, Leakitherium, Hyaenodon and Hyainailouros (Savage 1965; Ginsburg 1980; Barry 1988; Morales et al. 1998). In India and Pakistan, Dissopsalis, ?Metapterodon, and Hyainailouros are Miocene survivors, showing geographic relationships to both Africa and Europe (Pilgrim 1908, 1914; Colbert 1933; Barry 1980, 1988), but not to mainland Asia. The immediate ancestry of Hyaenodon weilini is unclear, for lack of a comparable form elsewhere. It seems likely that this Chinese survivor was derived from northern Eurasia stocks, instead of southern Asia.

Other taxa from Lanzhou, such as Ictiocyon, may also indicate European affinity, although materials are too limited to draw firm conclusions. A more definite assessment has to wait for improvement over the currently limited number of taxa available from the Lanzhou Basin.