''Hammatoceras'' is a genus of
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) ...
s belonging to the family
Hammatoceratidae
Hammatoceratidae is a family of lower and middle Jurassic ammonites included in the superfamily Hildoceratoidea.
Diagnosis
Hammatoceratidae comprises genera which are characterized by ribbed evolute shells (all whorls visible), some bearing keel ...
which lived during the
Toarcian
The Toarcian is, in the ICS' geologic timescale, an age and stage in the Early or Lower Jurassic. It spans the time between 182.7 Ma (million years ago) and 174.1 Ma. It follows the Pliensbachian and is followed by the Aalenian.
The Toarcian ...
stage of the Early/Lower
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 ...
between about 184 and 175 million year ago.
Taxonomy
''Hammatoceras'' is included in the subfamily Hammatoceratinae, which in the outdated 1957
Treatise on Invertebrate Paleontology
The ''Treatise on Invertebrate Paleontology'' (or ''TIP'') published by the Geological Society of America and the University of Kansas Press, is a definitive multi-authored work of some 50 volumes, written by more than 300 paleontologists, and co ...
was part of the Hammatoceratidae, but of the Phymatoceratidae in D.T. Donovan ''et al.'', 1981, a case of what to base the family name on. Both accordingly contain the earlier Phytmatoceratinae and derived Hammatoceratinae. The superfamily Hammatoceratoidea in which the Hammatocaratidae and related families are currently placed is abandoned in favor of the older, equivalent, Hildoceratoidea. (M. K. Howarth. 2013)
Species
Species within this genus include:
*?''Hammatoceras gabillyi''
Martinez, 1992
*''Hammatoceras insigne''
Schubler, 1831
*?''Hammatoceras costatum''
(Gabilly, 1973)
*''Hammatoceras pachu''
Buckman, 1921
*''Hammatoceras clausum''
Gabilly, 1973 WMSDB – Worldwide Mollusc Species Database
/ref>
*''Hammatoceras semilunatum'' Quenstedt, 1885
*''Hammatoceras roubanense'' Elmi, 1998
*''Hammatoceras bonarellii'' Parisch & Viale, 1906
*''Hammatoceras subplanatum'' De Brun, 1932
*''Hammatoceras speciosum'' Janensch, 1902
Fossil record
This genus is known in the fossil record in the Middle Jurassic, from 175.6 million years ago to about 171.6 million years ago. Fossil shells within this genus have been found in Canada, France, Germany, Hungary, Indonesia, Italy, Spain, Tunisia and the United Kingdom.[
]
Description
The shell of ''Hammatoceras'' varies from evolute to sub-involute, according to species and growth stage. All are compressed, i.e. discoidal, in form, with strong ribbing and a keeled ventor. Ribs arise from tubercles on the umbilical shoulder, the inner, dorso-lateral margin of the whorls, and bifurcate on the flanks, stopping at the ventral keel. Juvenile forms tend to be more evolute with more of the inner whorls showing, whereas mature forms tend to be more involute with outer whorls more strongly embracing.
References
* W.J, Arkell''et al.'', 1957. Mosozoic Ammonoidea. Treatise on Invertebrate Paleontology, Part L. Geological Society of America and University of Kansas Press.
* D.T.Donovan, J.H. Callomon, & M.K. Howarth, 1981. Classification of the Jurassic Ammonitina. The Ammonoidea, Systematics Association Special Volume no 18.
* Classification of Howarth 201
from M. K. Howarth. 2013.
* Treatise on Invertebrate Paleontology, Part L, Revised, Volume 3B, Chapter 4: Psiloceratoidea, Eoderoceratoidea, Hildoceratoidea.
{{Taxonbar, from=Q9285799
Early Jurassic ammonites of Europe
Ammonitida genera
Jurassic ammonites
Toarcian life
Hammatoceratidae