Nautilida

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(after Kummel 1953).]]
(after Kummel 1953).]]
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The Nautilida have a rich and complex evolutionary history. The details of [[taxonomy]] and [[phylogenetics]] remain obscure, but the general pattern is clear. This [[clade]], the last of the major groups of [[Palcephalopoda]] to evolve, are also the most successful. The following account is by Teichert (1988):
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The Nautilida have a rich and complex evolutionary history. The details of [[taxonomy]] and [[phylogenetics]] remain obscure, but the general pattern is clear. This [[clade]], the last of the major groups of [[Nautiloidea|Palcephalopoda]] to evolve, are also the most successful. The following account is by Teichert (1988):
:From modest beginnings in the Lower Devonian (Teichert ''et al.'', 1979), the number of genera increased from 1 or 2 in the [[Gedinnian]] to at least a dozen in the [[Enisian]] and about 22 in the Middle Devonian. After a decline in the Late Devonian, with only 3 genera recorded, the order rose to great prominence in the Carboniferous, when some 75 genera and subgenera in some 16 families are known (Shimanskiy, 1967, with additions). After the Carboniferous we witness a steady decline of the order to about 55 genera in 10 or 12 families in the [[Permian]], and about 35 genera in 8 families in the Triassic. Interestingly, the nautilids were much less affected by the great wave of extinctions at the end of the Permian than the contemporary [[ammonoidea|ammonoids]]: 3 families and at least 4 possibly 8 genera of nautilids passed from the Permian into the Triassic. Beginning in the Triassic, morphological differentiation of the order declined to a severe setback in the Late Triassic, when, just as today, only one genus, ''[[Cenoceras]]'' (above), survived (Kummel, 1953). This was followed by a slight recovery in the Late [[Jurassic]] and, especially, Cretaceous with 24 genera (Shimanskiy, 1975; Whetstone and Teichert, 1978), and a final decline during the [[Cenozoic]], at the end of which the order is reduced to a single genus ''Nautilus''.
:From modest beginnings in the Lower Devonian (Teichert ''et al.'', 1979), the number of genera increased from 1 or 2 in the [[Gedinnian]] to at least a dozen in the [[Enisian]] and about 22 in the Middle Devonian. After a decline in the Late Devonian, with only 3 genera recorded, the order rose to great prominence in the Carboniferous, when some 75 genera and subgenera in some 16 families are known (Shimanskiy, 1967, with additions). After the Carboniferous we witness a steady decline of the order to about 55 genera in 10 or 12 families in the [[Permian]], and about 35 genera in 8 families in the Triassic. Interestingly, the nautilids were much less affected by the great wave of extinctions at the end of the Permian than the contemporary [[ammonoidea|ammonoids]]: 3 families and at least 4 possibly 8 genera of nautilids passed from the Permian into the Triassic. Beginning in the Triassic, morphological differentiation of the order declined to a severe setback in the Late Triassic, when, just as today, only one genus, ''[[Cenoceras]]'' (above), survived (Kummel, 1953). This was followed by a slight recovery in the Late [[Jurassic]] and, especially, Cretaceous with 24 genera (Shimanskiy, 1975; Whetstone and Teichert, 1978), and a final decline during the [[Cenozoic]], at the end of which the order is reduced to a single genus ''Nautilus''.

Revision as of 23:50, 8 December 2011

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