Herbivores

Pachycephalosaurus wielded a dome-shaped skull up to 25 centimetres thick, made of solid bone. Debate continues about whether it used this for head-butting rivals (like bighorn sheep) or flank-butting. Analysis of bone texture reveals healed lesions consistent with high-impact head-to-head contact. Some researchers suggest the domes also served as species and sex recognition signals, as they varied greatly in size and shape between individuals.

Triceratops was one of the last non-avian dinosaurs to roam Earth before the mass extinction. It had a battery of up to 800 teeth arranged in stacks, constantly being replaced as old ones wore down from chewing tough vegetation — similar to shark teeth. Its three horns and large frill were likely used for both species recognition and combat, as fossilised skulls show healed puncture wounds from horn-to-horn fighting.

Stegosaurus measured about 9 metres long and weighed 2–4 tonnes, but its brain weighed only around 80 grams — roughly the size of a walnut. This gives it one of the lowest brain-to-body ratios of any known dinosaur. The iconic plates along its back were likely used for thermoregulation and species recognition rather than defence, and its spiked tail (thagomizer) was a formidable weapon.