Published Friday, August 21, 2026
by Violet shen & Ming Chuong

 

Editor’s Note :

Travel is more than movement—it is a way of reading the world.

Cultural Express launches Hidden Pattern, a new column by USC professor Cheng-Ming Chuong and Violet Shen, former Director of Clinical Research at Children’s Hospital of Orange County.

Through words and images, they explore landscape, culture, nature, and science—revealing the traces of time, the path of evolution, and the hidden order of the world.

This February, we traveled to Arizona for the annual Tucson Gem Show, one of the world’s largest gatherings of minerals, gems, and fossils.

Inside a fossil shop at Tucson’s famed gem show

During show season, Tucson transforms into a vast natural history museum, with gems, minerals, and fossils from around the world filling halls and hotels as collectors, scientists, and enthusiasts join a citywide treasure hunt.

Tucson Treasure • Fossil Mystery

Among thousands of specimens, one fossil stopped us in our tracks.

Embedded in stone was a straight-shelled cephalopod whose shell had begun to curve—as if caught at the very moment it started to coil.

It offered a rare glimpse into the evolutionary shift from straight shell to spiral, frozen in stone mid-turn. We bought it without hesitation and brought it home.

Ancient Nautiloid in Transition

At the same show, another fossil drew our attention: the Ammonite. Its spiral shell follows an elegant geometric rhythm, and some specimens shimmer with fiery, rainbow-like colors.

Iridescent Shell • Hidden Structure

Those colors are not pigment. Like the shimmer of peacock feathers or soap bubbles, they are structural colors, created when light interacts with microscopic layers within the shell.

Many brilliantly preserved ammonites come from Alberta, Canada. Today, some are cut and polished into gemstones known as Ammolite.

In these ancient shells, science and beauty meet.

Ammonite Fossil Unearthed in Alberta, Canada

What makes the spiral so compelling, however, is more than its graceful form. It embodies an order shared by both mathematics and life.

A spiral can expand or contract while preserving its proportions, reaching endlessly outward while drawing ever closer to its center.

This curious union of the finite and infinite appears throughout nature—from hurricanes and ocean currents to swirling galaxies; from the double helix of DNA to the Fibonacci patterns seen in seeds and plants.

Spiral Order • Evolution Unfolds

In the history of life, cephalopod shells offer one of nature’s most striking expressions of the spiral.

Nearly 500 million years ago, early nautiloid cephalopods cruised Paleozoic seas in long, straight shells.

Internal chambers and a siphuncle helped control buoyancy, letting them rise and sink through the water.

These straight-shelled hunters were among the dominant predators of ancient seas.

But straight shells had limits: they were less maneuverable and more prone to breakage. Over time, some lineages evolved increasingly curved shells, eventually coiling into spirals.

Coiling brought greater strength, balance, and control. Through hundreds of millions of years of evolution, the spiral became one of the cephalopods’ most successful designs.

Nautiloids and ammonites represent two famous branches of that evolutionary story. Both were cephalopods, but they followed different paths.

  Straight-Shelled Nautiloid Before the Evolutionary Turn

Ammonites appeared about 400 million years ago and flourished through the Jurassic and Cretaceous.

Their increasingly intricate shell sutures may have helped strengthen them against pressure.

But 66 million years ago, the end-Cretaceous mass extinction wiped them out—while nautiloid relatives survived. Why?

One possibility is metabolism. Nautiloids, with slower energy demands, may have endured food shortages and environmental upheaval better than ammonites.

The mystery remains—and deepens the fascination of these ancient spirals.

Our first encounter with them, however, was not in Tucson. It was seven years earlier, in Morocco.

Erfoud, Morocco—Fossil Country

Ancient Sea • Fossil Table

In spring 2019, we traveled to Erfoud on the edge of the Sahara.

Today it is desert. But during the Paleozoic Era, shallow seas repeatedly covered the region, leaving behind rich deposits of marine life.

Its rocks still hold trilobites, brachiopods, and cephalopods, making Erfoud a world-famous fossil region.

There, we bought a fossil table embedded with both coiled nautiloids and straight-shelled cephalopods.

Ming Choung's ancient cephalopod fossil table.

At the time, we simply thought they were beautiful.

We never imagined that seven years later, in Tucson, we would find a fossil showing a shell seemingly beginning to curve.

Suddenly, the two forms preserved in our Moroccan table no longer seemed merely decorative.

Together, they hinted at a much longer story—from straight to coiled, from fragile to more stable, from one form toward new possibilities.

Cephalopod fossils do not tell the story of a single species. They record nearly half a billion years of life experimenting, adapting, and reinventing itself through time

Perhaps that is why the spiral feels so familiar.

Growth rarely moves in a perfectly straight line. It may be more like a spiral—seeming to circle back, yet arriving somewhere new; returning, but at another level.

There may be no absolute beginning, and no final end.

Ancient Nautiloid Fossil

Two encounters—an ancient Sahara seabed and a fossil frozen mid-evolution in Tucson—revealed the same truth: nature writes its story in stone.

We travel to learn how to read it.

Prof. Ming Chuong (right) and Mr. Hsiao with a Stegosaurus fossil. Photo: Violet Shen

About the Authors

Dr. Cheng-Ming Chuong is a professor of pathology at the University of Southern California. With a scientist’s eye and a gift for  observation, he explores the hidden order of nature and the clues of life.

Violet Shen is the former Director of Clinical Research in Pediatric Brain Tumors at Children’s Hospital of OC.

Now devoted to travel and photography, she captures the beauty of landscape and human life through a discerning lens.

 

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