Mount up and trot after the animal (8)
I believe the answer is:
antelope
'the animal' is the definition.
(I've seen this before)
'mount up and trot' is the wordplay.
'mount' becomes 'etna' (Etna is an example).
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'and' is a charade indicator (letters next to each other).
'trot' becomes 'lope' (synonyms).
'etna' reversed gives 'ante'.
'ante'+'lope'='ANTELOPE'
'after' acts as a link.
(Other definitions for antelope that I've seen before include "One petal for this animal" , "Fast runner" , "grazing animal" , "Eg, gazelle or gnu" , "Gazelle or impala" .)