Reptile is around rocks (8)
I believe the answer is:
dinosaur
'reptile' is the definition.
(I have seen 'Prehistoric reptile ' mean 'dinosaur' so perhaps 'reptile' could also mean 'dinosaur')
'is around rocks' is the wordplay.
'rocks' is an anagram indicator.
'is'+'around'='isaround'
'isaround' is an anagram of 'DINOSAUR'.
(Other definitions for dinosaur that I've seen before include "Extinct monster like Barney, children's TV pal" , "Prehistoric monster found on Darius" , "Beast long gone" , "Eg, triceratops" , "is well out of date" .)