The Phylogeny of Anguinomorph Lizards

The phylogenetic relationships of anguinomorph lizards are reconsidered on the basis of the structure of the head musculature, of the skull, and of the atlas - axis complex. A basal dichotomy separates the Anguinomorpha into the Anguinoidea and Platynota. The most primitive Anguinoidea are gerrhonotiform lizards. They share common ancestry with a hypothetical common ancestor of the Anguinae and Diploglossinae. Anniella is most closely related to the Anguinae among the Anguinoidea. The relationships of XenosaulUs and ShinisaulUs are poorly determinable on the basis of present evidence. For reasons of parsimony, the two genera are included within the same family, the Xenosauridae, which is tentatively derived from the transitional field leading from the Gerrhono- tinae to the hypothetical ancestor of the Anguinae and Diploglossinae.
The Helodermatidae share many similarities with the Gerrhonotinae which indicate their primitive status. However, the Helodermatidae show diagnostic platynotan features and hence cannot be included in the Angui- noidea. On the basis of shared derived characters, the Lanthanotidae and the Varanidae are considered to share a common ancestry after the Helodermatidae split off from the lineage of platynotan evolution. Structurally, Lanthanotus is intermediate between Heloderma and Varanus.