Which big cats roar?
There are four big cats that can roar: lion, tiger, leopard and jaguar - all of which belong to the genus Panthera.
What causes a cat's roar?
In these species, the epihyal bone, part of the voice box, is replaced by a ligament. This can be stretched, creating a larger sound-producing passage and thus a wider range of pitch. The more the ligament extends, the lower the sound generated when air passes across the vocal cords. In addition, the cords are large, unbroken and fleshy, which produces deeper sounds.
Why can't cheetahs roar?
The bones of the cheetah's voice box form a fixed structure, with divided vocal cords that vibrate with both in and out breaths. This structure is the same for all the 'small' cats. While this design enables these cats to purr continuously, it limits the range of other sounds and prevents them from being able to roar.
Just because cheetahs are relatively large, that doesn't mean they can roar - they still have small-cat anatomy despite their size, and it's exactly the same for pumas/mountain lions.
Do big cats purr?
Big cats don't purr. Purring and roaring are mutually exclusive, so lions, tigers, leopards and jaguars are all incapable of purring, while every other cat can purr but not roar.
Are there any exceptions?
Interestingly, the snow leopard - also a member of Panthera along with lions etc - cannot roar. Its vocal cords lack an all-important layer of fatty, elasticated tissue, which, in other big cats, gives the vocalisations an uneven rumble that emerges as a roar. Some scientists therefore argue that the snow leopard deserves its own genus: Uncia.
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