''Harpoceras'' is an extinct 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) ...

belonging to the family

Hildoceratidae Hildoceratidae is a family of ammonoid cephalopods from the Lower Jurassic, lower Pliensbachian (''Jamesoni'' zone) to lower Bajocian (maybe even upper Bajocian) substages, generally with strongly ribbed, involute shells. They are combined with ...

. These

cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

s existed 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 ...

period, 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 ...

age from the Falciferum zone to the Commune subzone of the Bifrons zone.Sepkoski, Jac
Sepkoski's Online Genus Database – Cephalopoda
/ref> They were fast-moving nektonic carnivores.Paleobiology Database - Harpoceras
2017-10-16. Harpoceras NT

Description

Shells of ''Harpoceras'' species show strong dimorphism in their size. While microconchs reach 24–51 mm in diameter, macroconchs shells width is 115–430 mm. They are moderately evolute to involute and compressed. Whorl sides are flat and there is strong keel. Ribs are falcoid or falcate and thus biconcave, strong and projected. Sometimes, ribs can be broad and flat topped on outer part of whorl and in some species they can be striate on inner part of whorl. Some species have midlateral groove, or series of undulating depressions on inner half of whorl.

Distribution

Fossils of species within this genus have been found in the Lower Jurassic rocks of Europe, Northern Africa, Russia, Japan, Borneo, New Zealand, Indonesia, North and South America (Argentina; El Cholo and

Los Molles Formation The Los Molles Formation is a geologic formation of Early to Middle Jurassic age, located at northern and central part of Neuquén Basin at Mendoza Shelf in Argentina. It is overlain by the Niyeu–Lajas Formation.McIlroy et al., 2005 Descrip ...

s). Two species, ''Harpoceras serpentinum'' and ''Harpoceras falciferum'', are index fossils used for stratigraphic correlation and dating of rocks of the

stage of the Lower Jurassic.

References

Hildoceratidae Ammonitida genera Toarcian life Early Jurassic ammonites of Europe Jurassic Germany Fossils of Germany Posidonia Shale Early Jurassic ammonites of North America Early Jurassic ammonites of South America Jurassic Argentina Fossils of Argentina Neuquén Basin Early Jurassic ammonites of Asia Early Jurassic ammonites of Africa Fossil taxa described in 1869 {{Ammonitina-stub