希夏邦马峰地区三趾马化石对古高度和古环境重建的厘定

Improvement for the reconstruction of paleoaltitude and paleoenvironment based on the Hipparion fossils in Mount Shisha Pangma region

在第一次青藏高原科学考察中,于希夏邦马峰地区吉隆盆地晚中新世沃马组中发现的三趾马动物群化石成为证明青藏高原隆升历程的重要证据之一。在其后的考察中,希夏邦马峰周边以及青藏高原其他地区有若干三趾马新材料发现,持续对青藏高原隆升过程研究起到了非常重要的作用。本文研究了采集自希夏邦马峰地区吉隆盆地的三趾马新材料,其形态特征包括:门齿唇侧无纵沟;上颊齿原尖圆、小,无次尖收缩,褶皱较弱;下颊齿双叶近圆形,双叶谷浅,宽U形,外中谷在前臼齿中浅。这些特征与原来在吉隆盆地发现的福氏三趾马(Hipparion forstenae)的鉴定特征完全一致。自三趾马在晚中新世初期从北美迁入旧大陆以后,在众多的地点都有非常繁盛的三趾马动物群分布,其中的三趾马通常有多个种共存。然而,青藏高原腹地目前已知的三趾马动物群中均只有一种三趾马存在,这种现象非常罕见。在现代青藏高原,物种数量会随着海拔升高而发生变化,在中等海拔地段物种丰富度最高,在2500m以上的高海拔地区显著下降。本文通过高原腹地与泛第三极地区的青藏高原南缘、北缘、以东及以西区域三趾马物种多样性的比较,结果表明这一现象是青藏高原在新近纪时期的强烈隆升导致的特殊地形与气候环境所致。

In the first scientific expedition to the Tibetan Plateau,the discovery of the Hipparion fauna in the Late Miocene Woma Formation of the Gyirong Basin in the area of Mount Shisha Pangma became one of the most important pieces of evidence for the uplift process of the Tibetan Plateau.In the subsequent investigation,some new fossils of the Hipparion horse were discovered around Mount Shisha Pangma and other areas of the Tibetan Plateau,which still played a very important role in the study of the uplift process of the Tibetan Plateau.We studied the new Hipparion fossils collected from the Gyirong Basin in the area of Mount Shisha Pangma,that have the following morphological characters:the absence of longitudinal grooves on the labial side of the incisors and the hypocone contraction;the small protocone of the upper cheek teeth and the weak plications;the nearly rounded double knots of the lower cheek teeth with a shallow,wide and U-shaped linguaflexid;the shallow ectoflexid in the lower premolars.These characters are completely identical with the diagnosis of Hipparion forstenae,which was previously found in the Gyirong Basin.The diversity of the family Equidae has rapidly increased since 18Ma in the Miocene,as evidenced by the high adaptation of the forms with high-crowned teeth to radiation,and reached its peak with the spread of open grasslands.Since the migration of the Hipparion horses from North America to the Old World in the early Late Miocene,there has been a very prosperous distribution of the Hipparion fauna in many locations,among which the genus Hipparion usually had multiple species coexisting.Currently,there is only one species of Hipparion in the known Hipparion fauna from the hinterland of the Tibetan Plateau,which is a very rare phenomenon.In the modern Tibetan Plateau,the number of species vary with altitude,with the highest species richness in mid-altitude areas and a significant decrease in high altitude areas above 2500m.We compare the species diversity of Hipparion from the hinterland of the Tibetan Plateau with the northern and southern sides of the plateau as well as the eastern and western areas of the plateau in the Pan-Third Pole region.The results show that this phenomenon is due to the special terrain,climate and environment caused by the strong uplift of the Tibetan Plateau during the Neogene Period.