Kangaroo

Kangaroos are among the most recognizable animals in the world and among the most physiologically unusual. Their hopping gait becomes more efficient at higher speeds (the opposite of running in most animals), they're born at an embryonic stage that would be unrecognizable as a mammal, and females can maintain three offspring at different developmental stages simultaneously.

Facts you didn't know

• 1

  Kangaroo hopping becomes more fuel-efficient at higher speeds — the tendons in their legs store and return elastic energy like springs, meaning faster hopping costs less energy per meter than slower hopping. This is the opposite of how running works in most animals.

• 2

  Kangaroos are born at an embryonic stage after only 33 days of gestation — newborns are about 2cm long, blind, hairless, and without developed hind limbs. They crawl unaided to the pouch using their forelimbs and spend the next 8 months completing development there.

• 3

  A female kangaroo can simultaneously support: a joey in the pouch suckling, an older joey that has left the pouch but returns to nurse, and an embryo in diapause (suspended development) waiting for the pouch to become available. Three offspring, three developmental stages, one mother.

• 4

  Kangaroos cannot move their legs independently while on land — they always hop with both hind legs together. But in the water, they can kick each leg independently, and are capable swimmers.

• 5

  Kangaroos don't sweat — they lick their forearms to cool down. The saliva evaporates and carries heat away. The forearms have a high density of blood vessels near the surface for exactly this reason.