Abstract: The mammalian fossils (Mimolagus and Anagalopsis) from Shanmacheng in the Jiuxi Basin described by Bohlin in 1951 have long been enigmatic in systematics and controversial in the geological age. New survey in this area suggests the fossils were discovered from the Shanmacheng member of the Huoshaogou Formation. Comparisons of the Shanmacheng fossils with new specimens of Mimolagus from the Irdin Mahan Formation, and Anagalefrom the Late Eocene Ulan Gochu Formation, Nei Mongol, suggest an Eocene age for the Shanmacheng fossils. Reinterpretation of the fossil horizon and the paleomagnetic data of Dai et al. (2005) indicates the polarity zones from Huoshaogou section can be correlated to GPTS Chrons 13−18. Therefore, the Huoshaogou Formation may cover late Middle Eocene to Late Eocene and Bohlin’s fossil horizon can roughly be correlated to Chron18n (~39−40 Ma) of late Middle Eocene. The late Middle Eocene age of Mimolagus rodens narrows the time gap with its close relative Gomphos that have been recorded from Early to Middle Eocene. The archaic group Anagalidae may have become extinct before Oligocene. 

摘要： 步林(Bohlin, 1951)描述的酒西盆地骟马城(又译为十二马厂)化石(Mimolagus 和 Anagalopsis)在分类位置与地质年代上长期存在争议。步林认为仅依据这些化石无法确定其年代，只是推测可能为第三纪的早期。后人根据Anagalopsis与内蒙古发现的Anagale对比，认为该化石点大致时代为早渐新世。化石出自哪个层位也有不同的认识。有人认为化石发现在白杨河组下部，也有人认为化石层位属于火烧沟组。鉴于其重要意义，我们于2015年4月赴酒西盆地进行了调查。根据步林的地理位置描述与照片(Bohlin, 1940, 1951), 我们初步确定化石地点应位于骟马城沟内，火烧沟组下部骟马城段。对比内蒙古二连盆地伊尔丁曼哈组新发现的Mimolagus以及晚始新世乌兰戈楚组的Anagale, 认为步林描述的化石时代也应为始新世。根据对化石产出层位的重新认识，并对比戴霜等(2005)在火烧沟剖面的磁性地层学资料，推测火烧沟组的时代为中始新世晚期至晚始新世，骟马城化石层位的地质年代大致为中始新世晚期。Mimolagus的生存年代与其近亲Gomphos的差距大大减小，古老的Anagalidae也应该在渐新世之前就已全部灭绝。