Eureptilia was defined as a stem-based clade, specifically, the most inclusive clade containing Captorhinus aguti and Petrolacosaurus kansensis but not Procolophon trigoniceps, by Tsuji and Müller (2009).
Eureptilia je bio definsana kao matično bazirani kladus, specifično, najveobuhvatniji kladus koji sadrži Captorhinus aguti i Petrolacosaurus kansensis ali ne Procolophon trigoniceps, po predlogu Tsujia i Milera (2009).