Rebbachisauridae was coined without definition by Bonaparte (1996, 1997) and subsequently used without definition by Sereno et al. (1999:1344) and (Wilson 1999, 2002). The taxon has been attributed previously to Bonaparte (1997) in error (Wilson 2002, Taylor and Naisch 2005); both papers by Bonaparte were doubtless submitted for publication at about the same time. Taylor and Naisch’s (2005:3) attribution of Rebbachisauridae to Sereno et al. (1999) because Bonaparte (1997) “was only an abstract” is not reasonable. Bonaparte (1997:183) erected the taxon in the body of a long paper. Rebbachisauridae was first defined by Upchurch et al. (2004), who elected for a stem-based definition using Rebbachisaurus and Diplodocus as specifiers. The active definition is a first-order revision of that proposed by Upchurch et al. (2004).
The stem-based definition used here is patterned after the stem-based definitions of the other two diplodocoid families (Diplodocidae, Dicraeosauridae). Nigersaurus taqueti is used as the ingroup specifier rather than the eponymous Rebbachisaurus garasbae, because the former is so much more completely known; the latter is the type genus and, therefore, is used as a positive taxon qualifier. Yet it is too incomplete to serve as the basis for clade inclusion and is rarely used in phylogenetic analyses. Two external specifiers are used, one from each of the other diplodocoid clades. It seems unnecessary to add Saltasaurus or another titanosaurian as an external specifier, given the now discarded tradition of linking diplodocoids with titanosaurs; other diplodcoids are clearly more closely related and serve as external specifiers.