Most other octopuses lay eggs in caves ; Neale Monks and C. Phil Palmer speculate that , before ammonites died out during the Cretaceous-Paleogene extinction event , the argonauts may have evolved to use discarded ammonite shells for their egg laying , eventually becoming able to mend the shells and perhaps make their own shells .
It is made of calcite , with a 3-layered structure Most other octopuses lay eggs in caves , the argonauts may have evolved to use ammonite shells for their egg laying , eventually becoming able to mend the shells and perhaps even make their own .