Whales, Dolphins and Porpoises

• Whales, dolphins and porpoises are cetaceans (Class Mammalia, Order Cetacea)

• Of all the marine mammals, cetaceans (and sirenians) have made the most complete transition to aquatic life– Spend their entire lives in the water– The bodies of cetaceans are streamlined

and look remarkably fish-like; an example of convergent evolution

Convergent Evolution: Streamlining

Convergent evolution is the process by which unrelated species evolve similar physical characteristics because they have similar lifestyles

Whales, Dolphins, and Porpoises

• Cetaceans have a pair of front flippers, but the rear pair of limbs has virtually disappeared– Remain in adults as small, useless bones

– Most cetaceans have a dorsal fin, like fishes

– Their muscular tail ends in a pair of fin-like, horizontal flukes

Whales, Dolphins, and Porpoises

– Blubber provides cetaceans with insulation

– Cetacean nostrils are on top of the head, forming a single, or double opening called the blowhole

Whales, Dolphins and Porpoises

• There are ~90 species of cetaceans• All are marine, except for 5 species of

freshwater dolphins• Cetaceans are divided into two groups:– Toothed whales – includes dolphins & porpoises– Baleen whales; toothless, filter-feeding whales

Photos property of the Riverhead Foundation

Cetaceans: Toothed Whales

• The majority of cetaceans are toothed whales• Toothed whales use their teeth only to catch

and hold prey, not to chew it• Toothed whales have a single blowhole (one

opening) on the top of their head• Though they are all whales, most of the small

toothed whales are called dolphins or porpoises

Photo property of the Riverhead Foundation

Is it a dolphin or a porpoise?• The six species of porpoises are blunt-nosed

whales, having flattened teeth• The many more species of dolphins possess a

distinctive snout or ‘beak’ and have conical teeth

Porpoise(Family Phocenidae)

Dolphin (Family Delphinidae)

The Toothed Whale Whales

• The toothed “whales” include the sperm whale, beluga, pilot whales, beaked whales, and orca, each divided into their own families

A bottlenose whale? Yes!

Echolocation• All species of toothed whales are capable of

echolocation• Marine mammals echolocate by emitting

sound waves, and listen for the echoes reflected back from surrounding objects– The brain then analyzes the echoes– The time it takes the echoes to return tells the

animal how far away the object is– A type of biological sonar!

Echolocation

Baleen Whales

• Toothless whales are best known as baleen whales

• Instead of teeth, they have rows of flexible plates, or baleen, which hang down from the upper jaws

• Baleen is made of keratin• The inner edge of each plate consists of hair-

like bristles that overlap and form a dense mat

Baleen whales

Baleen Whales

Baleen Whales

• Baleen whales are characterized not only by their baleen, but by the double opening of their blowholes (double blowhole)

• Baleen whales can be further divided into the rorquals; rorquals feed by gulping up schools of fish and swarms of krill– The lower portion of the throat

expands during feeding, along distinctive grooves

Photo property of the Riverhead Foundation