The ability of fish to bite food from hard surfaces triggered a rapid increase in reef fish diversity about 50 million years ago. This evolutionary innovation allowed fish to access previously unavailable food sources. The study, published in *Proceedings of the National Academy of Sciences*, suggests that evolution occurs in bursts rather than at a constant pace.
Researchers at the University of California, Davis, found that fish lineages capable of scraping food from hard surfaces diversified more quickly. This includes algae, snails, and shellfish. Fish living in the open water column, where hard surfaces are absent, did not show the same acceleration in diversification. This feeding adaptation is a primary reason for the high number of coral reef fish species today.
To understand this pattern, researchers classified 9,560 fish species into seven habitat categories. They then used an existing evolutionary tree to estimate speciation and extinction rates over 350 million years. Around 50 million years ago, diversification rates for coral reef fish and bottom-dwelling fish increased by 1.5 to 1.7 times. Open-water fish showed stable evolution rates.
This evolutionary surge followed the Paleocene-Eocene Thermal Maximum (PETM), a period of global warming about 56 million years ago. The PETM caused significant changes in shallow-water species, including plankton and corals. This environmental shift created new opportunities for fish that could adapt their feeding strategies. The study found no evidence of increased coral diversification during this period, suggesting the change was driven by fish evolution.
Specific fish groups, such as parrotfish, butterflyfish, angelfish, surgeonfish, rabbitfish, and triggerfish, showed significant diversification. These species are known for biting the reef. Fish that feed in mid-water, like snappers and groupers, did not experience the same increase in speciation. This indicates that the unique feeding mode of biting contributed to the remarkable diversity of modern reef fishes.
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