An animal left twice as many appalled initially (5)
I believe the answer is:
llama
'an animal' is the definition.
(I know that llama is a type of artiodactyl)
'left twice as many appalled initially' is the wordplay.
'left' becomes 'l' (common abbreviation).
'twice' says to double the letters.
'initially' indicates taking the first letters.
The first letters of 'as many appalled' is 'ama'.
'l' doubled is 'll'.
'll'+'ama'='LLAMA'
(Other definitions for llama that I've seen before include "South American transport animal" , "Camel-like wool source" , "Animal related to camels but smaller and lacking a hump" , "S.American animal" , "S American animal like a camel with soft hair" .)