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 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, 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 Spath, 1923 Cetonoceras Wiedenmayer, 1977 Dactylioceratinae Hyatt, 1867 Reynesoceras Spath, 1936 Dactylioceras 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.