Amaltheidae is a family of

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 ...

n ammonitids from the Lower Jurassic consisting of genera characterised by stigated discoidal oxycones—narrow involute shells with narrowly rounded to angular venters that bear a series of grooves, or ridges, along broad flanks, which according to the

Treatise A treatise is a formal and systematic written discourse on some subject, generally longer and treating it in greater depth than an essay, and more concerned with investigating or exposing the principles of the subject and its conclusions."Treat ...

L, 1957, evolved into strongly ribbed planulates (discoidal evolute shells) with quadrate whorls, typically with crenulated keels; involving all together four genera. Donovan in Donovan ''et al.'' (1981) retains the Amaltheidae in the sense of Arkell, ''et al.'' 1957, as shown in the

but synonymizes ''Pseudoamaltheus'' with ''

Amaltheus ''Amaltheus'' is an oxyconic ammonite with a fairly open umbilicus, serrated keel, and slightly sigmoidal ribs from the Lower Jurassic, many of which are strigate. ''Amaltheus'', named by de Montfort, 1808, is indicative of the upper Pliensba ...

'', (a subgenus in the Treatise), reducing the number of valid genera to three. These are ''

'', ''

Amauroceras ''Amauroceras'' is an extinct genus of eoderoceratacean 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 clos ...

'', and '' Pleuroceras''. ''

'' is oxyconic, keeled, strigated, and ribbed on the outer flanks. ''

'' is smooth, compressed, without ribs or stigation, and the keel is reduced. '' Pleuroceras'' has a planulate shell with a quadrate whorl section, bearing strong radial ribs ending in ventro-lateral tubercles. The venter is tabulate with a strong serrated keel. The Amaltheidae are derived from the Liparoceratidae and have a principally

boreal Boreal may refer to: Climatology and geography *Boreal (age), the first climatic phase of the Blytt-Sernander sequence of northern Europe, during the Holocene epoch *Boreal climate, a climate characterized by long winters and short, cool to mild ...

distribution. Amaltheidae timeline

References

;Notes ;Bibliography * Arkell ''et al.'', 1957. Mesozoic Ammonoidea.

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 ...

, Part L; Geological Society of America and University Kansas press. * Donovan, Collomon,& Howarth. Classification of the Jurassic Ammonitina, in The Ammonoidea, M.R. House and J.R. Senior (eds) Academic Press 1981. Systematics Association Special Volume. 18

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