Fish colonized reefs in two distinct waves—before and after the mass extinction event that wiped out the dinosaurs about 66 million years ago.
The world’s reefs are hotbeds of biological diversity, including over 4,500 species of fish that represent one of the largest and most diverse assemblages of vertebrates, researchers say.
The fossil record of reef fish is patchy, so scientists traced their ancestry by developing a comprehensive family tree of the major group of modern ocean fish, the acanthomorphs or “spiny-finned fish,” and calculating the times when different groups migrated into or out of reef habitats.
The first wave of colonization occurred between 70 and 90 million years ago, before the end of the Cretaceous period. At that time, most of the world’s reefs were built not by coral but by mollusks called rudists.
Rudists disappeared in the mass extinction at the end of the Cretaceous, 66 million years ago, and corals became the world’s great reef builders. While the first-wave reef fish hung on to leave descendants in the present, a second wave of colonization took place as the world recovered from the extinction event.
The early wave of colonization began with lots of different-looking fish and over time there was an eventual filling of ecological niches accompanied by a decrease in colonization, says Samantha Price, a postdoctoral researcher in the evolution and ecology department at University of California, Davis and first author of the study that is published in the Proceedings of the Royal Society B.
By about 50 million years ago, the fundamentals of modern coral reefs, including the ancestors of most major families, such as clownfishes and parrotfishes, were in place, Price says.
“If you were able to dive on a coral reef 50 million years ago, the fishes would seem familiar, you would recognize it as similar to a modern reef.”
Researchers from Yale University, Towson University, Claremont McKenna College, University of Kansas, and University of Oxford contributed to the study. The National Science Foundation and the Natural Environment Research Council (UK) provided funding.
Source: UC Davis