Marsupials: The Most Evolved Mammals?

A new study challenges the idea that marsupials are more 'primitive' than mammals by showing their development has changed more than mammals since they last shared an ancestor. The findings suggest that the extremely young age of marsupial births represents the more specialized type of development that required greater changes in traits compared to our shared ancestor than our strategy of allowing young to develop within us for longer. The changes most likely reflect environmental demands or lack thereof.