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Studying Living Organisms

Australian Mammals: Evolutionary Development as a Result of Geographic Isolation

Deborah B. Asbell, Joseph L. Glick, Jr., and Donald C. Snyder, Jr.
Woodrow Wilson Biology Institute
1995


Target age or
ability group:
General Biology.
Class time
required:
45-50 minutes
Materials and equipment: Worksheets: Australia's Special Mammals Continental Map of Australia (containing Mammals) Continental Drift Student Worksheet
Summary of activity: After completion of this activity students will:
    1. know the difference between monotremes, marsupials, and placental mammals
    2. be able to compare and contrast these organisms (Australian mammals) with other mammals
    3. know mammalian characteristics
    4. will be able to identify Australian mammals
    5. learn about the unique variation and diversity of mammals located in Australia.
    6. learn about this unique development of mammals as a result of plate tectonics and geographic isolation.
Prior knowledge, concepts or vocabulary necessary to complete activity:
Vocabulary: flora, fauna, mammal, monotreme, marsupial, placenta, evolution, plate tectonics, continental drift, fossil, echnida, platypus, Aborigines, and kangaroo.
Concepts (Prior Knowledge):
    1. Students should be aware of plate tectonics.
    2. Students should know the characteristics common to all mammals.
    3. Students should be aware of evolution.

Teacher Instructions

Located after the Introductory section.

Introduction

Australian environments have been constantly changing through varying local geography and fluctuating climatic conditions, both local and worldwide. (Isolation from other major land masses and environmental change have been the main tools in shaping Australia's unique flora and fauna.)

The native mammals of Australia are derived from two sources. The oldest mammals are descendants of animals (monotremes and marsupials) that were on the continent when it was separated from Antarctica. The others, the bats and rodents, moved westward from Southeast Asia as Australia drifted northwards.

No fossil monotremes (platypus and echidna) have been found outside of Australia and new Guinea and only a few fossils are known. Although a piece of jaw, about 100 million years old, from an ancestral form of the platypus was recently discovered, very little is known about the evolution of these animals. The oldest known fossils of marsupials date from about 100 million years ago. They have been found in North America. From the fossil record it appears that marsupials then moved east into Europe as well as southward into South America. They died out in Europe and North America, possibly through competition with placental mammals, but were successful in South America. One species later re-invaded North America and it is believed that others traveled to the Australian continent by way of Antarctica, before the three continents broke up. Evidence in support of this theory comes from the discovery of a fossil marsupial in Antarctica in 1982. Generally, it is accepted that the opossums, or a similar group, were ancestral to the Australian marsupials. From this opossum-like stock many different kinds of marsupials developed, including native cats, bandicootes, kangaroos, wallabies, possums and wombats. Besides the 120 different species of marsupials living in Australia today, there were many more that are now extinct, including the so-called "giants". Many of these giants, or Mega-fauna, were larger varieties of animals that are alive today. For example, there were giant wombats, koalas, and kangaroos.

Some of these giants were still in existence about 10,000 years ago. The reason for their decline is not known; perhaps it was the change of climate that occurred at the end of the last Ice Age or perhaps they were hunted by the Aborigines. We may never know for sure.

As Australia drifted eastward to Southeast Asia, it became possible for other animals to cross the marine barriers and become established here. The first bats flew across no later that 15 million years ago, followed by rodents some 5-10 million years ago. The rodents would have floated across on storm debris such as mats of vegetation.

At present time, some of the most widespread and successful mammal species are those that have been introduced by humans. It is believed that the dingo accompanied Asian seafarers on their voyages, landing in Australia some 5,000 years ago. The feral cat, house mouse, black rat, rabbit, fox, horse, donkey, camel, goat, pig, feral cattle, and others were introduced by Europeans and are so well established that they must now be regarded as a part of Australia's mammal fauna.

Teacher instructions:

1. Prepare for each student the worksheet entitled: "Australia's Special Mammals" and the "Continental Map of Australia."

2. Review the vocabulary in the activity by discussing with class after they have read the worksheets.

3. Pass out "Student Activity Worksheet".

4. Assessment ideas:

    a. Student developed poster of Australian Mammals
      1. illustrating a mammal of their choice
      2. discussing their characteristics
    b. Student reports: Format
      1. 1-2 pages
      2. Each report must contain information about the characteristics of the mammal, habitat, range, history of its development, life span, and an illustration of the mammal.

STUDENT WORKSHEET

DIRECTIONS:Answerthe following questions based on the worksheets and our class discussion

1. Identify the following animal illustrations:

Word Bank: platypus, bat, wombat, Tasmanian Devil, kangaroo, echidna, koala

2. Define: mammal, evolution, placental mammal, monotreme, marsupial, flora, fossil, and fauna.

3. Describe three unique characteristics of Australian mammals..

4. What are the evolutionary reason(s) for Australian mammal development?

5. How are monotremes, marsupials, and placental mammals similar? different? Give two examples of each type of mammal.

6. What is plate tectonics? How has it contributed to the unique development of Australian mammals?

7. What are the native mammals of Australia? How did they evolve?

8. How could marsupials have possibly died out in North America and Europe?

9. How did the Mega-fauna die out in Australia?

10. What were the first two placental mammals introduced into Australia?

Australian Animals

Australia, South America and Africa occupy approximately the same range of latitudes and have a variety of habitats, yet they support quite different types of fauna.

