A homology that exists between humans and dolphins is the
structure of the human arm and the dolphin fin. They have very similar bone
structures each with five phalanges. Both species also have an ulna, radius, carpals
and humerus. It is clear that the dolphin bone structure is much more condensed
than the human arm, because of the fins design for forward movement. The
Pakicetus is the most likely common ancestor. While it did not have arms it
contained five phalanges in the leg similar to arm and fin structure today.
A good example of an analogous trait would
be the fins of a fish and penguin. The
fins are used to propel through water, but one is a fish and the other a bird.
While there are similar bones such as the humerus, radius, and ulna makes it
is clear they developed differently by looking at the bone structure. Even with the similarities the structures
formed independently due to environment. I could not find an exact common
ancestor, but it must have been a teleostomi species.
Austin,
ReplyDeleteVery interesting, I didn't realize that dolphins had phalanges within their flipper. No wonder they seem to have so much dexterity.
In general, good opening discussion on your homologous traits. You explain the reason for the shape of the dolphin, but what about the human? Why is the human forelimb shaped as it is?
ReplyDelete"The Pakicetus is the most likely common ancestor. While it did not have arms it contained five phalanges in the leg similar to arm and fin structure today."
Pakicetus is a possible ancestor of the dolphin but it is past the point where the two lines split off. Also, it did have a forelimb along with the phalanges.
That aside, you have the right idea for a common ancestor. Given the similarity in forelimb structure, and the fact that both animals are mammals, it is easy to conclude that the common ancestor was also a mammal and all mammals share that common forelimb structure from that common ancestor that arose from ancestral reptiles. That confirms that these traits are homologous.
Good image.
I'm confused by your analogous traits. Both sharks ARE fish, not birds, so I'm wondering if you mis-wrote something? Is it possible that you meant to compare sharks and penguins? I can't tell by your images what you might have meant.
I mistakenly wrote shark. I was originally looking at penguins and sharks and mistakenly wrote shark instead of penguin. I will correct this now.
DeleteOkay, then your pairing makes sense.
DeleteYour logic of looking at the skeletal material to determine whether or not the traits are genetically related is a good start, but remember that even this can be misleading so try to back it up with understanding of how these two organisms evolved. In particular, we know that birds developed their wings after the split from reptiles and penguin developed their "fins" after that, so we know that they acquired their fins independently from when and where fish inherited their fins, which (as you say) was from an ancient fish ancestor who likely DID possess these traits.