Temporal range: 270–0Ma Guadalupian - Holocene
In phylogenetic systematics, they are variously defined as the common ancestor and all its descendants of Younginiforms and "crown diapsids" (the common ancestor of lizards, crocodilians and birds, and all their descendants) [Callaway 1997], or all diapsids that are more closely related to Sauria than to Araeoscelidia (Laurin and Gauthier 2000).
Early or basal Permian neodiaspids were lizard-like, but already include specialised forms for swimming (Claudiosaurus) and gliding (Coelurosauravidae), as well as more conventional lizard-like forms (Youngina etc.). Before the end of the Permian, the neodiaspids give rise to the main branches of the diapsid evolutionary tree, the lepidosaurs and archosaurs.
The clade is defined by a number of details in skull and skeleton, for which see Laurin and Gauthier 2000.
- Callaway, J.M. (1997), Ichthyosauria: Introduction, in JM Callaway & EL Nicholls (eds.), Ancient Marine Reptiles. Academic Press, pp. 3–16.
- Laurin, Michel and Gauthier, Jacques A. (2000) Autapomorphies of Diapsid Clades