Middle Pleistocene to Holocene mammal faunas of the Ryukyu Islands and Taiwan: An updated review incorporating results of recent research

Abstract

This paper presents an updated review on Middle Pleistocene to Holocene land mammal fossil localities and their faunas in the main part of the Ryukyu Islands (Central and Southern Ryukyus) and in Taiwan. We reconstruct the successions of land mammal faunas from the Middle Pleistocene to Holocene mainly on Okinawa Island in the Central Ryukyus, and on Miyako and Ishigaki Islands in the Southern Ryukyus, as well as in Taiwan. We also discuss the faunal relationships among the three islands and Taiwan, and paleogeographic inferences based on the results. The fauna on Okinawa Island has been of an insular type, and has shown a high degree of endemism since the Middle Pleistocene. With the exception of the wild boar (Sus scrofa), no mammals have immigrated onto the island since the Middle Pleistocene, indicating that the island has been isolated from other regions by the sea since at least the Middle Pleistocene. The appearance of the wild boar in the later part of the Late Pleistocene is suggestive of human introduction. On Miyako Island, the presence of the steppe mammoth (Mammuthus trogontherii) in the Middle Pleistocene indicates that this species immigrated from Taiwan across a temporary land bridge formed between the island and Taiwan (probably via Ishigaki Island) during a cold stage of the late Middle Pleistocene. It is probable that this land bridge did not reach Okinawa Island. The Late Pleistocene faunas of Miyako and Ishigaki Islands are also of an insular type, and non-flying forms of the two faunas are markedly different from one another, and are also different from their counterparts on Okinawa Island. These observations indicate that Miyako and Ishigaki Islands were separated from one another and from Okinawa Island in the Late Pleistocene. The Holocene faunas of Miyako and Ishigaki Islands also indicate isolated conditions. As on Okinawa Island, it is suggested that humans introduced the wild boar, probably in the later part of the Late Pleistocene. The Middle Pleistocene to Holocene mammal faunas of Taiwan are of a continental type, and differ greatly from those of the Ryukyu Islands. Thus, Taiwan has been separated from the islands since the Middle Pleistocene, with the exception of the land bridge stage.