Loose piglets startled caveman? (12)
I believe the answer is:
speleologist
'caveman?' is the definition.
(I've seen this before)
'loose piglets startled' is the wordplay.
'startled' indicates an anagram.
'loose'+'piglets'='loosepiglets'
'loosepiglets' anagrammed gives 'SPELEOLOGIST'.
(Other definitions for speleologist that I've seen before include "he plumbs the depths" , "Caveman" , "Pigs let loose (anag) - one who studies caves" , "Caver" , "Potholer - I'll goose-step (anag)" .)