Beaver front teeth vs. Elephant tusks
Beaver:
Elephant:
- Upon examining these two structures, you see that each is just a modification of the basic incisor tooth structure. These homologous traits exhibit differences because over time, evolution adapted each of their incisors to preform certain functions. Beavers use their teeth for chewing through tree trunks while elephants use their tusks for digging, peeling back bark, fighting, among other things. They inherited these from a common ancestor (most likely a mammal) with incisor teeth.
Analogous Structures
Whale tail vs. Alligator tail
Whale:
Alligator:
- Although these two Structures may look similar and preform similar functions, they are not homologous because whales and alligators evolved separately. The whale tail is made of dense collagenous material, and two horizontal lobes make up the tail ends. Whales move their tales in an up and down motion to propel their bodies forward. Alligator rails, however, are made of bone and unlike whales, they make a side to side motion with their tails to propel themselves through the water. Not only that, but whales are mammals while alligators are of reptilian descent. It's is in fact possible that far enough back, their common ancestor could've had tails.
I never in a million years would have compared an Elephant's tusks with a beaver's teeth. Good find. Its a bit of a stretch, but since they are both mammals, I could see how it might have changed for the needs of both species.
ReplyDeleteAs for the alligators and whales, I think that it was a bit of a stretch to compare them even as analogous traits. The alligator tail is meant for swimming while barely submerged, while the whale's tail is meant for being submerged in thousands of gallons of water. I see where you made your comparison though, good job.
The opening sections, for both homologous and analogous traits, asks you to first describe (not just identify) the organisms you are comparing. This helps your reader understand the environments/selection pressures that produced the contrasted traits. Missing that as you jump straight into the discussion of the traits themselves.
ReplyDeleteGood discussion of your homologous pairing. You are correct the likelihood of the mammalian ancestry, but how do we know that this ancestor possessed the primitive form of this incisor trait? Is this incisor dentition pattern common to mammals in general?
I suggest that your decision to choose the alligator and whale for your analogous pairing may have been based upon a false understanding of the structure of the whale tale. The whale of a tale is constructed of vertebrae, just as the alligator tail is. Here is a link to an image (unfortunately I can't insert images in comments here):
http://www.ptmsc.org/boneatlas/images/skeleton_base_labeled.jpg
Looks a lot like an alligator tail, doesn't it. :-)
The tails of all mammals (including whales, primates, dogs, rats, etc) arose from a common archaic early mammal, and THAT mammal inherited its tail from its reptilian ancestor. So the common ancestor of a whale and an alligator was an archaic reptile who possessed the primitive tail structure of the traits you are comparing. So these traits arose from common descent with differences arising from differences in environment and function... in other words, these are actually homologous traits, not analogous.
You have the ancestry correct, but you were midlead by a misunderstanding of whale skeletal anatomy. Check out some skeletal images of these two organisms to understand this and let me know if you have any questions.
Like the previous person mentioned, I also would have never thought that both the elephant and the beaver belong under homology. It's quite interesting. Though I would have liked to at least know who was the proposed common ancestor of both. I'm sure it is a mammal like you stated but to exactly know the name of the mammal they came from would have been even more intriguing (:
ReplyDeleteAs for the Analogous Trait i really liked the two species you chose! very informative! (:
I could see the comparison as to why you chose a beavers front teeth to an elephants tusks. I never would have thought of such a comparison! Very infomrative and good brief descritoion on the teeth and tusks. Missing the common ancestors for first traits. However, nice analogus set of traits. Both tails but have complelety different functions. I like how you described the difference of how alligatrs swim to whales. Overall good blog post and very helpful.
ReplyDelete