PATHWAYS TO THE MARINE REALM IN SERPENTES

Despite the vast taxonomic diversity of extant and extinct snakes, few lineages have invaded the open ocean. Differences in the physical and chemical conditions on land versus in water likely explain why such invasions are relatively uncommon, as they require or favor different solutions to physiological challenges such as dehydration, thermoregulation, and salt balance as well as to other functions such as reproduction and locomotion. The goal of this study was to determine the traits of terrestrial lineages, if any, that facilitated the transition to fully marine lifestyles in certain lineages. To achieve this goal, we collected biome occupancy and tiering information from primary literature and regional guides to construct a habitat database spanning 1610 extant snake species. We also time-scaled an existing phylogeny of 1250 modern snakes using fossil calibrations. With the addition of previously collected data on reproductive strategy, body mass, and environmental temperature, we jointly reconstructed the ancestral states of these habitat, life history, and environmental characters across the Serpentes tree. We find that marine snakes evolved from generally fossorial ancestors that possessed larger-than-average body masses and lived in environments with higher-than-average temperatures. Furthermore, all but one lineage of marine snakes acquired viviparity before invading the ocean. In aggregate, invasion of the marine realm was facilitated by several ecological and physiological traits in combination, rather than by any single trait of the ancestral lineages.