How an Ancient Animal May Have Navigated Using Earth’s Magnetic Field

It is smaller than a single bacterial cell, shaped like a tiny spearhead, and it has been buried in the ocean floor for 97 million years. Now, scientists believe it was part of an ancient animal’s internal navigation system — a biological GPS that used Earth’s magnetic field to guide long-distance migration.

The discovery, published in Communications Earth & Environment, represents the first direct evidence that animals were navigating using the geomagnetic field at least 97 million years ago — pushing the known origins of this mysterious sense back to the age of the dinosaurs.

The fossils were recovered from ancient seafloor sediments in the North Atlantic Ocean. They are microscopic magnetite crystals — tiny particles of a strongly magnetic iron mineral — and they are shaped like spearheads, spindles, bullets, and needles.

Scientists are confident the structures are biological in origin. What they don’t know is what creature made them, or why. Until now.

The Breakthrough: Seeing Inside a Magnetic Fossil

To solve the mystery, researchers from the University of Cambridge and the Helmholtz-Zentrum Berlin did something nobody had managed before: they captured the first 3D images of the fossils’ internal magnetic structure.

The challenge was that giant magnetofossils — the larger class of magnetic fossils the team studied — are 10 to 20 times bigger than the magnetic particles used by bacteria. X-rays couldn’t penetrate them, which meant traditional imaging techniques simply didn’t work.

The team applied a new technique developed by co-author Claire Donnelly at the Max Planck Institute in Germany, carried out at the Diamond Light Source facility in Oxford. What they saw inside the fossil was remarkable.

The fossil’s interior harbored a closed loop of magnetization resembling a vortex — a stable, tornado-like pattern of magnetic moments swirling around a central line. The researchers determined that this structure was optimised to detect both the direction and the strength of Earth’s magnetic field.

That distinction matters. A simple compass needle tells you which way is north. A GPS tells you where you are. The fossil’s magnetic vortex was capable of the latter.

“We show that the large magnetization means it would be optimized to detect variations in the strength of Earth’s magnetic field from location to location,” said Rich Harrison, a professor at Cambridge’s Department of Earth Sciences and co-leader of the study. “This is a key part of building a natural ‘GPS system,’ enabling an animal to actually geolocate itself, not just know, for instance, which way is north”.

The Mystery Creature: Eels, Microbes, or Something Else?

The identity of the organism that produced these fossils remains unknown. But the researchers have some ideas.

The fossils were not associated with any other bodily remains, which makes identification difficult. What scientists do know is that the creature must have been a migratory marine animal — one common enough to leave behind abundant fossil remains across the ocean floor.

Harrison suggested eels as a possibility. Eels are famous for navigating across the Atlantic Ocean twice in their lifetimes: larval eels drift from the Sargasso Sea to coastal habitats across Europe and North Africa, and maturing adults migrate back to the Sargasso Sea to spawn and die.

The organism could also have been a microbe. Some of the particles closely resemble magnetite fossils produced by magnetotactic bacteria, which use chains of tiny magnetic particles to align with Earth’s magnetic field. But the giant magnetofossils are far larger than bacterial particles — and that size difference is what makes them so intriguing.

“It looks like this creature was carefully controlling the shape and structure of these fossils, and we wanted to know why,” Harrison said.

What This Means for Our Understanding of Navigation

The discovery has implications far beyond one unidentified ancient organism.

For decades, scientists have known that modern birds, fish, and insects use Earth’s magnetic field to navigate vast distances. But how they do it has remained one of biology’s most stubborn mysteries.

The leading theory is that magnetite crystals within an animal’s body align with the geomagnetic field, acting like microscopic compass needles. Certain bacteria possess a primitive form of this ability, using chains of magnetic particles to swim to their preferred depth in the water column.

But the newly discovered fossils are 10 to 20 times larger than the particles bacteria use. At just 50 to 100 nanometers wide, bacterial magnetite particles are, as Harrison put it, “the perfect compass needles”. The giant fossils shouldn’t work as compasses — they’re too big.

And yet, the 3D imaging proved they were optimised for navigation. The creature that made them wasn’t using them as compass needles. It was using them as something far more sophisticated: a magnetic map.

The Legacy of a 97-Million-Year-Old Sense

The magnetofossils were found in sediments dating as far back as 97 million years — meaning this navigation system evolved during the Cretaceous period, when dinosaurs still walked the Earth.

The discovery provides the earliest direct evidence of magnetoreception in animals. It suggests that the ability to sense Earth’s magnetic field — and use it to navigate across oceans — is far older than previously believed, and that it may have evolved from simpler bacterial magnetism into something approaching a true biological GPS.

“There has been a debate as to whether or not they were biological in origin,” Harrison told Reuters. “We show that the large magnetization means it would be optimized to detect variations in the strength of Earth’s magnetic field”.

The organism that produced these fossils is still unnamed. Its body is long gone. But the tiny magnetic structures it left behind — no larger than a bacterial cell — have survived for nearly 100 million years. And they tell a story of navigation that predates the dinosaurs’ extinction, a story that modern birds and fish are still living out today.

Whatever creature made these magnetofossils, we now know it was most likely capable of accurate navigation. And that changes how we think about the evolution of one of nature’s most extraordinary senses.