''Bifericeras'' is a Lower

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

ammonite belonging to the family Eoderoceratidae, and sometimes placed in the subfamily Xipherceratinae. Whorls are strongly depressed, but still evolute in coiling. The early growth state is prolonged, and smooth, followed by a late growth stage with rounded, straight, bituberculate ribs. ''Bifericeras'' was named by Buckman in 1913 and is found in Europe.

Biostratigraphic significance

The

International Commission on Stratigraphy The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigr ...

(ICS) has assigned the

First Appearance Datum First appearance datum (FAD) is a term used by geologists and paleontologists to designate the first appearance of a species in the geologic record. FADs are determined by identifying the geologically oldest fossil discovered, to date, of a particu ...

of ''Bifericeras donovani'' and of genus '' Apoderoceras'' the defining biological marker for the start of the

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 ...

Stage of the

, 190.8 ± 1.0 million years ago.

Distribution

Only found at Dimmer Camp,

Castle Cary Castle Cary () is a market town and civil parish in south Somerset, England, north west of Wincanton and south of Shepton Mallet, at the foot of Lodge Hill and on the River Cary, a tributary of the Parrett. History The word Cary derives fr ...

Somerset ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lor ...

References

;Notes ;Bibliography *Arkell ''et al.'', 1957. Mesozoic Ammonoidea, in Treatise on Invertebrate Paleontology, (Part L); Geological Soc. of America and University of Kansas press. *Donovan, D.T. Callomon and Howarth 1981 Classification of the Jurassic Ammonitina; Systematics Association

Jurassic ammonites Early Jurassic ammonites of Europe Fossil taxa described in 1913 {{jurassic-animal-stub