This expression shows the meaning of 'not even', 'not a single'.
Long explanation:
The grammar point 'たりとも~ない' (tari tomo ~nai) is used to express a strong negative assertion. It means 'not even one', 'not a single' or 'none at all'. It attaches to a noun to express something isn’t in a certain state, doesn’t exist or doesn’t occur, even by a little bit.