Animal found in alarming numbers (3)
I believe the answer is:
gnu
'animal' is the definition.
(thesaurus)
'in alarming numbers' is the wordplay.
'in' indicates a hidden word.
'GNU' is hidden within 'alarming numbers'.
'found' acts as a link.
(Other definitions for gnu that I've seen before include "Creature" , "Large heavy antelope" , "Strange gun for an antelope" , "hitherto unknown, we hear" , "Gun for a kind of deer" .)