The term 'died out' can be described by two crossword solutions: 'EXTINCT' (7 letters) and 'ENDED' (5 letters). EXTINCT means that a species of animal or plant has died out completely, with no living members of the species remaining. ENDED means that something has come to an end, usually referring to a period of time or an event. In this context, it can refer to the death of a species, meaning that the species has ENDED its existence.