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Howler Monkeys with Deeper Calls Have Smaller Balls

The smaller the testes in a howler monkey species, the larger the size of the animal's hyoid bone, which enables the monkeys to make booming calls.

Published On 10/27/2015
8:50 AM EDT
Hooting howler monkeys of the species Alouatta caraya make a racket. Howler monkey calls are as deep as those of much larger animals like tigers - a talent enabled by their enlarged hyoid bones. | Mariana Raño