Very occasionally, we still see a cetacean with legs. All whales and dolphins still have the genes for legs, and sometimes, the suppression of those genes doesn't happen, and...
Probably the most well known case of atavism is found in the whales. According to the standard phylogenetic tree, whales are known to be the descendants of terrestrial mammals that had hindlimbs. Thus, we expect the possibility that rare mutant whales might occasionally develop atavistic hindlimbs. In fact, there are many cases where whales have been found with rudimentary atavistic hindlimbs in the wild (see Figure 2.2.1; for reviews see Berzin 1972, pp. 65-67 and Hall 1984, pp. 90-93). Hindlimbs have been found in baleen whales (Sleptsov 1939), humpback whales (Andrews 1921) and in many specimens of sperm whales (Abel 1908; Berzin 1972, p. 66; Nemoto 1963; Ogawa and Kamiya 1957; Zembskii and Berzin 1961). Most of these examples are of whales with femurs, tibia, and fibulae; however, some even include feet with complete digits.
For example, Figure 2.2.1 shows the bones from the atavistic legs of a humpback whale. These bones are the remnants of one of two symmetrical hind-limbs found protruding from the ventral side of a female humpback whale, captured by a whaling ship from the Kyuquot Station near the west coast of Vancouver Island, British Columbia, in July 1919. Two officials of the Consolidated Whaling Company were understandably impressed by this discovery, and they removed one of the legs and presented the skeletal remains to the Provincial Museum in Victoria, B.C. (The other leg was evidently taken as a "souvenir" by crew members of the whaling ship). The museum's director, Francis Kermode, presented the bones to Roy Chapman Andrews from the American Museum of Natural History (AMNH) in New York. Andrews reported the findings, along with photographs of the whale from the whaling crew, in
American Museum Novitates, the journal of the AMNH. Andrews identified in the remains a shrunken cartiliginous femur, tibia, tarsus, and metatarsal. Both legs initially were over four feet long and covered in normal blubber and skin.