Perhaps the most difficult part of dinosaurs’ make-up to study is their senses. Were they slow and stupid, or were they alert and intelligent? Delicate organs such as brains and nerves do not fossilize well, and the bones associated with the sense organs are difficult to interpret. For example, it is impossible to find out about a dinosaur’s senses of taste or smell – structures in the nasal cavities may be to do with either smelling or breathing. However, it is possible to make educated guesses about how a dinosaur sensory system would have worked.
In the Cretaceous, a very interesting group of dinosaurs, the hadrosaurs (“duckbilled dinosaurs”), used their skulls to communicate. It seems very likely that the duckbills had a good sense of hearing, because the skulls look as though they belonged to animals that made plenty of noise. Parasaurolophus had a crest that consisted of tubes connected to the nostrils. Scientists’ tests show that air blown through the crest would have made a noise like a trombone. Duckbills with no crests may have had a flap of skin over their broad beaks that was inflated to make a noise, like the throat-pouch of a bullfrog.
Some dinosaurs, particularly those with big eyes, had a ring of tiny bones inside the eye. This is called the sclerotic ring. Many modern birds have this. It helps to support the eye and also helps it to focus or pinpoint something it is looking at. Sea reptiles of the Mesozoic had heavy sclerotic rings to protect their eyes from the pressure of the water. Dinosaurs that had a sclerotic ring probably had very sharp eyesight.
Hunting animals like birds of prey and people can see in three dimensions. Look at an object with only one eye, then the other. The object’s position will appear to change slightly. A person’s brain, and that of a bird of prey, can compare the binocular (two-eyed) images and use them to work out how far away the object is – useful if the object is moving prey. Several of the hunting dinosaurs may have had this ability.
The most famous dinosaur with binocular vision is the turkey-sized carnivore Troodon. Its eyes pointed forwards, although not as much as those of a modern cat or bird of prey. It also had a big brain for a dinosaur – almost as big as the brain of a modern running bird such as an emu. This would not necessarily have meant that it was very intelligent, but it would have had enough brain power to process the three-dimensional images that it received from its binocular vision.
A herbivore such as a horse does not need binocular vision. It finds it more useful to have a wide view of everything around it – mainly so that it can see any danger coming while it is eating. That is why a horse’s eyes are on the side the head and not pointing forwards. It does not see in colour, but it can see the difference between light and shade.
The herbivorous dinosaurs, such as Triceratops, had eyes on the side of the head. This gave them peripheral vision (a very wide field of vision). Without moving their heads, they could scan the landscape for danger and see predators coming early enough to take defensive action.