Wikipedia
Mamenchisauridae is a family of sauropod dinosaurs. The family was first named by Chinese paleontologists C.C. Young and X. Zhao in 1972, in a paper describing Mamenchisaurus. Other mamenchisaurids may include Chuanjiesaurus, Eomamenchisaurus, Hudiesaurus, Tienshanosaurus, Omeisaurus, and Tonganosaurus. Fossils of Mamenchisaurus and Omeisaurus have been found in the Shangshaximiao Formation, dating to the Oxfordian stage, around 161.2-155.7 Ma (million years ago). Chuanjiesaurus fossils date between 175.6-161.2 Ma, while those of Eomamenchisaurus were found in the Zhanghe Formation, believed to be around 175.6-161.2 million years old. Fossils of Tonganosaurus date to even earlier, from the Early Jurassic.
Long-bone histology enables researchers to estimate the age that a specific individual reached. A study by Griebeler et al. (2013) examined long bone histological data and concluded that the unnamed mamenchisaurid SGP 2006/9 weighed , reached sexual maturity at 20 years and died at age 31.