Animals

Scientists who are constantly studying dinosaurs have discovered the the larger dinosaurs’ hearing was sensitive to large noises rather then small ones, such as whistles. In fact they were given the ability to hear the footfalls of other dinosaurs from miles away.

But these massive reptiles may have had little or no hearing at higher sound frequencies, suggesting that the squeals of a smaller animal facing a Tyrannosaurus rex may have literally fallen upon deaf ears. The theory of how dinosaurs may have perceived sound comes from studies of hearing in birds, which are widely believed to be dinosaurs’ closest living relatives. “We know a lot about hearing in birds,” said acoustics researcher Robert Dooling of the University of Maryland, College Park.

“Big birds hear better at low frequencies, and small birds hear better at high frequencies.” Dooling’s latest work, in collaboration with two German scientists, suggests the relationship between size and hearing extends from tiny songbirds to the 75-ton (68-metric-ton) Brachiosaurus. That’s because the inner ear structure of all archosaurs, the group of related species that includes dinosaurs, birds, and crocodiles, is basically identical, the experts say.

“What makes this whole thing work is that the ears of dinosaurs and birds are all scale models of one another,” Dooling said. The scientist presented his team’s findings this week at the annual meeting of the Acoustical Society of America in Salt Lake City, Utah. The size of an auditory organ called the basilar papilla in the inner ear of birds is closely correlated with birds’ overall body size, Dooling said.

Knowing this, the researchers gave different bird species hearing tests by training them to peck at a key for a food reward in response to sound. From this the team established the sound frequencies at which birds hear best, and the high-frequency limit to their hearing. Comparing more than 30 bird species, Dooling’s team found a set of close correlations between basilar papilla length, frequency of optimal hearing, and the highest tone a species could detect.

Based on these relationships, the hearing capacity of most bird species can be accurately predicted from body size alone, Dooling said. German collaborators Otto Gleich of the University of Regensburg and Geoffrey A. Manley at the Technical University of Munich added to Dooling’s research. They used fossils to determine the average basilar papilla length of Archaeopteryx, a feathered reptile thought to be a prehistoric cousin to modern birds, along with those of two species of dinosaur.