''Hecticoceras'' is an

ammonite Ammonoids are extinct, (typically) coiled-shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living octopuses, squid, and cuttlefish (which comprise the clade Coleoidea) than they are to nautiluses (family N ...

genus belonging to the haploceratoid family

Oppeliidae Oppeliidae are compressed to oxyconic, sculptured Haploceratoidea, either unkeeled, unicarinate, bicarinate, or tricarinate; with sutures in great variety, but ribbing usually more or less falcoid or falcate. The Oppeliidae is the principal famil ...

, that lived during the

Middle Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek ...

and

Late Jurassic The Late Jurassic is the third Epoch (geology), epoch of the Jurassic Period, and it spans the geologic time scale, geologic time from 161.5 ± 1.0 to 143.1 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic stratum, strata.Owen ...

, from the

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 165.3 ± 1.1 Ma (million years ago) and 161.5 ± 1.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the ...

. ''Hecticoceras'' may be seen as a series of some nine subgenera, beginning with the lower Callovian ''H. (Hecticoceras)'' and ''H. (Hecticoceratoides)'' and ending with the lower Oxfordian ''H. (Pseudobrightia)'' and ''H. (Eochetoceras)''. ''Hecticoceras'' ''

sensu lato ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular co ...

'' and ''Prohecticoceras'' from the underlying

Bathonian In the geologic timescale the Bathonian is an age (geology), age and stage (stratigraphy), stage of the Middle Jurassic. It lasted from approximately 168.2 ±1.2 annum, Ma to around 165.3 ±1.1 Ma (million years ago). The Bathonian Age succeeds ...

form the oppeliid subfamily, Hecticoceratinae. ''Hecticoceras'', including its various subgenera, have a widespread distribution and have been found in the late Middle and early Upper Jurassic of Europe, North Africa, Somalia, India, Madagascar, and possibly Japan.

Subgenera

* ''Hecticoceras (Hecticoceras)'' * ''Hecticoceras (Hecticoceratoides)'' * ''Hecticoceras (Lunuloceras)'' * ''Hecticoceras (Sublunuloceras)'' * ''Hecticoceras (Kheraites)'' * ''Hecticoceras (Putealiceras)'' * ''Hecticoceras (Brightia)'' * ''Hecticoceras (Pseudobrightia)'' * ''Hecticoceras (Eochetoceras)'' ''Hecticoceras (Orbignyiceras)'' is sometimes distinguished from ''H. (Sublunuloceras)'' although the two are generally considered equivalent. ''H. (Chanasia)'' may be a fourth subgenus from the lower Callovian.

Descriptions

''Hecticoceras (Hecticoceras)'' which lived toward the end of the Middle Jurassic, during the early Callovian, is characterized by an evolute shell with a single keel and strong, paired ribbing that arises at the edge of the umbilicus and ends in a row of ventrolateral submarginal tubercles. ''(Chanasia)'', considered another subgenus, is characterized by a rapidly expanding, compressed, evolute shell with low broad ribbing on the outer flanks. ''Hecticoceras (Hecticoceroides)'', also from the lower Callovian, is like ''H. (Hecticoceras)'' except that it lacks a keel. ''H. (Lunuloceras)'', a third subgenus from the lower Callovian, has smooth inner whorls and sinuous ribbing on the outer whorls, but no tubercles. ''Hecticoceras (Kheraites)'' and ''H. (Sublunuloceras)'' are both known from the middle Callovian; ''H. (Kheraites)'' just from that interval, ''H. (Sublunuloceras)' into the lower Oxfordian (Upper Jurassic). ''(Kheraites)'' is strongly ribbed. ''(Sublunuloceras)'' has gentle sinuous ribbing and a single keel. ''Hecticoceras (Putealiceras)'' and ''H. (Brightia)'' from the upper Callovian differ in the detail of their ribbing. Ribbing in ''(Putealiceras)'' is generally straight and radial, bifurcating about mid flank and meeting at a distinct median keel on the venter. ''(Brightia)'' has large nodes on the inner half the whorl sides, and concavely curved ribs on the outer half. ''Hecticoceras (Pseudobrightia)'' from the lower Oxfordian is much like ''(Putealiceras)'' but tricarinate (three keeled). ''H. (Eochetoceras)'' from the same interval is stout whorled and unicarinate (single keeled), doubtfully distinct from ''(Putealiceras)''.

References

;Notes ;Bibliography * Arkell ''et al.'', 1957. Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology Part L. Geological Society of America and Univ. Kansas Press. {{Taxonbar, from=Q9286967 Haploceratoidea Ammonitida genera Late Jurassic ammonites Middle Jurassic ammonites Jurassic ammonites of Europe Callovian life Oxfordian life Callovian first appearances Late Jurassic extinctions