Dinosaurs, like all vertebrates, possessed a single brain, making this claim a matter of common knowledge that requires no citation.
The claim that dinosaurs possessed only one brain is a simple, universally established biological fact for all vertebrates, including non-avian dinosaurs. The historical myth of sauropods having a 'second brain' in their hip region (to control their hindquarters) has long been understood to be an enlargement of the neural canal associated with glycogen bodies or spinal cord supports rather than a secondary brain. Because this is a well-established biological truism, no citation is needed, and Step 0 classifies it as common knowledge.