Stegosaurus Had Two Brains? The Mystery of the Huge Canal in Stegosaurus' Hip

 

Image comparing Stegosauria pelvis to that of the Theropoda

For the longest time believe it or not, scientists thought stegosaurs had a second brain. Yes, you heard me right, a second brain. 

Stegosaurus, otherwise known as the "roof-lizard", were a species of herbivorous quadrupedal dinosaurs, that existed during the Late Jurassic. Most commonly known for their eye-grabbing plates placed on their back, and their spiky thagomizer attached to their tails, the stegosaur used all these alien features to help protect themselves, display affection and even regulate their own body temperature! 

Around 80 individual remains have been found of stegosaurus as of today. Along with the huge, spiked tail and thin thermoregulating plates, one more feature about the stegosaurus' body structure stumped many scientists in the past. That being, the abnormally large canal located in the pelvis of the stegosaur and many neighboring Genuses such as Camarasaurus.

Image of a complete Camarasaurus skeleton

The misconception all started when Yale paleontologist, Othniel Charles Marsh, was examining the remains of Sauropods and the Stegosauria in the late 19th century. He quickly noticed a large gap in the dinosaurs' pelvis which connected to the vertebrate of their spines. The cavity was significantly larger than that of the dinosaurs' brains which led Marsh to believe that maybe the crevice served as a slot for a "second brain". 

Yes, once again you heard me right, his only proof was that the gap he had discovered, was larger than that of the cavity that held the dinosaurs' brains, crazy right? Well, compared to other dinosaur skeletons at the time, a second brain didn't seem all that far off. 

For starters, Sauropods and Stegosauria had extremely small brain sizes compared to that of the rest of their body. To put it in perspective, Stegosaurus had a body roughly around the size of a bus, 30 feet long and 14 feet tall, with a brain the size of a mere peanut. For Sauropods, the difference was much larger. Their large size also meant a second brain could help with the stability and coordination needed to support their posterior. 

Suddenly, the absurd thought might make a little sense to you now. However, after later studies and findings it was concluded that NO DINOSAUR EVER DISCOVERED HAD A SECOND BRAIN! Even in some modern species today, it is not all that rare to see large gaps in the skeletons of organisms around their spine cord. Usually, these areas are packed with a hoard of neural tissue often utilized to carry out important functions such as the frequent movement of limbs.

So, what even is the cavity for? After the explanation I just gave, you might think, the storage of neural tissue used to aid in movement. But once again, this theory is wrong. 

The structure of the canal was not all that similar to the cavities in other animals or dinosaurs, filled with neural tissue. It was a great deal wider and much more open, suggesting that not only neural tissue filled that area. It had to have contained something else, or maybe even just that substance. 

The truth is as of today, it is not entirely proven what substance filled that gap. However, not all hope is lost. Leading theories from many scientists including some Sauropod experts, claims the gap most likely stored vital energy needed for survival, such as glycogen. 

After comparing many existing animals' hip structures, the Sauropod and Stegosauria pelvis most closely resembles those of modern-day birds. Ahhh, that makes so much sense now, after all, birds are dinosaurs. Sorry to break the news, even though the hip gap of birds contains these glycogen-rich deposits, we don't really know the use of them. Meaning we have little to know clue of what a glycogen storage would serve as in a sauropod or stegosaurus, or any dinosaur in fact. 

Maybe you might be the next paleontologist to discover what this gap was really used for.

Further information can be found in the sources, The Double Dinosaur Brain Myth and The Complete Dinosaur, authored by Michael K. Brett-Surman.