Omeisauridae is a family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of sauropods. Wilson, when naming the family in 2002, included Omeisaurus and Mamenchisaurus, but if Mamenchisaurus is included, Mamenchisauridae

Mamenchisauridae

Mamenchisauridae is an extinct family of sauropod dinosaurs. The family was first named by Chinese paleontologists C.C. Young and H.C. Chao in 1972, in a paper describing Mamenchisaurus. Other mamenchisaurids may include Bellusaurus, Chuanjiesaurus, Eomamenchisaurus, Hudiesaurus, Klamelisaurus,...

 has priority, as it was named in 1972. The term 'Omeisauridae' is unlikely to survive based on this, especially as Mamenchisaurus is firmly classified in Mamenchisauridae with other close relatives (i.e. Eomamenchisaurus

Eomamenchisaurus

Eomamenchisaurus is a genus of mamenchisaurid sauropod dinosaur from the Middle Jurassic of Yuanmou, Yunnan, China. The type species is E. yuanmouensis, described by Lu et al. in 2008....

, etc.) and Omeisaurus is often classified in both Euhelopodidae

Euhelopodidae

Euhelopodidae is a family of sauropod dinosaurs which includes the genus Euhelopus. The family name was first proposed by American paleontologist Alfred Sherwood Romer in 1956. The four genera Chiayusaurus, Omeisaurus, Tienshanosaurus, and Euhelopus were the original proposed euhelopodines...

and Mamenchisauridae in its present sense.