The family Dactylioceratidae comprises Early Jurassic ammonite genera with ribbed and commonly tuberculate shells that resembled later Middle Jurassic stephanoceratids and Upper Jurassic perisphinctids. Shells may be either evolute or involute.

Description

Ammonites with evolute, serpenticone to cadicone shells with ribs, sometimes with tubercules. Members of this family had no keels. while homeomorphic with stephanoceratids and perisphinctids, they had unique shell structure with double shells and flat-topped ribs on the inner shell. Based on suture differences, they are divided into 2 subfamilies. Reynesocoeloceratinae possess two major secondary lobes in dorsal side of external saddle. This saddle is not divided this way in Dactylioceratinae, while lateral lobe is deeply trifid.

Evolution

It has been suggested, that this family is polyphyletic, but this is now considered to be false. Reynesocoeloceratinae evolved in lower

Pliensbachian The Pliensbachian is an age (geology), age of the geologic timescale and stage (stratigraphy), stage in the stratigraphic column. It is part of the Early Jurassic, Early or Lower Jurassic epoch (geology), Epoch or series (stratigraphy), Series an ...

from '' Metaderoceras'' and died out in upper Pliensbachian. ''Reynesoceras'' oldest member of Dactylioceratinae evolved in upper Pliensbachian from ''Cetonoceras'', or ''Prodactylioceras''. This subfamily died out in middle

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 ...

, during Variabilis zone.M. K. Howarth 2013. Treatise on Invertebrate Paleontology, Part L, Revised, Volume 3B, Chapter 4: Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea.

Taxonomy

*Dactylioceratidae Hyatt, 1867 ** Reynesocoeloceratinae Dommergues, 1986 ***'' Reynesocoeloceras'' Géczy, 1976 ***'' Bettoniceras'' Wiedenmayer, 1977 ***''

Prodactylioceras ''Prodactylioceras'' is genus of ammonite that lived during the Pliensbachian stage of early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the e ...

'' Spath, 1923 ***'' Cetonoceras'' Wiedenmayer, 1977 ** Dactylioceratinae Hyatt, 1867 ***'' Reynesoceras'' Spath, 1936 ***''

Dactylioceras ''Dactylioceras'' was a widespread genus of ammonites from the Lower Jurassic period, approximately 180 million years ago ( mya). Etymology The name ''Dactylioceras'' comes from the Greek ''dactyl'', meaning “finger”, and refers to the shell ...

'' Hyatt, 1867 ****''D. (Dactylioceras)'' Hyatt, 1867 ****''D. (Orthodactylites)'' Buckman, 1926 ****''D. (Iranodactylites)'' Repin, 2000 ****''D. (Eodactylites)'' Schmidt-Effing, 1972 ***'' Nodicoeloceras'' Buckman, 1926 ***'' Peronoceras'' Hyatt, 1867 ***'' Zugodactylites'' Buckman, 1926 ***'' Porpoceras'' Buckman, 1911 ***'' Septimaniceras'' Fauré, 2002 ***'' Catacoeloceras'' Buckman, 1923 ***'' Collina'' Bonarelli, 1893 ***'' Tokurites'' Repin, 2016

References

;Notes ;Bibliography * W. Arkell ''et al.'', 1957. Mesozoic Ammonoidea, ''Treatise on Invertebrate Paleontology, Part L.'' Geological Society of America and University of Kansas, Press. Ammonitida families Eoderoceratoidea Early Jurassic ammonites Early Jurassic first appearances Early Jurassic extinctions {{ammonitina-stub