Hecticoceras
Encyclopedia
Hecticoceras is an ammonite
genus belonging to the haploceratacean
family Oppeliidae
, that lived during the Middle
and Late Jurassic
, from the early Callovian
to the early Oxfordian. 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 and Prohecticoceras from the underlying Bathonian
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.
H. (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.
H. (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.
H. (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.
H. (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.
H. (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).
Ammonite
Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct subclass within the Molluscan class Cephalopoda which are more closely related to living coleoids Ammonite, as a zoological or paleontological term, refers to any member of the Ammonoidea an extinct...
genus belonging to the haploceratacean
Haplocerataceae
Haplocerataceae is a superfamily of ammonoid cephalopods belonging to the Ammonitida that unites three families, the Strigoceratidae, Oppeliidae, and Haploceratidae, listed below....
family Oppeliidae
Oppeliidae
Oppeliidae are compressed to oxyconic, sculptured Haplocerataceae, either unkeeled, unicarinate, bicarinate, or tricarinate; with sutures in great variety, but ribbing usually more or less falcoid or falcate...
, that lived during the Middle
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....
and Late Jurassic
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
, from the early Callovian
Callovian
In the geologic timescale, the Callovian is an age or stage in the Middle Jurassic, lasting between 164.7 ± 4.0 Ma and 161.2 ± 4.0 Ma. It is the last stage of the Middle Jurassic, following the Bathonian and preceding the Oxfordian....
to the early Oxfordian. 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 and Prohecticoceras from the underlying Bathonian
Bathonian
In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 167.7 Ma to around 164.7 Ma...
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)
- H. (Hecticoceroides)
- H. (Lunuloceras)
- H. (Sublunuloceras)
- H. (Kheraites)
- H. (Putealiceras)
- H. (Brightia)
- H. (Pseudobrightia)
- H. (Eochetoceras)
H. (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.H. (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.
H. (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.
H. (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.
H. (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).