''Fontannesia'' is an

ammonoid 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 ...

cephalopod

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

with a small to medium size, evolute, discoidal shell that was

extant Extant or Least-concern species, least concern is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Exta ...

during the

Jurassic Period The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately 143.1 Mya. The Jurassic constitutes the second and m ...

. The sides are ribbed, the venter has a single median keel, and tubercles are lacking. ''Fontannesia'' is included in the

Sonniniidae Sonniniidae is a diverse family of Middle Jurassic ammonites ranging from those with stout evolute shells to those whose shells are sharply rimmed, oxyconic. The keel, which runs along the middle of the venter, is typically hollow. Sutures vary f ...

(

Hildoceratoidea Hildoceratoidea, formerly Hildoceratacaea, is a superfamily of compressed or planulate ammonites, some tending to develop acute outer rims; generally with arcuate or sigmoidal ribs. Aptichus were found in place are double-valved.Arkell ''et al.' ...

) and has been found widespread in Europe, western Australia, Canada, and Argentina.

References

* Arkell ''et al.'', 1957., Mesozoic Ammonoidea, Treatise on Invertebrate Paleontology Part L, Ammonoiea. Geological Society of America and University of Kansas Press. Ammonitida genera Sonniniidae Jurassic ammonites Ammonites of Australia {{ammonitina-stub