Two things to add to my post about convergent evolution
  1. Crabs have independently evolved so many times throughout history that there's a word for it:  Carcinisation (via Radiolab).  Put another way, Evolution Only Thinks About One Thing, and It's Crabs.
  2. New World vultures and Old World vultures aren't even really related, which means a flying animal that eats virus- and bacteria-laden decaying corpses has evolved on more than one occasion (again via Radiolab).