''Stephanoceras'' (meaning ''crown horn'') is an extinct genus of Stephanoceratoid ammonite which lived during the Bajocian (Middle Jurassic). It is the type genus of the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Stephanoceratidae Stephanoceratidae is a family of planulate and coronate ammonites within the Stephanoceratoidea.Arkell, Kummel, and Wright, 1957. Mesozoic Ammonoidea; Treatise on Invertebrate Paleontology, Part L, Mollusca 4. Shells are evolute so that all whorl ...

Type species

''Ammonites humphriesianum'' J. de C. Sowerby, 1825, subsequent designation by Buchman, 1898

Selected species

*''S. humphriesianum'' (J. de C. Sowerby 1825) - Type species *''S. blagdeni'' (Sowerby) *''S. brodeaei'' (J. Sowerby) *''S. mutabile'' (Quenstedt 1886) *''S. umbilicum'' (Quenstedt 1886) *''S. nodosum'' (Quenstedt 1886) *''S. macrum'' (Quenstedt 1886) *''S. pyritosum'' (Quenstedt 1886) *''S. triplex'' Weisert *''S. freycineti'' (Bayle) *''S. kreter'' (Buckman) *''S. leptogyrale'' (Buckman) *''S. boulderense'' Imlay 1982 *''S. coronatus'' (Bruguiere 1789) *''S. quenstedti'' Кoche 1939 *''S. skidegatense'' Whiteaves 1876

Description

''Stephanoceras'' has an evolute shell, as characteristic of the family, with well-developed ribbing and tubercles. The shell is coiled so whorls barely touch in most, but some have notable overlap. Primary ribs emerge from the umbilical seam, the line marking the inner edge of the particular exposed whorl, and divide on the flanks, usually in two, occasionally in three, forming secondary ribs that cross the outer rim of the shell, known as the venter, uninterrupted. Turbercles, elevated projections, form at the ends of the primary ribs where they bifurcate or sometimes trifurcate. ''Stephanoceras'' grew to be fairly large with a shell diameter as much as 27 cm and width as much as 6 cm across the outer whorl. Like many ammonites, ''Stephanoceras'' is dimorphic with a large, macroconch, form thought to be female and a small, microconch, form thought to be male. In most aspects the microconch is simply a smaller version of the macroconch. The primary difference lies in the aperture, which in the microconch has planar extensions on either side, lappets. That of the macroconch is generally simple, preceded by a constriction.

Distribution

Fossils of ''Stephanoceras'' are found in the

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), 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 J ...

marine strata of Canada, Mexico, Saudi Arabia and Spain. Some species, including ''S.coronatus'' and '' S.humphriesianum'' can also be found in rocks of the same age from England and Germany.

Gallery

File:S. humphriesianum - Clatcombe Dorset.jpg, ''Stephanoceras humphriesianum'', Jurassic, Inferior Oolite, ''Humphriesianum'' Zone, Clatcombe, Dorset, UK. Size of ammonite 275mm. File:Stephanoceratidae - Stephanoceras blagdeni.JPG, ''Stephanoceras blagdeni'' from Mid

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

''References''

*Arkell, ''et al.'' 1957. Mesozoic Ammonoidea, Treatise on invertebrate Paleontology, Part L, Mollusca 4. Geol Soc of America and Univ of Kansas press, Lawrence. *Galacz, A. 1991. Bajocian Sephanoceratid Ammonites from the Bakony Mountains, Hungary. Palaeontology, Vol 34, Pt 4, 1991, pp 859–885. *Sandoval, J. & Westermann, G. E. G. 1986. The Bajocian (Jurassic) ammonite fauna of Oaxaca, Mexico; Jour Paleo V.67, N.6, p. 1220, November 1986 Jurassic ammonites Jurassic ammonites of Europe Jurassic ammonites of North America Ammonitida genera Stephanoceratoidea {{ammonitina-stub