Ornithology/Gruiformes

The order Gruiformes is polyphyletic- the common ancestors of the birds in the group are not contained in the group. To compare, if "warm-blooded animals" was considered a group, then both Mammals and Birds would be in the group, but their last common ancestor would not be, because it would have most likely been cold-blooded. However, the American Ornithologist's Union still categorizes them as such, and the list follows them.