Bony Fish (bass etc.) and marine mammals (like dolphins) evolved some similar adaptations for survival in aquatic environments. However, they evolved separately and are not closely related evolutionarily. What type of evolution does this represent?

Convergent evolution

Explanation:

Convergent evolution is a type of evolution of similar features and/or structures between organisms that are not phylogenetically related. This type of evolution is known to create analogous structures/organs that exhibit similar or the same functions but were not present in the last common ancestor of these taxa. An example of analogous structures (and therefore also of convergent evolution) are the wings of bats and of insects (e.g., butterflies). Conversely, divergent evolution is a type of evolution where species phylogenetically related, i.e., species that share a common ancestor, evolve and accumulate differences over time.

they deliver oxygen to the blood