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These animals spread to the European coasts and Southern Hemisphere only much later, during the Pliocene. [54] The earliest known ancestor of arctic whales is Denebola brachycephala from the late Miocene around 9–10 million years ago. [55] A single fossil from Baja California indicates the family once inhabited warmer waters. [27] [56] [57]
It is divided into toothed whales (Odontoceti) and baleen whales (Mysticeti), which diverged from each other in the Eocene some 50 million years ago (mya). Cetaceans are descended from land-dwelling hoofed mammals, and the now extinct archaeocetes represent the several transitional phases from terrestrial to completely aquatic. [1]
It was a wolf-like mammal, [3] about 1–2 m (3 ft 3 in – 6 ft 7 in) long, [4] and lived in and around water where it ate fish and other animals. The name Pakicetus comes from the fact that the first fossils of this extinct amphibious whale were discovered in Pakistan .
Sperm whales have the largest brain mass of any animal on Earth, averaging 8,000 cm 3 (490 in 3) and 7.8 kg (17 lb) in mature males. [23] The brain to body mass ratio in some odontocetes, such as belugas and narwhals, is second only to humans. [24] In some whales, however, it is less than half that of humans: 0.9% versus 2.1%. [citation needed]
Whales are fully aquatic, open-ocean animals: they can feed, mate, give birth, suckle and raise their young at sea. Whales range in size from the 2.6 metres (8.5 ft) and 135 kilograms (298 lb) dwarf sperm whale to the 29.9 metres (98 ft) and 190 tonnes (210 short tons) blue whale, which is the
Whales have been kept in captivity by humans for research and entertainment for centuries. Particularly popular are killer whales. Conservation and animal rights organizations have been vehemently opposed to the captivity of these cetaceans. It is common for captive killer whales to display aggression towards other whales and their trainers.
The cetaceans (whales, dolphins and porpoises) are marine mammal descendants of land mammals. The pakicetids are an extinct family of hoofed mammals that are the earliest whales, whose closest sister group is Indohyus from the family Raoellidae. [20] [21] They lived in the Early Eocene, around 53 million years ago.
Artiocetus' name arises from a combination of cetus and artiodactyl, as this fossil was the first to show that early whales possessed artiodactyl-like ankles. Artiocetus belongs to the infraorder Cetacea, which includes whales, dolphins and porpoises. Cetus is a Latinized Greek word literally meaning "sea monster" and is used in biological ...