Dispersal of thermophilic beetles across the intercontinental Arctic forest belt during the early Eocene

Massive biological change occurred over the Eocene (65-33.9 million years ago) as the climate shifted from warm and equable to seasonal and latitudinally stratified. The warm and equable early Eocene remains the best and most recent analog for understanding the impact of human-caused climate change on biodiversity. Mild winter temperatures in the Arctic permitted a peculiar mixture of frost-intolerant groups such as alligators and palms until the end of the Eocene, and heat-requiring groups such as the primates and giant ants that were probably limited to the warmest early Eocene, especially during short-lived hyperthermal periods. Members of this strange community dispersed across continents via land bridges in the Arctic and today occur in highly disjunct populations in Asia and the Americas. Although Eocene climate change may have been one of the most important drivers of these ancient patterns in modern animal and plant distributions, its particular events are rarely implicated or correlated with group-specific climatic requirements. The authors sought to better understand Eocene climate change using a specialized group of rove beetle, which occurs only in humid subtropical to tropical forests, the dominant biome of the early Eocene. The authors assembled a diverse pool of evidence for analysis including Eocene fossils, comprehensive distributional data, Eocene and Modern climate data and DNA. They concluded that the direct ancestor of these beetles lived alongside early Eocene Arctic communities of now extinct types of primate and giant ants, and, unlike most other heat-requiring organisms, survived Eocene climate change as a moderately diverse group of 76 species.