Basics - Brainy Echidna Proves Looks Aren’t Everything - NYTimes.com
It's a shy, nocturnal, immaculate, pacifist that is nearly impossible for scientists to study in the wild. It has a huge brain, lays eggs and seems to be genetically half a bird.
. . . Reproductively, monotremes [the family echidnas belong to] are like a VCR-DVD unit, an embodiment of a technology in transition. They lay leathery eggs, as reptiles do, but then feed the so-called puggles that hatch with milk — though drizzled out of glands in the chest rather than expressed through nippled teats, and sometimes so enriched with iron that it looks pink.
Monotreme sex determination also holds its allure. In most mammals, a single set of XX chromosomes signifies a girl, a set of XY specifies a boy. For reasons that remain mysterious, monotremes have multiple sets of sex chromosomes, four or more parading pairs of XXs and XYs, or something else altogether: a few of those extra sex chromosomes look suspiciously birdlike. Another avianlike feature is the cloaca, the single orifice through which an echidna or platypus voids waste, has sex and lays eggs, and by which the group gets its name. Yet through that uni-perforation, a male echnida can extrude a four-headed penis.
However they conduct their affairs, monotremes do it remarkably well. Not only are they the oldest surviving mammalian group, but individual monotremes can live 50 years or longer. Peggy Rismiller of the University of Adelaide has studied the short-beaked echidna, or spiny anteater, since 1988. “One of the females we’ve been radiotracking since 1988 is at least 45, and she’s still reproducing,” Dr. Rismiller said.
The next time someone goes on and on about the lack of transitional forms in nature, slap them and scream ECHIDNA!