南京汤山驼子洞的马科化石及其意义

200 0年在南京汤山葫芦洞直立人地点附近的驼子洞堆积中发现了又一处哺乳动物化石点。其中的马科化石有两种 :黄河马Equushuanghoensis和中国 (长鼻 )三趾马Hipparion(Proboscidipparion)sinense。这是自 1 95 9年发现黄河马化石以来首次发现黄河马的颅骨和完整的颊齿列标本。这两种马的同时出现说明含驼子洞动物群的堆积形成于早更新世。因此驼子洞堆积的发现是江宁地区下更新统的首次记录。驼子洞的黄河马和长鼻三趾马均为这两类马在秦岭淮河以南的首次记录 ,并反映了在早更新世曾发生过北方动物群跨越长江的南迁事件。

FOSSIL EQUIDS (MAMMALS) FROM THE TUOZIDONG, NANJING (CHINA) AND ITS SIGNIFICANCE

After the discovery of Homo erectus and associated mammalian fauna from the Huludong Cave at Tangshan, Nanjing, Jiangsu Province (Mu et al., 1993; Huang, 1996; Dong, 1999), a new mammalian fauna was discovered in 2000 from the cave deposits at Tuozidong (32°03′N, 119°01′E) of 800 meters west of the Huludong. The relationship of these two faunas arose the interests of paleontologists. The recent study of the equids from Tuozidong shows that they are very significant and they are described below. 1 Systematic paleontology Equidae Gray, 1821 Equus Linnaeus, 1758 Equus huanghoensis Chow et Liu, 1959 (Figs. 1～2; Table 1) Holotype 3 upper premolars and 2 upper molars (IVPP V 2385～2389) from the Yellow River bank at the Sanmen Gorge, Pinglu County, Shanxi Province. The specimens are housed in the Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences. Revised diagnosis Skull robust, the zygomatic processus of the temporal is especially robust compared with that of the other large sized Equus. The teeth are also large. The protocone on the upper cheek teeth is relatively short, the occlusal shape of protocone is oval close to its root but appear triangular towards its top. Compared with the other species of Equus, the anterior edge of the protocone of their upper cheek teeth is located at the lingual side of posterior half of the protoconule, and never appear at that of anterior half of the protoconule. The length of the protocone is less than or equal to a third of the total length of the tooth in premolars, and a little larger than a third of the total length of the tooth in molars. The angle between the longitudinal axis of the cheek teeth and the protoloph or metaloph is very large. The hypocone is very close to the lingual side, and its size is similar to that of the protocone. Referred specimens A nearly complete cranium (JNTZ28389), a broken premaxilla with I1～2 (JNTZ28639), a left broken maxilla with P2～M3 (JNTZ6402), a nearly complete right maxilla with DP1～M3 (JNTZ6403), a broken left maxilla with P2～M3 (JNTZ29281), a broken right maxilla with P2～M3 (JNTZ26297). These specimens are housed in the Nanjing Museum. Remarks The cheek teeth in the listed specimens are very close to the holotype and included specimens of Equus huanghoensis (Yellow River horse) described by Chow and Liu (1959), e.g. short protocone, the anterior edge of the protocone of their upper cheek teeth is located at the lingual side of posterior half of the protoconule, and never appear at that of anterior half of the protoconule, the length of the protocone is less than or equal to a third of the total length of the tooth in premolars, and a little larger than a third of the total length of the tooth in molars, the angle between the longitudinal axis of the cheek teeth and the protoloph or metaloph is very large, etc. The differences between the type specimens and the Tuozidong specimens are that the caballine fold is strong in the type specimens but weak in the Tuozidong specimens. Nevertheless, the size of caballine fold is different between the holotype of Yellow River horse in the type specimens from Pinglu and included ones from Yushe (Chow and Liu 1959). This character is thus interspecifically variable. Compared with the Yellow River horse from Linyi, Shanxi Province (Chow and Chow, 1965), they are also very close to each other. Compared with the Yellow River horse from Xunyi, Shaanxi Province (Deng and Xue, 1999), they are very close to each other. It is therefore reasonable to assign the Tuozidong specimens to Equus huanghoensis. The presence of the complete cheek teeth dentition and nearly complete cranium materials from Tuozidong allow us to compare Equus huanghoensis further with the other Equus. The cranium of Equus huanghoensis shows that its zygomatic processus of the temporal is more robust than that in the other species, especially in dorsal and ventral views. And that in the other large horses such as Equus sanmeniensis (Teilhard de Chardin and Piveteau, 1930), Equ