Repeated evolution of limblessness and digging heads in worm lizards revealed by DNA from old bones

The evolutionary relationships of the burrowing amphisbaenians ('worm lizards') have long been controversial for several reasons: the rarity of museum specimens available for study, highly derived morphological conditions that can confound comparative studies and difficulty in obtaining tissues for molecular phylogenetic studies because of their secretive habits in the wild. We present a phylogenetic analysis of two nuclear genes obtained from both fresh tissues and museum specimens of worm lizards. We achieved sufficient taxonomic sampling for analysis by extracting DNA from museum specimens using a modified forensics protocol. Results show the limbless Rhineuridae to be the most basal lineage, whereas the limbed Bipedidae occupy a more derived position as the sister-taxon to a Trogonophidae-Amphisbaenidae clade. This pattern of relationships indicates widespread morphological convergence within the group, including three independent incidences of limb loss. Convergence in skull shape and scalation is also prevalent. Mosaic evolution in the skull versus postcranial skeleton parallels that seen in snake evolution.