Final answer:
The blowhole of a dolphin resembles a modified nostril, an evolutionary adaptation for breathing. Dolphins and fish have analogous body shapes, featuring convergent evolution due to similar environmental pressures, not a recent common ancestor.
Step-by-step explanation:
The blowhole of a dolphin looks like it could be a highly modified nostril. This modification is part of the evolutionary adaptations that enable dolphins to breathe air efficiently at the water's surface. Regarding the body shapes of dolphins and fish, this feature is more likely an analogous trait rather than a homologous one.
Although dolphins and fish have a similar body plan which is streamlined for swimming, these traits evolved independently in the two groups to serve the same function due to similar environmental pressures, rather than from a recent common ancestor. This phenomenon is known as convergent evolution. The concept of homologous traits, on the other hand, refers to features that arise from a common ancestor, such as the limb bones in different vertebrates.