Any of various armored ornithiscian dinosaurs of the group Thyreophora from the Jurassic and Cretaceous Periods, bearing bony plates or spikes, and including the ankylosaurians and the stegosaurians.
[New Latin Thyreophora, taxon name, Greek thureos, oblong shield; see THYROID + Greek -phora, neuter pl. of -phoros, -phore.]
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
The American Heritage Dictionary Blog
Check out our blog, updated regularly, for new words and revised definitions, interesting images from the 5th edition, discussions of usage, and more.