skeletal characteristic of monotremes (egglaying mammals of Australia and New Guinea) is the large epipubic bones in the pelvic region. They were originally thought to be related to having a pouch, but they are found in both males and females, and they also occur in all species of marsupials, whether they have a pouch or not. It is now thought that these bones are a relic of the skeleton of therapsids, wherein they provide extra attachments for abdominal muscles to support the weight of the hind quarters.