Cenozoic insect-plant diversification in the tropics.

E volution has done wonders with mass extinctions. Organic diversity has rebuilt itself at least five times during the history of life on Earth, fashioning novelty from the organic remnants of each catastrophe (1). Modern biodiversity arose from a global extinction event at the end of the Cretaceous period (the ‘‘K-T’’ extinction) that probably was caused by an asteroid or comet impact. This penultimate mass extinction [that before the recent and incipient human-caused extinctions (2)] eliminated 80% of large plant species, 20% of marine animal families, all dinosaurs except ancestors of present-day birds, and probably many specialized insect–plant associations (3). Some of the lineages that pushed through the end-Cretaceous bottleneck have done extremely well during the ensuing 65 million years of often favorable Cenozoic environments. Bony fishes, corals, and several invertebrate groups enjoyed net cladogenesis and speciation that greatly exceeded extinction. On land, groups with a good start before the end-Cretaceous extinction and impressive radiation since include birds, mammals, insects, and angiosperms. Stebbins (4) inspired modern research on recovery from extinction with the metaphor that plant communities are simultaneously ‘‘museums,’’ which preserve ancient lineages, and ‘‘cradles,’’ which foster speciation. The power of science to address these issues has been greatly increased by the advent of molecular phylogenetics, which when complemented by paleontology, biogeography, evolution, and ecology, can give a picture of the tempo of recovery. In this issue of PNAS, McKenna and Farrell (5) address the temporal trajectories of diversification rates and, by inference, the mechanisms of recovery from the end-Cretaceous mass extinction of the specialized and speciose Cephaloleia leaf beetles of Middle America. In a previous article (6) McKenna and Farrell brought together intensive taxonomy and the basic molecular phylogeny of this genus and its relatives. These are ancient beetles that have long specialized upon a single clade of monocots, the Zingiberales. The distinctive feeding damage of Cephaloleia ancestors on fossilized ginger leaves dating from late in the Cretaceous and early in the Eocene demonstrated that these radiations of leaf beetles began some 20 millions of years (Ma) earlier than the first body parts of leaf beetles are known in the fossil record (7).