柴达木盆地渐新世的鲤科鱼类化石

FIRST FOSSIL BARBIN(CYPRINIDAE,TELEOSTEI) FROM OLIGOCENE OF QAIDAM BASIN IN NORTHERN TIBETAN PLATEAU

记述了首次发现于柴达木盆地早渐新世晚期至晚渐新世早期(距今27～29 Ma)的鲤科鱼类化石。材料包括咽骨、咽齿、匙骨、腹鳍骨及一些零散的鳍条。咽骨及咽齿化石与原始鲃亚科鱼类及裂腹鱼亚科裂腹鱼属鱼类的相似;腹鳍骨化石与原始鲃亚科鱼类的更相似。鲃亚科鱼类现今分布于北纬35°以南的亚洲、欧洲南部及非洲北部;裂腹鱼属鱼类分布局限于青藏高原东、南、西面的边缘区域,在柴达木盆地没有分布。柴达木盆地水系现生鱼类仅见适于高寒环境的高度特化等级的裂腹鱼亚科鱼类及鳅科高原鳅属鱼类,鱼类组成与早渐新世晚期至晚渐新世早期的不尽相同。

Fossil cyprinid bones and teeth were unearthed from the latest Early to early Late Oligocene of Qaidam Basin in northern Tibetan Plateau. The specimens described here include： unbranched fin rays （IVPP V 15305） （ Fig. 4C） with serrations on its posterior edge from locality CD0301 （Fig. 1 ）, a wash called Wulan Husentu （also known as Hongliugou by local people） ; pharyngeal bones and teeth （ IVPP V 15131.1-2） （ Figs. 2-3） ; and detached incompleted cleithrum （V 15131.3） （Fig. 4A） and pelvic bone （V 15131.4） （Fig. 4B） from locality CD0407（Fig. 1 ）, which is 4.7 km southeast of CD0301, and is stratigrahically 150-200 m above CD0301. Both localities are in the latest Early to early Late Oligocene Lower Ganchaigou Formation and are paleomagnetically dated at c. 27 -29 Ma （Wang et al., in press）. The fossil from CD0301 can only be identified as Cyprinidae gen. et sp. indet. And the fossil from CD0407 can be identified as belonging to the subfamily Barbinae with the following characters： the length/width ratio of the pharyngeal bone is about 4 ; the length of its anterior and posterior limbs are almost equal; the pitted surface is moderately expanded, extending forward to a point opposite to the A2; the anterior edentulous process is about half the length of the dentigerous surface; the posterior edentulous process is laterally compressed, tapering to a blunt point, almost as long as the dentigerous surface. Teeth with 3 rows, the formula is / 5, 3, 2 ; A1 is not preserved, but its position can be judged by the pharyngeal bone; A2 is the largest one, some- what swollen at apex, with the tip somewhat recurved posteriorly and the grinding surface small; A3 is the second largest tooth, with its tip recurved posteriorly and the apical region somewhat expanded laterally and bent dorsally, the anterior margin convex and the posterior one concave, so the grinding surface is spoon-like and somewhat broad, with ridges on lateral edges; the following two teeth as well as teeth in the outer two rows resemble those of A3 except smaller in size; teeth on the outmost row are the smallest ones, teeth on the median row and A5 are the second, A4 is larger than A5 but smaller than A3. The anterior fork of pelvic bone may be shallow, judged from the long, unforked posterior part of the bone; the projecting facet in the posterior end of the pelvic bone is straight, with its length about twice of its width. Recent barbin fishes are distributed in the Yangtse River and the river systems south to it in China, with no species living in Qaidam Basin, northern Tibetan Plateau, where the Recent fish fauna only consist of Gyrnnocypris, Schizopygopsis （Schizothoracinae, Cyprinidae ）, and Triplophysa （Nemacheilinae, Cobitidae）. In other words, the Recent fish fauna from Qaidam Basin is very different from that of the latest Early to early Late Oligocene. This possibly means that the altitude and climate in this area have changed greatly since Oligocene.