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Ocean reefs may have emerged 20 million years earlier than previously thought

Felipe Daniel de Castro Sales Artist’s rendering of a marine animal of the genus NamacalathusFelipe Daniel de Castro Sales

Rocks some 550 million years old collected in northern Paraguay hold vestiges of what may have been the first ocean reefs formed by organisms visible to the naked eye. An international team of geologists and biologists have identified fossils of marine animals from three different genera that lived together, anchored in the sediment deposited by cyanobacteria at the bottom of a shallow ocean.  The fossils were found in limestones extracted in Puerto Valle Mi, near the border with the Brazilian state of Mato Grosso do Sul. These fossils, just a few centimeters long, are specimens of Corumbella, Cloudina and Namacalathus, the first living creatures with a skeleton, which lived between 550 million and 542 million years ago. It is the first time that fossils of these three genera have been found in rock samples from the same region, and the fifth occurrence worldwide—the first in South America—of organisms of the genus Namacalathus. The skeleton of Namacalathus, consisting of a small stem supporting a spheroidal cup, resembles the bud of a poppy (Precambrian Research, May 2017). “Until recently, scientists believed that the earliest reefs emerged around 530 million years ago and consisted of organisms similar to calcareous sponges called archaeocyathids,” says geologist Lucas Warren, a researcher at São Paulo State University (Unesp) in Rio Claro and first author of the article. “The fact that these 550 million-year-old organisms are present in the same type of rock suggests that they were already capable of congregating and growing on the same substrate, in the same manner as present-day corals on a reef,” he explains.