There are a few mammals--the monotremes--that lay eggs and do not have breasts, but they do produce milk for their young. (Live birth also occurs in a variety of non-mammalian species; it is not a diagnostic characteristic for class mammalia.) |
There are a few mammals--the monotremes--that lay eggs and do not have mammary glands, but they do produce milk for their young. (Live birth also occurs in a variety of non-mammalian species; it is not a diagnostic characteristic for class mammalia.) |
There are a few mammals--the monotremes--that lay eggs and do not have mammary glands, but they do produce milk for their young. (Live birth also occurs in a variety of non-mammalian species; it is not a diagnostic characteristic for class mammalia.)
Kingdom Animalia, Phylum Chordata, Class Mammalia
Therapsids? are the direct ancestors of mammals, but some scientists consider them to be mammals. In this case, Pelycosauria? are the direct ancestors of mammals.
The names Prototheria, Metatheria and Eutheria expressed theory that Placentalia? were descendants of Marsupialia, which were in turn descendants of Monotremata. Because this theory has been refuted, these names are rarely used nowadays.