Homologus
Traits
The Homologus trait between a bird and a rabbit is that they
both share that same forelimb that consists of the humerus, radius and the ulna. The
forearm of a bird and the forearm of a rabbit seem to be completely different however,
they are made up of the same bones. Obviously the main difference between the
two animals is that a rabbit cannot fly like a bird can. These homologus traits
seem to look different on the outside, but on the inside their bone structure
is the same. Throughout its evolution, birds evolved into having long and thin
forearms better suited for flying. However, in the meantime rabbits evolved
into having more weight bearing forearms to help them hop around better and
move faster to avoid predators. In this example, the Eusthenopteron is the
common ancestor between all tetrapods. This is known because this is where the
development of the humerus, radius and the ulna began
Analogous
Traits
An example of an analogous trait is fins. For example, both
dolphins and sharks have fins and they both serve the same purpose to help the
animal swim. Because of several similarities, such as living in the sea and
having fins you would think they are closely related but they are not. These
fins are similar in shape, size and purpose, however, just because they have
the same fins, does not mean they have the same direct ancestor. In fact a
dolphin is considered a mammal while a shark is a fish. The fact that they are
both two different animal types shows us that they cannot share a common
ancestor but it is possible that if you go far enough back they will at some
point share an ancestor. It is possible that the same ancestor would have a
fin, but it is hard to tell.
