Article borne by diminutive, climbing, pack animals (6)
I believe the answer is:
llamas
'pack animals' is the definition.
(I've seen this before)
'article borne by diminutive climbing' is the wordplay.
'article' becomes 'a' (the indefinite article in English).
'borne by' means one lot of letters goes inside another (to bear can mean to carry).
'diminutive' becomes 'small' (similar in meaning).
'climbing' says the letters should be written backwards (in a down clue, letters climb up).
'a' placed within 'small' is 'samall'.
'samall' reversed gives 'LLAMAS'.
(Other definitions for llamas that I've seen before include "South American animals like the camel" , "South American animals related to camels but humpless" , "domesticated guanacos" , "Camel-like animals" , "Andean pack animals" .)