[robbrown451]

Mammals are tetrapods, which are indeed under Osteichthyes (unless you consider Ostreichtyes to be paraphyletic).

If you look at the cladogram on the wikipedia page I linked, you see a picture of a salamander near the top representing the category Tetrapodomorpha. We (and whales) are also on that branch. Sharks are outside of that whole cladogram, as they are cartilaginous fish. ( * )

In other words, any clade which includes all bony fish also includes mammals.

[*] which means that the most recent common ancestor of sharks and goldfish lived longer ago than the most recent common ancestor of whales and goldfish