Lystrosauridae Broom, 1903

Kammerer, Christian F. & Angielczyk, Kenneth D., 2009, A proposed higher taxonomy of anomodont therapsids, Zootaxa 2018, pp. 1-24 : 14-15

Lystrosauridae Broom, 1903 a

Definition: All taxa more closely related to Lystrosaurus murrayi ( Huxley, 1859) Broom, 1932 , than Dicynodon lacerticeps Owen, 1845 , or Kannemeyeria simocephala ( Weithofer, 1888) Broom, 1913 a.

Taxonomic comments: The relationships between Lystrosaurus , kannemeyeriiforms, and various Dicynodon -like Permian taxa (e. g., Vivaxosaurus , Dinanomodon ) remain unresolved, with some analyses recovering a Lystrosaurus +kannemeyeriiform sister-group relationship ( Angielczyk 2001, 2002; Surkov 2000; Surkov et al. 2005; Ray 2006; Fröbisch 2007; Fröbisch & Reisz 2008) and others placing Lystrosaurus outside a clade containing Vivaxosaurus and kannemeyeriiforms ( Angielczyk & Kurkin 2003a, 2003b; Angielczyk 2007) or even basal to Dicynodon ( Maisch 2002a) . Although the relative position of Lystrosauridae is uncertain, the monophyly of this group (containing Lystrosaurus Cope, 1870 , with at least four species, and the monospecific genus Kwazulusaurus Maisch, 2002 a) has not been challenged, and we define it here as a stem-based taxon using Dicynodon (representing Permian dicynodontoids) and Kannemeyeria (representing kannemeyeriiforms) as external specifiers.

Revised diagnosis: As currently defined, Lystrosauridae includes only the genera Lystrosaurus and Kwazulusaurus . The latter taxon has only been included in one phylogenetic analysis ( Maisch, 2002a). Therefore, in addition to listing autapomorphies from the analyses of Angielczyk (2007), Fröbisch (2007), and Fröbisch & Reisz (2008), we also include autapomorphies identified by Maisch (2002a). Maisch (2002a) identified two autapomorphies of Lystrosauridae : (1) ectopterygoid absent; (2) snout region short and deep, strongly extended ventrally. Autapomorphies recognized in common by Angielczyk (2007), Fröbisch (2007), and Fröbisch & Reisz (2008) are: (1) parietals widely exposed on the skull roof; (2) anterior portion of the palatine does not contact the premaxilla. Cluver (1971) provided a detailed diagnosis of Lystrosaurus in his thorough treatment of the cranial morphology of the genus, and Maisch (2002a) presented the only diagnosis of Kwazulusaurus to date. The most distinctive character of lystrosaurids is the steeply downturned snout, although this feature is more strongly developed in Lystrosaurus than Kwazulusaurus .