The smallest vertebrate ever found is a 7.7mm frog

Look how tiny it is compared to a dime! The frog was discovered in Papua New Guinea. It's scientific is Paedophryne amauensis. It holds the record for being the smallest vertebrate in the world. 

It dethroned the previous record holder, a Sumatran fish, only a month after it was officially described! Scientists now believe that tiny frogs are not that uncommon. They've found that 27 of the 29th smallest frogs 'jump' straight from tadpoles to adults, and their moist environment benefit and help them be so small.

(Source)