One, and it's about the size of a walnut. Actually, scientists thought for a while the stegasaurus may have had a brain-like structure in it's tail. The expansion of the spinal column in the pelvis gave rise to the incorrect idea that dinosaurs had two brains. Yes, the size of a walnut!
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When it was found that there was a large cavity in the pelvic region of the spinal column, large enough to house 20 times the nerves that the brain had, scientists theorized that perhaps there was a secondary "brain" there. However, we now know that the cavity near the pelvis housed a glycogen body. Birds have a similar cavity, and its purpose is believed to be to supply glycogen to the nervous system. Thus, like all other vertebrates, Stegosaurus had only one brain.
Yes some of these prehistoric reptilians had 2 brains along with memory's and messages inside their microscopic or enormous brains, the pharasorolophus, stegosaurus, stegoceras, iguanadon, phaceycefolosaurus, miasauria and the edmontosaurus all had 2 brains one in the head and one just below the spine. All of the dinosaurs that had 2 brains were herbivores.
No vertebrates have more than one brain. That includes Brontosaurus, which only had one brain.
No vertebrates, including Brontosaurus, have or have ever had two brains.
BTW: Brontosaurus is an invalid name for Apatosaurus excelsus.
Yes they do, they do have two brains, one of the brains is in the head like regular animals, and the other brain is in the stegosauruses stomach near the hip or leg.