Many lizards can hear well, but there are also species that have no hearing at all. They perceive sounds only through the vibrations from the ground, pressing their whole body against the ground to do so. The development of hearing depends on the location of the eardrum. In some lizards it lies open on the sides of the head, in others it is hidden under the scales, while in others it is covered with skin or even reduced together with the tympanic cavity.
All vertebrates and even some insects have the ability to hear. It is not necessary to have well-developed hearing to perceive sound vibrations.
Lizards and salamanders hear with their lungs
A team of American scientists led by Professor Thomas Hetherington of Ohio University discovered that hearing-impaired frogs use their lungs to perceive sounds. Now, studying four species of salamanders and three species of lizards, Hetherington has found that their lungs also help them hear. Both salamanders and lizards have an inner ear that can process sounds. Als transmit signals to neurons, but salamanders lack an outer and middle ear.
In the experiments, the animals were placed in an isolated chamber where a loudspeaker played sounds of different frequencies. The sound caused the animal’s chest to vibrate, and the air that filled the lungs carried those vibrations to the inner ear. To measure skin movements during tones of different frequencies, a laser beam was aimed at the animals’ chests. The laser beam served as a highly sensitive detector. Skin vibrations were most pronounced at low frequencies: in small newts (genus Salamander).
The peak amplitude of movement was in the range of:
- 1600 to 2500 hertz
- in larger salamanders 1250 to 1600 hertz
- and in lizards 1000 to 2000 hertz
Lizards have a middle ear where the hammers are located, and the skin in this area vibrates at frequencies of 2000 to 3000 hertz.
Sound can enter the body in a variety of ways, but the lungs are most sensitive to sound waves. Apparently, the lungs are important as a hearing organ for animals that do not have medium-sized ears, especially small amphibians and reptiles. Their lungs have thin, muscular walls that are more sensitive to sound and can absorb a wider range of frequencies.