As an animal that spends a great deal of time making small-scale local manoeuvres in its complex, three-dimensional watery home, Inia is especially telling in that it may actually be taking part in a trend toward hyperdactyly, as it bears an extra bone in its flipper that is to all intent and purposes a sixth digit.    From Wordnik.com.  [Did ichthyosaurs fly? Probably not, no] Reference