It sounds impossible at first. How can the remains of sea creatures end up on mountain peaks, hundreds of kilometers from the nearest shore? Yet across Southeast Asia—from Langkawi in Malaysia to the uplands of Brunei and Sumatra in Indonesia—scientists have found fossils of marine animals embedded in rocks high above sea level.
These discoveries reveal one of Earth’s greatest geological stories. The mountains and islands of the region were once part of the ocean floor. Over millions of years, the slow collision of tectonic plates lifted ancient seabeds skyward, turning what was once underwater into mountain ranges. The fossils left behind—corals, shells, fish bones, and microscopic traces—are the last whispers of long-lost seas that once covered this part of the world.
How the ocean rose to the mountains
About 400 to 500 million years ago, most of Southeast Asia lay beneath warm, shallow seas. These waters teemed with life—corals, shellfish, trilobites, and early forms of fish. When these organisms died, their remains settled on the seafloor and became trapped within layers of mud, sand, and lime. Over millions of years, those layers hardened into sedimentary rocks rich in fossils.
Outcrops in Sabah, Malaysia, showing tilted layers of ancient marine sediments where scientists discovered trace fossils—evidence of deep-sea life that once thrived on the ocean floor before these rocks were uplifted into mountains. Locations include Inanam, Sepangar, and Sulaman areas, with visible “way-up” directions marked by arrows indicating the original seabed orientation.
Source:
Bulletin of the Geological Society of Malaysia, Volume 71, May 2021.
But Earth’s crust never stands still. The movement of tectonic plates—the slow drift and collision of the planet’s surface—pushed those oceanic rocks upward. The seabed folded, cracked, and rose to form hills and mountains. In some places, like Borneo and Sumatra, parts of the old seafloor now sit thousands of meters above the current ocean. The fossils preserved within them are direct evidence of this transformation.
Malaysia: Ancient oceans in Langkawi and Sabah
Langkawi, known today for its beaches and limestone caves, holds one of Malaysia’s most important fossil records. The Tenjong Dendang Formation, a rocky layer dating back more than 440 million years, contains fossils of trilobites and brachiopods—small marine creatures that lived in ancient seas long before the age of dinosaurs. These fossils were discovered in limestone that once formed the seabed, showing that Langkawi was submerged in a warm tropical ocean during the Late Ordovician period.
Far to the east, in Sabah, the story continues in the Crocker Range. The rocks here are part of what used to be a deep-sea basin. Fossilized burrows and feeding trails found in these rocks reveal the activity of marine animals that lived on the ocean floor tens of millions of years ago. Today, those deep-sea sediments have been uplifted to form the mountainous backbone of northern Borneo.
Brunei: Fossil sharks from the Miocene sea
In Brunei, paleontologists studying the rocks of northern Borneo have unearthed fossils of sharks, rays, and other fish species dating back around 10 million years, during the Miocene epoch. These fossils were found in layers of marine sediment that have since been tilted and raised above sea level by tectonic activity.
The findings paint a picture of a time when Brunei’s hills were part of a shallow, tropical sea filled with marine life. Over time, as the land rose, those marine sediments hardened into rock and preserved traces of the creatures that once swam there. Today, these fossils help scientists reconstruct ancient ecosystems and understand how rising and falling sea levels shaped the island’s evolution.
Indonesia: Clues from Sumatra, Java, and Kalimantan
In Indonesia, marine fossils appear across several islands, often hidden within limestone hills or exposed in river valleys. In Sumatra, for instance, the Merangin Geopark in Jambi Province preserves a remarkable mix of marine fossils and ancient plant remains. The rocks here tell of a time when Sumatra lay beneath a shallow sea before being lifted and folded into the land we see today.
Rocky riverbanks inside Merangin Geopark, Jambi, Indonesia, where layers of ancient marine limestone preserve fossils of corals and other sea life from hundreds of millions of years ago. These rocks were once part of a shallow ocean floor before tectonic forces lifted them into the present-day highlands.
Source:
blog.bookingtogo.com
Similar stories emerge in Java and Kalimantan, where scientists have reported fossilized shells, corals, and fish remains inside sedimentary rock formations. These discoveries show that much of Indonesia’s current landscape—now covered by forests and volcanoes—was once part of an ancient seafloor shaped by long, slow geological forces.
What these fossils tell us
Each fossil found in the mountains of Southeast Asia is a piece of the region’s deep-time puzzle. They reveal where oceans once spread, how islands formed, and how the continents themselves have moved. The trilobites of Langkawi, the shark teeth of Brunei, and the coral fossils of Sumatra all tell the same story: the sea was here long before us.
For scientists, these fossils are valuable clues that help reconstruct the history of our planet’s surface. For everyone else, they are reminders that the land beneath our feet is always changing. The mountains we hike today were once coral reefs. The limestone cliffs that tower over us were once underwater worlds.
