Creature on the Serengeti developing a growth (7)
I believe the answer is:
warthog
'creature on the serengeti' is the definition.
(some warthogs live on the Serengeti)
'developing a growth' is the wordplay.
'developing' indicates anagramming the letters (letters developed into a new form).
'a'+'growth'='agrowth'
'agrowth' is an anagram of 'WARTHOG'.
(Other definitions for warthog that I've seen before include "A growth (anag) - African animal" , "Wild boar of Africa" , "African wild pig" , "African native" , "Beast" .)