Animal found in growing numbers (3)
I believe the answer is:
gnu
'animal' is the definition.
(type of antelope)
'in growing numbers' is the wordplay.
'in' indicates the answer is hidden within the clue.
'GNU' is hidden within 'growing numbers'.
'found' acts as a link.
(Other definitions for gnu that I've seen before include "hitherto unknown, we hear" , "Wildebeest" , "Gun for a kind of deer" , "Antelope sounds as if it has knowledge" , "Animal" .)