Unit 2: Cetaceans

The Classification of Cetaceans

Whales and dolphins are members of the kingdom Animalia, phylum Chordata, and class Mammalia. That means that whales and dolphins are mammals, not fish. They give birth to their young rather than lay eggs. They nurse their young through mammary glands, and they give extensive parental care to their offspring. Collectively, we place all of the 80-90 whales and dolphins in the order cetacean. Cetus from the Latin meaning whale. Cetaceans are generally placed into two distinct sub-orders the Mysticeti (whales with baleen) and Odontoceti (toothed whales.)

The Evolution of Whales

The fossil record of Whales and dolphins shows us that they are decedents of land based mammals. Although they have been extremely successful, whales have a lot of features that are not ideally suited for life in the ocean. To start with, whales and dolphins breathe air, limiting them to life at the surface. They are warm blooded and most species struggle to maintain high body temperatures. They have a spine and pelvis that moves up and down like other mammals, rather than the side to side movement of fish. The bone structure of their fins matches that of hoofed land mammals rather than fish. They nurse their young with milk and most species have hair or fur. Additionally, many whales have residual leg bones that are no longer attached to their pelvis.

A great diversity of whale and whale ancestor fossils tell a compelling evolutionary story of the movement from land to water. Ancient whale ancestors most likely moved into the water to take advantage of abundant food resources and gradually over time evolved into highly successful modern whales. Watch a video clip from PBS Evolution to learn more about whale evolution.

The embryological development of whales living in the present also tells a story of their evolutionary history. In many embryonic whales, external hind limb buds are visible for a time but then disappear as the whale grows larger. Some whale embryos will develop hair and rudimentary ear pinnae, which disappear before birth. In some whale species developing embryos start off with nostrils in the front of their head like land mammals, only to have these migrate backwards to the blow hole position as the embryonic whale continues to develop.

Mysticeti (Baleen Whales)

Description: Mysticeti are the largest living animals that have ever existed on Earth. They are larger than elephants, and some even larger than the largest of the dinosaurs. Blue Whales, the largest whale species on Earth, have an average adult length of 80 feet (24 meters) and have been measured to 98 feet (30 meters). It is impossible to weigh such an animal, but estimates have put the large ones near 190 metric tons. What gets lost in that size is how long and sleek these animals are. Blue whales are also some of the fastest swimming animals in the ocean, reaching 50 kilometers per hour for short distances. All baleen whales have large convex skulls with attached baleen plates hanging down from the maxilla of their skull. Baleen whales also have a large double nostril blow hole on the top of their head through which they breath.

 

Feeding: Aside from their size, the mysticeti’s most distinctive feature is the baleen plates that hang down from their top jawbone. Whales use these baleen plates to filter out food items such as small fish, krill, and plankton from immense quantities of water. It may seem strange that the largest animals on earth would feed on organisms that are frequently less than an inch long, but from an ecological perspective it makes perfect sense. Krill, copepods, and other types of plankton are some of the most abundant (by weight) forms of life on Earth.

All baleen whales are filter feeders, but different whales use a variety of different strategies for capturing food. Some whales, such as bowhead whales and right whales, have exceptionally long baleen. They will skim the surface of the water with mouths agape, gathering small phytoplankton in their mouths. (YouTube Clip) Some whales, such as blue and fin whales, will swim quickly into schools of prey, gulping up huge schools of prey at a time and filtering out the water as they close their very large mouths. (YouTube Clip) Gray whales, who have very short and stiff baleen, feed by scraping the side of their heads along the bottom, sucking up mouthfuls of sediment and filtering out the crustaceans living in the mud. Humpback whales have some of the most interesting feeding style of all. They will often feed in small groups producing nets of bubbles to entrap schools of fish. (YouTube Clip)

Life Cycles: The life cycle of most baleen whales includes late reproductive maturity, long gestational periods, and calves every 3-4 years. Baleen whale mothers will nurse their calves for up to two years. Most species of baleen whales make great migrations with calving often taking place in calm shallow and protected waters. Most baleen whales feed in the colder and more nutrient rich waters of the higher latitudes. Baleen whales are generally considered less social than their gregarious cousins the tooth whales, but they will form small feeding or mating groups. Baleen whales have a variety of courtship styles; they are can be highly competitive, often elaborate, and sometimes aggressive. Male humpbacks, the most unique in this regard, participate in an annual “sing off” to attract potential female mates.

