似希腊鼻原角龙(角龙亚目:原角龙科)在内蒙古阿拉善地区的发现

Occurrence of Protoceratops hellenikorhinus (Ceratopsia: Protoceratopsidae) in Alxa region, western Inner Mongolia, China

本文记述了内蒙古西部阿拉善右旗阿拉腾敖包镇巴音塔拉一带上白垩统乌兰苏海组中的2件原角龙属Protoceratops头骨化石,头骨全长超过700 mm、齿骨腹缘近于平直、上颌骨侧面近水平向的嵴较直且较弱、无上颌骨齿,表明其应归入似希腊鼻原角龙P.hellenikorhinus。该种鉴定特征被修订为:原角龙属个体较大的种,头骨全长超过700 mm,鼻骨角突发育,无前颌骨齿,上颌骨侧面前后方向的嵴相对平直且较弱,鳞骨腹突伸长且与方轭骨相接触,齿骨腹缘平直,前齿骨前缘与腹缘形成一明显夹角,隅骨后缘由一向后的三角形面形成。这是似希腊鼻原角龙在阿拉善地区的首次确切记录,阿拉善右旗巴音塔拉也成为该种化石继内蒙古乌拉特后旗巴音满都呼之后的第2个分布区,大大扩展了该种的地理分布范围,并为两地晚白垩世恐龙动物群的对比研究提供了关键信息。

Two new protoceratopsid specimens excavated from the Late Cretaceous Wulansuhai Formation at Bayan Tal near the town of Alaten Obo, Alxa Right Banner, Alxa League, western Inner Mongolia can be further included within Protoceratops hellenikorhinus based on their features such as: skull total length more than 700 mm, ventral edge of the dentary nearly straight, horizontal ridge on the maxillary lateral side relatively straight and reduced, and premaxillary teeth absent. Here the diagnosis of this species is revised as follows: large-sized species of the genus Protoceratops with skull total length exceeding 700 mm in adult, dorsally prominent nasal horns, lack of premaxillary teeth, straight and strongly reduced rostrocaudal ridge on the lateral side of maxilla, long projection of the squamosal contacting the quadratojugal, straight ventral edge of dentary, evident angle between the anterior and ventral edges of predentary, and caudal edge of the angular formed by a caudally facing triangular surface. The new specimens are the first occurrence of Protoceratops hellenikorhinus from Alxa region, western Inner Mongolia, showing Bayan Tal, Alxa Right Banner to represent the second area yielding this species following Bayan Mandahu, Urad Rear Banner. The new discovery expands the geographical distribution of this taxon, and provides the crucial information for the correlation of dinosaur faunas between the two areas.