Sponges may have lived in oceans up to 890 million years ago, a study that identifies sponge-like structures within ancient reefs has suggested.
If verified, the findings could represent the earliest known fossilised animal body and may pre-date the next-oldest undisputed sponge fossils by around 350 million years, an expert said.
Sponges are simple animals, and genetic evidence from modern sponges suggests they emerged during the early Neoproterozoic era (1,000 million to 541 million years ago).
However, there have not been a lot of fossilised sponge bodies from this period.
Professor Elizabeth Turner, from Laurentian University in Ontario, Canada, examined rock samples from 890-million-year-old reefs in north-western Canada that were built by calcium carbonate-depositing bacteria.
She found branching networks of tube-shaped structures that contained, and were surrounded by, crystals of the mineral calcite.
These structures were found to closely resemble the fibrous skeleton found within horny sponges — a modern type used to make commercial bath sponges.
They were also similar to structures previously identified in calcium carbonate rocks that are thought to have been created by the decay of horny sponge bodies.
Prof Turner said the structures may be the fossilised remains of horny sponges that lived on, in and beside calcium carbonate reefs approximately 90 million years before Earth’s oxygen levels increased to levels thought to be necessary to support animal life.
The findings could imply that the evolution of early animals occurred independently of this oxygenation event and that early animal life survived severe ice ages that occurred between 720 million and 635 million years ago, if the structures are accepted as sponge body fossils.
The study published in Nature said: “If vermiform microstructure is in fact the fossilised tissue of keratose sponges, the material described here would represent the oldest body-fossil evidence of animals known to date, and would provide the first physical evidence that animals emerged before the Neoproterozoic oxygenation event and survived through the glacial episodes of the Cryogenian period.”