The point of the case is less about any placental parallels beyond Australia… and more about 3 closely related “kinds” of Marsupials (measured by genotype, not phenotype). It is believed that conditions in Australia were optimum because there were no rival placental occupants in the niches the placental sub-grouos increasingly exploited!
I have posted this thread already. Just go to my profile and search my posts for: marsupial Australia mole.