The idea that any dinosaur possessed two brains is a misconception, often encountered in popular culture. This notion stems from early misinterpretations of their anatomical features, providing insight into the neurological structures of these ancient creatures.
The Stegosaurus Misconception
The “two-brained” myth is most famously associated with the Stegosaurus, a large, herbivorous dinosaur known for its distinctive plates and tail spikes. This misconception originated in the 1870s when paleontologist Othniel Charles Marsh identified an unusually large neural canal in the pelvic region of the Stegosaurus’s spinal cord. This cavity was significantly larger than the space occupied by the brain in its skull. Early scientists, puzzled by how such a massive animal could function with a relatively small brain, speculated that this pelvic enlargement housed a “second brain” to help control its hind limbs and tail.
However, this interpretation was later disproven. Modern understanding reveals this substantial pelvic cavity did not contain a second brain, but likely held a neural ganglion, a concentration of nerve cells. This ganglion aided in coordinating the complex movements of the large hindquarters, legs, and powerful tail, which was equipped with spikes for defense. Similar, though less pronounced, enlargements of the spinal cord are found in many vertebrates, including humans, facilitating limb innervation. The idea of a “sacral brain” was abandoned by scientists not long after its proposition, but it persisted in popular media.
Beyond the Myth: Dinosaur Brains
While the “two brains” theory is incorrect, it prompts a closer look at what scientists know about dinosaur brains. Dinosaur brains were generally small in proportion to their large body sizes, especially in immense herbivores like sauropods. For instance, a Stegosaurus’s brain was roughly the size of a dog’s or a lemon, despite the animal weighing many tons. This contrasts with mammals and birds, which typically have larger brains relative to their body mass.
The study of dinosaur brains relies on examining endocasts, molds of the brain cavity within fossilized skulls. These endocasts provide insights into the size and shape of different brain regions, indicating the development of senses like smell or vision. Dinosaur nervous systems were complex enough to manage their massive bodies and behaviors. Neural ganglia, like the one in Stegosaurus’s pelvis, were common and coordinated localized functions, such as limb movement or tail control, without being centers of complex thought.
Recent research suggests that while dinosaurs were not as intelligent as primates, some theropods, like Tyrannosaurus rex, had more complex brain structures than previously thought, with capabilities for sensory-motor processing similar to modern birds and alligators. The overall intelligence of dinosaurs varied widely depending on the species and its lifestyle, with predatory dinosaurs generally exhibiting larger brains relative to their body size compared to herbivores. The “two-brained” dinosaur myth highlights the scientific journey to understand the neurology of these ancient animals.