Dactylioceras commune (Sowerby 1815)

Taxonomy

Ammonite

Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Ammonitida
Family: Dactylioceratidae
Genus: Dactylioceras
Species: Dactylioceras commune
Author Citation Sowerby 1815

Geological Time Scale

Eon: Phanerozoic
Era: Mesozoic
Period: Jurassic
Sub Period: None
Epoch: Early
International Age: Early Toarcian

Biostratigraphy

Bifrons zone
Commune subzone

Provenance

Collector: Roger Furze
Date Collected: 08/14/2008
Acquired by: Field Collection

Dimensions

Diameter: 5 cm

Location

Fuegerolles quarry
Calvados
Normandy
France

• a13a
• a74
• a335
• dactylioceras commune
• france
• fuegerolles
• lower jurassic
• lower toarcian
• normandy

Comments

This species was one of the most common of its time, but nevertheless it is used as the index fossil for the subzone since its occurence is practically limited to it. It is not easy to differentiate it from the species D.athleticum, which occurs in the same subzone. One main difference is that D.commune has a more rounded whorl section than D.athleticum, which is more oval. Another is that the number of ribs per whorl by D.athleticum remains constant, whereas D.commune has less ribs on the outer whorls as on the inner ones. The first specimen is from France (4 photos), the next 2 photos show a pyritized version in a concretion from a site near Whitby, Yorks., UK as well as the cut and polished version in the last photo. Both come from the Whitby Mudstone Formation. It's always interesting to observe how the same species can be preserved so differently depending in the particular conditions under which they were fossilized.

 

Literature: Howarth, M.K. (1973): The Stratigraphy and Ammonite Fauna of the Upper Liassic Grey Shales of the Yorkshire Coast. Bulletin of the British Museum

                  (Natural History) Geology. Vol.24 No.4