Final answer:
Bony fishes, or Osteichthyes, make up the largest class of vertebrates, with approximately 30,000 species. Given that there are about 50,000 vertebrate species in total, bony fishes represent approximately 75% of the vertebrate population, which corresponds to answer C).
Step-by-step explanation:
The question asks about the proportion of vertebrates that bony fishes represent. Bony fishes are members of the clade Osteichthyes, and they are characterized by having a bony skeleton. It is noted that the majority of modern-day fish species belong to this group, with an estimated number of species around 30,000, signifying that bony fishes constitute the largest class of vertebrates in existence today. Looking at the total number of vertebrate species, which is approximately 50,000, bony fishes represent a substantial proportion of the vertebrate population.
Therefore, the correct answer to the question 'What proportion of the vertebrates is represented by bony fishes?' is C) Approximately 75%. This means that out of the entire vertebrate group, three quarters are made up by bony fishes, indicating their overwhelming prevalence in the vertebrate world.