Significance

Humans have been influencing the composition of animal communities over millennia, having led to the extinction of primarily large‐bodied terrestrial vertebrates through hunting and land conversion. However, the legacy of human pressure history is often ignored in studies that focus on contemporary diversity. Here, we analyse 11,377 tetrapod species of the Western Hemisphere to test whether millennial‐scale human pressures have left an imprint on contemporary body mass distributions throughout the tetrapod clade. We find that human pressures over the last 12,000 years explain a small but significant portion of geographical variation in contemporary body mass distributions that cannot be explained by ecological constraints alone. Overall, the median body mass of tetrapod assemblages is lower than expected in areas with a longer history of high human population density and land conversion, but there are important differences among tetrapod classes. Ignoring spatial variation in the history of human pressure is likely to lead to bias in studies of the present‐day functional composition of tetrapod assemblages, at least in areas that have long been influenced by humans.