Lytoceratidae is a taxonomic family of

ammonoid Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

cephalopods belonging to the suborder

Lytoceratina Lytoceratina is a Suborder (biology), suborder of Jurassic and Cretaceous Ammonitida, ammonites that produced loosely coiled, evolute and gyroconic shells in which the sutural element are said to have complex moss-like endings. Morphologic chara ...

, characterized by very evolute shells that generally enlarge rapidly, having whorls in contact but mostly overlapping very sightly, or not at all. Surface ornament may consist of various combinations of straight or crinkled growth lines, flares, constrictions, and, more rarely, plications. Sutures are highly complex and moss-like, but with few major elements. Lateral lobes are widely splayed and blunt, or with obliquely deflected end. The external, ventral, lobe is short. The Lytoceratinae have a worldwide distribution and a stratigraphic range extending from the middle Lower Jurassic (

Pliensbachian The Pliensbachian is an age of the geologic timescale and stage in the stratigraphic column. It is part of the Early or Lower Jurassic Epoch or Series and spans the time between 190.8 ± 1.5 Ma and 182.7 ± 1.5 Ma (million years ago). The Plien ...

) to the early Upper Cretaceous (

Cenomanian The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous Epoch or the lowest stage of the Upper Cretaceous Series. An age is a unit of geochronology; it is a unit of time; the stage is a unit in the s ...

Subfamilies

The Lytoceratidae has been divided into four subfamilies, as follows. *

Lytoceratinae Lytoceratinae is a subfamily of ammonoid cephalopods that make up part of the family Lytoceratidae. Description They are characterized by shells in which the whorls bear growth lines or lamellar folds, or both, commonly corresponding to constric ...

Neumayr 1875 (

) ** ''

Ammonoceratites ''Ammonoceratites'' is an extinct genus of ammonoid cephalopod known from the Albian (upper Lower Cretaceous) of British Columbia, Madagascar, New Zealand, and Japan, included in the Lytoceratidae. The shell of ''Ammonoceratites'' is evolute, sm ...

'' Bowditch 1822 ** ''

Argonauticeras ''Argonauticeras'' is an extinct ammonoid cephalopod genus that lived during the latter part of the Early Cretaceous, included in the Lytoceratida and found in lower and possibly middle Aptian marine sediments. It has been thought of as a subgenu ...

'' Anderson 1938 ** '' Carinolytoceras'' Wiedmann 1962 ** ''

Eulytoceras ''Eulytoceras'' is an extinct genus of ammonoid cephalopods belonging to the family Lytoceratidae. These fast-moving nektonic carnivores lived in the Cretaceous period, from Hauterivian age to Barremian age.Sepkoski, JacSepkoski's Online Genus D ...

'' Spath 1927 ** ''

Hemilytoceras ''Hemilytoceras'' is a lytoceratin ammonite genus with round inner whorls, outer whorls becoming depressed and in some developing high lamellae (ribs) that bend forward over the venter. The type species ''H. immanae'' came from the Tithonian of ...

'' Spath 1927 ** ''

Lytoceras ''Lytoceras'' is an ammonite genus that was extant during most of the Jurassic and Cretaceous periods, and is the type genus for the family Lytoceratidae. These cephalopods were fast-moving nektonic carnivores. Description Shells of ''Lytoceras' ...

'' Suess 1865 ** '' Metalytoceras'' Spath 1927 ** ''

Pictetia ''Pictetia'' is a genus of about eight species of trees and shrubs in the legume family with Thorns, spines, and prickles, spiny stems and (in six of the eight species) spine-tipped leaflets.Beyra & Lavin (1999), pp.36–38 The genus is endemism, ...

'' Uhlig 1883 ** ''

Protetragonites ''Protetragonites'' is an extinct genus of ammonoid cephalopods belonging to the family Lytoceratidae. These fast-moving nektonic carnivores lived from the Jurassic period Tithonian age to the Cretaceous period Aptian age.Sepkoski, JacSepkoski' ...

'' Hyatt 1900 ** '' Pterolytoceras'' Spath 1927 Lytoceratids with whorls that bear growth lines or lamellar flares, or both, and in which there are only two lateral lobes in the external suture, on either side, and the dorsal lobe is cruciform (cross like). *

Megalytoceratinae Megalytoceratinae is a subfamily of lytoceratids ammonites consisting of planulate forms, i.e. those with moderately evolute compressed shells with bluntly rounded venters, in which the outer whorls become smooth and sutures tend to resemble tho ...

(

Toarcian The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian. The Toarcian ...

–

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stratig ...

) Planulate lytoceratids in which whorls and sutures tend to lose lytoceratid character and resemble those of the perisphinctidae. * Villaniinae (

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...

) Plantulate lytoceratids with sutures like those in the Lytoceratinae, but without the dorsal lobe being cruciform. * Alocolytoceratinae Spath 1927 (

–

) ** ''

Alocolytoceras ''Alocolytoceras'' is a lytoceratid ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living ...

'' ** ''

Audaxlytoceras ''Audaxlytoceras'' is an extinct genus of lytoceratid ammonites. Taxonomy The Middle Jurassic '' Nannolytoceras'' is its closest relative. '' Aegolytoceras'' and '' Peripleuroceras'' Tutcher and Trueman 1925 are synonyms. Fossil record This ge ...

'' ** '' Derolytoceras'' ** ''

Lobolytoceras ''Lobolytoceras'' is an extinct genus of ammonite in which only the inner whorls have large swollen ribs, later whorls have wrinkled growth lines which coarsen somewhat, near the aperture. The genus is known from the Lower Jurassic Toarcian of Eu ...

'' ** '' Pachylytoceras'' ** '' Pleurolytoceras'' Lytoceratids with many deep constrictions resulting and capricorns in middle whorls. Outer whorls become more smooth and involute. Capricorn: a shell encircled by blunt, wide spaced ribs separated by subequal rounded interspaces, resembling a goat's horn .

References

* Ammonitida families Jurassic ammonites Pliensbachian first appearances Cenomanian extinctions {{Ammonitida-stub