The night before, Nguyễn Thế Vĩnh dreamed once again that he had unearthed a crocodile.
Not just scattered bones, but a nearly complete skeleton, perfectly preserved, resting beneath the earth of the Na Dương basin for more than 30 million years. In his dream, he gently brushed away layers of soil and carefully lifted the fossilised skull with both hands.
The next morning, the dream still lingered as he and his colleague, Nguyễn Minh Chuyển, both palaeontologists from Lạng Sơn Provincial Museum, set off on their old motorbike toward the Na Dương coal mine.
The road snakes through slopes coated in grey coal dust. In the sweltering summer heat, layers of red and yellow earth formed a geological record stretching back millions of years. No crocodile awaited them that day, but only the quiet hope that a fresh excavation or recent downpour might reveal creatures long hidden from the sun.
It is a hope that keeps drawing them back.
The exposed slopes of the Na Dương coal mine in northern Việt Nam preserve one of Southeast Asia's richest late Eocene fossil deposits. Every newly uncovered layer offers palaeontologists a rare opportunity to reconstruct an ecosystem that flourished 35–40 million years ago.
Palaeontologists Nguyễn Minh Chuyển (right) and Nguyễn Thế Vĩnh begin another day of fieldwork, descending into the open-pit mine where newly exposed sediment layers may reveal fossils preserved for tens of millions of years.
"In the palaeontology community, the Na Dương basin is considered one of Southeast Asia's richest fossil sites," Chuyển said.
"The late Eocene sediments here preserve an entire ecosystem from 35 to 40 million years ago, a vast landscape of lakes, swamps and forests teeming with crocodiles, turtles, coal beasts (anthracotheres) and diverse plant life."
Chuyển's assessment is echoed by international researchers who have spent years studying the basin. In a landmark review of the site, Prof. Madelaine Böhme, a German palaeontologist and terrestrial palaeoclimatologist at the University of Tübingen, described Na Dương as "one of the few localities in Southeast Asia allowing for multi-focused investigation" of Eocene ecosystems, citing its extraordinary diversity of vertebrate, invertebrate and plant fossils.
For Vĩnh and Chuyển, every expedition is more than a search for museum specimens. Each fossil is a potential piece in reconstructing a vanished world.
Mining has made many of Na Dương’s fossil discoveries possible by exposing sedimentary layers that would otherwise remain buried. Yet it is also steadily erasing the landscape in which those fossils have survived for millions of years. With limited personnel, equipment and time, palaeontologists must reach each newly exposed section before machinery, rain and exposure to the air destroy the evidence it contains.
They parked at the edge of the sprawling mining site and shouldered backpacks filled with basic tools: hammers, chisels, small brushes, specimen bags, water and packets of peanut candy to keep them going through the day.
After a quick exchange, they split up, each taking one side of the exposed slope. Heads bowed, they walked slowly, eyes scanning the rocky ground.
There was no high-tech equipment, no ground-penetrating radar. They relied solely on experience and subtle clues: a fossilised leaf imprint, a petrified tree trunk or traces of ancient crocodile dung.
Palaeontologist Nguyễn Thế Vĩnh scans the exposed slopes for subtle clues, a change in colour, texture or shape, that might reveal fossils hidden beneath the surface. Years of experience have taught him to read a landscape that most people see as nothing more than rock.
