Upchurch (1995) was first to use the superfamily. He included Quaesitosaurus and Nemegtosaurus (see also Upchurch 1998, 1999; Upchurch et al. 2004); the definition later employed followed that of the initial definition (Sereno 1998:63). The two aforementioned genera are likely synonyms and more likely represent a titanosaurian (Wilson 2002, in press). They are not used in the active definition and are regarded as lying outside Diplodocoidea.
Recently Taylor and Naisch (2005:2-3) discussed in detail the history of the taxon Diplodocoidea and also used the defnition of Sereno (1998). The active definition is a first-order revision of Sereno (1998:63) that uses species instead of genera. Wilson and Sereno (1998) used a very similar definition but list two other genera (Rayososaurus, Amphicoelias). These genera, however, are not necessary to include in the definition and have their own taxonomic complications. Here they are excluded from the definition and allowed to fall where they may.
The earliest record for any currently known diplodocid or dicraeosaurid is Kimmeridgian-Tithonian in age (McIntosh 1990). The latest well established bone record is Rebbachisaurus garasbae, from the Cenomanian-age Kem Kem beds in Morocco (Sereno et al. 1999); the latest dental record includes teeth from the Bauru Group (Campanian-Maastrictian) of Brazil (Kellner 1996), which are very similar to teeth of the earlier diplodocoid Nigersaurus taqueti (Sereno et al. 1999; Sereno and Wilson in press).
A similar age (Campanian-Maastrichtian) dentary attributed to Antarctosaurus wichmannianus (Huene 1929) also may pertain to the Diplodocoidea (Wilson and Sereno 1998) rather than the Titanosauria (Upchurch et al. 2004). The squared shape of the jaw, nonetheless, has recently been shown to characterize some titanosaurians.
Dates are rounded to the nearest million, the earliest and latest from the boundary between the two stages indicated for earliest and latest records (Gradstein et al. 2004).