There is something adorable about a kangaroo joey sticking their head out of the pouch. I remember visiting a zoo where we were able to walk through the kangaroo pen. It was raining.
A joey hopped out of its mother’s pouch and decided to explore the world. Well, mom, being smart, was in their rain shelter.
The joey hopped out of the shelter, stopped dead, looked up, and dived back all the way into the pouch with such force they rocked mommy back on her tail. I swear she rolled her eyes.
So, why did marsupials take such a different evolutionary course from placental mammals like us?
How did they get those pouches?
All The Different Pouches
First of all, the pouch, which is correctly called the “marsupium” (just as a womb is technically a “uterus”) is not the same across the wide variety of marsupials.
Some marsupials have pouches that face backwards, such as wombats. They burrow and don’t want to throw dirt on the baby.
Opossums have a pouch that’s a slit down the center of their body.
The Koala pouch opens straight outwards (and also has a strong spinchter so the joey doesn’t fall to its death from whatever tree they’re sitting in).
And some marsupials don’t have pouches at all, and from them we get our first clue.
Phascogales, also known as mousesacks or wambengers, have three surviving species, the brush-tailed, red-tailed and northern brush-tailed. I guess the tails are the easiest way to tell these critters apart. They’re about the size of rats, and are arboreal. I.e., they are basically marsupial squirrels.
And they’re weird.
First of all, the males live a year or so before they, uh…okay. They mate to death. They literally mate so much that they stress themselves ill. In captivity, the males can be kept alive for three years by restricting their mating, but they can’t breed after that. The females live for three years but also only breed once.