[N] 2013 A theropod left metatarsal from the Shishugou Formation
He, Y.-M., Clark, J.M. & Xu, X. (2013) A large theropod metatarsal from the upper part of Jurassic Shishugou Formation in Junggar Basin, Xinjiang, China.
Vertebrata PalAsiatica 51: 29-42
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 inds 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 Junngar Basin. V 18060 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 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.