"Indeed, the human and the nine-banded armadillo are the only known mammals that produce monozygotic gestations, although some species occasionally deliver a two-headed or six-legged offspring."Not content with producing monozygotic ("identical") twins, the nine-banded armadillo's normal means of reproduction is actually identical quadruplets.
Unfortunately, the quote from the article appears to be...what's the word?...wrong. For example, here is an article (with the impressive title "Monstrous Dolphins") referencing identical twin dolphins.
I'm reading through the scientific literature for an upcoming blog post on factors influencing twinning rates and finding some truly bizarre stuff.