陕西蓝田灞河组的小羚羊

DORCADORYX TEILHARD ET TRASSAERT, 1938 (BOVIDAE, ARTIODACTYLA) FROM THE BAHE FORMATION OF LANTIAN, SHAANXI PROVINCE, CHINA

描述了牛科小羚羊(Dorcadorys Teilhard et Trassaert,1938)一新种:D.orientalis sp. nov.。材料发现于陕西蓝田Loc.6,晚中新世灞河组中部。它和属型种Dorcadoryx triquetricor- nis的主要不同在于它的角心长,向上分散度大,角后窝深而狭长,眼眶向头骨两侧突出不明显,下颌骨水平支低而纤细,颊齿窄和前臼齿列相对长等。Dorcadoryx是中国北方和蒙古地区晚中新世至早上新世的特有类型之一。我国山西晚中新世的?Tragoreas(Bohlin,1935)、蒙古新近纪晚期的Tragoreas sp.2和sp.3以及Olonbulukia(?)sp.(Dmitrieva,1977)可能是它的成员。经修订,属的主要特征是个体小至中等大小,头骨狭长,角基之间的额面不向上隆起,头骨弯曲发生在额顶骨之间,眶上孔小,眶前窝大,颅顶部狭长,基枕部具中沟,前结节不明显,角心位于眼眶之上、不旋转,内外侧扁,分散度不大,稍向后弯曲,角柄长,角后窝存在, 前臼齿列退化以及p4的下后尖和下前尖相连等。它可能属于山羊亚科,包含4—5种。新种可能是其中的一个早期类型。

A new bovid, Dorcadoryx orientalis sp. nov. , is described in this paper. The materials were found from the middle part of Bahe Formation Loc. 6, Lantian County, Shaanxi Province, China. The holotype is a frontlet with two horn cores （IVPP V 14413, Fig. 1A）. It is characterized by the horn cores being long, situated above the orbits, lacking torsion, laterolaterally compressed, divergent in anterior view, inclined backwards in side view and elliptical in cross section. The postcornual fossa is narrow and deep. The frontal is not raised between the horn bases. The supraorbital foramen is small. The premolar row is short relative to the length of molar row and the paraconid is fused with metaconid on p4. Dorcadoryx was first established by Teilhard and Trassaert in 1938 on the basis of materials from “Zone 1” of Yushe Basin, Shanxi Province. It contains one species, D. triquetricornis. Solounias （1982） referred it to Protoryx Major, 1891. Actually, it is a valid genus. Although it is similar to Protoryx in the size of the supraorbital foramina and the morphology of the horn cores, it can be distinguished from the former in the following features： small in size; the horn cores slenderer; postcomual fossa present; the frontal between the horn bases not elevated, the highest point of the skull situated at the frontoparietal suture behind the horn cores; the preorbital fossa more prominent; the side of the cranial slightly inflated; short premolar row in relation to the length of molar one and the metaconid fused with the paraconid on p4 etc. Similarly, Dorcadoryx differs in the aforementioned features from Pachytragus Schlosser, 1904 and Pseudotragus Schlosser, 1904 from the Late Miocene of Europe, and Olonbulukia Bohlin, 1937 from the Late Miocene of Northern China. Bohlin （ 1935 ） described ？ Tragoreas from the Baodean of Gansu and Shanxi. It contains four species. Among them, ？ Tragoreas sp. （Bohlin, 1935, figs. 84 - 85） was considered by Teilhard de Chardin and Trassaert （1938） to be a junior synonymy of Dorcadoryx triquetricornis. ？ Tragoreas lagrelii Bohlin, 1935 was referred by Gentry （ 1971 ） to Dorcadoryx and was regarded as a distinct species. I agree with their opinions. The other two species, ？Tragoreas palaeosinensis （Schlosser, 1903 ） and ？ Tragorea sp., may be referable to Dorcadoryx as well. They are similar to Dorcadoryx in size and shape in the cross section of the horn bases. However, the former （？ Tragoreas palaeosinensis ） is distinguishable from Dorcadoryx triquetricornis in its larger size, its longer and narrower muzzle, its longer premolar row in relation to the molar row and its paraconid being not fused with metaconid on p4. The latter （ ？ Tragoreas sp. ） is also distinct from Dorcadoryx triquetricornis in the horn cores with a slight torsion. Dmitrieva （1977） reported the Tragoreas sp. 2, Tragoreas sp. 3 and Olonbulukia （9） sp. from the Upper Miocene and the Lower Pliocene of Mongolia. According to the size and morphology of the horn bases, they are closely related to Dorcadoryx. Therefore, it is possible that Doreadoryx contains D. triquetrieornis, D. lagrelii, D. orientalis , 9. D. palaeosinensis and ？ Dorcadoryx sp. etc. D. orientalis differs from D. triquetricornis in that its horn cores are longer and more divergent in anterior view; the postcornual fossa is narrow and deep, the orbits projecting is less prominent, the mandible is slenderer, the cheek teeth are narrower and the premolar row is long relative to molar one etc. It differs from D. lagrelii in having the narrow and deep postcornual fossa, the orbits projecting less prominent, much slender mandible and narrower cheek teeth etc. It is distinct from ？ D. palaeosinensis （Schlosser, 1903） in its smaller size, slenderer mandible, smaller teeth and shorter premolar row relative to molar one. So far, Dorcadoryx is known only from the Upper Miocene and Lower Pliocene of northern China and Mongolia. It seems to be an endemic form in the East Asia. The new species D. orientalis appears in the middle Late Miocene of Lantian, China. It may be an early form of the genus. Systematically, Dorcadoryx is more similar to a caprine than an antilope because it possesses some features of Caprinae, such as its cranial axis angled with the axis of face at the frontoparietal suture, the supraorbital foramina small and closely positioned, the premolar row short in relation to the length of molar one, an additional small cavity present between the two lobes on the worn upper molars, the metaconid situated posterior to the protoconid and the paraconid fused with metaconid on p4.