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Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. March Learn how and when to remove this template message The two parvorders, baleen whales Mysticeti and toothed whales Odontocetiare thought to have diverged around thirty-four million years ago.
Baleen whales have bristles made of keratin instead of teeth. The bristles filter krill and other small invertebrates from seawater. Grey whales feed on bottom-dwelling mollusks.
Rorqual family balaenopterids use throat pleats to expand their mouths to take in food and sieve out the water. Most mysticetes prefer the food-rich colder waters of the Northern and Southern Hemispheres, migrating to the Equator to give birth. During this process, they are capable of fasting for several months, relying on their fat reserves.
The parvorder of Odontocetes — the toothed whales — include sperm whales, beaked whales, killer whales, dolphins and porpoises. Generally the teeth are designed for catching fish, squid or other marine invertebratesnot for chewing them, so prey is swallowed whole.
Teeth are shaped like cones dolphins and sperm whalesspades porpoisespegs belugastusks narwhals or variable beaked whale males. Female beaked whales' teeth are hidden in the gums and are not visible, and most male beaked whales have only two short tusks. A few toothed whales, such as some killer whalesfeed on mammals, such as pinnipeds and other whales.
Toothed whales have well-developed senses — their eyesight and hearing are adapted for both air and water, and they have advanced sonar capabilities using their melon. Their hearing is so well-adapted for both air and water that some blind specimens can survive. Some species, such as sperm whales, are well adapted for diving to great depths.
Several species of toothed whales show sexual dimorphismin which the males differ from the females, usually for purposes of sexual display or aggression.
Anatomy[ edit ] Dolphin anatomy Cetacean bodies are generally similar to that of fish, which can be attributed to their lifestyle and the habitat conditions.
Their body is well-adapted to their habitat, although they share essential characteristics with other higher mammals Eutheria. Almost all have a dorsal fin on their backs that can take on many forms depending on the species.
A few species, such as the beluga whalelack them.
Both the flipper and the fin are for stabilization and steering in the water. The male genitals and mammary glands of females are sunken into the body. In larger species, it can reach a thickness up to half a meter 1.Diffusion of responsibility is a sociopsychological phenomenon whereby a person is less likely to take responsibility for action or inaction when others are present.
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Established in the 's and incorporated in , the Arlington Youth Football Club (AYFC) has a long history of supporting the youth of Arlington County through Football and Cheer.