"Extreme" Animal Embryos Revealed

Red Kangaroo: Embryo Outside the Womb?

Some day this little guy or girl will be about as tall as a man. But for now the weeks-old red kangaroo joey is roughly cherry-size, essentially an embryo outside the womb.

Red kangaroos--along with three other species featured in the National Geographic Channel's new Mother's Day 2009 documentary In the Womb: Extreme Animals--have evolved ingenious adaptations for coping with what would seem to be gestational hazards.

Even at this early stage, the red kangaroo's forearms are fully functional, its inner ear can tell up from down, and its sensitive nose makes up for unseeing eyes--the better to find and latch on to the tiny teat that will nourish the kangaroo almost continuously for six months, according to the documentary.







Emperor Penguin: Inside the Breathing Egg

Kicking back before getting down to the hard work of hatching--a several-day process--a late-stage emperor penguin embryo (shown in a digital illustration) breathes easy inside its egg, which is resting on the father penguin's feet while Mom is on a months-long fishing trip.

Unlike developing humans, a baby penguin can't tap into the oxygen in its mother's bloodstream. Instead, its umbilical cord is linked to blood vessels in a membrane attached to the egg's inner wall. Oxygen enters the embryo's blood via microscopic holes in the shell--turning the egg into a kind of surrogate lung.

After 64 days of development, the baby penguin will slowly smash its way out, and its mother, with any luck, will be waiting with fish.



Demon Shark: Sac to "Stem"

Shown about halfway through its 12-month gestation period in a computer-generated illustration, a lemon shark--like a human embryo--is literally connected to its mother via an umbilical cord attached to a placenta. But it wasn't always so.

Until about three months in the womb, baby sharks feed off a yolk sac. Once the embryo has depleted the yolk, the collapsed sac settles against the womb wall and shoots blood vessels into the wall, tapping into the mother's circulatory system.

By the time the embryo is six months old (pictured), it has a sense of smell 10,000 times sharper than a human's. This and other sensory adaptations--including electro-sensors that detect the faint voltage of other animals--will one day allow the shark to detect even a fin flick hundreds of feet away.