[ păk′ĭ-sĕf′ə-lə-sôr′əs ]
A large herbivorous dinosaur of the genus Pachycephalosaurus of the late Cretaceous Period. It grew to about 7.6 m (25 ft) long and had a domed skull up to 25.4 cm (10 inches) thick that was lined with small bumps and spikes. The thick skull may have been used for head-butting during mating displays.
The American Heritage® Science Dictionary Copyright © 2011. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.