Geoscience Reference
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wings and are warm-blooded, a greater number of characteristics
provide evidence that bats are more closely related to other mammals
than they are to birds. Bats have hair, nurse their young with milk, have
three bones inside their ears, and have teeth of different shapes like
other mammals. Birds do not share these characteristics, and in fact,
the wings of birds and bats are constructed quite differently. Whereas
five fingers of the hand support the membrane that forms a bat's wing,
the feathers of a bird's wing are attached to the arm and only one fin-
ger of the hand. This difference is interesting, but the number of sim-
ilarities shared by bats and mammals is more important for
interpreting the genealogy of bats. Using the principle of parsimony,
we can see that most of the anatomical evidence suggests that bats are
more closely related to mammals. Consequently, birds and bats are not
as closely related, even though they both have wings and are warm-
blooded. In the end, cladistic methodology compares only similarities
shared among different groups, then uses the principle of parsimony
to choose the genealogical interpretation that is supported by the
larger number of similarities.
The previous example may seem rather obvious, since most biology
students have learned that bats are mammals and birds are not, but
cladistics and the principle of parsimony have shed new light on
other evolutionary puzzles that had previously proved more difficult
to solve. One of these is the evolutionary relationship of birds to croc-
odiles, lizards, and other reptiles. At first glance, crocodiles look
much more like lizards than birds. Crocodiles and lizards have a
scaly, reptilelike body, whereas birds have a feathered body with
wings. Yet, despite the obvious differences seen in crocodiles and birds,
a closer examination reveals that crocodiles and birds share many more
physical similarities than crocodiles and lizards do. For example,
crocodiles and birds share a series of air holes in their middle ear that
are not found in lizards. Birds and crocodiles also share a robust rib
cage that is strengthened by short struts of cartilage called uncinate
processes. In birds and some theropod dinosaurs, these uncinate
processes ossify. Another feature found in crocodiles and birds is a
muscular stomach or gizzard that processes food. Lizards do not
have gizzards. Consequently, when we apply the principle of parsi-
mony, crocodiles and birds are more closely related than crocodiles and
lizards on the family tree of vertebrates. The similar reptilian appear-
