An animal lies on a rock (3,4)
I believe the answer is:
sea lion
'an animal' is the definition.
(I have seen 'Marine animal' mean 'sea lion' so perhaps 'animal' could also mean 'sea lion')
'lies on a rock' is the wordplay.
'rock' indicates anagramming the letters.
'lies'+'on'+'a'='liesona'
'liesona' is an anagram of 'SEA-LION'.
(Other definitions for sea lion that I've seen before include "Large-eared marine mammal, sometimes performing" , "Acrobatic aquatic mammal" , "Large marine mammal" , "Is alone (anag.)" , "Aquatic mammal - code name for planned German invasion of England, 1940" .)