Strange union, a dog and a dinosaur (9)
I believe the answer is:
iguanodon
'dinosaur' is the definition.
(I know that iguanodon is a type of dinosaur)
'strange union a dog and a' is the wordplay.
'strange' is an anagram indicator.
'and' is a charade indicator (letters next to each other).
'union'+'dog'='uniondog'
'uniondog' put after 'a' is 'auniondog'.
'auniondog' with letters rearranged gives 'IGUANODON'.
(Other definitions for iguanodon that I've seen before include "Massive dinosaur of the early Cretaceous period" , "Long-tailed bipedal dinosaur" , "reptile now extinct" , "fossil" , "It used to eat plants" .)