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A black horny sponge (Scalarispongia scalaris) growing off the coast of France. Some types of horny sponge are today harvested for bath sponges. Credit: Biosphoto/Alamy
Most major groups of animals — including arthropods, molluscs and worms — first appear in the fossil record during the Cambrian explosion, 541 million years ago. But according to a paper published today in Nature1, sponge fossils from northwestern Canada could be 350 million years older, significantly pushing back the date of Earth’s earliest-known animals.
The ancient discovery is igniting debate among palaeontologists, who have long contested when complex animal life first evolved.
“If I’m right, animals emerged long, long before the first appearance of traditional animal fossils,” says study author Elizabeth Turner, a sedimentary geologist at Laurentian University in Sudbury, Canada. “That would mean there’s a deep back history of animals that just didn’t get preserved very well.”