Start of month: turned up North American lizard (6)
I believe the answer is:
iguana
'lizard' is the definition.
(I know that iguana is a type of iguanid)
'start of month turned up north american' is the wordplay.
'start of' becomes 'i' (I can't explain this - if you can you should give a lot more credence to this answer).
'month' becomes 'Aug' (abbreviation for August).
'turned up' is a reversal indicator.
'north american' becomes 'na'.
'aug' in reverse letter order is 'gua'.
'i'+'gua'+'na'='IGUANA'
Can you help me to learn more?
(Other definitions for iguana that I've seen before include "Herbivore" , "Tropical spiny lizard" , "Large lizard of tropical Amercia" , "Type of lizard" , "Tropical tree-lizard" .)