Approximately how many known vertebrates are there?

• A. 5,200
• B. 520
• C. 520,000
• D. 52,000

Answer: (D)

Estimating the number of known vertebrate species. Vertebrates are animals with backbones, including fish, amphibians, reptiles, birds, and mammals. The count is a rough figure because new species are described regularly and classifications change with new research. About fifty-two thousand living, described vertebrate species is a commonly cited estimate used in introductory biology because it covers all five vertebrate classes without claiming there are too many or too few. Remember that different databases may give slightly different numbers, but this range reflects widely taught estimates of described vertebrates.

This helps explain why the other options aren’t as good: under five thousand would miss many major groups of vertebrates, while hundreds of thousands would overshoot what is commonly documented in current catalogs.