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Canada's species


Chipmunk. Photo: Peter MirejovskyAn offshoot of the reptiles, mammals first arose 200 million years ago and were tiny until the ruling dinosaurs died out 65 million years ago. That resulted in an explosive radiation for the mammals, who are now the dominant vertebrate group on land.

Mammals can be distinguished by their hair, internal heat regulation (warm-bloodedness), specialized teeth, and the fact that mothers nourish their young with milk. A few species, known as the Monotremata (duckbilled platypus and echidna), actually lay eggs, but the vast majority give birth to live young. Of these some, known as the marsupials (opossums and kangaroos, for instance), give birth to young that finish developing in external pouches, while the Placentata (most mammals, including humans) develop within their mother.

There are about 4500 species of mammals. In the placental mammals, these include the orders Insectivora (shrews and moles), Primata (apes, monkeys and humans), Chiroptera (bats), Carnivora (such as dogs, cats, and weasels), Proboscidea (elephants), Cetacea (whales and dolphins), and more. Groups such as the whales, dolphins, seals and manatees have actually returned to the ocean, where their distant ancestors the amphibians emerged long ago and their even more distant ancestors the fish still live.

Page 2 Rodents (order Rodentia)

Page 3 Carnivores (order Carnivora)

Page 4 Aquatic mammals (orders Cetacea and Pinnipedia)

Page 5 Other mammals