The blue whale is not only the largest animal on the planet — it is the largest living creature ever recorded in Earth’s history, reaching up to 27 metres in length. The fin whale follows at 22 metres, and the North Atlantic right whale, despite its considerable weight, has a maximum length of 18 metres. The minke whale is the smallest Mysticeti at just 10 metres. By comparison, the largest Odontoceti — the sperm whale — reaches 18 metres, approaching the size of medium-sized baleen whales.
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Roston, R. A., Lickorish, D., & Buchholtz, E. A. (2013). Anatomy and age estimation of an early blue whale fetus. Anat Rec 296: 709–722. https://doi.org/10.1002/ar.22678