The fossil record shows that members of the group of dinosaurs known as lambeosaurs had large bony crests on top of their heads. The shape of the crests varied from species to species, but all lambeosaur crests contained extended hollow passages. No one really knows exactly what function the crests served, but scientists have offered several theories.

Sense of smell

One theory holds that the primary purpose of the crests was to improve the dinosaurs' sense of smell. Examination of the fossils has suggested that the crests contained many blood vessels. The nose bones of modern animals with a highly developed sense of smell have a similar inner structure characterized by a high density of blood vessels. Thus, it is reasonable to conclude that the crests were primarily used to enhance the sense of smell.

Cooling

A second theory maintains that the crests served to prevent overheating by lowering lambeosaurs' body temperature. The addition of a crest had the effect of increasing the surface area of the lambeosaur's body, thereby allowing body heat to escape more rapidly. Other warm-climate dinosaurs, stegosaurs for example, also had bony crestlike plates on parts of their body that increased the body surface area. It has long been believed that the bony plates of stegosaurs were adaptations to improve cooling, so it seems likely that the crests of lambeosaurs served the same purpose.

Sound

A third possibility is that lambeosaurs used the crests to make sounds, perhaps for communication with other lambeosaurs. It was definitely possible to make low sounds by forcing air through the crests. This theory is supported by a finding suggesting that lambeosaurs had a good sense of hearing: paleontologists recently discovered remains of a lambeosaur that had a highly developed inner ear. A good sense of hearing would be necessary for animals communicating by sound.