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Two major concepts of comparative anatomy are:
- Homologous structures - structures (body parts/anatomy) which are similar in different species because the species have common descent. They may or may not perform the same function. An example is the forelimb structure shared by cats and whales.
- Analogous structures - structures which are similar in different organisms because they evolved in a similar environment, rather than were inherited from a recent common ancestor. They usually serve the same or similar purposes. An example is the torpedo body shape of porpoises and sharks. It evolved in a water environment, but the animals have different ancestors.
Although spoken of less than the above in comparative anatomy and physiology, heterogeneous structures (structures which are dissimilar), are also present even when there is a common ancestor and a similar environment. For instance the comparative anatomy of dolphins and fish.
The rules for development of special characteristics which differ significantly from general homology were listed by Karl Ernst von Baer (the Baer laws).
Examples of Comparative Anatomy
- Did you know the Panda is not a bear, more closely related to the Raccoon and has no thumb? It lacks the phalanges that comprise the thumb, instead it has some exaggerated meta-carpals that function similar to the thumb.
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