''Arkelloceras'' is an early

Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...

(

Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stratig ...

stage) Stephanoceratoid (Ammonitina) genus from arctic Canada, Alaska, and Siberia belonging to the family

Otoitidae Otoidtidae: stephanoceratoid ammonitina from the early Middle Jurassic that begin as cadicones but become more planualte with age; derived from the Hammitoceratidae (Hildoceratoidea), probably through '' Erycites'' by way of ''Abbasites''. Sh ...

(Imlay 1984, Westermann 1965) ''Arkelloceras'' seems to be a direct descendant of ''

Abbasites ''Abbasites'' is an extinct genus of ammonites from the early Middle Jurassic epoch, included in the ammonitid family Erycitidae. Description ''Abbasites'' is small and subglobular with ribbing that divides high on its sides and which has an int ...

'' and is thought to have given rise to ''

Ermoceras ''Ermoceras'' is a genus of ammonite belonging to the Thomboceratidae family of the Middle Jurassic ( u Baj) found in deposites of central Arabia, Sinai, and Algeria with strong primary and secondary ribs and a single row of lateral tubercles ...

'' 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 132

* 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. {{Taxonbar, from=Q4791959 Jurassic ammonites