U.S. scientists say a detailed map of a dinosaur brain suggests faculties for complex behavior, and possibly the ability to make sounds to communicate.

Soft tissues like brain matter are not preserved in fossils, but faint impressions left on the insides of fossilized skulls can yield "endocasts" giving clues of the size and shape of the outermost brain parts, they said.

To recreate a dinosaur brain, the researchers analyzed the brains of alligators -- which came from a lineage that predated many dinosaurs -- and those of birds, which evolved after the dinosaurs.

The dinosaur brain should have evolved to be somewhere in between, Duke University researcher Erich Jarvis said.

"In the popular mind, dinosaurs may be underrated in the complexity of their behavior," Jarvis told a meeting of the Society of Neuroscience in San Diego this week.

The analysis of alligator and bird brains allowed Jarvis and Duke colleague Chun-Chun Chen to piece together the innermost regions of the dinosaur brain, including six areas that are specialized for complex behavior such as processing visual information and learning and making sounds.

"It suggests that the dinosaur brain had the capacity for complex sensory motor processing, just like we see in birds and alligators," Jarvis said.

It also suggest dinosaurs had sufficient brain complexity to communicate with sounds, Jarvis said, although he acknowledged there is currently no evidence of a dinosaur that did this.

"But all the brain subdivisions to support vocal learning are there, so I'd argue the capacity to evolve vocal learning did exist in dinosaurs," he said.