Nautiloidea is the oldest subclass of cephalopods. They originated in the Paleozoic era in the Cambrian period. The earliest Nautiloid fossils (which come from China) demonstrate that they were a very diverse subclass of animals. Many of these early species died out, but one family Ellesmeroceratidae made past this initial hurdle and into the subsequent Ordovician period. All the other cephalopods from this period onward are descendants of the Ellemeroceratidaes.