Australia's Amazing Animals.
Where in the world can you find an animal that shoots venom from its ankle, a lizard with "water pipes" on its skin, and a "bear" that isn't a bear? Think Australia, home to creatures like the platypus, the thorny devil, and the koala. How did they end up (or down) there?
"Ancestors of these animals evolved millions of years ago, when the island belonged to a supercontinent called Gondwana," explains Michael Archer, a zoologist (animal scientist) and director of the Australian Museum in Sydney. This vast landmass once consisted of what is now Australia, Antarctica, South America, Africa, and India. Over 100 million years, the ceaseless shifting of continental plates (slabs of Earth's crust) caused the landmass to rupture and break apart. "Between 45 and 38 million years ago, Australia severed its last ties to Gondwana to become the island continent it is today," Archer says.
Surrounded by water, many Australian animals have evolved in total isolation. "In Africa and South America, for example, lion populations swapped back and forth each time sea levels lowered," says Archer. But on the remote island of Australia, animals evolved undisturbed over eons of time, gradually developing into species found nowhere else on Earth. Today, some of these species face unprecedented threats--like shrinking habitats and diminishing food supplies due to urbanization and pollution. Read on and meet some of these amazing creatures.
ONE: WEIRD SIGHT
What has four legs, a furry body, beady eyes, a wide beaverlike tail, a duck's bill, and webbed feet? When scientist George Shaw at the British Museum first laid eyes on a preserved platypus in 1799, he didn't know what it was. Shaw thought somebody had surgically attached miscellaneous animal parts together as a joke, and even tried to pry the bill off!
Even stranger, the female platypus, unlike other mammals (warm-blooded animals that nurse their young with milk), lacks teats or milk-dispensing nipples. Instead, a platypus mom secretes milk through pores in her belly. And rather than carry her young internally, she lays eggs!
These two biological traits are so rare in mammals that scientists classify the platypus, (along with one other Aussie animal in the world, the echidna) as monotremes (meaning "one hole"). Both creatures possess a single cavity or cloaca, through which they expel eggs, feces (solid waste), and urine---a characteristic usually associated with reptiles.
Since the platypus is nocturnal, or active at night, a big challenge for scientists is to find one in the first place. The animal spends most of its active hours diving underwater for food. Researchers have found that the solitary platypus swims in night waters with eyes and ears shut! How does it find food or avoid smashing into rocks? The rubbery bill is pressure-sensitive and can detect obstacles ahead. It's also packed with electro-receptors (nerve endings sensitive to electric currents) that can zero in on weak electrical signals produced by moving prey: aquatic invertebrates, or animals without backbones, like crayfish and shrimps.
When not splashing in water, the platypus snoozes--up to 17 hours a day in underground burrows dug by rivers in eastern Australia and Tasmania. Locating the burrows is no small feat for researchers. "The entrances are usually well disguised," says Melody Serena of the Australian Platypus Conservancy.
The creatures are even harder to spot now, since water pollution is causing the platypus to struggle with habitat loss. But a recent waterway cleanup has drawn platypuses to a most unlikely place: Melbourne--Australia's second largest city. To find them "living near busy roads and factories has been a very exciting discovery," Serena says. This spells encouragement for environmentalists.
Another creature-feature: the adult male platypus is one of the only venomous (poisonous) mammals in the world. On each ankle lies a sharp, hollow, 15 nun (0.6 in.)-long spur that secretes venom produced by a thigh gland. Venom comes in handy when males compete for mates. Ouch!
CALL ME: UGLY
Australia boasts nearly 750 species of snakes and lizards, and in the continent's harsh interior desert these critters must devise survival "smarts" to avoid becoming chow for crafty predators. Meet one lizard whose survival strategy is to look so scary it's named the thorny devil.
To scare off larger lizards, the thorny devil inflates itself with air and "puffs up" with a threatening display of spiky skin. But the thorny devil is only 10 to 15 cm (4 to 6 in.)long, slow moving, and basically a coward--when really scared, the lizard tucks its head between its front legs. Then a knoblike spiny protrusion on the back of its neck comes to the rescue to sit in place of the real head! "This certainly makes thorny devils hard to swallow for most predators, even snakes," says Eric Pianka, a herpetologist (expert in reptiles) at the University of Texas at Austin.
Like its fake head, the thorny devil's spiky skin performs double duty. The lizard sports a hygroscopic (taking up moisture) system of skin grooves. The thousands of grooves and spikes collect rainwater and dew during cold desert nights. A thorny devil's gulping motions moves water down grooves (like a pipe system) directly into its mouth. How resourceful!
WE'RE: NOT BEARS
With faces like teddy bears, koalas are often mistakenly called beam--but they're not even relatives. These tree-huggers, along with more than 270 mammal species (including the kangaroo), are marsupials, or mammals that usually feature pouches in which to nurse or carry their young.
