Marine mammals in Antarctica can be divided into two major groups: the pinnipeds and the cetaceans. Pinnipeds can be further divided into two groups, true seals in the family Phocidae and sea lions in the family Otariidae, while cetaceans are either toothed, or Odontocetes, or baleen whales, the Mysticetes. We have all four of these groups of marine mammals in Antarctica that are briefly described here. Four of the phocid seals are endemic to Antarctica and adapted to breed on sea ice. Cetaceans include four different types of orcas, or killer whales (actually more related to dolphins) that may represent up to three species. Minke and humpback whales are the most common of the baleen whales in Antarctica, feeding mainly on krill.