Lituitida
Encyclopedia
The Lituitida are the Lituitidae of the Treatise (Furnish & Glenister,1964), reranked as an order and combined with other orthoceratoids.. They are considered to be more closely related to the Orthocerida
than to the Ascocerida
or Pseudorthocerida
which are also included.
Lituitids are characterized by smooth to annulate shells in which the juvenile portion near the apex is coiled or cyrtoconic. The adult portion is straight or slightly sigmoidal and may be expanded. Growth lines show a deep hyponomic sinus and lateral ocular sinuses. The siphuncle is subcentral with layered connecting rings. Cameral deposits are prevalent and concentrated more ventrally. The apex is small and spherical and lacks a cicatrix.
The Lituitida, which were originally included in the Tarphycerida as the Lituitidae (Furnish and Glenister) have their beginnings in the Early Ordovician with forms like Ancistroceras
. Their diversity increased after the late Arenigian extinction (Floian-Dapingian) at the end of the Canadian Epoch
and take a tumble following the early Cincinnatian (Sandbian) in the early Late Ordovician, from which the group never recovers.
It is thought that they had a planktonic juvenile stage in their life cycle and that mature adults lived in the shallow waters of the open ocean.
Some 8 genera have been described, all from the Baltic region of northern Europe. One genus, Holmiceras, is limited to the Lower Ordovician and one, Ancistroceras, comes from both the lower and middle of the period. Five genera included the type genus, Lituites
, are known only from the Middle Ordovician and one, Tyrioceras, is known from the Middle and Upper Ordovician, the last of its kind.
Orthocerida
Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...
than to the Ascocerida
Ascocerida
The Ascocerida are comparatively small, bizarre nautiloids known only from Ordovician and Silurian sediments in Europe and North America, uniquely characterized by a deciduous conch consisting of a longiconic juvenile portion and an inflated breviconic adult portion that separate sometime in...
or Pseudorthocerida
Pseudorthocerida
Pseudorthocerida are generally straight longiconic nautiloids with a subcentral to marginal cyrtochoanitic siphuncle composed of variably expanded segments which may contain internal deposits that may develop into a continuous parietal lining.. Cameral deposits are common and concentrated ventrally...
which are also included.
Lituitids are characterized by smooth to annulate shells in which the juvenile portion near the apex is coiled or cyrtoconic. The adult portion is straight or slightly sigmoidal and may be expanded. Growth lines show a deep hyponomic sinus and lateral ocular sinuses. The siphuncle is subcentral with layered connecting rings. Cameral deposits are prevalent and concentrated more ventrally. The apex is small and spherical and lacks a cicatrix.
The Lituitida, which were originally included in the Tarphycerida as the Lituitidae (Furnish and Glenister) have their beginnings in the Early Ordovician with forms like Ancistroceras
Ancistroceras
Ancistroceras is one of the two ancestral lituitids from the late Early Ordovician . The other being Holmiceras.The shell is weakly annulate, starts off with 1.5 to 2 contiguous or slightly separated whorls followed by a rapidly expanding orthocone with an apical angle of about 30 deg...
. Their diversity increased after the late Arenigian extinction (Floian-Dapingian) at the end of the Canadian Epoch
Canadian Epoch
The Canadian is the Lower or Early Ordovician in North America. The term is common in the older literature and has been well understood for more than a century...
and take a tumble following the early Cincinnatian (Sandbian) in the early Late Ordovician, from which the group never recovers.
It is thought that they had a planktonic juvenile stage in their life cycle and that mature adults lived in the shallow waters of the open ocean.
Some 8 genera have been described, all from the Baltic region of northern Europe. One genus, Holmiceras, is limited to the Lower Ordovician and one, Ancistroceras, comes from both the lower and middle of the period. Five genera included the type genus, Lituites
Lituites
Lituites is an extinct nautiloid genus from the Middle Ordovician and type for the Lituitidae, a tarphycerid family that in some more recent taxonomies has been classified with the orthocerids and listed under the order Lituitida...
, are known only from the Middle Ordovician and one, Tyrioceras, is known from the Middle and Upper Ordovician, the last of its kind.