Nautiloid: Difference between revisions
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Revision as of 13:33, 16 November 2012
| Nautiloids Temporal range: Upper Cambrian 495 mya – Recent
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|---|---|
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| Orthoceras | |
| Scientific classification | |
| Kingdom: | Animalia
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| Phylum: | Mollusca
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| Class: | Cephalopoda
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| Subclass: | Nautiloidea
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Nautiloids are a large and diverse group of marine cephalopods (Mollusca) belonging to the subclass Nautiloidea. They began in the later Cambrian, and are represented today by the living Nautilus.
Nautiloids flourished during the early Paleozoic era, when they were the main predatory animals. They developed an extraordinary ramge of shell shapes and forms. Some 2,500 species of fossil nautiloids are known, though only a few species survive today.[1]
Taxonomic relationships
Nautiloids are among the group of animals known as cephalopods, an advanced class of molluscs which also includes ammonoids, Belemnites and modern coleoids such as octopus and squid. Other molluscs include gastropods, scaphopods and pelecypods.
Traditionally, the most common classification of the cephalopods has been a three-fold division (by Bather, 1888), into the nautiloids, ammonoids, and coleoids. This article is about nautiloids in that broad sense, sometimes called Nautiloidea sensu lato.
Cladistically speaking, nautiloids are a paraphyletic assemblage united by shared primitive (plesiomorphic) features not found in derived cephalopods. In other words, they are a evolutionary grade that is thought to have given rise to both ammonoids and coleoids. They are defined by the exclusion of both those descendent groups. Both ammonoids and coleoids have traditionally been assumed to have descended from bactritids, which in turn arose from straight-shelled orthocerid nautiloids.[1]
The ammonoids (a group which includes the ammonites and the goniatites) are extinct cousins of the nautiloids which evolved early in the Devonian, some 400 million years ago.