Megaptera novaeangliae (humpback whale) 5
Northern right-whale dolphin image by: James St. John
Megaptera novaeangliae Borowski, 1781 – humpback 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.
From museum signage:
"Humpback whales aren’t actually humpbacked. They were probably named for their diving style. These whales curve their backs when they dive, exposing a large bulge above water. Humpbacks also do backflips, breaching the water in graceful arcs. Their long flippers – about one-third their body length – make them excellent acrobats. Humpback whales can reach a length of 52 feet and a weight of 44 tons. Individuals can be identified by unique patterns of white markings on the undersides of their flukes."
Classification: Animalia, Chordata, Vertebrata, Mammalia, Artiodactyla, Cetacea, Mysticeti, Balaenopteridae
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