Abstract: The Shishugou Formation in the Junggar Basin was deposited during the late Middle Jurassic to the early Late Jurassic. It is known as a rich source of vertebrate fossils, including specimens of several different kinds of theropod. Here we report an isolated theropod left metatarsal IV (IVPP V 18060) from the upper part of the Shishugou Formation, exposed at the Wucaiwan Locality in the northeastern part of the Junggar Basin. Based on comparisons with the fourth metatarsals of other theropods, we refer this specimen to Allosauroidea. Similarities to the equivalent bone in other allosauroids include: the proximal end has a subtriangular outline with a tongue-like, posteriorly directed posteromedial process; the shaft has a gentle outward curve; a semi-lunate concave of muscle attachment is present on the posterolateral side of the shaft; and the cross-section of the shaft is triangular. Within Allosauroidea, V 18060 is most similar to the fourth metatarsal of Sinraptor dongi, a taxon that occurs in the same formation in the Jiangjunmiao area of the Junggar Basin. V18060 displays several specific resemblances to S. dongi: the outline of the distal end is subtrapezoidal; the depression for muscle attachment on the posterior side of the shaft that borders the shaft’s lateral side lacks a well defined ridge. However, V 18060 also differs in some respects from the fourth metatarsal of S. dongi: V 18060 is much more robust, and the lateral condyle on the distal end is smaller than the medial one. These morphological differences could be ontogenetic variation or due to sexual dimorphism, taxonomical variations. We prefer the interpretation that V 18060 is a new species that has a close relationship to S. dongi, and a cladistic analysis based on the morphology of metatarsal IV supports this inference. The discovery of V 18060 suggests that the theropods from the Shishugou Fauna are more diversified during the Mid-Late Jurassic than previously thought. The presence of different sinraptorid species in the neighboring areas of Wucaiwan and Jiangjunmiao points to the possibility that these two regions within the Junggar Basin were geographically isolated or ecologically distinct from one another during the Mid-Late Jurassic.

摘要： 准噶尔盆地中侏罗世晚期到晚侏罗世早期沉积的石树沟组产出过包括多种兽脚类恐龙在内的大量脊椎动物化石。描述了一件新的采自准噶尔盆地东北缘五彩湾地区石树沟组上部的兽脚类恐龙左第四跖骨标本(IVPP V 18060)。通过与其他兽脚类恐龙第四跖骨对比，该标本可归入异特龙超科(Allosauroidea)。它与其他异特龙超科第四跖骨的相似性包括：近端关节面三角形并有一向后方延伸的舌状突出，向外侧轻微弯曲的骨干，位于骨干后方靠近外侧边的半月形肌肉凹陷，三角形骨干横截面。在异特龙超科当中，V 18060与准噶尔盆地将军庙地区石树沟组中发现的董氏中华盗龙(Sinraptor dongi)最为相似(除了以上相似性，V 18060和董氏中华盗龙的相似性还包括远端关节轮廓呈近梯形，骨干后部肌肉凹陷与周围边界呈半开放状态)。但是，V 18060和董氏中华盗龙也存在着一些明显的区别：V 18060明显比董氏中华盗龙的第四跖骨粗壮，远端内外两髁大小差异相反。这些形态差异可能是由于个体发育或者性双形造成的，也可能代表分类学差异。对比研究和基于第四跖骨形态信息进行的分支系统学分析结果更偏向后一种解释：V 18060代表一个不同于董氏中华盗龙但与后者亲缘关系很近的新的兽脚类恐龙。新材料的发现增加了中晚侏罗世石树沟动物群兽脚类恐龙的分异度。在五彩湾和将军庙地区发现不同的中华盗龙类恐龙指示了晚侏罗世早期准噶尔盆地中相邻地区可能存在着一定的生态分异性或者地理隔离。