陕西首次发现中华鳖化石及其意义

FOSSIL OF PELODISCUS(TRIONYCHIDAE, TESTUDINATA) WAS FIRST DISCOVERED IN SHAANXI

在陕西宝鸡簸箕庄下更新统三门组中发现中华鳖化石,鉴定为一个新种宝鸡中华鳖Pelodiscus baojiensis sp.nov.。该化石主要特征为甲壳近圆形,上拱,个体较小,长宽相近;肋板8对,第8对收缩,背甲表面布满不规则的蠕虫状的脊和凹坑纹饰,边缘变平,在缝合线附近凹坑明显纵向拉长,表面未见纵向的脊或纵向的瘤粒;肋条突出于肋板之外,骨骼明显比现代中华鳖粗壮。已记录的8属18种中国鳖科化石(不包括本文新种),分属21个地点,在地质时代上自白垩纪晚期开始,经过古近纪、新近纪一直延续到第四纪,除早、中更新世尚无报道以外,其它各地质时代基本都有发现,且以全新世报道最多,多达70余个考古地点中都记载了鳖科遗存。这是陕西鳖类化石的首次报道,也是中国第四纪早期鳖类化石的首次报道。宝鸡中华鳖的发现地点位于中国新生代鳖类化石分布的最西侧。化石证据表明,三门古湖在早更新世期间应该一直延伸到了渭河盆地西缘的宝鸡地区。

The fossils of Early Pleistocene Pelodiscus baojiensis sp. nov. were discovered at the bottom of loess in Boqizhuang section, Baoji, Shaanxi Province. It have be developed some small-sized bodies with similar length and width and subcircular carapace which is convex upwards. There are eight pairs of costal bones of which the last one seems reduced. Its surface is decorated with irregular worm-like ridges and pits;the edge of the dorsal carapace is flat which show distinct elongation near the suture lines, without longitudinal ridges or tumor grains on the surface. Free-ends of ribs protrude from the ribbed plates and the fossil skeletons are obviously stronger than those of modern turtles in China. At present, 8 genera and 18 species have been reported(not including the new species of this paper)which are distributed in 21 localities from the Late Cretaceous, Paleogene, Neogene to Quaternary except the Early and Middle Pleistocene. The majority materials of Trionychidae are mainly found in the Holocene and it has been recorded in more than 70 archaeological sites. This is the first report of soft-shelled turtle fossils from Shaanxi and also the Early Quaternary China. The site of Pelodiscus baojiensis sp. nov. is located at the westernmost part of the paleogeographical distribution of the taxon in Cenozoic China, which indicates that the Sanmen Lake extended to Baoji area of the western edge of Weihe Basin during the Early Pleistocene.