Dinosaur dung fleece has in lining (9)
I believe the answer is:
iguanodon
'dinosaur' is the definition.
(I know that iguanodon is a type of dinosaur)
'dung fleece has in lining' is the wordplay.
'dung' becomes 'guano' (excrement of sea birds).
'fleece' becomes 'do' (I've seen this in other clues).
'has' says to put letters next to each other.
'lining' means one lot of letters goes inside another (eg 'tree-lined' means surrounded by trees).
'guano'+'do'='guanodo'
'guanodo' inserted within 'in' is 'IGUANODON'.
(Other definitions for iguanodon that I've seen before include "reptile now extinct" , "Long-tailed bipedal dinosaur" , "It used to eat plants" , "big beast" , "Old lizard" .)