13-626: The Lituitidae are a family of evolved tarphycerids characterized by a long orthoconic section that follows a coiled juvenile portion at the apex, along with a generally tubular siphuncle, which like that of the barrandeocerids is composed of thin connecting rings. Flower and Kummel (1950) included the Lituitidae in the Barranderocerida which are now included in the Tarphycerida as a number of derived families. Furnish and Glenister (1964) removed
26-486: A benthic lifestyle as they became older. Younger, wholly coiled forms were probably more active, nektobenthic, certainly more maneuverable. The Tarphycerida comprise three phylogenetically related groups of families. They are: the tarphyceratid group consisting of the Estonioceratidae , Tarphyceratidae , Trocholitidae , and Ophidioceratidae ; the barradeoceratid group, derived from Centrotarphyceras , consisting of
39-565: A complex aperture with lappets as in Litoceras . The earliest known lituitids are Ancistroceras and Holmiceras which made their first appearances in the latter part of the Early Ordovician, well before Rhynchorthoceras . The precise ancestry for either is unknown, although evolutionary possibilities can be found in various tarphyceratid and trocholitid genera. The tendency for the adult tarphycerid shell to unwind, or straighten out,
52-453: A less active, bottom-dwelling stage with shells that diverge during which they mated and produced, probably a single litter of young, like the modern but unrelated coleoids . Uranoceratidae See text The Uranoceratidae is a family of Silurian barrandeoceroids that tend to become uncoiled with age and in which siphuncle segments tend to be expanded into the camerae . Shells of uranoceratids are gyroconic . Early stages of
65-456: Is represented by Litoceras , which first appears later in the early Middle Ordovician . The coiled juvenile portions of the Lituitidae are characterized by a deep hyponomic sinus and lateral salients at the aperture, indicating a high degree of mobility. The orthoconic adult portions are characterized by a shallow hyponomic sinus as in Ancistroceras indicating a more passive lifestyle, or
78-403: Is well documented. This even occurs in some ammonoids, in the ammonitid Bacultidae and in the ceratitid Choristoceratidae. Nowhere is there any direct evidence of orthoconic forms developing coiling at their apexes nor does any obvious advantage exist for them to have done so. Tarphycerida The Tarphycerida were the first of the coiled cephalopods , found in marine sediments from
91-872: The Barrandeoceratidae , Bickmoritidae , Nephriticeratidae , and Uranoceratidae ; and the plectoceratid group, derived from Campbelloceras , consisting of the Plectoceratidae , Lechritrochoceratidae , and Apsidoceratidae . The tarphyceratids comprise the Tarphycerida of the Treatise on Invertebrate Paleontology Part K to which Flower added the ancestral Bassleroceratidae. The Estonioceratidae, Tarphyceratidae, and Trocholitidae are primitive forms characterized by siphuncles with thick-walled connecting rings. The Ophidioceratidae are derived offshoots. The barrandeoceratid and plectoceratid families were once combined in
104-562: The Silurian Ophidioceratidae . The Tarphycerida evolved from the elongated, 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
117-536: The Barrandeocerida, determined to be invalid due to having multiple ancestors in the Tarphyceriatidae and therefore abandoned. The common characteristic of these forms is the thin-walled connecting rings in their siphuncles. A 1988 classification divides the Tarphycerida into suborders Tarphycerina and Barrandeocerina, which were previously defined as separate orders. Tarphycerids are more closely related to
130-553: The Lituitidae to the Tarphycerida on the basis of observed similarities in the structure of the siphuncle. Other taxonomies, e.g. Dzik (1981) include the Lituitidae in the Orthocerida partly on the basis of the subcentral siphuncle and thin connecting rings, on the misconception that Rhynchorthoceras is ancestral. The Lituitidae comprise two basic groups, based on general form. One is represented by Ancistroceras and Holmiceras and probably includes Angelinoceras . The other
143-551: The Lower Ordovician (middle and upper Canad ) to the Middle Devonian . Some, such as Aphetoceras and Estonioceras , are loosely coiled and gyroconic; others, such as Campbelloceras , Tarphyceras , and Trocholites , are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular, as much as half the length of the containing whorl in most, greater than in
SECTION 10
#1732858655730156-613: The diverse Oncocerida , through the ancestral Bassleroceratidae in the Lower Ordovician, than to the other nautiloid orders. The Oncocerida, in turn, gave rise to the Nautilida which include the recent Nautilus and Allonautilus . This puts the Tarphycerida in the broad group that includes the nautilids. It makes them also separate from the groups that include the Discosorida , Actinocerida , Endocerida , and Orthocerida , and from
169-429: The superficially similar Ammonoidea . The tarphycerid animal must have been rather elongated, like squid, although no close relationship is implied. Either that or it was able to retreat deep into its portable lair. As for whatever arms or tentacles they may have had, no indication has been found. They probably went through two stages, first a younger more active and swimming stage with simple coiled shells, followed by
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