Sadistic cladistics

Classification of vertebrates more complex than believed

source: Graham Lawton
New Scientist vol 210 no 2813, May 21 2011 p30

Cladistics is a taxonomy system developed by Willi Hennig, an entomologist from Germany, during the 1960s. Hennig focused on genetic relationships of species, looking at their evolutionary ancestry. Mammals were developed from just one ancestral species, which neatly diverged from the tree of evolution at a single point. This is also true for birds. Mammals can therefore be defined as a clade, as is the case with birds. Amphibians can also be seen as a clade, if extinct species are excluded. Reptiles, however, do not form a true clade, because their common ancestor was also the ancestor of birds and mammals. Classifying fish is also more complex than thought. Biologists generally use traditional, less accurate classifications in their everyday work, because they are less cumbersome.