Arkelloceras
Encyclopedia
Arkelloceras is an early Middle Jurassic
(Bajocian
stage) Stephanoceratacean (Ammonitina) genus from arctic Canada, Alaska, and Siberia belonging to the family Otoitidae
(Imlay 1984, Westermann 1965)
Arkelloceras seems to be a direct descendant of Abbasites
and is thought to have given rise to Ermoceras
and possibly to Thamboceras. (Westermann 1965)
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....
(Bajocian
Bajocian
In the geologic timescale, the Bajocian is an age or stage in the Middle Jurassic. It lasted from approximately 171.6 Ma to around 167.7 Ma . The Bajocian age succeeds the Aalenian age and precedes the Bathonian age....
stage) Stephanoceratacean (Ammonitina) genus from arctic Canada, Alaska, and Siberia belonging to the family Otoitidae
Otoitidae
Otoidtidae: stephanoceratacean ammonitina from the early Middle Jurassic that begin as cadicones but become more planualte with age; derived from the Hammitoceratidae , probably through Erycites by way of Abbasites....
(Imlay 1984, Westermann 1965)
Arkelloceras seems to be a direct descendant of Abbasites
Abbasites
Abbasites is an extinct ammonite genus from the early Middle Jurassic included in the ammonitid family Erycitidae.-Description:Abbasites is small and subglobular with ribbing that divides high on its sides and which has an interruption on the venter that replaces the keel, generally characteristic...
and is thought to have given rise to Ermoceras
Ermoceras
Ermoceras is a thomboceratid ammonite from the Middle Jurassic of central Arabia, Sinai, and Algeria with strong primary and secondary ribs and a single row of lateral tubercles; described as having a deep ventral groove...
and possibly to Thamboceras. (Westermann 1965)
References
- Imlay, Ralph W. 1984. Early and Middle Bajocian (Middle Jurassic) Ammonites from Southern Alaska;U.S.G.S PP 1322 http://www.dggs.dnr.state.ak.us/webpubs/usgs/p/text/p1322.PDF
- Westermann, G. E. G. 1965.Septal and Sutural Patterns in Evolution and Taxonomy of Thamboceratidae and Clydoniceratidae (M Jurassic Ammonitina). Jour of Paleontology 39(5)864-874, Sept.