A friend and mourner recalled that, growing up, she believed cats and dogs were the same animal, but that cats were the females and dogs the males. This is entirely credible.

Anna Quindlen (b. 1953) American journalist, novelist

Article (1991-04-07), “Mr. Smith Goes to Heaven,” New York Times
    (Source)

Part of an obituary for her dog, Jason Oliver C. Smith. Reprinted in Thinking Out Loud (1993).