A new diapsid reptile, Malerisaurus langstoni, n.sp., from the Late Triassic Dockum Formation of Texas, was a small, gracile, longnecked animal similar to modern bipedal lizards in size, proportions, and inferred activities. The skull is diapsid with an incomplete lower temporal arcade and a fixed quadrate. A similar configuration of the cheek region is known in many longnecked Permo-Triassic protorosaurs (= Prolacertiformes) that paralleled the squamates in the loss of lower temporal bar without any phyletic relationships to the latter group. The protorosaurs were very successful during the Permo-Triassic period, being recorded from all continents except South America. The number of neck vertebrae and its length are diagnostic characters for classifying the two families of protorosaurs. The family Protorosauridae (including Protorosaurus, Prolacerta, Kadimakara, Macrocnemus, Malerisaurus and the unnamed Yerrapalli form) has a moderately long neck, with 8 vertebrae. The family Tanystropheidae (including Tanystropheus and Tanytrachelos) has an extremely long neck with 12 vertebrae. The ankle structure is the most important derived feature that distinguishes protorosaurs, rhynchosaurs, and trilophosaurs from the traditional lepidosaurs, and unites them with archosaurs in a larger assemblage, the Archosauromorpha.