# Lituitidae

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{{Short description|Family of molluscs}}
{{Automatic taxobox
| name = Lituitidae
| fossil_range = late L [Ord](/source/Ordovician) - ? [Sil](/source/Silurian)
| image = Trilacinoceras discors,l.png
| taxon = Lituitidae
| authority = 
}} 
The '''Lituitidae''' are a family of evolved [tarphycerids](/source/Tarphycerida) 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](/source/Tarphycerida) is composed of thin connecting rings.

==Taxonomic position==
Flower and Kummel (1950)<ref>Flower & Kummel, 1950. A Classification of the Nautiloidia. Jour Paleontology, V.24, N.5, pp 604-616, Sept</ref> included the Lituitidae in the Barranderocerida which are now included in the  Tarphycerida as a number of derived families. Furnish and Glenister (1964)<ref name = Furnish>Furnish & Glenister, 1964, Nautiloidea -Tarphycerida. [Treatise on Invertebrate Paleontology](/source/Treatise_on_Invertebrate_Paleontology) Part K</ref> removed the Lituitidae to the Tarphycerida on the basis of observed similarities in the structure of the siphuncle. Other taxonomies, e.g. Dzik (1981)<ref>Dzik, 1981. Origin of the Cephalopoda. Acta Palaeont. Polonica 26, 2, 161-191</ref> include the Lituitidae in the [Orthocerida](/source/Orthocerida) partly on the basis of the subcentral siphuncle and thin connecting rings, on the misconception that ''[Rhynchorthoceras](/source/Rhynchorthoceras)'' is ancestral.

==Classification==
The Lituitidae comprise two basic groups, based on general form. One is represented by ''[Ancistroceras](/source/Ancistroceras)'' and ''[Holmiceras](/source/Holmiceras)'' and probably includes ''[Angelinoceras](/source/Angelinoceras)''.  The other is represented by ''[Litoceras](/source/Litoceras)'', which first appears later in the early [Middle Ordovician](/source/Middle_Ordovician).<ref name = Furnish/>

==Characteristics==
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 a complex aperture with lappets as in ''Litoceras''.<ref name = Furnish/>

==Derivation and evolution==
The earliest known lituitids are ''[Ancistroceras](/source/Ancistroceras)'' and  ''[Holmiceras](/source/Holmiceras)'' <ref name = Furnish/>  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.<ref name = Furnish/>  The tendency for the adult tarphycerid shell to unwind, or straighten out, is well documented. This even occurs in some ammonoids, in the [ammonitid](/source/Ammonitida) Bacultidae and in the [ceratitid](/source/Ceratitida) Choristoceratidae.<ref>Arkell et al 1957, Mesozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L.</ref>  Nowhere is there any direct evidence of orthoconic forms developing coiling at their apexes<ref>a)Treatise on Invertebrate Paleontology Part K, Teichert & Moore (eds);chapters on the Endocerida, Actinocerida, and Orthocerida b)Flower R. H 1957. Studies of the Actinocerida, Mem 2, New Mexico Bureau of Mines and Mineral Resources (NMBMMR) c) Flower R. H 1962 Notes on the Michelinocerida, Mem 10, NMBMMR.</ref>  nor does any obvious advantage exist for them to have done so.

==References==
{{Reflist}}

{{Taxonbar|from=Q6653367}}

Category:Prehistoric nautiloid families
Category:Early Ordovician first appearances
Category:Silurian extinctions

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Adapted from the Wikipedia article [Lituitidae](https://en.wikipedia.org/wiki/Lituitidae) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Lituitidae?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.