The Spiny Anteater, an Egg-Laying Monotreme.

Greetings. Echidnas, known as spiny anteaters, are native to New Guinea, Australia, and Tasmania. Having initially evolved between 20 and 48 million years ago, the four species of echidnas and the duck-billed platypus are the sole representatives of the ancient order Monotremata.

Covered in hair and quills, echidnas are solitary and extremely shy animals. The quills are made of keratin, which makes up fur, claws, nails, and horn sheaths in animals. Despite having evolved from an aquatic platypus-type ancestor, spiny anteaters are terrestrial animals, but are fully capable swimmers when necessary. Echidnas are powerful diggers, and possess short, strong limbs armed with long claws, with the hind claws having a backwards curve to assist in the digging process. 

Echidnas have the second-lowest active body temperature of any mammal, at 33° Celsius, behind only the duck-billed platypus. With a diet of ants, worms, termites, and insect larvae, echidnas have no problem finding nourishment in their terrestrial habitats. While appearing to be similar to hedgehogs and porcupines, echidnas are not related in any way to those placental mammals, although they do have some behavioral similarities. 

Echidnas inhabit forests and woodlands, sheltering under roots, debris piles, and vegetation, and are intolerant of extreme temperatures. With a natural lifespan of about 16 years, echidnas are somewhat long-lived animals, thanks to their low metabolism and climate adaptability. All four species are sexually dimorphic, with males being about 33% larger than females, attaining weights of 6 kilograms. Males have large spurs on their hind feet, although the spurs are non-poisonous, unlike the highly poisonous spurs of the platypus.

Fossil evidence suggests that the oviparous (egg-laying) mammals and viviparous (young internally developing) mammals separated during the Triassic Period, approximately 225 million years ago, with echidnas diverging from platypuses approximately 48 million years ago during the Paleogene. The evolution of echidnas suggests that they transitioned from aquatic environments to a terrestrial existence, which placed the animals in direct competition with marsupials.

Despite the erroneous perception that the egg-laying mammals are somehow primitive, the Monotremes are a tough and successful order of mammals that have outlived the non-avian dinosaurs, the pterosaurs, the Pleistocene megafauna, and many of their mammalian kin. 

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