Stegosaurus had a second brain located in its hip or rear, in addition to its head brain.
Stegosaurus had only one brain, located in its skull. However, the sacral plexus (a cluster of nerve tissue in the hip region) was unusually large, leading some early paleontologists to speculate about a 'second brain.' This hypothesis was thoroughly debunked by the mid-20th century. The sacral plexus, common in large dinosaurs, controlled the hind limbs and tail but was not a true brain. Modern paleontological understanding confirms that all dinosaurs had centralized brains in their skulls.