If you imagine the earliest animals on Earth, you might picture something simple but sturdy. Maybe a sponge-like creature anchored to the sea floor, reinforced with tiny glass needles. That image turns out to be wrong.
According to a major new study led by scientists at the University of Bristol, the first sponges were soft-bodied animals without mineral skeletons. No glass needles. No hard support. Just flexible bodies quietly filtering seawater more than 600 million years ago.
And that small shift in perspective helps solve one of the biggest puzzles in early animal evolution.
Sponges are among the oldest animal lineages still alive today. They play a huge role in marine ecosystems, recycling nutrients, stabilizing habitats, and filtering oceans. Because they sit so close to the base of the animal family tree, understanding when and how they evolved matters far beyond sponges themselves.
For decades, scientists have been stuck with a contradiction. Genetic studies and chemical biomarkers suggested sponges evolved as early as 650 million years ago. But the fossil record told a different story. The oldest undisputed sponge fossils, tiny glass-like structures called spicules, only appear around 543 million years ago. That left a gap of more than 100 million years. Too big to ignore. So where were the sponges hiding?
The new research, published in Science Advances, suggests a surprisingly simple answer. Early sponges did exist. They just did not have hard skeletons that could fossilize.
Dr Eleonora Rossi and her international team approached the problem from two angles. First, they built a new evolutionary timeline using genetic data from 133 protein-coding genes across 70 sponge species, combined with carefully selected fossil evidence. This placed the origin of sponges between about 600 and 615 million years ago, during the early Ediacaran Period. That already narrowed the gap.
But the real breakthrough came when the researchers looked closely at the sponge skeletons themselves.
Modern sponges often rely on spicules, microscopic needles made of silica or calcium carbonate. These structures fossilize easily, which is why they dominate the sponge fossil record.
The team tested a critical assumption. Were spicules present in the very first sponges?
Using advanced statistical models that track how traits evolve over time, the answer came back clearly. No.
Early sponges were soft-bodied. They lacked mineralized skeletons entirely. Spicules evolved later, not once but independently across different sponge lineages.
In other words, sponges did not start with skeletons and diversify from there. They experimented. Multiple times.
This helps explain why the fossil record seems to start so late. Soft-bodied animals are notoriously bad at leaving fossils. Without hard parts, they decay quickly, leaving little trace behind.
Dr Rossi summed it up simply. We do not see sponge fossils before 543 million years ago because there was nothing durable to preserve.
That absence is not evidence that they did not exist. It is evidence that they were soft.
The study also challenges another long-held idea. Many scientists assumed that spicules were a key innovation that drove sponge success and diversification. The data say otherwise.
When the team analyzed diversification rates across sponge evolution, they found no clear signal that the appearance of spicules triggered major evolutionary explosions. Some sponge groups diversified dramatically, but long after spicules appeared.
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Spicules helped with structure and defense. They were useful. But they were not the engine of sponge evolution.
Something else drove early sponge success. What that was remains an open question. Beyond sponges, the implications are much bigger.
Sponges may represent the earliest branch of the animal tree, or at least one of the earliest. Understanding their evolution sheds light on how complex animal life began, how early reefs formed, and how life started reshaping Earth’s chemistry.
As Professor Davide Pisani from Bristol explains, this research is not just about ancient sea creatures. It is about how life and the planet co-evolved, eventually setting the stage for animals like us.
There is also a broader lesson here about how science works.
For years, molecular data and fossils appeared to contradict each other. Instead of favoring one, this study looks at what happens when researchers examine biology more closely. They explore development, materials, and how traits form. Sometimes, the conflict goes away.
Early sponges did not vanish from the fossil record due to their faults. They were absent because they were soft.
Quiet, fragile, and easy to erase, they still existed. They changed the world nonetheless.
Journal Reference
- Rossi, M. E., Keating, J. N., Kenny, N. J., Giacomelli, M., Álvarez-Carretero, S., Schuster, A., Cárdenas, P., Taboada, S., Koutsouveli, V., J. Donoghue, P. C., Riesgo, A., & Pisani, D. (2026). Independent origins of spicules reconcile paleontological and molecular evidence of sponge evolutionary history. Science Advances. DOI: 10.1126/sciadv.adx1754
