Except for the five species of monotremes (egg-laying mammals), all modern mammals give birth to live young. Most mammals, including the six most species-rich orders, belong to the placental group. The three largest orders in numbers, are first Rodentia: mice, rats, porcupines, beavers, capybaras, and other gnawing mammals; then Chiroptera: bats; and then Soricomorpha: shrews, moles and solenodons. The next three orders, depending on the biological classification scheme used, are the Primates including the humans; the Cetartiodactyla including the whales and the even-toed hoofed mammals; and the Carnivora, that is, cats, dogs, weasels, bears, seals, and their relatives.

How many species of mammals do not have a live birth?