The researchers will use mice instead of opossums or humans to determine whether the cells of the ear bones originated from the same embryonic cells as the cells that form the jaw in other vertebrates because in this type of experiment, organisms that are ideal are the ones that have a short life span, easy to be researched on and easy to mantain.
It will be very tedious and demanding to use opossums and humans in this type of practical experiment because,it is against the culture and norms guilding human living and existence to use humans as model organisms,opossums as well are very bad model organisms because unlike the mice,opossums are long lived and it will be very difficult to raise and maintain an opossum in a laboratory.
Humans and mice are both mammals just that human is a higher mammal but they share similar features in terms of pattern of development,though there is a clear difference during their early development,so because of the common ancestry shared by the mice and humans,the result of the experiment on the mice with share a close similarity with the pattern that is expected in humans.