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Any of various extinct jawed fishes of the group Placodermi of the Silurian and Devonian Periods, having bony plates of armor covering the head and thorax. Placoderms were among the first jawed vertebrates.

[New Latin Placodermī, class name : Greek plax, plak-, flat stone, plate; see plāk- in Indo-European roots + -derm.]
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.


(Palaeontology) any extinct bony-plated fishlike vertebrate of the class Placodermi, of Silurian to Permian times: thought to have been the earliest vertebrates with jaws
[C19: from Greek plac-, plax a flat plate + -derm]
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014


(ˈplæk əˌdɜrm)

any of various extinct jawed fishes of the class Placodermi, chiefly of the Devonian Period: many were armored in bony plates.
[1855–60; < New Latin Placodermi name of the class, pl. of placodermus=placo- (< Greek; see placoid, -o-) + -dermus -derm]
Random House Kernerman Webster's College Dictionary, © 2010 K Dictionaries Ltd. Copyright 2005, 1997, 1991 by Random House, Inc. All rights reserved.
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.placoderm - fish-like vertebrate with bony plates on head and upper body; dominant in seas and rivers during the Devonian; considered the earliest vertebrate with jaws
aquatic vertebrate - animal living wholly or chiefly in or on water
class Placodermi, Placodermi - extinct group of bony-plated fishes with primitive jaws
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References in periodicals archive ?
Among the major algal groups inhabiting the bromeliad phytotelmata are the desmids, especially Cosmarium Corda ex Ralfs considered the largest desmid genus in terms of number of species (over 2,000), and one of the oldest names among the placoderm desmids (Prescott et al., 1981; Sophia et al., 2004; Bicudo and Menezes, 2017; Brook and Johnson, 2011).
Antiarchs (Placoderm fishes) from the Devonian Aztec Siltstone, Southern Victoria Land, Antarctica.
Churchill-Dickson (2007) reviewed vertebrate records from the Silurian--Devonian of Maine, noting Silurian records of 'fish teeth' (probably conodonts) from the Edmunds Formation and acanthodian spines from the Ames Knob Formation, as well as Devonian placoderm remains ('Asterolepis') from the Chapman Sandstone.
Along with a different placoderm fossil found in 2013, the new find, named Qilinyu rostrata, is helping rewrite the story of early vertebrate evolution, says paleontologist John Maisey of the American Museum of Natural History in New York City.
Matt Friedman, a paleobiologist at Oxford University, said: "If you look at just the top of the skull and the body, it looks like a placoderm.
The scientists studied the skull of Romundina, an early armoured fish with jaws, or placoderm, from arctic Canada.
These morphological transitions, they note, are concomitant with radiations of shell-crushing placoderm and chondrichthyan fish.
Psammosteid heterostracans (Pteraspidomorpha) predominate in number among species-level taxa, but the specimens of antiarch placoderm remains are most numerous.
They were interpreted as the result of placoderm fish dragging or pushing off the sediment.
Qilinyu and Entelognathus - another placoderm from the same period found in 2013 in the same region - exhibit the first instance of distinct maxillary, premaxillary and dentary bones.