1. Sympatric distribution of oviparous and viviparous squamates
We merged a dataset of squamate distribution (IUCN Red List Spatial Data; http://www.iucnredlist.org/) and a dataset of squamate parity modes (Pyron & Burbrink 2014) to extract regions where oviparous and viviparous squamates are sympatric. [Note: we reclassifiedS. lundelli as viviparous and S. aeneus as oviparous (Maet al. 2018).] We first matched the two datasets by species name (bi-mode species were removed; 4,939,090 matched records [species × grid cells] of 2919 species remained). Then, we calculated the number of oviparous and viviparous species present in each 0.1° × 0.1° grid cell (0.1° corresponds to 11.13 km at the equator) respectively. We mapped grids with only oviparous species, only viviparous species, or both oviparous and viviparous species respectively (Fig. 1). We also calculated number of oviparous species, which had distribution overlaps with viviparous species, and number of viviparous species, which had distribution overlaps with oviparous species.