While many countries have their own unique fauna, Australia (and Papua, New Guinea) are unusual in that they include:

    a. 70% of the world's marsupials

    b. all of the world's monotremes

    c. a tiny percentage of the world's placentals

    d. an enormous diversity of parrots and other birds

    e. fascinating range of reptiles, amphibians, and fish

    f. countless unusual invertebrates

There are a number of reasons why Australia has many unique species.

Australia has been isolated for long periods of time, so there has been little exchange of animals with the rest of the world. For example Australia has no native hoofed animal.

Australia's climate is often unpredictable. There may be long periods of drought, frequent floods or fires. These sorts of problems require adaptations. For example, the red Kangaroo can suspend the development of its embryo until conditions improve.

Rain forest pockets still contain examples of very ancient animals (like the Cuscus), from a time when much of Australia was covered by rain forests.

Generally, our knowledge of Australian fauna is quite poor. It is believed that between 200,000 and 300,000 species are in Australia, but so far only about 100,000 have been described.

Australia's Special Mammals

What are mammals?

Mammals all produce milk to suckle their young.
Mammals have fur or hair.

There are three types of mammals:

a. Monotremes are mammals that lay soft-shelled eggs. They are only found in Australia and New Guinea. The Platypus and the Echidna are the only monotremes left today.

b. Marsupials are mammals that give birth to young which are in an immature state. The females often have pouches in which to carry the young. Only 30% of the world's marsupials are found outside Australia. The main groups of the 180 species of Australian marsupials are:

    1.Macropods --Kangaroo and Wallabies
    2.Carnivorous marsupials -- Numbats, Moles, Dasyurids
    3.Possums, Gliders, and Cuscus
    4.Bandicootes and Bilbies
    5.Koalas and Wombats

c. Placentals are mammals that produce a well developed placenta which allows the young to be born in a more developed state. Most species are found in other parts of the world. Only the following few are found in Australia:

    1.Native mice and rats
    2.Bats
    3.Dingoes
    4.Seals
    5.Whales, Dolphins, and Dugongs

Continental Drift Worksheet

The land masses of the world have not always been where they are today. At one time all the continents were joined together in one land mass called Pangaea. Geologists working on theories of continental drift (more correctly called the "Theory of Plate Tectonics") agree that the continents, as we now know them, have been constantly on the move, merging with each other, breaking into different groupings and joining again.

The rigid crust of the Earth is considered to have broken into a number of "plates" that are moving independently in different directions. The continents themselves are lighter rocks sitting on top of these plates. Where two plates collide the softer, upper layers of rock are compressed and folded to become mountain ranges. Erosion by ice, rain and wind then produces the mountain shapes familiar to all of us. The Himalayas and the Andes are examples of mountain ranges recently formed in this manner.

The movements of the continents have been recorded by particular rocks. Certain magnetic minerals behaved as compasses and point to where the magnetic poles were, at the time the rocks were formed. This information along with other geological and biological evidence enables scientists to construct maps of the world for different times in the past. These maps are called Paleogeographic maps.

Geologists have established that 200 million years ago one single continent, Pangaea, existed. During a period of 20 million years Pangaea broke up into two separate land masses:
the northern continent, known as Laurasia, consisted of North America, Asia and Europe; the southern continent, Gondwana, included Antarctica, Australia, India, Africa and South America.

Over the next 100 million years Gondwana broke up. Africa and India moved northward while South America, Antarctica and Australia remained connected. Eventually the three continents broke away from each other, with Australia and Antarctica separating about 45 million years ago. At present, Australia is moving north toward the tropics at about 10 mm per year. About 60 million years from now, we will collide with Asia.

As Australia has drifted across the globe, the land and its climate has changed. For example, during past ages there have been many variations in sea levels and at times, much of what is now dry land was covered by shallow seas in which sediments and fossils collected. In fact, in the past, Australia has been so dissected by shallow seaways that it was reduced to several large islands. At other times the land mass has been high above the surrounding oceans with land connecting Tasmania, Kangaroo Island and New Guinea to the Australian mainland.

Bibliography

Continental Drift Worksheet from "Australia's Life of the Past," developed by the South Australian Museum, Adelaide, South Australia 1992.

Continental Map of Australia (containing mammals) developed by the Taronga Zoo, Sydney, New South Wales, Australia 1992.

Australia's Special Mammals Worksheet developed by the Taronga Zoo, Sydney, New South Wales, Australia 1992

Continental Map of Australia with Mammals

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