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The ancestors of coleoids (including most modern cephalopods) and the ancestors of the modern nautilus, had diverged by the Floian Age of the Early Ordovician Period, over 470 million years ago. We know this because the orthocerids were the first known representatives of the neocephalopoda, [ 40 ] were ultimately the ancestors of ammonoids and ...
The ancestors of coleoids (including most modern cephalopods) and the ancestors of the modern nautilus, had diverged by the Floian Age of the Early Ordovician Period, over 470 million years ago. [ 145 ] [ 147 ] The Bactritida , a Devonian–Triassic group of orthocones, are widely held to be paraphyletic without the coleoids and ammonoids, that ...
The Reudemannoceratidae are the ancestral and most primitive of the Discosorida, an order of cephalopods from the early Paleozoic.The Reudemannoceratidae produced generally medium-sized endogastric and almost straight shells with the siphuncle slightly ventral from the center.
Orthoceratidae is an extinct family of actively mobile carnivorous cephalopods, subclass Nautiloidea, that lived in what would be North America, Europe, Asia, Africa, and Australia from the Ordovician through Triassic from 490—203.7 mya, existing for approximately
Plectronoceras is the earliest known shelled cephalopod, dating to the Late Cambrian. [ 1 ] [ 2 ] [ 3 ] None of the fossils are complete, and none show the apex or aperture of the shell. [ 3 ] Approximately half of its shell was filled with septa; 7 were recorded in a 2 centimetres (0.79 in) shell. [ 4 ]
Antarcticeras is an extinct genus of enigmatic cephalopod from the Eocene of Antarctica.It contains a single species, A. nordenskjoeldi.It is either considered the last of the "orthocone"-type cephalopods, the only member of its subclass Paracoleoidea & a descendant of the orthoceratids, and a remarkable example of convergent evolution with coleoid cephalopods, or an oegospid squid and a ...
Endoceratidae is a family of large to very large straight-shelled nautiloid cephalopods belonging to the order Endocerida that lived during the Middle and Late Ordovician. They include the largest known Paleozoic invertebrates, represented by Endoceras and Cameroceras .
The Cymatoceratidae is a family of Mesozoic and early Cenozoic nautiloid cephalopods and the most abundant of their kind in the Cretaceous. They are characterized by ribbed, generally involute shells of varied forms - coiled such that the outer whorl envelops the previous one, as with Nautilus, and sutures that are variably sinuous.