2. Both the dolphin and the herring, predators in the water, have streamlined bodies with a dorsal fin on top which helps them survive and thrive as they search for food in the water. However, these are analogous traits because while the herring is a species of Osteichthyes (bony fish), the dolphin is a mammal from the Cetecea order. Dolphins are actually mammalian carnivores which eat fish. If we look back in the ancestry tree we can see that both the dolphin and the herring are vertebrates, which would be where they share the vertebral column which eventually developed into their streamlined bodies and top fins, but there does not seem to be a shared ancestor possessing the specific traits of streamlined body and top fin (although other Osteichtyes have these traits). Other species in the Dolphin's Cetacea class are the porpoises and whales and neither of these species possess both the streamlined bodies and top dorsal fin (porpoises have the fin but are not streamlined) of the dolphin. This is perhaps because it was unnecessary until it evolved independently as a means of survival for these two species who needed to moved quickly and turn adeptly to ward of predators and find food.
Nice work! I like how you made it personal -- made it more interesting to read. I never noticed those similarities and I have two dogs so I'm going to keep an eye out! I also like your second post on the dolphin and the herring. I feel like I got a lot from it.
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DeleteWithout you describing each species, I conjectured that in the homologous comparison you were referring to humans and dogs. I think you could have described the structure differences more in depth, and perhaps provided images of the similar structures. Cute pictures of your dog, but I can't really see the connection. I believe the common ancestor of humans and dogs is Boreoeutheria. Does this shrew or mole ancestor have the same traits?
ReplyDeleteIn your analogous example, the dolphin is a carnivore, so I see where you say they are both predators, however the dolphin is a large mammal, whereas, the herring is a small bait type fish, for predators, that forage for and feed on plankton. How does the dorsal fin help each of them survive? What is the function of the dorsal fin? I wasn't really sure where you were going on this comparison.
Hi Jonathan,
ReplyDeleteThank you very much for your input on my post. I actually see what you are saying. I decided to compare my dog and myself because there are so many different species that have homogolous traits, as we can see from the myriad offerings on others' posts and I was kind of thinking of this real world example of me and my own dog - so different and yet here we are sharing a trait that evolved from a shared ancestor. I was pointing out how I use mine differently than my dog does because he walks on all fours and hence the trait evolved differently for him than for me, but yes, I definitely could have provided more detail into how our apendages evolved and work. I was keeping it less academic and more playful, while still trying to show the homologous traits, but thank you for tracing our common ancestor to the Boreoeutheria! Awesome! As for the herring and the dolphin, I'm looking at the combination of their streamlined bodies and the placement of that dorsal fin on those bodies. I think it is a valid comparison as an analogous trait and feel I supported it well by discussing other members of the dolphins class and also showing the side by side picture of a herring and a dolphin. You can really see from the picture how streamlined the bodies are and where the dorsal fin is placed, and I that was really my take on the entire exercise (what she was trying to get us to take away from this whole thing) - at first glance you might think these traits would mean the dolphin and the herring shared a common ancestor, but no, they don't. And evolution obviously helps these two species as it does every species adapt and thrive (in this case, to eat and stave off preditors), but yet when I look at my dog and myself (again getting to my personal take on the exercise) I wouldn't think we had any ancestoral link, but voila, we do. I presented this more from a lay-person perspective, while trying to fulfill all the criteria of the assignment. Thank you for your critique because it gave me a chance to reflect on my post and defend it, which is very rewarding and also how we help each other grow and learn!
Tracy, Good clarification! well done
DeleteGood interaction. :-) This is how it's supposed to work!
DeleteI like how you were able to incorporate your dog into the discussion! Good background and analysis, particularly the ancestral component. The only thing that would have been more helpful would have been an image of the structures you were comparing, such as drawings of the skeletal design of the human and canine forelimb.
ReplyDeleteI was particularly drawn to your ancestral discussion on your analogy pairing. You managed to take your organisms all the way back to their fishy common ancestor, but remember even if the common ancestor possessed the trait in question, remember that this doesn't matter if we know that one of the organisms in the pairing developed the trait independently. In this case, the herring inherited and retained the body shape from the ancestor, BUT we know that the dolphin was originally a land mammal and developed it's streamlined body shape after it made the move into the water environment. That's how we know these are analogs, because one organism evolved it independently.
Other than this point, good post.