Xenosauridae Cope, 1886

Conrad, J. L., 2008, Phylogeny And Systematics Of Squamata (Reptilia) Based On Morphology, Bulletin of the American Museum of Natural History 2008 (310), pp. 1-182 : 113

Xenosauridae Cope, 1886

(figs. 54D, 55D, 56C)

DEFINITION: All taxa sharing a more recent common ancestor with Xenosaurus grandis than with Anguis fragilis , Carusia intermedia , or Varanus varius .

DIAGNOSIS: Xenosaurids share two unambiguous synapomorphies: 126(1) ectopterygoid exposed on the lateral skull surface posterior to the maxilla and 212(3) presence of ‘‘shoulders’’ or incipient cusps on the posterior marginal teeth.

COMMENTS: Common usage and phylogenetic definitions of Xenosauridae have been anchored to Xenosaurus and Shinisaurus ( McDowell and Bogert, 1954; Gauthier, 1982; Estes, 1983; Estes et al., 1988; Presch, 1988; Wu et al., 1996; Lee, 1998; Lee and Caldwell, 2000). However, Shinisaurus shows morphological affinities with platynotans (see below) and no special affinity for xenosaurids ( Conrad, 2004a, 2004b, 2005a, 2006a, 2006b) (figs. 54–56). Recent molecular work supports a similar hypothesis, suggesting that Shinisaurus is related to varanids ( Townsend et al., 2004) (fig. 10A).

Restes rugosus is usually considered to have affinities with Xenosaurus and was initially considered a species of Exostinus ( Gilmore, 1942a; Estes, 1965, 1975). Although Conrad (2006b) was unable to resolve the placement of R. rugosus , perhaps due to the incompleteness of that and other taxa, the current analysis supports the hypothesis that it is a xenosaurid.

The current definition of Xenosauridae takes into account the problematic relationships of both Shinisaurus and Restes . Although the data analyzed here strongly suggest that Shinisaurus is not a member of the xenosaurid radiation, the current definition of Xenosauridae would allow inclusion of Shinisaurus should the topology of, for example, Lee and Caldwell (2000) (fig. 7) prove accurate.

Note that Xenosaurus is included here as a composite taxon based on observations of X. grandis and X. platyceps . Future versions of this data matrix may include codings for some individual Xenosaurus species.