page_title: Dinosaur brains and intelligence
section_title: Stegosaurus
hierarchical_section_title: Dinosaur brains and intelligence / Stegosaurus
caption_attribution_description: Brain cavity of Stegosaurus stenops (holotype USNM 4934)[1] marked with red. Funded by the U.S. Geological Survey.
context_page_description: Dinosaur brains and intelligence are interesting topics. Dinosaurs were once regarded as stupid animals, but it is now realised that some of the smaller carnivores had above average intelligence for reptiles. This idea led to exaggerated portrayals in films like Jurassic Park.
context_section_description: The idea that Stegosaurus had a "brain the size of a walnut" (an oft-repeated phrase), was not quite accurate. It had a brain the size of a dog's, but in proportion to its body, the brain was very small. In the 1880s a well-preserved Stegosaurus braincase allowed Othniel Charles Marsh to get a cast of the brain cavity, which gave an idea of the brain size. The endocast showed that the brain was indeed small: relative to body size, maybe the smallest among the dinosaurs. The fact that an animal weighing over 4.5 metric tonnes (5 short tons) could have a brain of no more than 80 grams (2.8 oz) led to the idea that dinosaurs were unintelligent, an idea now largely rejected.
  Marsh also noted a large canal in the hip region of the spinal cord, which could have accommodated a structure up to 20 times larger than the famously small brain. This may have been used to coordinate the hind region in defence against theropod attack. This function for the "second brain" is not proved by any direct evidence.
caption: Brain cavity of S. stenops is in red
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