Long before dinosaurs left their first footprints, a creature without brain, organ, or nerve was already quietly filtering the ancient seas. Sponges — among Earth's oldest animals, possibly 700 million years in existence — have endured not through complexity but through a radical simplicity that science is only beginning to fully appreciate. Their story, written in fossil spicules and living cells that can reassemble themselves after being torn apart, asks us to reconsider what it means to be alive, to persist, and to matter in an ecosystem.
Ancient sponges: Earth's oldest animals reveal secrets of survival
creatures that can be unmade and remade
Mark
So sponges have been around for 700 million years, but we only have fossils from 543 million years ago. How do we know the older ones existed at all?
Mimi
Genetic analysis suggests sponges diverged from other early animals much earlier than the fossil record shows. The theory is that early sponges were soft-bodied with no hard skeletons, so they didn't fossilize. Once they evolved spicules—those needle-like structures—we can finally see them in the rocks.
Luke
But that's still an inference, right? We're reading the genetic clock and saying it must mean something, but we don't have physical evidence of those soft-bodied sponges. It's a reasonable hypothesis, but it's not the same as finding them.
Mimi
True. That's why Eleonora Rossi's work is important—she's laying out the logic of why the gap exists. But you're right that we're working backward from what we know.
Mark
And now we're discovering new sponge species all the time. How many are actually out there?
Mimi
Scientists estimate around 15,000 species total, but only about half have been formally described. So there could be 7,500 sponges we've never even named yet.
Luke
That's a huge range of uncertainty. Is that estimate based on sampling rates, or is it more of an educated guess?
Mimi
It's based on discovery patterns and the diversity we see in different ocean zones, but you're right—it's not a precise figure. We simply don't know the ocean well enough yet.
Mark
What about those sponges that can live 15,000 years? How do we even measure that?
Mimi
Scientists use radiometric dating on the sponge tissue itself, looking at isotope ratios that accumulate over time. The giant volcano sponge is the record holder we know of.
Luke
And "may have been alive for thousands of years" for that giant glass sponge near Hawaii—that's an estimate too, not a confirmed age?
Mimi
Correct. We found it in 2015, so we can't have observed its full lifespan. We're inferring age from size and growth rates.
Mark
But the reaggregation thing—that's been tested directly, right?
Mimi
Yes. Scientists have actually broken sponges apart and watched them reassemble. That's not inference; that's observation.
Luke
And it only works for sponges? No other animal can do that?
Mimi
Not to that degree. Sponges are unique in being able to disaggregate down to individual cells and still come back together as a functional organism.
El Pulso
- For centuries, scientists debated whether sponges were animals at all — a confusion that hints at how profoundly they defy our expectations of life.
- A gap of roughly 100 million years between genetic evidence and the fossil record suggests the earliest sponges were so soft they vanished without a trace, leaving science to piece together their origins from near-nothing.
- Without a single organ or nerve, sponges nonetheless sustain entire coral reef ecosystems — filtering water and excreting nutrients that feed organisms throughout the food web.
- The discovery of a car-sized glass sponge near Hawaii, potentially thousands of years old, underscores how much of this ancient world remains hidden in the deep ocean.
- Of an estimated 15,000 sponge species, roughly half remain undescribed — meaning thousands of living chapters in Earth's oldest animal story are still waiting to be read.
Long before dinosaurs left their first footprints, a creature without brain, organ, or nerve was already quietly filtering the ancient seas. Sponges — among Earth's oldest animals, possibly 700 million years in existence — have endured not through complexity but through a radical simplicity that science is only beginning to fully appreciate. Their story, written in fossil spicules and living cells that can reassemble themselves after being torn apart, asks us to reconsider what it means to be alive, to persist, and to matter in an ecosystem.
Sponges don't look like much — fixed to the ocean floor, motionless, easy to mistake for rock or plant. For centuries, scientists made exactly that mistake, and it wasn't until the mid-1700s that the scientific community accepted them as animals. Beneath their unremarkable surface, however, lies one of the most extraordinary survival stories on Earth.
Researchers now believe sponges appeared more than 608 million years ago, with some genetic evidence pushing that figure to around 700 million years — hundreds of millions of years before dinosaurs. The fossil record only preserves sponges back to about 543 million years ago, in the form of tiny needle-like structures called spicules. Eleonora Rossi of the University of Bristol proposed a compelling explanation for the gap: the earliest sponges were entirely soft-bodied, with no mineralized skeleton to leave behind. They lived and died without a trace, invisible to stone.
