Final answer:
The similarities in body shape between sharks and dolphins are analogous, resulting from convergent evolution to adapt to a similar aquatic environment. They don't have a close evolutionary relationship and their common body shape does not imply a recent common ancestor.
Step-by-step explanation:
The similarities between sharks and dolphins in body shape are analogous traits rather than homologous. This is because, despite both being vertebrates, sharks are fish and dolphins are mammals, indicating that their similar streamlined bodies are not due to a recent common ancestry but instead are due to convergent evolution. Convergent evolution occurs when different species evolve similar traits independently of each other to adapt to similar environments or ecological niches. In this case, the hydrodynamic shape of dolphins and sharks is an adaptation to living and moving efficiently through water.
Homologous structures, on the other hand, have a similar embryonic origin and are found in species with a common ancestor, even if their current functions differ. For example, the bones in the front flipper of a whale are homologous to the bones in the human arm. These fish and mammalian structures serve different purposes but have a common ancestral origin.
To summarize, the similarities in body shape between sharks and dolphins are examples of analogous structures due to adaptation to similar environmental pressures, not a close evolutionary relationship, and thus, the correct answer is Option 2: B - Analogous.