A new juvenile specimen of Guanlingsaurus (Ichthyosauria, Shastasauridae) from the Upper Triassic of southwestern China

ABSTRACT

A new nearly complete skeleton from the Wayao Member of the Falang Formation (lower Carnian, Upper Triassic) of Guizhou, South China, is described and ascribed as a juvenile individual of Guanlingsaurus liangae. The new specimen supplies hitherto unknown information on this species: a complete pelvic girdle shows that the ilium was misidentified as the ischium by previous authors; complete hyoids show that their length was overestimated previously; unlike in other shastasaurids, the obturator foramen on the pubis is widely open as part of the obturator fossa; and the fibula has a posterior flange, similar to that of Shonisaurus. Guanlingsaurus liangae was reassigned to the genus Shastasaurus and was suggested to be a suction feeder due to its short snout, lack of teeth, and hyoid. However, the new specimen of Guanlingsaurus described here shows much smaller hyoids compared with Shonisaurus, which was thought to be a suction-feeding ichthyosaur. Suction feeding in ichthyopterygians as a whole requires scrutiny: the group lacks an ossified hyoid corpus that is typically expanded in suction-feeding cetaceans, which suggests that ichthyopterygian hyoids were insufficiently robust for suction feeding. A phylogenetic analysis of Ichthyopterygia based on a revised data matrix clarifies the shastasaurid affinity of G. liangae as a sister taxon of Shonisaurus, with Shastasaurus as their sister group, and Shonisaurus is reestablished as a genus containing Shonisaurus sikanniensis as traditionally held. It suggests that the assignment of Guanlingsaurus and Shonisaurus sikanniensis to Shastasaurus unnecessarily confuses existing taxonomy.a

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ACKNOWLEDGMENTS

T.-F. Hu prepared GNG dq-50. Projects 40920124002, 40672002, and 40302009 were supported by the National Natural Science Foundation of China. C.J. was supported by a grant from the China Scholarship Council for 1-year research in the U.S.A. and thanks L.-T. Wang (GMR), X.-H. Chen and L. Cheng (YIGMR), P. Holroyd (UCMP), B. Strilisky (RTMP), and B. Adams (NSM) for their help in providing access to the specimens in their care and P. M. Sander for helpful suggestions on the manuscript.

Handling editor: Robin O’Keefe