Apparently, some fossils can be altered by geological processes, leading to mistaken identification:
“While it holds true sponges are the only living organism which can produce these steroids, chemical processes can mimic biology and transform common and abundant algae sterols into ‘animal’ sterols,” he said.
“These molecules can be generated in the lab when simulating geological time and temperatures, but we also showed such processes did happen in ancient rocks.”Australian National University, “True origin of oldest evidence of animals” at ScienceDaily
This find, if it checks out, leaves more time for the evolution of algae but less for the evolution of animals. Which returns the Cambrian explosion to its “remarkable” status.