SYDNEY -- Once upon a time, millions of years ago, the humble hedgehog spread over Africa, Asia and Europe, while a freak of nature gave Australia the spiky echidna.

Australia is home to the dianthus erinaceus or hedgehog plant, the chocolate hedgehog cake, the common hedgehog slug, and U.S. porn star Ron "Hedgehog" Jeremy calls Australia home, but the lovable hedgehog is nowhere to be found on the vast continent which was cast adrift at least 200 million years ago.

Curiously, the hedgehog made famous by writer Beatrix Potter and Australia's echidna often fall victim to mistaken identity, along with the spiny porcupine familiar to North Americans.

Yet they are, in fact, one of the world's clearest examples of convergent evolution, say scientists.

Convergent evolution, the emergence of chance look-alikes, involves an evolutionary pattern in which completely unrelated species share similar traits because each has independently adapted to similar ecological and environmental conditions.

"If you were a little animal and you eat insects you have to be on the ground, then one of your main problems in life is that you get eaten by big things, so you have to come up with a defense mechanism," said Erna Walraven, senior curator at Sydney's harbourside Taronga Zoo.

"Both hedgehogs and echidnas, independently, have come up with spikes," Walraven said.

The hedgehog is essentially an insect-eating mammal and the porcupine is a large plant-eating rodent, while the echidna is part of an elite group of monotremes -- along with the Australian platypus -- which are a mixture of mammal and reptile.

"If you go back 200 million years ago, you have a number of different animal mammal groups evolving in different spots and in different ways," said Anne Musser, convergent evolution specialist at the Australian Museum. **** Breakup of Gondawana**** About 350 million years ago, Antarctica, India, Australia, Africa and South America formed a single landmass, a southerly "supercontinent" named Gondawana by scientists.

Australia, Antarctica and South America were all joined as East Gondawana before Australia separated and moved north as the landmass broke up, while Antarctica moved south and froze over.

"As Gondawana separated the animals that were marooned were the ones that were able to evolve into what we have now -- marsupials made it south in time to get aboard the ark that was Australia," Musser said.

The hedgehog became part of northern hemisphere history and the American porcupine flourished in its own ark.

While people often refer to Australia's echidna as a cousin of the hedgehog, Taronga Zoo's Walraven said hedgehogs and echidnas were as far removed from each other as they could be.

The reproductive system is what typifies the difference.

The echidna, a monotreme, has a pouch, lays eggs and then suckles its young.

The hedgehog gives birth to "hoglets", usually four to six offspring at a time. Their tiny spines are covered with a membrane which shrivels away and hardens within hours.

The young echidna hatches after about 10 days incubation and will then remain in its mother's pouch for seven to eight weeks. During this time it gradually becomes spiky.

There are many species of hedgehogs, given their almost global distribution, but the one most commonly referred to -- and fictionalized by children's writer Beatrix Potter with her Mrs Tiggy-Winkle hedgehog character -- is the erinaceus europaeus.

Hedgehogs are usually brown and yellow and have an immensely developed stomach muscle which allows them to curl up into a ball for protection when they are frightened. It eats bugs and berries and has a penchant for slugs, bird eggs and snakes.

Australia's echidna is about 40-55 cm (15-21 inches) long, the erinaceus europaeus hedgehog 20-25 cm (seven-nine inches) long with a round body, stiff spines and a hairy underbelly.

The echidna, one of the oldest unchanged creatures in the world, likes to live in the bush and comes out at night to eat ants and termites with its sticky tongue.

There are more than a dozen species of hedgehog found throughout Africa, Asia and Europe, including the British Isles, where they feast on the eggs of now endangered birds.

The American porcupine, about 75 cm (29 inches) long when fully grown, has quills protecting its back, sides and tail, which usually lie flat against its body until the animal is faced with danger.