Stegosaurus (“plated lizard”), which lived about 150 million years ago, had a brain weighing only 2.5 oz. – 0.00002% of its computed body weight of 3.25 tons. This compares with a percentage of 0.0006 for an elephant and 1.88 for a human. It is possible that the brains of some sauropods were proportionately even smaller. The picture is from the movie The Lost Word: Jurassic Park (USA, 1997).