1) Homology
a. A dolphin and a sheep have the same skeletal structure, eventhough, one is adapted for swimming and the other for running.
b. The majority of tetrapods have the same forelimb bone arrangement: one arm bone (humerus), two forearm bones (radius and ulna), a number of wrist (carpal) bones and five metacarpals (located in the palm) joined to five sets of phalanges (bones of the fingers).
c. I believe that the common ancestor could have been a reptile. A reptile can be adapted for both water and land thus creating these two animals.
2) Analogy
a. The wings of various unrelated flying animals, such as insects and vertebrates( known as birds) resemble one another superficially, but their structures are very different.
b. Vertebrate (bird) wings are modified forelimbs supported by bones. Insect wings are outgrowths of the upper wall of the thorax and are supported by chitinous veins.
c. I believe that the ancestores of the bird and insect both possesed the same trait. The reason for this is because they were both designed for aviation.
A reptile was indeed a common ancestor of both the dolphin and the sheep, but they also had a more recent common ancestor who was a mammal. Doesn't change the homologus status of the trait, however.
ReplyDeleteIf the wing of an insect and the wing of a bird are analogous traits (not homologus) would you expect their common ancestor to have the same trait? Think about the definition of "analogous".
Very interesting! I would have never thought a dolphin and sheep would have a shared homologous trait, but your intake on this and posting of the subject, makes a good trait to point out.
ReplyDeleteIf the wing of an insect and the wing of a bird are analogous traits, I would not expect their common ancestor to have the same trait. It could be a possibility that their common ancestors had to mutate to be able to survive in that specific environment. Maybe the number of preditors increased causing both the bird and insect to mutate for survival.
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