Modern-day animals make extensive use of sounds in their interactions with others. Some so...

Modern-day animals make extensive use of sounds in their interactions with others. Some sounds are meant primarily for members of the same species, like the cooing calls of a pair of doves, the long-range infrasoimd communication between elephants, or the songs of the hump-backed whale. Other sounds may be used as a threat to other species, such as the Tattle of a rattlesnake or the roar of a lion.

There is little doubt that extinct animals used sounds in much the same ways. But how can we ever hear the call of a long-vanished animal like a dinosaur when sounds don’t fossilize? In some cases, basic physics may have the answer.

Consider, for example, the long-crested, duck-billed dinosaur Parasaurohplus walkeri, which roamed the Earth 75 million years ago. This dinosaur possessed the largest crest of any duck bill—so long, in fact, that there was a notch in P. walker’s spine to make room for the crest when its head was tilted backward. Many paleontologists believe the air passages in the dinosaur’s crest acted like bent organ pipes open at both ends, and that they produced sounds P. walkeri used to communicate with others of its kind. As air was forced through the passages, the predominant sound they produced would be the fundamental standing wave, with a small admixture of higher harmonics as well. The frequencies of these standing waves can be determined with basic physical principles. Figure 14-43 presents a plot of the lowest ten harmonics of a pipe that is open at both ends as a function of the length of the pipe.

The long crest of Parosaurolophus walkari played a key role in its communications with others.

FIGURE 14-41 Standing wave frequencies as a function of length for a pipe open at both ends. The first ten harmonics (n = 1-10) are shown.

Paleontologists believe the crest of a female P. walkeri was probably shorter than the crest of a male. If tills was the case would the fundamental frequency of a female be greater than less than, or equal to the fundamental frequency of a male?