Eoderoceratidae is the ancestral and most primitive family of the

Eoderoceratoidea Eoderoceratoidea is a superfamily of true ammonites (suborder Ammonitina) from the Lower Jurassic, comprising seven phylogenetically related families, characterized in general by having ribbed evolute shells that commonly bear spines or tubercle ...

; lower Jurassic

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) ...

cephalopods, characterized by evolute, commonly serpenticonic, shells that had long body chambers and would have had no stable floating position; and thus resemble contemporary

Psiloceratoidea Psiloceratoidea is a superfamily of Early Jurassic ammonoid cephalopods proposed by Hyatt in 1867, assigned to the order Ammonitida. They were very successful during Hettangian and Sinemurian. Last of them, family Cymbitidae and genera '' Hypox ...

. Spines, or tubercles, are typically found in two rows on the inner and outer parts of the whorl sides, joined by radial ribs. These are often more developed on the inner and middle whorls, becoming less so or absent on the outer. Sutures are highly complex. The Eoderoceratidae can be divided into two subfamilies, the Xiphoceratinae which is the earliest and in which there is an early maximum development of spines of the inner whorls, and the Eoderoceratinae. Two other subfamilies were included in the Treatise 1957 but are now regarded as families in their own right, These are the Phricodoceratidae and Coeloceratidae Genera that have been attributed to the Xiphoceratinae are ''

Bifericeras ''Bifericeras'' is a Lower Jurassic ammonite belonging to the family Eoderoceratidae, and sometimes placed in the subfamily Xipherceratinae. Whorls are strongly depressed, but still evolute in coiling. The early growth state is prolonged, and sm ...

'', '' Microderoceras'', and '' Xiphoceras''. Those attributable to the Eoderoceratinae include '' Crucilobiceras'', '' Eoderoceras'', '' Neomicroderoceras'', and '' Promicroceras'' All can be regarded simply as eoderoceratids.

References

*Arkell ''et al.'', 1957. Mesozoic Ammonoidea, ''in'' Treatise on Invertebrate Paleontology, (Part L); Geological Soc. of America and University of Kansas press. *Donovan, D.T. Callomon and Howarth 1981 Classification of the Jurassic Ammonitina; Systematics Association

Ammonitida families Eoderoceratoidea Sinemurian first appearances Early Jurassic extinctions {{Ammonitina-stub