Empty seashells became the ocean’s first ready-made homes 470 million years ago

An international study led by the University of Tartu shows that about 470 million years ago, empty mollusc shells began serving as homes for small sea creatures.

During the earlier Cambrian Period, the inside of empty shells remained uninhabited; the first animals moved into shells during the Middle Ordovician, about 460 million years ago.

These tiny residents included bryozoans, brachiopods, sponges, graptolites, and cornulids, which filtered food particles from water.

Shell shape influenced the size and diversity of resident communities, with larger nautiloid shells being colonized first.

This ecological innovation laid the groundwork for how ocean ecosystems function today.