South American native mammal or reptile, not one wanting company (7)
I believe the answer is:
guanaco
'south american native mammal' is the definition.
(I know that guanaco are native to South America)
'reptile not one wanting company' is the wordplay.
'reptile' becomes 'iguana' (type of lizard).
'not' suggests deleting specific letters.
'one' becomes 'I' (Roman numeral).
'wanting company' becomes 'co' (abbreviation. I am not sure about the 'wanting' bit.).
'iguana' with 'i' removed is 'guana'.
'guana'+'co'='GUANACO'
'or' is the link.
(Other definitions for guanaco that I've seen before include "Llama-like animal" , "One of the 30 [RUMINANTS]" , "South American resident" , "Hoofed mammal" , "wool producer" .)