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.
more than one lynx is call lynxes
you call them possums if your talking about more than 1
More than one fisherman is fishermen
alligators
swans
Fish
Ants
Atria
Pegasi I think.
Vampiresses.
Polygamy.