a. The two species that I identified as having a homologous trait were humans and Felis Catus (common house cat). The domestic cat is a small, typically furry, carnivorous mammal. Humans are also mammals that are characterized by erect posture, movement on two feet, manual dexterity, increased tool usage compared to other mammals and a general trend towards larger, more complex brains and societies.
b. The homologous trait that they share is between the tailbone in humans and the tail of the cat. In humans, the tailbone has become a vestigial structure. The coccyx, also known as the tailbone, is a "small, triangular bone resembling a shortened tail located at the bottom of the spine. It is composed of three to five coccygeal vertebrae or spinal bones. The vertebrae may be fused together to form a single bone; however, in some cases, the first vertebra is separate from the others" (Healthline). The tailbone functions as "an attachment site for tendons, ligaments, and muscles. It also functions as an insertion point of some of the muscles of the pelvic floor. The coccyx also functions to support and stabilize a person while he or she is in a sitting position" (Healthline). In domestic cats, the tail plays a much different role. The purpose of their tails is primarily for balance, marking their territory, and communication (Factual facts). The cat’s tail has "19 to 23 vertebrae, about 10 percent of the total number of bones in her body. An extensive group of muscles, ligaments, and tendons hold the tail together and provide its amazing mobility" (Catster). These homologous traits that the human and Felis Catus possess because of how each of the two species use them. The domestic cat uses its tail for a variety of reasons, many of which are for balance and communication, and the human only uses its tailbone for stabilization when in certain positions and support for the pelvic floor.
c. The common ancestor of humans and domestic cats is the first mammal to exist. All mammals possess this same homologous trait for a tail. Humans express this trait as a vestigial one as it is not used as a traditional tail like a domestic cat would.
d.
2.
a. The two species that I identified as having an analogous trait were dolphins and sharks. Dolphins are "highly intelligent marine mammals...(that are)...found worldwide, mostly in shallow seas of the continental shelves, and are carnivores, mostly eating fish and squid" (Defenders). Sharks belong to a family of fish that have skeletons made of cartilage, breathe through a series of five to seven gill slits located on either side of their bodies and have multiple rows of teeth. (Defenders).
b. The analogous trait that the dolphin and shark share is their dorsal fins. In dolphins, the dorsal fin, located on the top of the animal, is "filled with a fibrous connective tissue. It serves to keep the animal upright and prevents "roll". Also, it has a thermo-regulation (body temperature adjustment) function" (Understand dolphins). Shark's dorsal fins do much of the same things for the animal. The only difference is that sharks have a pair of dorsal fins instead of just one. The first dorsal fin is "located on the top of a shark’s back and is used to stabilize the shark in the water. Lined with strong, flexible dorsal fibers, the first dorsal fin keeps a shark from rolling on it’s back and helps it make sharp turns while swimming fast" (Shark insider). The secondary dorsal fin "helps to stabilize the shark in the water. The second dorsal fin helps the shark swim steadily and maneuver the back of it’s body more easily" (Shark insider).
c. If you go far enough back in time, you will find a common ancestor of the shark and the dolphin. But, sharks are classified as fish and dolphins are classified as mammals. So, even though they both possess the same trait of having a dorsal fin that provides very similar functions for them, it is still an analogous trait. This is because it is not a result of common genetic history. It is, however, a result of common environmental pressure that caused both species to develop a similar adaptation to that stress.
d.
http://www.sharksider.com/understanding-shark-fins/
Hello classmate, I enjoyed reading you blog post, I almost chose the same animals as you, but instead of the cat I used the dog as an example of homologous trait. How interesting is that human beings have so much in common with animals (not just apes), not just bones with different functions that makes them unique, but also have common ancestors. The analogous trait that sharks and dolphins shared to me was a big surprise, I’ve always thought they were somehow related, because of their environment and the similarity in their bodies. When you see the structures of their dorsal fins you can clearly see the difference between both, and also a sharks dorsal fin will have a straighter trailing edge while the dolphin and porpoise have a very curved trailing edge dorsal fin.
ReplyDeleteVery good opening description of your homologous species pairing and excellent description of your homologous traits. Good explanation of the relationship between function and structure.
ReplyDeleteJust a side note: Scientists have been trying to explain the loss of the ape tail structure for a long time. It isn't clear if it was lost due to lack of use or if there was some type of positive, adaptive pressure that caused it to be reduced in size. Interesting question.
Very good explanation as to how ancestry provides support for this claim of homology.
Good description on your analogous species and very good description of your analogous traits.
With regard to ancestry, you are almost there. :-) You are still asking your reader to make some assumptions to accept that these are analogous traits, namely that these traits are not the result of a common genetic history. What do we know about dolphin evolution, in particular, that can support this claim of analogy?
For example: The common ancestor of the dolphin and shark is an archaic fish, who did possess these fin structures and also passed that trait onto extant shark species. So the question is, did the dolphin also inherit it's fin from that common ancestor? Dolphins "fins" evolved after dolphins split off from terrestrial mammals, i.e., long after the split with ancient fish. This provides us with the evidence we need to confirm that this trait did evolve independently in at least one of these organisms, making these traits analogous.
Good images. Other than that last point on ancestry, good post.
Nice post I really like the how you related the cat and human tailbones, thats something i would have never thought of! to be honest I didn't even know the coccyx was useless. The only thing thing i don't really get is how we know the shark and dolphins traits aren't from a common ancestor directly aside from the fact that dolphins are mammals
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