In the phylogenetic system, the Synapsida include Mammalia and all other amniotes more closely related to Mammalia than to Reptilia. Nonmammalian synapsids form an extensive series of taxa that are successively more closely related to mammals and are often collectively referred to as ‘mammal-like reptiles’. This vernacular term alludes to the superficially ‘reptilian’ appearance of many primitive synapsids. It has become scientifically meaningless because Synapsida and Reptilia are now interpreted as two entirely distinct evolutionary lineages of Amniota.