There’s no shortage of dinosaur myths. Paleontologist Dave Hone recently compiled a list of eight persistent falsehoods over at the Guardian–from the misapprehension that all dinosaurs were huge to the untenable idea that Tyrannosaurus could only scavenge its meals–but there was one particular misunderstanding that caught my attention. For decades, popular articles and books claimed that the armor-plated Stegosaurus and the biggest of the sauropod dinosaurs had second brains in their rumps. These dinosaurs, it was said, could reason “a posteriori” thanks to the extra mass of tissue. It was a cute idea, but a totally wrong hypothesis that actually underscores a different dinosaur mystery.
I remember in early elementary school, I was taught that all dinosaurs may have had second brain at the end of their tails. That was way off. I was too young to realize my teacher didn't have an amazing understanding of all topics. I never bought into the "second brain" idea, but from what I gather now, we don't really know much more than professor Marsh. There's a "distinct cavity" in Stegosaurus and sauropods and we don't really know what it was for. Marsh found this in Camarasaurus and basically made a good guess as to what it was. Not necessarily a second brain, but some sort of neural booster pack. That could make sense. We're talking about fauna from the mid Jurassic, who really knows what it could be. All we have are guesses.
Also, paleontologist Jack Horner makes some pretty valid points about Tyrannosaurus rex being a scavenger.