Egg-laying Mammal Is Living Link to Reptiles - may be the strangest mammal in the world

ngm ^ | May 18,2010 | Christy Ullrich

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Related to the platypus, this nocturnal worm-eater is the largest egg-laying mammal in the world. An echidna can weigh up to 36 pounds. Photograph by Tim Laman It may be the strangest mammal in the world—spiky hairs, pointy beak, no nipples, four-headed penis. The long-beaked echidna, found in the rain forest of New Guinea’s Foja mountains, has adapted in remarkable ways. A monotreme, from a group of egg-laying mammals that have been around since the time of the dinosaurs, this primitive animal serves as a living link between mammals and reptiles.

Short-beaked echidnas and platypuses are the only other living monotremes. Weighing up to 36 pounds, echidnas have powerful bodies that allow them to dig easily. Muscular shoulders, strong arms, and five-clawed feet enable them to dig straight down into the ground, disappearing from sight within minutes.

Says Kristofer Helgen, mammal curator at the Smithsonian Institution, “they’re impenetrable.” When an echidna senses danger, “it tucks in its head, forms a ball, and starts to disappear into the ground right in front of you,” he says.

Its peculiar-looking elongated beak is an outgrowth of its skull. The echnida uses its beak to overturn rocks and root around for its favorite meals—earthworms, beetles, and millipedes—then devours its food with its long sticky tongue. Echidnas are also said to have “a sixth sense,” says Helgen. The skin of their sensitive beaks is innervated, which gives them the ability to detect electrical fields and navigate gradients in moist soil that leads them to the bodies of earthworms.

The echidna has a single hole, the cloaca, for excretion, egg-laying, and mating. Scientists believe that probably only two of the males’ four penis heads are active during copulation. A dozen males may pursue a female echidna, and she likely mates multiple times. Since females don’t have nipples, they produce milk from mammary patches on their stomachs that their young lap up.

Echidnas are known as slow movers, and though they waddle, they can forage across long distances. Humans and dogs are their only real predators today, which is why national parks and remote areas, like the Foja mountains, remain important sanctuaries for these critically endangered animals. The long-beaked echidna thrives in the mountain rain forest of the Fojas, with its earthworm-filled soils.

“Unlike porcupine quills, which can stab, the echina’s spines are like spiky armor—a kind of discouragement,” Helgen says. The modified hairs come from a long root that originates in a muscular layer of the animal’s body. This feature allows the echidna to move its hair individually or in groups.

Much about this fascinating animal continues to elude scientists, including the echidna's mating behavior. No one has ever reported seeing a baby long-beaked echidna.

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