File:Mesoplodon mirus (True's beaked whale) 10 (30840724990).jpg

Mesoplodon mirus True, 1913 - True's beaked 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 mysticete and the odontocete whales. Mysticete whales are the baleen whales - they include the blue whale, finback whale, humpback whale, gray whale, right whale, minke whale, sei whale, etc. The odontocetes are the toothed whales and include the sperm whale, killer whale, dolphins, porpoises, and belugas. Toothed whales have smaller bodies than the baleen whales. They have one blowhole atop the head and have prominent teeth - they feed on fish and squid and other large animals.

From museum signage: "The True's beaked whale is an offshore inhabitant. Almost everything known about these small whales comes from strandings. This whale washed ashore in North Carolina in 1940. This skeleton is so rare that is is one of only 18 in research collections around the world.

True's beaked whales are rarely sighted at sea. The only information we have about this species comes from stranded whales that have washed ashore along the Atlantic Coast of the United States.

True's beaked whales grow up to 17 feet. They have only one pair of teeth in their lower jaws [located on the tip of its lower jaw]. In females, the teeth never become exposed. [They] "gum" their prey to death. It is thought that most male beaked shales use their teeth to fight one another for mates. True's beaked whales are unique because they typically lack the scars that are evidence of this behavior.

Beaked whales eat squid, but little else is known about their behavior. Their mysteriousness makes this specimen - the only pregnant True's beaked whale found - particularly valuable.

Museums and other research institutions collect stranded whales for study and preservation. In 1940 huge waves from a sudden storm at sea tossed this museum's one-and-a-half ton whale onto Gull Shoal Beach. Stranded on the sand, she soon died. As they stripped the flesh from her carcass, researchers made a surprising discovery: the whale was pregnant.

Scientists buried the mother's bones in sand so that the remaining flesh would be removed by natural processes. They created a model of the 200-pound fetal whale by casting its shape in plaster.

Models of mother and baby hung in the old museum for more than 50 years, as did the mother's skeleton, which is now on display here. There are only fifteen True's beaked whale specimens in U.S. museum collections, and fewer on display."

Classification: Animalia, Chordata, Vertebrata, Mammalia, Artiodactyla, Cetacea, Odontoceti, Ziphiidae

See info. at: <a href="https://en.wikipedia.org/wiki/True's_beaked_whale" rel="nofollow">en.wikipedia.org/wiki/True%27s_beaked_whale</a> and <a href="https://en.wikipedia.org/wiki/Toothed_whale" rel="nofollow">en.wikipedia.org/wiki/Toothed_whale</a> and