''Hecticoceras'' is an

ammonite Ammonoids are a group of extinct marine mollusc animals in the subclass Ammonoidea of the class Cephalopoda. These molluscs, commonly referred to as ammonites, are more closely related to living coleoids (i.e., octopuses, squid and cuttlefish) ...

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 and

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the name ...

, from the

Callovian In the geologic timescale, the Callovian is an age and stage in the Middle Jurassic, lasting between 166.1 ± 4.0 Ma (million years ago) and 163.5 ± 4.0 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 and stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian Age succeeds the Bajocian Age and precedes the Callovian Age. Strat ...

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