Big lizard droppings collected by one academic (9)
I believe the answer is:
iguanodon
'big lizard' is the definition.
'iguanodon' can be an answer for 'lizard' (I have seen 'Old lizard' mean 'iguanodon' so perhaps 'lizard' could also mean 'iguanodon'). I'm not certain of the 'big' bit.
'droppings collected by one academic' is the wordplay.
'droppings' becomes 'guano' (term for bird droppings).
'collected by' means one lot of letters go next to another (I've seen this in other clues).
'one' becomes 'i' (Roman numeral).
'academic' becomes 'don' (type of academic - especially at Oxbridge).
'guano' put after 'i' is 'iguano'.
'iguano'+'don'='IGUANODON'
Can you help me to learn more?
(Other definitions for iguanodon that I've seen before include "Herbivorous dinosaur" , "Massive dinosaur of the early Cretaceous period" , "big beast" , "Large dinosaur" , "Massive dinosaur with long heavy tail" .)