Big Dinos Heard Deep, Low Tones

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May 11, 2007 — The audio world of dinosaurs, especially larger species like T. rex, was deep and low, according to new research on hearing in archosaurs, a group that includes birds, crocodiles, alligators and the extinct dinosaurs.

The discovery reveals how similar the ear anatomical structure is among living birds, crocodilians and their distant dino relatives.

The findings, which will be presented in June at the Acoustical Society of America Meeting in Utah, also suggest that dinosaurs produced noises that were similar to the sounds they could hear.

"As a general rule, animals can hear the sounds that they produce," lead author Robert Dooling told Discovery News.

Dooling is a professor of psychology and co-director of the Center for the Comparative and Evolutionary Biology of Hearing at the University of Maryland at College Park. He conducted the comparative study on archosaur ear data with German neuroanatomists Otto Gleich and Geoffrey Manley.

In addition to gathering inner ear measurements for living animals, the team took these same measurements from fossil remains of brachiosaurus, allosaurus and archeoptryx.

The researchers found that an animal’s body mass is significantly correlated to the size of the individual’s internal ear structure, which in turn is linked to what that creature could hear.

This determination allowed the scientists to extrapolate the hearing of the smallest bird, which weighs just around a third of an ounce, to that of huge dinos like brachiosaurus, which weighed 75 tons.

Dooling and his team believe hearing in such large dinosaurs was restricted to low frequencies with a high frequency limit below 3 kilohertz.

Smaller dinosaurs, however, likely could hear and emit higher frequency sounds since, as Dooling explained, "large organisms (in general) hear best and produce sounds at lower frequencies, while smaller organisms hear best and produce sounds at higher frequencies."

He likened large dinosaur sounds and hearing to today’s very large mammals, such as elephants. Since elephants can hear the footsteps of other elephants over great distances, it is probable that "dinosaurs also could hear the footsteps of other dinosaurs."

Richard Fay, director of the Parmly Hearing Institute at Loyola University, told Discovery News that the team's findings make sense.

Fay adds, however, that it's possible dinosaurs were the "strong, silent type," since "vocalizations evolved to match hearing range, and not the other way around."

Both Fay and Dooling suggested there is even a human link to dinosaur hearing, since, like elephants, humans possess a very low frequency range, which becomes more evident with age.

"Interestingly, we sometimes irreverently refer to aging humans as dinosaurs," said Dooling. "In fact, as we humans age in the noisy environment in which we live, we begin to lose our hearing at high frequencies."

He added, "So, in a sense, our hearing becomes more like that of the dinosaurs."