Dugongs are large mammals that look like a cross between seals and walruses but are actually more closely related to elephants. They live in the coastal areas of the Indian Ocean, the Indonesian archipelago, and the southwestern Pacific around the Philippines.

Dugongs are threatened in almost all of their habitat, but they thrive in Western Australia's Shark Bay, where an estimated 10,000 dugongs eat sea grass and try to avoid tiger sharks, their primary predator.

In this lesson, students will compare and contrast the physical appearance and adaptations of dugongs with those of elephants, and they'll consider the evolutionary relationship between these two animal species. They will discuss how the dugong's adaptations have made it well suited to life in the ocean, and they will conclude by writing paragraphs about the things they've discussed and learned.

Geography, life sciences

Standard 8: "The characteristics and spatial distribution of ecosystems on Earth's surface"

Two hours

• Computer with Internet access

Students will

• look at pictures of animals and try to determine which are most closely related to one another;
• discuss the actual relationships between these animals and the basis by which scientists determine relationships;
• look at and discuss an elephant evolutionary tree and the elephant's relationship to dugongs;
• compare and contrast photographs of a dugong and an elephant, and list and discuss their findings;
• discuss how dugongs' physical characteristics help them live in the ocean; and
• write paragraphs explaining the relationship, similarities, and differences between dugongs and elephants and the dugong's special adaptations to life in the ocean.

Ask students to name some animals that are related to each other despite being members of different species and despite living in different habitats. Some of the numerous examples include African and Asian elephants; polar bears and grizzly bears; lions and leopards; etc.

Have students look at the pictures of animals at the following Web sites and determine to the best of their judgment which ones are the most closely related. Ask them to list their decisions. Try to limit this exercise to 10 to 15 minutes, as it's not the central focus of the lesson. It's OK if students don't get to all of them.

National Geographic: Creature Feature—African Elephants
National Geographic: Creature Feature—Crocodiles
National Geographic: Creature Feature—Emperor Penguins
National Geographic: Creature Feature—Mountain Gorillas
National Geographic: Creature Feature—Ring-Tailed Lemurs
National Geographic: Sights & Sounds—Sulu-Sulawesi Seas (Click "Begin" and then scroll over the interactive map to find a link to a picture of a dugong.)
Nine-Banded Armadillo
Everything You Always Wanted to Know About Kangaroos
The Horseshoe Crab: Putting Science to Work to Help "Man's Best Friend"
Animal Facts: Brown Recluse Spider
Sloth Photo Gallery
PossumRescue

Relationship answers:

• Dugong/elephant
• Spider/horseshoe crab
• Crocodiles/birds
• Kangaroo/opossum
• Sloth/armadillo
• Lemur/gorilla

Discuss students' lists as a class. They should realize that even animals that at first seem very different may be related. They will also notice that an animal might be less closely related to an animal it resembles than to another animal that looks quite different.

For example, did many students guess that the lemur was most closely related to the sloth? Lemurs are primates and therefore are more closely related to gorillas than to sloths, but this is not obvious from looks alone.

Explain that when we talk about one animal species being related to another species, we generally mean that the two species share a common ancestor. For example, lemurs and gorillas are related because gorillas are part of a primate group (the suborder Anthropoidea) that scientists believe evolved from the primate group that includes lemurs (the suborder Prosimii).

This happened during the Eocene period, about 34 million to 50 million years ago. Thus, scientists believe that primitive lemurs were the ancestors of gorillas (and chimpanzees, orangutans, and humans).

Remind students that dugongs and elephants share a common ancestor and were the best match in the exercise they did a few minutes ago. Have them go to the Elephant Evolution page and scroll down until they see the evolutionary tree. Explain that dugongs branched off from this elephant family tree in or before the Eocene, which is the geologic period at the earliest (bottom) part of the tree.

It's essential for students to realize that elephants did not magically transform into dugongs, nor did they give birth to dugong babies. Rather, this was an incredibly slow process in which animals were born with slightly different traits than their parents had. If these traits allowed them to live more easily in the ocean, they'd survive and pass the traits on to their offspring. Eventually, more and more animals had these traits.

Have students look at the pictures of dugongs and elephants at these Web sites. Ask them to list the similarities and differences they notice just from observing these photographs.

National Geographic: Creature Feature—African Elephants
National Geographic: Sights & Sounds—Sulu-Sulawesi Seas (Click "Begin" and then scroll over the interactive map to find the dugong.)

Discuss students' lists as a class. What are the main differences between these two species? Did students notice any similarities?

Have students go to this dugong fact sheet and scroll down to see the map of the dugong's geographic range. Ask them to name the continents where they could travel to see dugongs.

Review students' observations of dugongs and the physical features that make them well suited to ocean life. Then pose these questions to the class and discuss their ideas about the best answers:

• How does a dugong's fluked tail help it in the water?
• How do its paddlelike forelimbs ("arms") help it in the water?
• Dugongs can hold their breath for up to 20 minutes, although they usually only stay under for about seven minutes. Why is this adaptation important?
• How might dugongs' small tusks be helpful?
• What might be an advantage of their dolphinlike shape?
• A dugong's nostrils are covered with a valve that helps keep the nostrils closed while the dugong is underwater. What are the advantages of this?
• How might the position of the dugong's mouth on its head help it feed?

Have students write paragraphs answering these questions:

• How are dugongs and elephants similar and different?
• How can animals with such differences be related?
• How is the dugong specially adapted to life in the water?

Have students compare dugongs with manatees, their North American and Caribbean cousins. They should look at pictures and read about both species at the following Web sites. Ask them to draw sketches of both animals and to write captions or paragraphs comparing and contrasting the two.

National Geographic: Creature Feature—West Indian Manatees
National Geographic: Sights & Sounds—Sulu-Sulawesi Seas (Click "Begin" and then scroll over the interactive map to find a link to a picture of a dugong.)
Animal Diversity Web: Family Dugongidae (Click on "premaxillae" in the third paragraph to see pictures of a manatee skull and a dugong skull; the manatee is Trichechidae, and the dugong is Dugongidae.)

This material is based on work supported by the National Science Foundation under Grant No. 0229817.

Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

Dugong dugon
Elephant Evolution
National Geographic: Creature Feature—African Elephants
National Geographic: Crittercam Chronicles
National Geographic: Sights & Sounds—Sulu-Sulawesi Seas