A marine creature is a lone ranger? (3,4)

I believe the answer is:

sea lion

I'm a little stuck... Click here to teach me more about this clue!

'a marine creature' is the definition.

'is a lone ranger?' is the wordplay.
'is a lone' can be anagrammed to 'SEA LION'.
But, I'm not clear how this is indicated.

Can you help me to learn more?

(Other definitions for sea lion that I've seen before include "one often immersed in salty water" , "Large-eared mammal of Pacific Ocean, like Leo" , "Marine animal, used as a circus performer" , "Creature" , "Acrobatic aquatic mammal" .)

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