10 Facts About Dolphins

10 Facts About Dolphins

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Dolphins are well known for their intellect, their gregarious nature, and their acrobatic abilities. But there are many lesser known qualities that make a dolphin a dolphin. Here we'll explore ten characteristics of dolphins and learn more about these much-loved marine mammals.

1. Dolphins belong to a group of mammals referred to as cetaceans (or Cetacea). The cetaceans are further broken down into two main groups, the toothed whales (or Ondontoceti) and the baleen whales (Mysticeti). Dolphins are classified as toothed whales (Ondontoceti). Other toothed whales include killer whales, pilot whales, beluga, narwhal, sperm whales, and several groups of river dolphins.

2. The term 'dolphin' refers to a diverse assortment of marine mammals. The term dolphin is not restricted to a single taxonomic class and therefore is an unspecific term. The groups of toothed whales whose members are often referred to as dolphins include the oceanic dolphins (Delphinidae), river dolphins (Iniidae), and the Indian river dolphins (Platanistidae). Of these groups the oceanic dolphins are by far the most diverse.

3. Oceanic dolphins are also referred to as 'true dolphins' and are the most diverse group of cetaceans. The species of dolphins that belong to the Family Delphinidae are referred to as 'oceanic' or 'true' dolphins. The Delphinidae group includes about 32 species and is the largest of all subgroups of the cetaceans. Species of oceanic dolphins (Delphinidae) inhabit the open ocean, though this is not a strict rule for the group (in some cases, oceanic dolphins inhabit coastal waters or riverine habitats).

4. Some oceanic dolphins have a prominent beak also known as a 'rostrum'. The snout of some oceanic dolphins is long and slender due to their elongated, prominent jaw bones. Within the dolphins' elongated jaw bone sits numerous conical teeth (some species have as many as 130 teeth in each jaw). Species that have prominent beaks include, for example, Common Dolphin, Bottlenose Dolphin, Atlantic Humpbacked Dolphin, Tucuxi, Long-Snouted Spinner Dolphin, and numerous others.

5. A dolphin's forelimbs are known as 'pectoral flippers'. The forelimbs of a dolphin are anatomically equivalent to the forelimbs of other mammals (for example, they are analogous to arms in humans). But the bones within the forelimbs of dolphins have been shortened and made more rigid by supporting connective tissue. Pectoral flippers enable dolphins to steer and modulate their speed.

6. Some dolphin species lack a dorsal fin. The dorsal fin of a dolphin (located on the back of the dolphin) acts like a keel when the animal swims, giving the animal directional control and stability within the water. But not all dolphins have a dorsal fin. For example, the Northern Rightwhale Dolphins and the Southern Rightwhale Dolphins lack dorsal fins.

7. Dolphins have a unique sense of hearing. Dolphins do not have prominent external ear openings. Their ear openings are small slits (located behind their eyes) which do not connect to the middle ear. Instead, scientists suggest that sound is conducted to the inner and middle ear by fat-lobes located within the lower jaw and by various bones within the skull.

8. Dolphins have excellent vision in and out of the water. When light passes from air to water, it changes speed. The creates an optical effect referred to as refraction. For dolphins, this means their eyes must correct for these differences if they are to see clearly in both conditions. Fortunately, dolphins have specially adapted lens and cornea that enable them to see clearly in and out of the water.

9. The Baiji is a critically endangered river dolphin that inhabits the murky waters of the Yangtze River in China. The Baiji has suffered dramatic population declines over recent decades due to pollution and heavy industrial use of the Yangtze river. In 2006, a scientific expedition set out to locate any remaining Baiji but failed to find a single individual in the Yangtze. The species was declared functionally extinct.

10. Dolphins probably do not have a very strong olfactory sense. Dolphins, like all toothed whales, lack olfactory lobes and nerves. Because dolphins do not possess these anatomical features, they most likely have a poorly developed sense of smell.
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Ancestors of Inia geoffrensis were a relatively successful marine group, but were displaced during the Miocene period by the appearance of more advanced delphinids. Inia may have entered the Amazon from the Pacific Ocean approximately 15 million years ago, or from the Atlantic Ocean between 1.8 million and 5 million years ago. Their long beaks (often lined with tiny hairs), small eyes, disproportionately large flippers and highly flexible bodies -- once considered "primitive" features -- are now recognized as specialized adaptions to a complex environment.

Soltalia fluviatlis is a warm-water coastal species distributed from the eastern coast of Central America down along the northeastern coast of South America. No one knows for sure when some of these delphinids began to occupy and adapt to freshwater river systems. They are one of the few delphinid species which can move freely between fresh, brackish, and marine waters.
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