Nearly half a billion years ago, in the ancient seas of the Ordovician, small marine creatures made a quiet but consequential decision: to move into the empty shells left behind by the dead. Researchers from the University of Tartu and their international collaborators have traced this moment of ecological ingenuity to approximately 470 million years ago, revealing how a simple behavioral shift — shelter-seeking — helped architect the seafloor communities that persist to this day. In the long story of life on Earth, it is a reminder that transformation often begins not with grand invention, bu