7-677: Amaltheidae is a family of eoderoceratoidean 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 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
14-483: 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 tubercles. Adult shell size ranges from 2 or 3 cm to giants reaching 50 cm in such genera as Apoderoceras , Epideroceras , and Liparoceras . The earliest known eodoceroceratoidean
21-515: Is the eoderoceratid genus Microderoceras . Although its origin is uncertain, it is likely that it is derived from the Psiloceratoidea . It has also been proposed, with some imagination, that Microderoceas has its origin some earlier Jurassic lytoceratid such as Analytoceras . Seven families are included, beginning with the Eoceroceratidae, which gave rise at about the same time to
28-532: The Amaltheidae in the sense of Arkell, et al. 1957, as shown in the Treatise but synonymizes Pseudoamaltheus with Amaltheus , (a subgenus in the Treatise), reducing the number of valid genera to three. These are Amaltheus , Amauroceras , and Pleuroceras . Amaltheus is oxyconic, keeled, strigated, and ribbed on the outer flanks. Amauroceras is smooth, compressed, without ribs or stigation, and
35-745: The Phricodoceratidae, Coeloceratidae, Liparoceratidae, and Polyhmorphitidae. The Phricodoceratidae left no descendants but the Coeloceratidae later gave rise to the Dactylioceratidae and the Liparoceratidae to the Amaltheidae. The Polymorphitidae became the source for the superfamilies Hildocerataceae beginning with the Hildoceratidae. The more recent taxonomy of Donovan et al. (1981) with seven families, differs from that of Arkell, et al. in
42-633: The Treatise (1957) which included just five families. The phricodoceratids and coeoloceratids were then considered as subfamilies (Phricodoceratinae and Coeloceratinae, respectively) of the Eoderoceratidae. As later (1981) the Liparoceratidae and Polyhmorphitidae were derived from the Eoderoceratidae but the Dactylioceratidae were derived separately (1957) from the Lytoceratidae - a source since then largely rejected. This Ammonitina -related article
49-510: 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 distribution. This Ammonitina -related article is a stub . You can help Misplaced Pages by expanding it . Eoderoceratoidea Eoderoceratoidea
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