B. The 20' tall extinct megafauna that was a mash-up of rhinoceros, giraffe and dinosaur. The largest-ever land mammal!
If so, you should check out this hilarious video, made even funnier by the after-market Japanese sub-titles. It features computer-animated projectile birthing, computer-animated fresh-kill pooping, a vicious giant scavenger-hog, a horse-monster that grazes from the treetops - so you know it's from the BBC. Unfortunately, since this is Miocene Mongolia, no elephant-sized ground sloths (S. America) nor ridiculously chandelier-antlered elk (Europe). I love how they treat it like a real documentary - night vision filters, lens flare, even the film crew "disturbing" the big baby's sleep at one point. So awesome.