See question title. After doing some looking around on my own I haven't found much so I figured I'd ask some experts.
closed as too broad by J. Musser, The Last Word, MattDMo, WYSIWYG, Chris♦ Jun 22 '14 at 9:09
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The smallest vertebrate (if that's what you mean; there are many invertebrates with endoskeletons that are not made of bone) is Paedophryne amanuensis, a Papua New Guinea frog that's about 7 mm long.