From Sara Reardon at Nature:
Wallabies are kicking over scientific conventions surrounding mammalian placentas, the organ responsible for protecting and nourishing a developing fetus. A study finds that contrary to what scientists thought previously, mother tammar wallabies (Macropus eugenii) have both a functioning internal placenta and milk that performs some of the organ’s usual roles.
Taxonomists usually separate marsupials — including kangaroos, wallabies and wombats — from placental mammals, also known as eutherians, such as mice and people. The separation is based partly on a supposed lack of a placenta in marsupials. But many researchers think that this distinction is incorrect, noting that marsupials develop simple, placenta-like structures during the end of pregnancy, just before the underdeveloped baby crawls from the uterus into the mother’s pouch. More.
Which they presumably developed without reference to placental mammals.
See also: Lee Spetner: What challenges do convergent evolution and antibiotic resistance pose to Darwinian evolution?
Evolution appears to converge on goals—but in Darwinian terms, is that possible?