Dactylioceratidae

Dactylioceratidae
Temporal range: early Jurassic
Ammonites of genus Dactylioceras from Schleifhausen (Germany)
Scientific classification
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Eoderocerataceae
Family: Dactylioceratidae
Hyatt, 1867

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

Prodactylioceras cf. davoei

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.[1]

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.[1]

Approximate timeline of Dactylioceratidae genera.

Taxonomy

[1][2]

References

  1. 1 2 3 M. K. Howarth 2013. Treatise on Invertebrate Paleontology, Part L, Revised, Volume 3B, Chapter 4: Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea.
  2. http://fossilworks.org/?a=taxonInfo&taxon_no=273835 accessed 11. june 2016


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