Did egg-laying boas break Dollo's law? Phylogenetic evidence for reversal to oviparity in sand boas (Eryx: Boidae).

Re-evolution of lost complex morphological characters has been proposed for several characters, including insect wings, limbs, eyes in snakes, and digits in lizards, among others. There has also been much interest in whether the transition from oviparity to viviparity is reversible, particularly in squamate reptiles where the transition to viviparity has occurred more times than in any other lineage. Here, we present a phylogenetic analysis of boid snakes based on a concatenated multigene study of all genera of erycines, New and Old World boines, plus other groups thought to be closely related with boines such as monotypic species Calabaria and Casarea. We reconstruct ancestral parity mode on this phylogeny and present statistical evidence that oviparity reevolved in a species of Old World sand boa in the genus Eryx nearly 60 million years after the initial boid transition to viviparity. Remarkably, like other viviparous boas hatchlings of oviparous Eryx lack an egg-tooth providing independent evidence that oviparity is a derived state in these species.