Placodermi

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Antiarchi †

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Arthrodira †

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Petalichthyda †

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Phyllolepida †

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Ptyctodontida †

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Rhenanida †

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The Placodermi are armored prehistoric fishes known from fossils dating to the Devonian period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked. Placoderms were the first of the jawed fishes, their jaws evolving from the first of their gill arches.

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The first identifiable Placoderms evolved in the late Silurian; they disappeared in the Late Devonian extinctions. The first appearance of late Silurian placoderm fossils, in China, show the fishes already differentiated into antiarchs and arthrodires; apparently placoderm diversity originated long before the Devonian, though earlier fossils, of basal placodermi, have yet to be discovered.

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The earliest studies of placoderms were published by Louis Agassiz, in his five volumes on fossil fishes, 1833 &ndashh; 1843. The work of Dr. Erik Stensio, at the Swedish Museum of Natural History, Stockholm, from the late 1920s established the details of placoderm anatomy, and identified them as true jawed fishes related to sharks.

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Prehistoric fish: Prehistoric fish are various groups of fishes that lived before recorded history. A few, such as the coelacanth still exist today and are considered living fossils....

Devonian: Disambiguation: Devonian is also an adjective relating to the English county of Devon or the people there....

Silurian: The Silurian is a major division of the geologic timescale that extends from the end of the Ordovician period, about 443.7 million years ago (mega years ago, mya), to the beginning of the Devonian period, about 416.0 mya (ICS 2004). As with other geologic periods, the rock beds that define the perio...