This taxon may have been first defined by Apesteguia (2004), who although not providing a numerical cladistic analysis, argued for a close relationship between Nemegtosaurus, Quaesitosaurus, Rapetosaurus, and Bonitasaura and referenced the phylogenetic analysis and use of Nemegtosauridae by Wilson (2002). Unaware of this definition, Wilson (2005) proposed an identical definition, while clarifying further the anatomy and relationships of the key genus Nemegtosaurus.
Upchurch et al. also defined Nemegtosauridae in 2004. In their analysis, the taxon encompassed Nemegtosaurus and Quaesitosaurus, which they placed within Diplodocoidea. The latter genus may eventually shown to be a junior synonym of Nemegtosaurus (Wilson 2005). More problematic is the use of Diplodocus as an external specifier.
An useful active definition may eventually be constucted from a first-order revision of that in Apesteguia (2004) and Wilson (2005) using species rather than genera.