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Sinraptorid metatarsal from Upper Jurassic in Junngar Basin, China



From: Ben Creisler
bcreisler@gmail.com


A new paper (in Chinese) in open-access Vertebrata PalAsiatica:



HE Yi-Ming, James M. CLARK & XU Xing (2013)
A large theropod metatarsal from the upper part of Jurassic Shishugou
Formation in Junggar Basin, Xinjiang, China.
Vertebrata PalAsiatica 51: 29-42
http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/201301/P020130131395888802283.pdf



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 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
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.