Many biologists will talk about the group known as Ungulates

Many biologists will talk about the group known as Ungulates, or hoofed mammals. This group includes species as diverse as pigs (Sus), elk (Cervus), cows (Bos), hippos (Hippopotamus), extinct species (e.g., Elomeryx and Archaeotherium), and even rhinos and horses (Equus). Based upon the tree above and assuming this tree is correct, is this group (Ungulates) monophyletic?

Solution

b.  Yes, because all of these species share a most recent common ancestor

All the members of the group of interest are more closely related to each other than they are to the outgroup. Hence, the outgroup stems from the base of the tree. An outgroup can give you a sense of where on the bigger tree of life the main group of organisms falls. It is also useful when constructing evolutionary trees.