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When did the first vertebrates appear?
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Animal
The fallow deer (Dama dama) has been introduced in many areas ever since the Neolithic Period.
The first vertebrates appeared much earlier than previously thought, with the discovery of Early Cambrian fossils in South China. While an extensive vertebrate fossil record begins approximately 400 million years ago, these earlier findings push the timeline back into the Cambrian Period.12
Prior to this discovery, the oldest generally accepted vertebrate fossils were fragments of jawless fishes (Agnatha) dating to the Upper Ordovician Period, roughly 450 million years ago. Because the earliest ancestors of these fish were likely soft-bodied and lived in environments where fossilization was rare, their complete evolutionary history remains incomplete, and many early remains may never be recovered.31