西藏聂拉木达涕盆地晚中新世的三趾马化石及其古生态和古高度意义

HIPPARION FOSSILS OF THE DATI BASIN IN NYALAM, TIBET, CHINA AND THEIR PALEOECOLOGICAL AND PALEOALTIMETRY IMPLICATIONS

西藏自治区聂拉木县达涕盆地是一个小型的山间盆地,沉积了新近纪晚期的河湖相地层.早期的工作中曾报道有三趾马化石的线索,据此进行的新的考察发现了更多的哺乳动物化石,其中包括1件带有颊齿列的三趾马上颌.达涕盆地的三趾马体型中等,其上颊齿具有原尖小而圆,前、后端较尖,褶皱中等发育,前附尖和中附尖不特别加宽,无次尖收缩等特点.与之前发现的下颌骨相结合,证明达涕盆地的三趾马属于福氏三趾马（Hipparion forstenae）.通过与西藏吉隆和山西保德发现的福氏三趾马的时代对比,显示达涕盆地含福氏三趾马层位的年龄约为7Ma,因此将原定的上新世达涕组的时代纠正为晚中新世.与近距离的吉隆沃马盆地福氏三趾马的生态对比,指示达涕盆地在7Ma的古海拔高度约为2400 ～ 2900m,该地区自那时以来快速上升了至少2000m,这一结果与构造学的证据吻合.

The Dati Basin is a small intramontane basin on the south side of the Nainnainxuonla tableland, 45km north of Nyalam eountyseat, Tibet Autonomous Region, China where the Late Neogene fluvial and lacustrine strata were deposited. In the previous expedition, a fossil of Hipparion was reported from the Dati Basin. Based on the clue, a new excavation discovered more mammalian fossils, including a maxillary of Hipparion with cheek teeth. The Hipparion horse from Dati is middle-sized, and its upper cheek teeth has small and rounded protocones with sharp anterior and posterior ends, moderate enamel plications, narrow para- and mesostyles, and no hypoeonal constriction. Combined with the mandible found previously, the Hipparion fossils of the Dati Basin were proved to belong to H. forstenae. According to chronological correlation to H. forstenae of Gyirong, Tibet and Baode, Shanxi, the age of the horizon bearing H. forstenae fossils in the Dati Basin is about 7Ma. As a result, the original Pliocene Dati Formation is revised to be the Late Miocene. Compared with the ecology of H. forstenae from the nearby Woma Basin in Gyirong, the paleoelevation of the Dati Basin was about 2400-2900m at 7Ma. Since that time, this area has rapidly risen at least 2000m, which is consistent with the tectonic evidence.