辽宁西部早白垩世义县组一新驰龙类(英文)

A NEW DROMAEOSAUR (DINOSAURIA: THEROPODA)FROM THE EARLY CRETACEOUS YIXIAN FORMATION OF WESTERN LIAONING

我国辽西早白垩世义县组底部陆家屯层近年来产出大量恐龙和其他脊椎动物化石 ,其中包括兽脚类恐龙当中的伤齿龙类和窃蛋龙类 (Xu ,2 0 0 2 )。本文报道该层位产出的一件驰龙类化石标本。通过对比研究 ,我们确认这一标本不同于热河群已知的其他 3种驰龙类 ,并建立了驰龙类的一个新属种 :陆家屯纤细盗龙 (Graciliraptorlujiatunensisgen .etsp .nov .)。驰龙类最初发现于北美晚白垩世地层中 (MatthewandBrown ,1 92 2 ) ,随后在蒙古晚白垩世地层中也有发现 (Osborn ,1 92 4 ) ;现在已知驰龙类的化石记录主要集中在北美和中亚地区的白垩纪地层中 (Xu ,2 0 0 2 )。千禧中国鸟龙 (Sinornithosaurusmillenii)曾代表最早的确定无疑的驰龙属种 (Xuetal.,1 999) ,其生存时代大约为 1 2 5Ma (Swisheretal.,1 999)。陆家屯纤细盗龙正型标本产于义县组底部陆家屯层 ,其上覆和下伏岩层的同位素年代分别为 1 2 8Ma和 1 39Ma (Swisheretal.,2 0 0 1 )。因此 ,陆家屯纤细盗龙代表已知最早的驰龙属种。陆家屯纤细盗龙和其他驰龙类共享以下近裔特征 :尾椎前关节突和脉弧极度加长、上颌齿后缘锯齿明显大于前缘锯齿和指节III- 2明显缩短。陆家屯纤细盗龙的以下近裔特征区别于其他驰龙类

A specimen collected from the Early Cretaceous lowest part of Yixian Formation of Liaoning, northeastern China, represents a new genus and species of dromaeosaurid theropod. It comprises a fragmen tary maxilla with some teeth, a few caudals, almost complete fore limbs, and partial hind limbs and is here named Graciliraptor lujiatunensis gen. Et sp. Nov. Distinctive characteristics of the new species include a laminal structure connecting the postzygapophyses of middle caudals, middle caudals extremely long and slender, small manual ungual I, proximal end of metacarpal Ⅲ strongly expanded, proximal tibiotarsus shaft rectangular in cross section, astragalar medial condyle significantly expanded posteriorly, metatarsal Ⅱ dis tally much wider than the other metatarsals and long and slender pedal phalanx Ⅲ-1. Being the earliest def initive dromaeosaurid species known to date, G. Lujiatunensis provides new information important for under standing the early evolution of the group. On one hand, G. Lujiatunensis displays a few features similar to those of basal birds, such as caudals significantly elongated, semilunate carpal small and primarily contact ing metacarpal Ⅱ, and manual digit Ⅰ short, providing further evidence for a close relationship between the Dromaeosauridae and the Aves; on the other hand, it is similar to troodontids in some features on the cau dals. The discovery of G. Lujiatunensis also indicates a high diversity of the Dromaeosauridae in the Early Cretaceous Jehol Biota. Combined with other lines of evidence, it is inferred that the Dromaeosauridae rap idly diversified taxonomically but remained relatively stable morphologically in the early evolution of the group.