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.
The whole peripheral nervous system makes decisions without adult supervision from the brain all the time. I’d consider that to be a sort of distributed second brain in a way