Behavior: Observing whales can be an exciting experience. This is despite the fact that they spend much of their time underwater. Several obvious behaviors can be observed when whale watching. Whales will often stick their heads out of the water to look around in a move called spy hopping. Sometimes they throw themselves completely out of the water in a move called breaching. Whales may also slap their fins or flukes (tails) to make sounds that can be heard for great distances.

Odonticeti (Toothed Whales)

Description: With the noted exception of the sperm whale, the toothed whales are smaller than the baleen whales. They have highly developed brains and are aggressive predators. Toothed whales have concave skulls with a large bulbous organ called a melon, which they use to focus sound.

Behavior: Toothed whales are defined by their social groups that are typically large extended families led by a matriarchal head. Males, especially male sperm whales, are more likely to be isolated into bachelor groups.” Smaller groups will often come together to form larger “super pods” for the purpose of mate selection. Dolphins and toothed whales give the appearance of being highly playful, putting on frequent aerial and acrobatic displays. Dolphins are often observed riding the waves, pushed by the front of boats in a behavior called bow riding or even surfing.

Feeding: As in all things, toothed whales feed in groups. Often, working collectively as unit, they are highly adapted hunters. Dolphins have been observed to successfully corral fish into shallow areas where they are easy to eat. Even more remarkably, killer whales will sometimes beach themselves onto shallow beaches when going after pinnipeds or penguins. Toothed whales make extensive use of echolocation to locate, and in some cases can use sound to disable or “stun” their prey. Sperm whales, in particular, have a large arsenal of sounds to locate and disable their prey. Their skills at hunting are so well adapted that large schools of tuna will often follow below pods of dolphins, taking advantage of the dolphins ability to locate prey through echolocation. Some groups of toothed whales are migratory, and others prefer to stay in local habitats. Toothed whales will often dive to great depths in the search for prey (particularly squid). Most notably, sperm whales can dive to depths of three kilometers and stay down for over an hour.

Questions to Research

Use the reading above and slide deck for this unit to help you answer these questions.

1. Read about the evidence that whales have evolved from land mammals. Or watch “When Whales Watched on YouTube.”  Describe two pieces of fossil evidence that link whales to land mammals.
2. Based on the reading above describe two differences between Mysteceti and Odonticeti whales.  One difference should be in anatomy and the other in feeding or behavior.  Pay attention to the 3d skulls of the two groups available in the  reading.
3. Watch a short video from NOAA on tagging whales in Antarctica.  Describe how they tag whales as well as what they learn about the whales behavior from these tags.
4. Many cetaceans take part in long migrations between feeding and breeding grounds.  Open up this infographic.  Examine it closely and describe the migratory routes of one species of whale found in the Pacific Ocean.
5. A new population of blue whales (the largest animals on earth) were recently discovered by scientists.  Where were they discovered, and how were they identified?
6. North Atlantic Right Whales were considered to be the “right” whales to hunt because of their slow moving behavior and the tendency of their bodies to float when killed.  Although they are no longer hunted, explain what risks these most endangered of whales are facing.  If you need a feel good moment, watch a NOAA team liberate a North Atlantic Right Whale from fishing gear in which it had become entangled (YouTube).
7. Cetaceans are the largest animals to have ever lived on earth (larger even than the dinosaurs.  Describe how large blue whales, sperm whales, fin whales, and bowhead whales are.  This infographic may help you.  Finally, just for fun, type “blue whale skeleton, Santa Cruz, CA” into google maps. Zoom in all the way in. Comparing this reconstructed skeleton to the cars and buildings should help you understand how big these animals are.
8. Whales as ecosystem engineers.  What is meant by that term and how do whales stabilize ecosystems?
9. As cetaceans go, gray whales are distinctive in their appearance and in their feeding style.  They spend their summers feeding in Alaska’s food rich waters where they are studied by NOAA biologists.  Describe two things you learn about how Gray Whales are unique.
10. Odonticeti (toothed whales) are long lived, intelligent, and highly social.  They typically live in matrilineal groups led by older females.  As such, different family groups, develop different cultural rules and behaviors.  Describe two cultural differences between transient and resident orca groups.