Marine tetrapod macroevolution: Physical and biological drivers on 250 Ma of invasions and evolution in ocean ecosystems

Abstract

The dominant consumers in today's ocean ecosystems are marine mammals, including cetaceans, sirenians, and pinnipeds, and other marine carnivorans. The ecological dominance of marine mammals can be traced back to at least seven independent transitions during the Cenozoic, when different lineages of terrestrial mammals underwent land to sea evolutionary transformations. However, the evolution of marine mammals represents only the most recent set of marine invasions by tetrapods over the past 250 million years. During the Mesozoic, over a dozen different reptile lineages (e.g., mosasaurs, ichthyosaurs, turtles, snakes) evolved obligate marine lineages, including a few lineages that persist to today, such as sea turtles. Birds, which are phylogenetically nested among diapsid reptiles, have also repeatedly adapted to marine life since the Cretaceous. Attempts to understand the common patterns of marine tetrapod evolution, and the processes that have shaped them, have largely been limited to individual groups. Placed in a broad comparative view from the Mesozoic to the Cenozoic eras, the macroevolution of marine tetrapods reveals evolutionary drivers at different scales, along with morphological parallels, unique evolutionary innovations, and the strong influence of historical constraints. Major physical, environmental drivers appear to be responsible for some patterns in marine tetrapod evolution at some temporal and geographic scales, but these drivers are not unique causes, as biological drivers (e.g., escalation) likely also play a role. The culmination of this trophic ascendancy has been dramatically altered by human hunting (especially of marine mammals), underscoring the need for historical datasets that extend into deep time to understand the ecological history of marine tetrapods.