Sharks are basically my favorite animal, excluding mythological ones. And assuming I can PICK a favorite, since I pretty much love them all.
Here's the craziest thing I know about sharks. Baby sharks come out of mom three different ways: live birth (long science word: viviparous), laying eggs which then hatch (long science word: oviparous), and ovoviviparous, which is as cool as it sounds. The young form in eggs which stay inside the mother until they are developed enough. They then hatch-- still inside mom-- and she gives birth to the live young.
THIS IS NOT THE CRAZY PART. That's still frickin' cool, right? But it gets better. SO MUCH BETTER. Er. Well, it gets SO MUCH CRAZIER.
So there's a shark called the sand tiger. Not to be confused with the plain ol' tiger shark. The sand tiger is more of a shallower-water species. But that doesn't stop it from having the CRAZIEST FETUSES IN THE HISTORY OF THE WORLD.
See, sand tiger sharks are ovoviviparous (the eggs-hatch-inside-mom-and-live-young-swim-out thing). Like all female sharks, they have TWO uteri. The two uteri have independent openings but share the birth canal. And mom will develop eggs in both uteri at the same time.
That's still not the crazy part. The crazy part is that those eggs are literally in a race for survival. Whichever egg hatches first will EAT the rest of the young in its uterus before being born live. Typically only one pup from each uterus survives.
So every sand tiger shark born is already a winner.
Isn't nature amazing???