 The clade Flagellicaudata was erected by Harris and Dodson (2004) for the diplodocoid clade formed by Dicraeosauridae and Diplodocidae in their paper describing a new genus of sauropod dinosaur, "Suuwassea".The authors carried out a phylogenetic analysis and noted that "Suuwassea", although more derived than Rebbachisauridae, is in a trichotomy with other families belonging to Diplodocoidea (Diplodocidae and Dicraeosauridae).Flagellicaudata was defined as a node-based clade consisting of the most recent common ancestor of "Dicraeosaurus" and "Diplodocus" and all of its descendants.