Mama koalas possess pouchlike folds surrounding the teats to protect nursing babies. That's because marsupial babies (joeys) are born highly underdeveloped--blind, hairless, and very tiny--measuring between 1.27 to 2.54 cm (0.5 to 1 in.) in length. Joeys crawl instinctively from the birth canal into the pouch to nurse on their mothers' teats.
Before a 6-month old koala is fully weaned from milk and starts an adult diet of eucalyptus leaves, the furry creature begins a monthlong transition diet of cecal feeding: The koala leans out to eat mom's excrement directly from her anus. What joeys are eating is called pap--runny, partially digested food broken down by mom's intestines. Pap is rich in microorganisms (tiny organisms including bacteria) that are essential in breaking down hard-to-digest eucalyptus leaves. So pap readies a baby's digestive system for adult food.
Millions of koalas once roamed Australia, but since the arrival of European settlers in the 1780s, 80 percent of the koalas natural habitat--eucalyptus-tree forests--has been destroyed. Add urban sprawl, and today's 100,000 remaining koalas are forced to share backyards with resident Aussies. Australian laws protect koalas but not their habitat. But last May unexpected pressure for better koala protection came when the U.S. government classified the koala as a threatened species (could be in danger of extinction) under the U.S. Endangered Species Act. Says Ann Sharp of the Australian Koala Foundation, "This sends a strong message to our government that the koala is in urgent need of protection."
Name: Thorny Devil or Moloch (Moloch horridus)
Home: Interior deserts of southern and western Australia
Length: 10 to 15 cm (4 to 6 in.)
Weight: 33 to 88 g (1 to 3 oz)
Life span: Up to 20 years
Head count: Unknown
Wacky fact: Named after Moloch, a god who demanded human sacrifice, and "horridus"--which means dreadful in Latin.
Name: Platypus or duck-billed platypus (Ornithorhynchus anatinus)
Home: Freshwater lakes and rivers of eastern Australia and Tasmania
Length: 40 to 56 cm (1.3 to 1.8 ft)
Weight: 1 to 2.5 kg (2.2 to 5.5 lb)
Life span: Around 12 years
Head count: So elusive, impossible to estimate
Wacky fact: One way researchers rate platypus health is to run a "squeeze test" on the tail to check for fat. The tail stores up, to 50 percent of body fat and provides energy when food is scarce.
Name: Koala (Phascolarctos cinereus)
Home: Northeast and southeast Australia
Length: 65 to 82 cm (2 to 2.7 ft)
Weight: 5 to 12 kg (11 to 26.5 lbs)
Life span: 13 to 18 years
Head count: 100,000 (estimated)
Wacky fact: The word "koala" is derived from the language of the Katang aborigines (earliest known inhabitants of the area) meaning "no drink." Koalas get most of their liquid supply from eucalyptus leaves.
Language Arts: Read and report on a novel set in Australia.
Did you Know?
* Koalas are the only non-primates (humans, gorillas) with unique sets of fingerprints. About 4,000 koalas are killed each year by cars or dogs.
* The thorny devil dines exclusively on ants. Using the tongue, it flicks one ant into its mouth at a time--up to 45 per minute, and around 2,000 ants per meal!
* The platypus swims with one forearm at a time, as in the crawl stroke. Hind limbs are only used for steering.
CHECK FOR UNDERSTANDING, p. TE4 Australia's Amazing Animals
1. False; the echidna and the platypus are the only two monotremes in the world. 2. True 3. False; nocturnal animals are active at night. 4. False; Marsupial babies are born blind, bald, tiny, and highly under-developed. Born To Run Life * Physical Science: Cellular Respiration * Muscles * Energy
Australia's Amazing Animals
Directions: True or false? Circle the correct letter, then rewrite false statements to make them true.
T F 1. The echidna and the platypus are the only two marsupials in the world.
T F 2. Monotremes are mammals that lack teats and lay eggs.
T F 3. Nocturnal animals are only active when the sun is up.
T F 4. When marsupial babies are born they look like mini-adults, complete with a full head of hair.
T F 5. A herpetologist is an expert in reptiles.
National Science Education Standards
Grades 5-8: structure and function in living systems * diversity and adaptation of organisms * population, resources, and environments
Grades 9-12: interdependence of organisms * environmental quality * natural and human-induced hazards
Australian Koala Foundation www.savethekoala.com
Ausralian Platypus Conservancy www.austmus.gov.au/index04.htm
Australian Museum (education section) www.austmus.gov.au/index04.htm
Mammals of Australia edited by Ronald Strahan (Smithsonian Institution Press, 1995)
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|Date:||Sep 4, 2000|
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