4-565: See text 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 Pliensbachian stage in Europe, north Africa, Caucasus, Siberia, N. Alaska, Canada, Oregon, and possibly Honduras; and is the type for the Amaltheidae and
8-560: A member of the Eoderoceratoidea. Two subgenera are recognized. One, A.(Amaltheus) is already described. The other A. (Pseudoamaltheus) , sometimes expressed as genus, is a late derivative of ( Amaltheus ) with an early loss of keel and ribbing and an extreme development of strigation. This Ammonitina -related article is a stub . You can help Misplaced Pages by expanding it . Ammonitida Ammonitida or "True ammonites" are an order of ammonoid cephalopods that lived from
12-744: The Jurassic through Paleocene time periods, commonly with intricate ammonitic sutures . Ammonitida is divided into four suborders, the Phylloceratina , Lytoceratina , Ancyloceratina , and Ammonitina . The Phylloceratina is the ancestral stock, derived from the Ceratitida near the end of the Triassic . The Phylloceratina gave rise to the Lytoceratina near the beginning of the Jurassic which in turn gave rise to
16-673: The highly specialized Ancyloceratina near the end of the Jurassic. Both the Phylloceratina and Lytoceratina gave rise to various stocks combined in the Ammonitina. These four suborders are further divided into different stocks, comprising various families combined into superfamilies. Some like the Hildoceratoidea and Stephanoceratoidea are restricted to the Jurassic. Others like the Hoplitoidea and Acanthoceratoidea are known only from
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