Wikipedia
The Tarphycerida were the first of the coiled cephalopods. They are found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some like Aphetoceras and Estonioceras are loosely coiled, gyroconic, others like Campbelloceras, Tarphyceras, and Trocholites are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular (Furnish and Glenister 1964), as much as half the length of the containing whorl in most, greater than in the Silurian Ophidioceratidae.
The Tarphycerida evolved from the elongate, compressed, exogastric Bassleroceratidae, probably Bassleroceras, around the end of the Gasconadian through forms like Aphetoceras. Close coiling developed rather quickly and both gyroconic and evolute forms are found in the early middle Canadian.
Tarphycerids tend to uncoil in the late mature stage of their growth, indicating they settled into a benthic lifestyle as they became older. Younger, wholly coiled forms were probably more active, nekto-benthic, certainly more maneuverable