n. 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-1 in the Appendix of Indo-European roots + -DERM.] |
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