O. Gy. Dely szerk.: Vertebrata Hungarica 23. (Budapest, 1989)
Cao, van Sung: On the problem of zoogeographical division of the rodent fauna of Vietnam (Mammalia, Rodentia) 57-66. o.
North Truong-son has a transitory character. Here runs the southern limit of certain northern species as Rattus flavipect us, Callosciurus erythraeus, Hystrix hodgsoni , Callosciurus pygerythrus and the northern one for some southern species as Callosciurus flavi manus, Tamiops rodolphei, Menetes berdmorei, Rattus exulans etc. South Truong-son is also of transitory character, with dominance of southern faunal elements: Hystrix brachyurus, Hylopetes spadiceus , Hylopetes lepidus, Menetes berdmorei, Berylmys berdmorei. District Nam Bo has a typically Indo-Malayan character, with a major share of Sundan elements ( Hylopetes spadiceus , Hylopetes lepidus, Menetes berdmorei, R atufa affinis, Callosciurus notatus, Callosciurus n igrovittatus, Sundasciurus hippurus) . As it is well-known zoogeography has not only the task to describe the present distribution of animals, but that one to reveal the history and origin of the fauna, too. That vill be shown in the following part of this paper. History and origin of the rodent fauna of Vietnam With respect to its species composition and origin the rodent fauna of Vietnam may be considered as very complex. Up to date a very few paleontological data have been gathered and that is the reason why it is very difficult to elucidate the phases of the history, origin and evolution of the Vietnamese rodent fauna. The basic and most characteristic core of the local fauna is made up by the ancestral group of endemic forms, which are in addition of relict character and form the main part of the Indo-Chinese fauna (Callosciurus erythraeus, Callosciurus pygerythrus , Callosciurus finlaysoni, Callosciurus flavimanus, Rattus osgoodi, Rattus germaini, Ratufa bicolor) . Besides these a significant contribution of Chinese faunal elements (Rattus flavipectus , Rhyzomys sinensis ) and that of Indo-Chinese ones (Ratufa bi- color, Mus cooki ), but especially of that one of Malayan elements ( Menetes berdmorei, Ra tufa affini s , Sundasciurus hippurus , Callosciurus notatus, Rattus exulans etc. ) can be established. This can be explained only by the complicated linkage of past and present periods. The fact that the rodent fauna of Vietnam has absorbed to such a large extent different elements shows clearly that this territory excelled during geohistorical processes with similar ecological conditions, physicographical factors, but especially with its uniformity. The presence of endemic rodent species is characteristic not only for Vietnam, but for the whole Oriental realm, too; this seems to prove the former existence of an ancestral, independent faunogenetic center. Besides the ancestral elements the territory of Vietnam was invaded by certain species from other regions, too, as Micromys minutus, Niviventer confucianus, Eothenomys melanogaster etc. from the northern Palearctic, Hystrix brachyurus, Hylopetes spadiceus, Rattus exulans , Berylmys berdmorei and Menetes berdmorei from the Malayan region, or Mus cooki. Mus pahari , Cannomys badius, Rhyzomys pruinosus , Rattus koraten- sis , Bandicota indica and Vandeleuria oleracea from the west. It might have been sufficiently shown by recorded data that the rodent fauna of Vietnam is the result of a long and complicated self-dependent evolution. The rodent fauna of Vietnam has been isolated from the surrounding territories by such natural barriers as the Pacific from Indonesia, whereas the rivers running in the west-eastern direction prevented in fact the immigration of the animals of China into the southern areas. It is worth of mentioning that some species of China's temperate zone having a wide distribution (the genera Apodemus, Microtus) as well as that ones of India's semidesert zone (Meriones, Cricetulus etc. ) are absent from Vietnam since the conditions of this country are quite different. On the contrary a number of relict species were able to survive in Vietnam until present; they were preserved by the favourite life conditions and the isolation of the fauna. On the wide highlands of Tay nguyen xerophilic forests and xerophilic grasslands developed. In these areas such thermophilic species of southern origin settled that were able to adapt themselves to the severe habitat, as Menetes berdmorei, Hylopetes spadiceus , Ta miops rodolphei. It deserves attention that some rodent species originating from very far countries are represented in Vietnam by locally highly differentiated forms, each having an isolated area of its own. We may refer to the four subspecies of the red-bellied Squirrel (Callosciurus erythraeus erythraeus , C. e. erythrogaster , C. e. castaneoventris, C. e. cucphuongis) as
