How much does a stegosaurus brain weigh?
Stegosaurus had a brain that weighed about 2.8 oz, the same as a dog's brain. That is very small considering that the Stegosaurus was 30 feet long and weighed 5.5 tons. People often say that its brain was the size of a walnut or a pea, but that exaggerates its small size.
Stegosaurus had one of the smallest brain to body ratios of any animal known to have existed. Therefor, Ankylosaurus had a larger brain to body ratio. This does not necessarily mean that Stegosaurus were not as smart, however. The actual intelligence of an animal can not truly be determined by only fossils, because some animals are smarter than others that have larger brain to body ratios, although it is relatively rare.