Definition of "ostracoderm" []

• Any of several groups of extinct primitive jawless fishes of the Ordovician through the Devonian periods in North America and Europe, having bodies that were encased in an armor of bony plates. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "The oldest fossil related to all modern vertebrates, the ostracoderm a jawless, bony-plated fish, dates to about 490 million years ago."
• "[[ostracoderm]] s jawless fish related to present-day [[lamprey]]"
• "[[ostracoderm]] s jawless fish related to present-day [[lamprey]] s and"