What sponges lack in complexity, they more than compensate for in ecological power. With no brain, organs, or nervous system, they filter bacteria, plankton, and organic material from the water, quietly maintaining the health of marine ecosystems. In nutrient-poor coral reefs, certain species excrete waste that other organisms feed on, effectively fertilizing the entire reef system — all without any of the biological machinery most animals depend on.
Their longevity is almost incomprehensible. The giant volcano sponge can live for around 15,000 years, and in 2015 researchers found the largest known sponge near Hawaii — a glass sponge the size of a car, potentially thousands of years old. Scientists estimate some 15,000 species exist globally, but only half have been formally described, leaving thousands still unknown to science.
Perhaps most astonishing is the sponge's capacity for self-reconstruction. If broken apart — even reduced to individual cells — a sponge can reassemble itself. Cells passed through fine cloth and left in seawater for a few days will find one another, recognize each other, and reform into a functioning animal, each cell returning to its original role. Mix cells from two different species and they will sort themselves out and rebuild separately. This process, called reaggregation, is unique among all animals on Earth — a quiet testament to a creature that has been unmade and remade, in one form or another, for hundreds of millions of years.
Sponges don't look like much. They sit on the ocean floor, immobile and unremarkable, nothing like the fish that dart past them or the crustaceans that scuttle through the water. For centuries, scientists weren't even sure they were animals at all—it wasn't until the mid-1700s that researchers accepted what seems obvious now: these creatures are living beings, not plants or geological formations. But beneath their humble appearance lies something far stranger than anything that swims or crawls.
These ancient animals have been on Earth far longer than we once thought. Researchers believe sponges appeared more than 608 million years ago, making them among the planet's earliest animals. Some genetic evidence pushes that timeline even further back, suggesting sponges have existed for around 700 million years—hundreds of millions of years before dinosaurs walked the land. The fossil record, however, tells a different story. The oldest sponge remains scientists have found are about 543 million years old, and they consist of tiny, needle-like structures called spicules. Nothing older appears in the rocks. This discrepancy puzzled researchers until Eleonora Rossi, an honorary research associate at the University of Bristol's School of Biological Sciences, proposed an explanation: the first sponges were soft-bodied creatures with no mineralized skeletons. They evolved roughly 100 million years before the fossil record could preserve them. When those early sponges died, they left no trace—no spicules, no hard parts, nothing for stone to remember.
What makes sponges truly remarkable is not their age but their design. They have no brain, no organs, no nervous system. They don't hunt or flee. Instead, they remain fixed to a hard surface for life, drawing water through their bodies and filtering out bacteria, plankton, and organic material. This simple feeding mechanism performs an outsized ecological service: sponges clean the water and maintain the health of marine ecosystems. In coral reefs starved of nutrients, certain sponge species excrete a form of waste that other organisms feed on, essentially fertilizing the reef and sustaining productivity throughout the entire system. They accomplish all this without the biological machinery most animals require to survive.
Their longevity is staggering. The giant volcano sponge can live for around 15,000 years, with some individuals potentially reaching 23,000 years old. In 2015, researchers discovered the largest known sponge in the world near Hawaii in the Pacific Ocean—an ancient glass sponge the size of a car, measuring 3.5 metres long, 2 metres high, and 1.5 metres wide. It may have been alive for thousands of years. Scientists estimate roughly 15,000 sponge species exist on the planet, but only about half have been formally described. That means thousands of sponges remain unknown to science, waiting in the deep ocean or hidden in coral crevices.
Perhaps the most extraordinary ability sponges possess is their capacity to rebuild themselves. If a sponge is broken apart—even reduced to individual cells—it can reassemble. Experiments have shown that a sponge can survive being passed through fine cloth, its cells scattered and separated. When those cells are left in seawater for a few days, they recognize each other and begin to come together again, reforming into a functional sponge. Each cell returns to its original role. If cells from two different sponge species are mixed together, they sort themselves out and rebuild as separate individuals. This process, called reaggregation, is unique to sponges among all animals on Earth. They are, quite literally, masters of reinvention—creatures that can be unmade and remade, that have survived for hundreds of millions of years in oceans that have changed beyond recognition, and that continue to thrive in the deepest, darkest parts of the sea where few other animals can endure.
Citas Notables
The first sponges were soft-bodied and lacked mineralised skeletons. That's why we don't see sponge spicules in rocks from around 600 million years ago—there simply weren't any to preserve.— Eleonora Rossi, University of Bristol's School of Biological Sciences
Sponges are the only animals that if broken down to the level of their cells, can reassemble themselves. Experiments have shown that a sponge can survive after being passed through a fine cloth to break apart its individual cells.— National Museum of Ireland
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