There are three types of mammals: monotremes and marsupials evolved before the placental mammals. Monotremes are represented by the duckbilled playpus and the spiny anteater, both of which are found in Australia. They lay thcir eggs, which resemble reptilian eggs, in burrows in the ground. The female incubates the eggs, as do birds, but after hatching the young are dependent upon the milk that seeps from modified sweat glands on the abdomen of the female. The male platypus also produces milk.