Cover image: Pictured are echinoid (sea urchin) specimens representative of the vast morphological diversity within this 265-million-year-old group of animals. Using phylogenetic analysis, Melanie J. Hopkins and Andrew B. Smith found that diversification of echinoids has been episodic. Evolutionary rates were lowest during the initial Triassic diversification and generally increased over time, but were punctuated by periods of high evolutionary rates that coincided with major shifts in echinoid feeding strategies, demonstrating that rates of evolution may be highly heterogeneous over time. See the article by Hopkins and Smith on pages 3758–3763. Image of C. exquisitus courtesy of Simon Coppard (The Natural History Museum, London).