File:Balaenoptera musculus (blue whale) 1 (31068434305).jpg

Balaenoptera musculus (Linnaeus, 1758) - blue whale skeleton (real). (public display, North Carolina Museum of Natural Sciences, Rayleigh, North Carolina, USA)

Mammals are the dominant group of terrestrial vertebrates on Earth today. The group is defined based on a combination of features: endothermic (= warm-blooded), air-breathing, body hair, mother's milk, four-chambered heart, large brain-to-body mass ratio, two teeth generations, differentiated dentition, and a single lower jawbone. Almost all modern mammals have live birth - exceptions are the duck-billed platypus and the echidna, both of which lay eggs.

Mammals first appear in the Triassic fossil record - they evolved from the therapsids (mammal-like reptiles). Mammals were mostly small and a minor component of terrestrial ecosystems during the Mesozoic. After the Cretaceous-Tertiary mass extinction at 65 million years ago, the mammals underwent a significant adaptive radiation - most modern mammal groups first appeared during this radiation in the early Cenozoic (Paleocene and Eocene).

Three groups of mammals exist in the Holocene - placentals, marsupials, and monotremes. Other groups, now extinct, were present during the Mesozoic.

Whales are members of Order Cetacea, which includes the dolphins and porpoises. Cetaceans have intermediate- to very large-sized bodies that are streamlined (cigar-shaped) and have a thick blubber layer for heat insulation purposes. They are evolutionarily derived from terrestrial mammals that had four legs. The former front legs are now flippers. The hind legs are highly reduced and non-functional in whales. The skull is elongated, with one or two blowholes atop the head. The tail is horizontally-oriented, unlike the vertically-oriented caudal fin ("tail") of a fish. Vertical movement of a whale's tail provides propulsion. Whale bodies have a soft outer skin layer with almost no hair - this improves water flow around the body.

Whales are famous for being deep and long divers. Sperm whales can dive to over 9,200 feet deep. Northern bottlenose whales can hold their breath for over two hours. Unlike humans, whales have evolved mechanisms for coping with diving diseases such as nitrogen narcosis and decompression sickness.

Cetaceans are subdivided into two groups - the odontocete whales and the mysticete whales. The odontocetes are the toothed whales and include the sperm whale, killer whale, dolphins, and porpoises. Mysticete whales are the baleen whales - they include the blue whale, finback whale, humpback whale, gray whale, right whale, minke whale, sei whale, etc. Baleen whales have much larger bodies than toothed whales and have two blowholes atop the head. They eat low on the food pyramid - their dominant food is krill, which is an abundant, small crustacean (Animalia, Arthropoda, Crustacea). Baleen whales usually feed near the surface. Instead of having teeth, these animals have baleen - parallel rows of keratin plates hanging down from the upper jaw. Baleen is used to concentrate small prey and separate them from seawater. Individual baleen plates can be up to 14 feet long.

The blue whale is the largest animal on Earth - it is a baleen whale. This organism is more massive than even the largest dinosaur. The heaviest sauropod dinosaur was about 150 tons. The heaviest known blue whale was about 200 tons.

Blue whale skeletons are rarely on display. The example shown above is in North Carolina's natural history museum in Rayleigh.

From museum signage: "Named for its motley blue-gray color, the blue whale is known for its enormous size. At over 100 feet and weighing as much as 160 tons, it is the largest mammal ever to live on Earth. It has a long, broad head with two blowholes and long, slender flippers. Because diatoms sometimes make its underside yellow, the blue whale is nicknamed "Sulfur Bottom".

How do you feed a blue whale? With at least two tons of tiny shrimp, called krill, every day. Blue whales swim near the surface and lunge after schools of prey. As they take in huge volumes of water, the grooves that line their throats expand like giant balloons. When they push the water out through the baleen, a filtering system, the krill are trapped. The whales use their tongues to lick the krill from the baleen.

Why is the skull of this whale darker than the rest of its skeleton? The bones of whales contain oil, most of which is removed when the bones are cleaned. The skull contains a lot more oil than the smaller bones and will continue to seep for many years.

Blue whale females remain pregnant for about a year. At birth, calves are 25 feet long, weigh more than two tons, and grow at the rate of 200-250 pounds a day.

Blue whales migrate seasonally between their tropical or temperate breeding grounds and their polar feeding grounds worldwide. They commonly stay far from shore, making it difficult to track their migrations or study behavior.

In the early 1900s, whalers found great profit in whale oil. Because blue whales could produce about six times more oil than smaller species, they were hunted nearly to extinction. Blue whales are now completely protected by international agreement and their numbers are increasing. Lamp oil and other products once made from whale oili are now made from vegetables and petroleum. "

Classification: Animalia, Chordata, Vertebrata, Mammalia, Artiodactyla, Cetacea, Mysticeti, Balaenopteridae

See info. at: <a href="https://en.wikipedia.org/wiki/Blue_whale" rel="nofollow">en.wikipedia.org/wiki/Blue_whale</a> and <a href="https://en.wikipedia.org/wiki/Baleen_whale" rel="nofollow">en.wikipedia.org/wiki/Baleen_whale</a> and