Surprisingly young age for the mamenchisaurid sauropods in South China

Abstract

Mamenchisauridae, a sauropod group named after the largest known proto-Asian sauropod Mamenchisaurus, is generally believed to range from the Early to the Late Jurassic in age. Fossil remains of Mamenchisaurus are primarily found in the Upper Shaximiao Formation and less frequently in the overlying Suining Formation in the Sichuan Basin. An accurate absolute age for Mamenchisaurus is critical for understanding the evolution and radiation of the mamenchisaurids. However, reliable age determinations for the Mamenchisaurus-bearing formations are lacking. In this study, we provide robust detrital zircon U/Pb ages (mean ages of 114.4 ± 1.1 Ma; Aptian) for rocks from the classic fossil outcrops of the Suining Formation in the Sichuan Basin. Our data indicate an extremely long chronological gap between M. anyuensis (114.4 ± 1.1 Ma) and the earlier Mamenchisaurus (Late Jurassic). This indicates mamenchisaurids may have lived at least 30 million years longer than previously thought.