One of the Oldest Known Animals Is This Tiny, Ancient Sponge

A new fossil find pushes back the start of the evolution of multicellular animals

Sponge-like fossil
A scanning electronic microscope image of the 600 million-year-old sponge-like fossil Image courtesy of Zongjun Yin

Sponges seem like humble creatures—especially if you associate them with the synthetic pads we use to clean—but they are actually awesome. True, they don’t have nervous, digestive or circulatory systems. But the simple sponge represents the most ancient lineage of multicellular animals on Earth. Now, a new fossil dug up in Southern China pushes the advent of the first animals back even earlier in history.

The Earth is nearly four billion years old and for much of that long history, life was basically just bacteria, plankton or algae—small, simple creatures. But about 570 million to 530 million years ago, something sparked and suddenly (in geological time, anyway) the complex, multicellular life we see around us started appearing during the Cambrian explosion. Sponges were a major part of that evolutionary flowering of complexity.

The new fossil is 600 million years old, according to the paper published in Proceedings of the National Academy of Sciences, meaning it predates that explosion. That puts it in a time period earlier than many scientists expect to find sponges and could shake up what we know about the timing of animal evolution.

While the fossil can’t be properly classified in any of the major sponge classes we see today, the porous surface and tubes of the fossil make it unmistakably sponge-like, the researchers say, according to International Business Times. It is "just over 1 millimeter high and wide, the size of a small bead, and was found in a phosphorus-rich geological formation known for preserving animal fossils in an excellent state," reports Michael Balter for Science

The fossil represents a possible ancestor not only of the many sponges we know today but of all animals. And at the very least, organisms like this one may have helped turn the oxygen-poor environment of the early Earth into one more conducive to the evolution of complex life because they helped munch excess organic matter, which would have drawn oxygen from water as it decayed. It seems we have a lot of reasons to thank the primitive sponge.

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