Hoofed mammal, one following pensioner round end of park (5)
I believe the answer is:
okapi
'hoofed mammal' is the definition.
(okapi is a kind of hoofed mammal)
'one following pensioner round end of park' is the wordplay.
'one' becomes 'i' (Roman numeral**).
'following' is a charade indicator (letters next to each other).
'pensioner' becomes 'oap'.
'round' indicates putting letters inside.
'end of' says to take the final letters.
The final letter of 'park' is 'k'.
'oap' enclosing 'k' is 'okap'.
'i' put after 'okap' is 'OKAPI'.
(Other definitions for okapi that I've seen before include "Type of giraffe" , "Animal, a sort of zebra/giraffe cross" , "Giraffe family member" , "One of the giraffe family" , "Animal of central Africa" .)