Extant cetaceans exhibit hyperphalangy, a condition where the finger have an increased number of bones. The first digit, however,has a reduced number of bones (so hypophalangy) and is actually absent in several baleen whales; only Pilot Whales have hyperphalangy on this digit. The fifth digit generally has the ancestral number of bones for baleen whales but toothed whales typically have reduction; Kogia is an exception with hyperphalangy. In toothed whales, the second and third digits have the most number of bones whereas in baleen whales it is the third and fourth digits.
First Image: (A) Orca, (B) Sperm Whale, (C) North Atlantic Right Whale, (D) Humpback Whale, (E) Ichthyosaur (Stenopterygius sp.)
Second Image: (A) Orca, (B) North Atlantic Right Whale, (C) Sei Whale
Cooper, L. et al. (2007) Evolution of Hyperphalangy and Digit Reduction in the Cetacean Manus. The Anatomical Record 290 654–672