More than one platypus is two or more platypuses. The plural is not 'platypi'.
unfortunately, you misspelled platypus. it is a common mistake though. more than one platypus are platypi.
There has never been more than one species of platypus (except for a prehistoric platypus as shown by fossil remains). Platypuses in the north, like the koala, are smaller than their southern counterparts, but they are still a single species.
That would be the plural using Greek rules: both platypus and octopus are from Greek, and do not (as is commonly assumed) use the Latin plurals platypi and octopi.The correct English plural is either platypuses or the same word platypus (used as a group noun, like sheep or trout).
more than one lynx is call lynxes
you call them possums if your talking about more than 1
More than one fisherman is fishermen