Jurassic Period

Ornithischian Dinosaurs

Why were stegosaurs originally thought to have had a “second brain”?

The dinosaurs that made up the Stegosauria, such as Stegosaurus and Kentrosaurus, had extremely tiny brains. For example, the Stegosaurus, an animal that weighed approximately 1 to 2 tons (0.9 to 1.8 metric tons), had a brain only weighing 0.15 to 0.18 pounds (70 to 80 grams) and thought to be about the size of a walnut. Paleontologists also found an enlarged part of spinal cord in fossils of the stegosaur sacrum. This swelling, larger than the brain cavity, was originally thought to be a “second brain.” Currently, scientists believe this area is associated with nervous and connective tissue and fat, not a second brain.


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