亚洲土著类群硅藻鼠科的演化

硅藻鼠科是仅分布于亚洲的啮齿类类群,头骨具豪猪型咬肌结构,下颌则为松鼠型。该类群代表了一个从梳趾鼠类分化出的区域性支系,虽与豪猪次目相近,但并不是它的成员。最早的硅藻鼠化石记录发现于Baluchistan渐新世陆相地层中,稍晚的记录发现于南业晚渐新世。印度次大陆连续的地层为该科的演化历史提供了主要的化石依据。早中新世晚期至中中新世,硅藻科化石也发现了泰国、中国以及日本。其后的硅藻鼠种类少且鲜有化石记录。晚中新世早期在巴基斯坦有一个种,中国南部晚中新世也可能有一个种。尽管在最早的化石地点发现的标本较多,但其后的时段内除泰国李盆地外化石并不丰富,这指示了其特殊的生活习性或其生活区域化石保存的偏差。已知的化石记录并没有指示出该类群的多样性,也可能是缺少石化作用的结果。硅藻鼠类在水系外围区域延续生存与最近在老挝中部多岩石地带发现的现生Laonastes也是一个硅藻鼠的假设相一致。

EVOLUTION OF THE DIATOMYIDAE, AN ENDEMIC FAMILY OF ASIAN RODENTS

The Diatomyidae are a distinctive rodent family of Asian distribution. The skull is characterized by hystricomorphous musculature, and the jaw is sciurognathous in morphology. The group represents a local radiation of ctenodactyloid rodents closely related to, but not a member of Hystricognathi. The fossil record first yields Diatomyidae in the Oligocene terrestrial sediments of Baluchistan, followed by younger occurrences elsewhere in the late Oligocene of southern Asia. Successive deposits of the Indian subcontinent illustrate much of what is known of the history of the family. By the late Early Miocene and Middle Miocene, Diatomyidae are also known from Thailand, China, and Japan. Thereafter, diatomyids are rare and infrequently recorded as fossils. One taxon is known from the early Late Miocene of Pakistan, and there is a possible record in the late Miocene of southern China. Although abundant where found in the oldest fossil sites, diatomyids are not numerous as fossils in later localities, except Li, Thailand. This suggests special habitat preference or bias against preservation at sites where they do occur. The known fossil record does not indicate taxonomic diversity of the group, but this may be an artifact of lack of fossilization. Survival of Diatomyidae as specialized rodents of habitat peripheral to fluvial systems is consistent with the hypothesis that the recently recognized extant Laonastes of rockv terrain in central Laos is a diatomyid.