Reefs composed of sponges and microbial mats appeared 1.5 million years after the end-Permian mass extinction, reports a paper published online in Nature Geoscience. Previously, it was thought that reefs constructed by animals were absent for the first 5 million years after the extinction event.
Arnaud Brayard and colleagues report fossils from Utah and Nevada that they interpret as reefs built by sponges and microbial communities. Various molluscs, ammonoids and urchin spines were also found in the reef deposits. They report that the deposits were formed only 1.5 million years after the extinction, and contain a record of abundant animal life on the sea floor during a period previously thought to be largely devoid of bottom-dwelling animals.