Zhang et al. (2001) were first to define Therizinosauroidea. The stem-based definition overlaps with that given previously for Therizinosauria by Russell (1997). Russell’s Therizinosauria has precedence and also may be the better stem-based taxon to encompass the entire clade of specialized theropods (see Therizinosauria).
Clark et al. (2004), in contrast, proposed a node-based definition for Therizinosauroidea, which is followed here. Inclusion of the basal therizinosaurian Falcarius from western North America currently differentiates Therizinosauria from the less inclusive Therizinosauroidea. The active definition is a first-order revision of that in Clark et al. (2004) that uses species as specifiers.