4-523: The family Dactylioceratidae comprises Early Jurassic ammonite genera with ribbed and commonly tuberculate shells that resembled later Middle Jurassic stephanoceratids and Upper Jurassic perisphinctids . Shells may be either evolute or involute. Ammonites with evolute, serpenticone to cadicone shells with ribs, sometimes with tubercules. Members of this family had no keels. while homeomorphic with stephanoceratids and perisphinctids, they had unique shell structure with double shells and flat-topped ribs on
8-506: 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 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
12-815: 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 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
16-786: The inner shell. Based on suture differences, they are divided into 2 subfamilies. Reynesocoeloceratinae possess two major secondary lobes in dorsal side of external saddle. This saddle is not divided this way in Dactylioceratinae, while lateral lobe is deeply trifid. It has been suggested, that this family is polyphyletic, but this is now considered to be false. Reynesocoeloceratinae evolved in lower Pliensbachian from Metaderoceras and died out in upper Pliensbachian. Reynesoceras oldest member of Dactylioceratinae evolved in upper Pliensbachian from Cetonoceras , or Prodactylioceras . This subfamily died out in middle Toarcian , during Variabilis zone. This Ammonitina -related article
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