Evolutionary Origins of Viviparity in the Reptilia. II. Serpentes, Amphisbaenia, and Ichthyosauria

Superimposition of reproductive mode data from the literature over phylogenetic classification systems reveals that viviparity (live-bearing reproduction) has evolved on at least 35 independent occasions among the Serpentes, once in the Amphisbaenia, and once in the Ichthyosauria. Of the ophidian origins of the live-bearing mode, at least fourteen have occurred in the Colubridae, twelve in the Viperidae, three in the Hydrophiidae (used in the sense of Smith et al., 1977), and one in each of the following groups: Boidae, Acrochordidae, Tropidophiidae, Uropeltidae, Typhlopidae, and Elapidae. Previous analysis has distinguished and defined 45 origins of viviparity among the lizards. Here, ten additional saurian origins are recognized on the basis of unpublished and recently published evidence, three in the Iguanidae, two in the Scincidae, and one in each of the following groups: Agamidae, Chamaeleontidae, Anguidae, Xenosauridae, and Anniellidae. As phylogenetic relationships are clarified, further origins seem likely to be detected, particularly in the Colubridae, Hydrophiidae, Scincidae, and Iguanidae. At present, however, at least 92 origins of viviparity can be recognized within the class Reptilia. Reptilian viviparity has arisen on multiple occasions in each of the six major biogeographic regions, with a majority of the origins having occurred in the Old World. Nearly 19% of the extant reptile species are probably live-bearers, including more than 20% of the snakes and over 19% of the lizards. About 71 % of the viviparous species belong to either the Scincidae, Colubridae, Viperidae, or Iguanidae. The discontinuous distribution of the origins of viviparity among the reptilian families supports the hypothesis that selective pressures, preadaptations, and constraints vary at high taxonomic levels.