Ammonites are like biological clocks embedded in stone
For hundreds of millions of years, ammonites ruled the seas with shells engineered to rival modern submarines — and then disappeared, leaving behind something perhaps more enduring than their living forms: a record written in stone. Scientists now read these fossilized shells as chronological markers, anchoring entire geological layers to specific moments in Earth's long history. In Mexico and beyond, researchers are translating that ancient record into digital form, ensuring that creatures extinct for sixty-six million years continue to illuminate the planet's past — and perhaps its future.
- Each ammonite species lived briefly but spread across entire ocean basins, embedding a precise biological timestamp into the rock layers wherever it died — making them indispensable tools for dating Earth's deep history.
- Their chambered shells, regulated by a siphon system that balanced air and water, represent a buoyancy engineering solution so elegant that modern submarine design arrived at the same principles independently.
- The fragility of the fossil record creates urgency: these irreplaceable specimens, formed over millions of years, risk damage or inaccessibility without new methods of preservation and study.
- At UNAM's National Institute of Geology, paleontologist Josep Anton Moreno Bedmar's team is digitizing ammonite fossils into high-resolution 3D models, opening the archive to researchers worldwide without risking the originals.
- The effort is landing as a shared global resource — one that connects vanished oceans to present-day climate science, turning extinction into an ongoing conversation about how life and Earth have shaped each other.
Millions of years ago, ammonites — marine mollusks distantly related to octopuses and squid — dominated the seas with shells so biomechanically sophisticated that modern engineers might study them with admiration. They vanished at the end of the Cretaceous period, but what they left behind has proven extraordinarily useful: fossilized shells embedded in rock layers across the planet, functioning as a kind of master calendar for Earth's history.
Geologists call them index fossils, though the reality is more poetic than the term suggests. Each ammonite species lived briefly but spread widely across marine territories, leaving a biological timestamp wherever it died. When a researcher finds an ammonite in a rock layer, that discovery anchors the entire formation to a specific moment in geological time. "Ammonites are like biological clocks embedded in stone," says Josep Anton Moreno Bedmar, who leads the paleontology department at Mexico's National Institute of Geology and specializes in Lower Cretaceous ammonites.
The shells themselves reveal a creature of remarkable engineering. Divided into chambers connected by a thin tube called a siphon, the shell allowed the ammonite to regulate its own buoyancy by adjusting the balance of air and water within — the same principle that governs modern submarine design. Different species solved the problem of ocean survival differently: some developed thin, streamlined shells for speed; others grew globular and heavy, trading agility for resilience.
Today, Moreno Bedmar's team is extending the ammonite's usefulness into the digital age. By creating high-resolution three-dimensional models of fossil specimens, they are building an archive that researchers anywhere in the world can access without ever handling the originals. Creatures that took millions of years to fossilize and survived countless geological upheavals can now be studied across continents — deepening our understanding of ancient climate shifts and what the deep past might teach us about the world we inhabit now.
Millions of years ago, the oceans belonged to creatures whose engineering was so sophisticated that modern submarine designers might study them with envy. Ammonites—marine mollusks distantly related to today's octopuses and squid—dominated the seas for an enormous stretch of geological time, then vanished at the end of the Cretaceous period. What makes them remarkable now is not what they were, but what they tell us. Their fossilized shells, scattered through rock layers across the planet, have become something like a master calendar for Earth's history. Scientists use them to date ancient stone with surprising precision, to map the contours of vanished oceans, and to trace the climate shifts that reshaped our world.
Geologists call them index fossils—a technical term for something quite poetic in practice. Each species of ammonite lived for a relatively brief window of time, yet spread across vast marine territories, leaving behind a kind of biological timestamp. When a researcher cracks open a rock and finds an ammonite shell, that discovery anchors the entire layer to a specific moment in Earth's past. The precision is remarkable. "Ammonites are like biological clocks embedded in stone," explains Josep Anton Moreno Bedmar, who heads the paleontology department at Mexico's National Institute of Geology and specializes in Lower Cretaceous ammonites. The metaphor captures something essential: these creatures, through their very existence and extinction, became markers of time itself.
The fossilization process that preserved them is delicate and strange. When an ammonite died, its shell sank to the seafloor and gradually filled with sediment. Over millions of years, the surrounding material hardened into rock, encasing the shell within it. When scientists carefully break open that rock today, they find internal molds—perfect impressions of the animal's body, a ghost of something that swam in oceans that no longer exist. These impressions reveal not just the shape of the creature, but hints of how it lived.
That life was governed by an engineering principle that would not be formally understood until humans invented submarines. The ammonite shell was divided into a series of chambers, connected by a thin tube called a siphon. By regulating the amount of air and water in these compartments, the animal could adjust its buoyancy and move up or down through the water column at will. It propelled itself through a form of jet propulsion, expelling water to move backward. Different species developed different solutions to the problem of survival: some had thin, streamlined shells built for speed; others were globular and heavy, slower but more resistant to pressure and damage. Each design represented a distinct answer to the question of how to live in the sea.
These ancient creatures are not merely historical curiosities. They continue to serve science in new ways. At the National Institute of Geology in Mexico, Moreno Bedmar's team has begun digitizing ammonite fossils into high-resolution three-dimensional models. The work is painstaking, but the payoff is significant: researchers anywhere in the world can now study these specimens without ever touching the originals. A fossil that took millions of years to form and survived countless geological upheavals can now be examined, measured, and analyzed by scientists separated by continents and oceans. The digital archive becomes a shared resource, accelerating discovery and deepening our understanding of how the planet's climate has changed, how life has adapted, and what the deep past can teach us about the present.
Citas Notables
Ammonites are like biological clocks embedded in stone— Josep Anton Moreno Bedmar, head of paleontology at Mexico's National Institute of Geology
La Conversación del Hearth Otra perspectiva de la historia
Why do scientists care so much about ammonites when there are so many other fossils to study?
Because ammonites are like a filing system for time. If you find one in a rock layer, you know almost exactly when that rock formed. Most fossils don't give you that precision.
But they're extinct. What does an extinct creature tell us about the world today?
Their shells record the chemistry of ancient oceans—the temperature, the salt content, even the oxygen levels. When you read enough of them across different time periods, you see the story of how Earth's climate has shifted.
You mentioned they had this flotation system. Did they invent it, or did evolution just stumble onto it?
Evolution doesn't invent anything—it solves problems. The ammonite that could control its depth had an advantage. Over millions of years, that advantage shaped the design. It's biomechanics born from necessity.
And now you're turning them into digital models. What changes when a fossil becomes data?
Everything becomes shareable. A paleontologist in Tokyo can study a specimen from Mexico without asking permission or risking damage. Science moves faster when the barriers come down.
Do you think understanding how ammonites engineered their shells teaches us anything practical?
Maybe. Engineers have always looked to nature. But more importantly, it reminds us that life solves complex problems in elegant ways. That's worth paying attention to.