Stegosaurus Had a Brain the Size of a Walnut Relative to Its Body
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.