ROADSIDE FOSSILS: TRIASSIC PAPER CLAMS FROM PINE PASS

Triassic Paper clams, Pardonet Formation

In the rugged foothills of Pine Pass, near the small northern British Columbia town of Chetwynd, the rocks tell a story from over 200 million years ago—a story written in shell just a short walk from the main road. 

Here, in outcrops of the Pardonet Formation, the remains of once-living bivalves called paper clams—or “flat clams”—paint a vivid picture of life in the Late Triassic seas.

During the Triassic, roughly 237–201 million years ago, these delicate-shelled bivalves of the genus Moinotis, specifically Moinotis subcircularis, thrived in shallow marine environments. 

Their thin, flattened shells resemble wafer-like sheets, earning them the common name “paper clams.” 

Despite their fragile appearance, they were ecologically tough, colonizing vast seafloor regions after the Permian-Triassic mass extinction—Earth’s most catastrophic biodiversity crisis. In the wake of devastation, paper clams became pioneers in new marine ecosystems, spreading widely across the Triassic world.

At Pine Pass, the Pardonet Formation captures this resilience in stone. The strata—composed mainly of silty shales and fine-grained sandstones—represent an ancient seabed deposited along the western margin of Pangea. These rocks are part of the larger Western Canada Sedimentary Basin and are well known for their rich fossil assemblages, including ammonoids, conodonts, and marine reptiles. Yet, among these Triassic relics, it’s the paper clams that often dominate.

A short scramble up the rocky slope near the highway reveals bedding planes glittering with thousands of tiny, overlapping shells. They lie perfectly preserved, their paper-thin forms cemented into the matrix as though frozen in a whisper of time. Each shell records a pulse of ancient life in a warm, shallow sea teeming with invertebrates.

Our field stop at Pine Pass was a spontaneous detour en route to a paleontological conference in nearby Tumbler Ridge—a region equally famed for its dinosaur tracks and marine fossils. What was meant to be a quick roadside break became a fossil feast. 

Within minutes, we were crouched among the rocks, gently tracing our fingers over Moinotis subcircularis—delicate, symmetrical, and as hauntingly beautiful as the day they settled on the Triassic seafloor.