Homology and Analogy
In the pictures above, all of these species possess the ability to swim under water with the use of a variety of adaptations. They each, specifically, share two side fins that aid in maneuverability in the water. Dolphins and the whales are homologous because they anatomically posses bones in their pectoral fins that are very similar to the human arm. According to Smithsonian Institution, dolphins and whales use their pectoral fins to steer and guide through the water, and they both have the major skeletal elements of the forelimbs of land mammals. These homologous traits exhibit difference between the two species because the fins are shortened and modified compared to each mammal due to their size and environment. According to the University of Bristol, these Cetacea are considered to be descendants of land mammals, largely due to the bones found in the fins and their need to breathe air from the surface. Also, the University of Bristol states that whales and dolphins were close relatives to the largest hoofed carnivores on land known as Rodhocetus.
As compared to dolphins, sharks possess the analogous pectoral fins. Although, sharks use their pectoral fins to maneuver up while swimming. Sharks are considered fish and not mammals; therefore, their fins are rigid, not flexible, and the fins are supported by rods made of cartilage, according to PBS.org. In this way their fins are analogies. Sharks are classified as Chondrichthyes (jawed fish with paired fins). They first appeared 450 may, and they have no bones. Their skeletal structure is made up of cartilage. As sharks have remained in equilibrium for a large amount of time, their ancestors have shared the analogous trait of pectoral fins.
Analogous structure first: Good example of the forelimbs/fins of dolphins and sharks and great logical argument in the discussion on ancestry. Well done.
ReplyDeleteFor your homologous structure, keep in mind that the two species need to have common ancestry (you have that) and also key structural differences that are caused by environmental differences. You don't really demonstrate this, even you suggest these differences exist. The shape and structure of forelimbs of whales and dolphins have more similarities than differences due to the environment in which they live. A better example would have been one you alluded to early in the paragraph, namely comparing human forelimbs with whales/dolphins. These are homologs because of their clear anatomical differences and would have been a better way to go here.