Flagellicaudata

Flagellicaudata is a node-based clade of diplodocoid sauropod dinosaurs, comprising the families Dicraeosauridae and Diplodocidae along with their most recent common ancestor and all of its descendants. The name refers to the long, whip-like tails characteristic of its members, from the Latin flagellum, meaning "whip," and cauda, meaning "tail." Its two constituent families span a broad range of body forms: dicraeosaurids are unusual among sauropods for having re-evolved short necks, an apparent adaptation for browsing close to the ground, whereas diplodocids include some of the longest and most slender animals ever known, with greatly elongated necks. Together they represent a more derived grouping within Diplodocoidea, nested above the rebbachisaurids.