|
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 ==Composition and taxonomy== The Tarphycerida comprise three phylogenetically related groups of families. They are: the tarphyceratid group consisting of the Estonioceratidae, Tarphyceratidae, Trocholitidae, Lituitidae, and Ophidioceratidae; the barradeoceratid group, derived from ''Centrotarphyceras'' (Flower 1984), consisting of the Barrandeoceratidae, Bickmoritidae, Nephriticeratidae, and Uranoceratidae; and the plectoceratid group, derived from ''Campbelloceras'' (''ibid''), consisting of the Plectoceratidae, Lechritrochoceratidae, and Apsidoceratidae. The tarphyceratids comprise the Tarphycerida of the Treatise on Invertebrate Paleontology Part K (Furnish and Glenister 1964) to which Flower added the ancestral Bassleroceratidae. The Estonioceratidae, Tarphyceratidae, and Trocholitidae are primitive forms characterized by siphuncles with thick-walled connecting rings. The Lituitidae and Ophidioceratidae are derived offshoots. The barrandeoceratid and Plectoceratid families were once combined in the Barrandeocerida (Sweet, 1964), determined by Flower (1984) to be invalid due to having multiple ancestors in the Tarphyceriatidae and therefore abandoned. The common character of these forms are the thin-walled connecting rings in their siphuncles. Some recent classifications (e.g. Teichert 1988) divide the Tarphycerida into to suborders, the Tarphycerina and Barrandeocerina, which were previously defined as separate orders. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tarphycerida」の詳細全文を読む スポンサード リンク
|