Why can some cats roar while others can’t?
There are actually only four well-known living species of cat that can roar: the lion, tiger, jaguar and leopard. This comprises about half the Pantherinae subfamily–the big (roaring) cats.
Up to the present time, the accepted theory was that the ridgity or flexibility of the hyoid bone (a U-shaped bone in the throat suspended above the larynx) was the main determining factor on whether or not a cat could roar. This was because each of the four roaring cats have a flexible segment in their hyoid bone. And, non-roaring species (cheetahs, clouded leopards and all small cats) have inflexible, fully-ossified hyoid bones. However, this theory was subsequently shot down due to the fact that snow leopards have the same flexible hyoid bones as the roaring cats, but they can’t roar. So, more studies needed to be done.
After much research, scientists have recently determined that the reason lions, tigers, jaguars and leopards can roar and no other species can is actually due to other morphological features, especially of the larynx. To test this theory, they compared the larynx of each of the four roaring cats with those of several species of non-roaring cats (most notably the snow leopard, but also several species of small cats). They found that while a snow leopard has similar undivided thyroartenoid folds and that its larynx is similar in size to that of a small jaguar, they lack the pad of fibro-elastic tissue that increase the length and mass of its vocal fold which roaring cats have.
This pad of fibro-elastic tissue is what allows roaring cats the gradual transition of sound energy from a high to a low air resistence resulting in a better transfer of acoustical energy which efficiently radiates the sound. In short, the sound-producing mechanism of the snow leopard and all other non-roaring cats is less efficient due to shorter vocal folds, and poorer due to the lack of ability to radiate sound because they don’t have the pad of fibro-elastic tissue. This is why snow leopards, clouded leopards, cheetahs and small (purring) cats can’t roar.
Source: The larynx of roaring and non-roaring cats, M.H. Hast, J Anat. 1989 April; 163: 117–121.