Comparative Anatomy
Comparative Anatomy is the study of the similarities and differences in the anatomy of difference species. It has long served as one of the main evidences for evolution, due to the fact that it is very concrete, and does not require extensive technology.
A simple example of comparative anatomy is this: You look at two animals. They both have feathers, wings, and beaks. What type of animal are these two organisms? Do you think they are related, and why or why not?
A simple example of comparative anatomy is this: You look at two animals. They both have feathers, wings, and beaks. What type of animal are these two organisms? Do you think they are related, and why or why not?
Scientists will go more in depth than just looking at the outer appearences of organisms. Many times, scientists use bones to determine similarities and differences in comparative anatomy. There are two types of structures you will now research. These have both been used to determine whale evolution.
The first are Homologous Structures. These are parts of the body in organisms that have similar structure to other organsisms' comparative parts. One example of this is the bone structure in limbs of different mammals, shown below.
The first are Homologous Structures. These are parts of the body in organisms that have similar structure to other organsisms' comparative parts. One example of this is the bone structure in limbs of different mammals, shown below.
You can see that even though some bones are slightly different lengths and shapes, all limbs above share the same bone structure. This points to the fact that even though each animal shown has a specialized limb used for different things, all of these mammals have descended from one organism.
The second type of structure is a Vestigial Structure. These are structures that, over time, have lost much of their ancestral function. One example in humans is the appendix. The appendix was once an enlarged part of the digestive system, used to digest leaves in primates who were herbivores. As evolution occured and the appendix was no longer needed, it shrank in size and function over a very long time. By looking at the reduced appendix in humans, and its similarity to a functional appendix in some primates, scientists can infer that there was a common ancestor between the two structures.
The second type of structure is a Vestigial Structure. These are structures that, over time, have lost much of their ancestral function. One example in humans is the appendix. The appendix was once an enlarged part of the digestive system, used to digest leaves in primates who were herbivores. As evolution occured and the appendix was no longer needed, it shrank in size and function over a very long time. By looking at the reduced appendix in humans, and its similarity to a functional appendix in some primates, scientists can infer that there was a common ancestor between the two structures.
Comparative Anatomy of Whales
We can first look at the homologous structures in whales. One major homolgous structure is the fin of a whale. If you look at the skeleton of a whale's fin, notice that all of the bones match up to comparative bones in other mammals. This is evidence that whales, as mammals, share a common ancestor with other mammals.
Another example of a homologous structure in whales is their inner ear bones. The inner ear bones of a whale are extremely similar to land mammals, but the one difference is that they are fused together. Instead of several, detatched earbones, the ear bones of whales are attached, which helps in hearing under water. There is another mammal with fused ear bones as well, the hippo.
Now lets take a look at an example of a vestigial structure in whales. As you know, land mammals have hind (back) legs. Whales do not have hind legs. What they do have though, are small skeletal structures that look like shrunken hind legs. As ancestral cetaceans began to transition from land to water, their legs were pushed back further for swimming, and eventually reduced in size due to lack of use. Below are pictures of the skeletons of these (extinct) species, from the earliest to the most modern. Note the transition of the hind legs:
Some other anatomical features of whales that indicate common ancestry with mammals include the following:
Lungs
Placenta (for developing embryos)
Chambered Stomach (very similar stomach found in hippos)
At this point, please continue on to Transitional Fossils!