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.
Ancestral cephalopod had just two tentacles | X-Ray Magazine Credit: Marianne Collins / University of Toronto Nectocaris is a genus containing one species (N. pteryx) of early cephalopod known from the Middle Cambrian Burgess Shale. It was not until 1976 that it was formally described. The head had two stalked eyes, one pair of tentacles, and an oval carapace or shield at the rear. Fleshy fins supported by internal spines ran along the sides of the flattened, kite-shaped body
Fossil of the trilobite genus Ceratarges, found in the Devonian (about 360 million years old) Hamar Laghdad Formation near Alnif, Morocco. Fossil is about 6 cm in length. Collection of the Sauriermuseum Aathal, Aathal, Switzerland.