So I built a stegosaurus model kit, which included some factoids in the instructions. One of these factoids was that stegosaurs are not believed to have had a secondary brain in the hips to help them control their rear half after all. That was wild to me, since the whole stegosaurs and sauropods with their tiny heads needing a secondary brain for their huge bodies was commonly accepted back when I was a kid. So I looked it up, and indeed, the current hypothesis is that the cavity that the second brain was thought to occupy is used for a thing called a glycogen body. But what exactly does a glycogen body do? We’ll get back to you on that, apparently.
When I was a kid I didn’t read about a “2nd brain” but a series of ganglions that acted like relays down the spine. Supposedly the belief was the size of dinosaurs made it impossible for nerve signals to reach the brain from distant parts of the body in a timely manner so they had these relays that made it easier to have reflex responses while the signal was being passed on to the brain.
i mean, that is true in so much as all animals have them, that’s precisely why reflexes happen before we even realize it
i’d imagine even the tiniest field mice work like this, because it’s something the first animals evolved and it’s highly useful regardless of how long it takes signals to reach the brain.
This was more than just simple reflexes though, like minibrains.