Contents of volume 70A number 4 1981

Abstract

Several species of mammals belonging to terrestrial groups have become facultative or obligate members of the marine ecosystem. The polar bear (Ursus maritimus; family Ursidae) and the arctic fox (Vulpes lagopus; family Canidae) range widely over the north polar pack-ice. Two species of bats (order Chiroptera) also catch fish in coastal waters, the greater bulldog bat (Noctilio leporinus; family Noctilionidae) of the neotropics and the fishing bat (Myotis vivesi; family Vespertilionidae) of the Gulf of California. Four clades of placental mammals (class Mammalia: cohort Placentalia) independently evolved adaptations for life in the oceans. These are the still-living pinnipeds (sea lions, walruses, and seals), cetaceans (whales, dolphins, and porpoises), and sirenians (manatees and dugongs), and the extinct desmostylians. The pinnipeds are amphibious animals capable of terrestrial locomotion and must haul out on shore to give birth. The cetaceans and sirenians (except for a few primitive Eocene species) are aquatic, having lost their hindlimbs and evolved huge muscular tails with terminal flukes for swimming. The extinct desmostylians were quadrupedal amphibious creatures. The pinnipeds and cetaceans are carnivorous; the sirenians and desmostylians are herbivorous. Although primarily oceanic, several members of each of the three living groups have secondarily invaded freshwater habitats. The systematics of all of these sea mammals, living and fossil, is a flourishing field of research; many details are currently contested, and several paraphyletic groupings await resolution, so changes in the prevailing classification may be anticipated.