A simple dichotomous key used to identify different groups of mammals is provided. An organism that initially keeps its live young in a pouch and spends the majority of its time on the ground is discovered. Using this dichotomous key, determine which group it is most likely to belong to.
Dichotomous keys are used to help identify organisms. To answer this question, let’s first learn how to use a dichotomous key using a very simple example. Let’s assume we want to work out what this flower is and that there exist only three different types of flowers, (A), (B), or (C).
We can use a simple dichotomous key to figure out what flower this might be. A dichotomous key follows a simple system using yes or no questions. The key starts with something we know, in this case that we have a flower. And it allows us to use observable traits to work out what flower this is. Let’s assume flower petals can only take one of two colors, pink or white. So first, we ask ourselves, does the flower have pink petals or white petals? The petals are pink. So we then follow that branch and look at the next applicable question. The next question asks if the flower has leaves or not. It does not. So we follow the according branch and see that the specimen in question is specimen (B), according to the dichotomous key.
Note that the dichotomous key only helps us to identify something in which we can observe characteristics, for example, which group a mammal belongs to. It is not a tool for determining evolutionary relatedness. Let’s now return to our original question to apply our skill of reading a dichotomous key. We already know that the organism is a mammal. On the first branch, we need to decide if the organism lays eggs or gives birth to live young. Our organism gives birth to live young, so we’ll travel down this branch.
Now, we need to know whether our organism has a pouch or not. It has a pouch. So we can narrow the choices down further. Let’s have a look at the final question. Is the organism ground dwelling or tree living? It is ground dwelling. Therefore, we can say that the organism in question belongs to the group macropodidae.