Courtesy Ken Zirkel via FlickrLook at the top photo. That's the famous and rightly impressive life-size model of a blue whale at New York's American Museum of Natural History. The blue whale (Balaenoptera musculus) is the largest living vertebrate known on Earth, reaching up to 109 feet in length and weighing around 210 short tons. (Some sauropod dinosaurs were probably larger in some dimensions but they're extinct so they don't count.)
Courtesy Christopher Austin et al/PloS OneNow look at the bottom photo. That's a cute little frog named Paedophryne amauensis. The frog averages about 0.27 of an inch in length - about the size of a housefly (I gave up trying to find its average weight, if you find it, add it to the comments). Anyway, because of its extreme diminutive size, Paedophryne amauensis now holds the title of the world's smallest vertebrate. It was discovered recently in New Guinea by researchers from Louisiana State University. The previous record holder for smallest vertebrate was a tiny Indonesian fish named Paedocypris progenetica. The LSU team, led by Chris Austin, curator of herpetology at LSU's Museum of Natural Science, published its research in a recent issue of PLoS One. Since we're flinging around superlatives, New Guinea is the world's largest and tallest tropical island. Oh, and even though the frog's existence was just announced a couple days ago, a challenger to the "tiniest" title has already come forward.