Modiolus is strikingly similar to modern mussel shells. Indeed, many modern bivalve shells have ancestors that are millions of years old. Nautilus, the spiral-shelled creature similar to the ammonites, is always quoted as a ‘living fossil’ but in fact many forms of life that we are familiar with today are also living fossils. Many bivalves can trace their ancestry back at least 200 million years.
Find out more about bivalves on the molluscs pages.