Cover image: Pictured is a gray whale (Eschrichtius robustus) diving to dredge for food. Fossils suggest that around 150 species of cetaceans (whales, dolphins, and porpoises) were present 10 million years ago, whereas only 89 species exist today. Hélène Morlon et al. analyzed the molecular phylogeny of present-day cetaceans to infer their evolutionary history, and the authors confirmed the dramatic species loss suggested by the fossil record. Molecular approaches are critical for analyzing how diversity varies over evolutionary time, especially in groups or regions that lack a detailed fossil record. See the article by Morlon et al. on pages 16327–16332. Image courtesy of Minette Layne.