Russell (1997) coined and defined a new taxon, Therizinosauria, for this widespread, diverse Laurasian clade that is becoming much better known in recent years. There seems little reason to restrict the taxonomy of this interesting clade to family-group taxa by using Therizinosauridae or Therizinosauroidea. Therizinosauria, in contrast, parallels Ornithomimosauria and Oviraptorosauria in form and definitional type (stem-based with multiple external specifiers), as defined by Russell (1997). The active definition is a first-order revision of Russell’s definition that uses species as specifiers.
Zhang et al. (2001) and Xu et al. (2002) coined a similar stem-based definition for Therizinosauroidea but were unaware of Russell’s earlier definition. Therizinosauroidea can be used within the clade as relationships between Asian and North American representatives become better resolved. Therizinosauridae can continue to be used as defined by Zhang et al. (2001) and Xu et al. (2002) for a more restricted clade of advanced therizinosaurians.