The Ancient Architects of Wembury
At Wembury Point in South Devon, the rocky foreshore reveals an extraordinary story of ancient life. The wave-cut platforms are composed of Lower Devonian rocks, mudstones and siltstones laid down approximately 400 million years ago. These rocks, part of the Dartmouth Group, contain trace fossils that have changed our understanding of animal behavior. The fossils in question are not bones, but burrows: smooth, date-shaped borings known by the ichnospecies name Gastrochaenolites torpedo. These structures provide some of the earliest evidence of bivalves—in this case, ancient clams—drilling into hard rock.
This behavior, a form of bioerosion, was previously thought to have evolved much later. The Wembury fossils demonstrate that clams had developed the ability to bore into rock substrates during the Devonian Period, a time when the first forests were beginning to appear on land and fish were diversifying in the oceans. The borings are typically 15 to 30 millimeters long and 8 to 12 millimeters wide, with a rounded, torpedo-like shape. They were created by clams that used a combination of mechanical abrasion with their shells and chemical dissolution to create a secure home within the rocky substrate, a strategy still used by modern piddock clams.