By tooth and scale
The Silurian period was warm, and compared to the periods around it, rather gentle. Plants on land became a bit more sophisticated, with roots and stems and the ability to move water an nutrients around their bodies. Giant sea scorpions, the largest arthropods of all time, cruised the waters, probably chowing down on our early vertebrate ancestors. The fish developed jaws and moved into fresh water, and apparently, Changed some scales into teeth.
Here are a couple of articles with general information about the Silurian.
And here’s some articles about how our teeth may have come from modified fish scales.